Drainage Xxxx

State of Qatar - Public Works Authority Drainage Affairs

Volume 4 TSE System Design Page i 1st Edition June 2005 - Copyright Ashghal

Contents

1.0 General ................................................................................................................................... 1

1.1 Introduction ................................................................................................................................ 1 1.2 Standards .................................................................................................................................. 1 1.3 Master Planning of Landscape and TSE Irrigation Systems ..................................................... 1

1.3.1 Landscape Development Master Plan ....................................................................................... 1 1.3.2 Irrigation Budgets ....................................................................................................................... 1 1.3.3 Irrigation Master Plan ................................................................................................................. 2

1.4 Irrigation Water Quality .............................................................................................................. 2

1.4.1 General ....................................................................................................................................... 2 1.4.2 Public Health Factors in Effluent Use ......................................................................................... 2 1.4.3 Quality of TSE for Landscape Irrigation ..................................................................................... 3 1.4.4 Recommended TSE Quality for Landscape Irrigation ................................................................ 4

1.5 Documentation .......................................................................................................................... 4 1.6 Environmental Impact Assessment ........................................................................................... 4 1.7 Building Permit .......................................................................................................................... 4

2.0 Design of TSE Transmission and Distribution System ..................................................... 7

2.1 Definitions .................................................................................................................................. 7 2.2 Standards and Sources of Information ...................................................................................... 7 2.3 Principles of Design ................................................................................................................... 8 2.4 Sizing and Flow Estimation ....................................................................................................... 8 2.5 Pipeline Materials .................................................................................................................... 14

2.5.1 Ductile Iron Pipes ..................................................................................................................... 14 2.5.2 Polyethylene Pipes ................................................................................................................... 14 2.5.3 GRP Pipes ................................................................................................................................ 15 2.5.4 Asbestos Cement Pipes (Safety Note) ..................................................................................... 15

2.6 Hydraulic Analysis ................................................................................................................... 15 2.7 General Design Considerations .............................................................................................. 20

2.7.1 Pipeline Horizontal Alignment .................................................................................................. 20 2.7.2 Pipeline Vertical Alignment ....................................................................................................... 21 2.7.3 Internal Pipe Pressures and Restraint of Thrust ...................................................................... 21 2.7.4 Air Release ............................................................................................................................... 22 2.7.5 Pipeline Maintenance – Draining .............................................................................................. 22 2.7.6 Isolation Valves ........................................................................................................................ 22 2.7.7 Flow Metering and Remote Sensing ........................................................................................ 23

2.8 Pumping Installations .............................................................................................................. 25

2.8.1 Pumping Plant .......................................................................................................................... 25 2.8.2 Plant Layout .............................................................................................................................. 28 2.8.3 Primary Movers ........................................................................................................................ 29 2.8.4 Variable Speed Drives (VSD) ................................................................................................... 30 2.8.5 Motor Control Centre (MCC) .................................................................................................... 31 2.8.6 Instrumentation and Control ..................................................................................................... 33


Page ii Volume 4 TSE System Design 1st Edition June 2005 - Copyright Ashghal

2.8.7 Pump Suction and Delivery Design ......................................................................................... 37 2.8.8 Surge Protection ...................................................................................................................... 38 2.8.9 Air Valves ................................................................................................................................. 40 2.8.10 Filtration ................................................................................................................................... 40 2.8.11 Ventilation and Air Conditioning ............................................................................................... 41 2.8.12 Standby Generation ................................................................................................................. 43 2.8.13 Maintenance Access and Lifting Gear ..................................................................................... 43 2.8.14 Geotechnical Information ......................................................................................................... 44 2.8.15 Sub- and Superstructure Design.............................................................................................. 45

2.9 TSE Towers ............................................................................................................................ 47 2.10 TSE Ground Tanks ................................................................................................................. 47 2.11 Site Facilities ........................................................................................................................... 49

3.0 Design of Irrigation Systems .............................................................................................. 50

3.1 Definition and Scope ............................................................................................................... 50

3.1.1 System Layouts ....................................................................................................................... 50 3.1.2 Pipework Materials ................................................................................................................... 52 3.1.3 Pipework Sizing ....................................................................................................................... 52 3.1.4 Minimum and Maximum Pressures.......................................................................................... 52 3.1.5 Irrigation Rates ......................................................................................................................... 54 3.1.6 Irrigation Equipment ................................................................................................................. 54 3.1.7 Control Systems ....................................................................................................................... 58 3.1.8 Co-ordination of Irrigation and Landscape Design .................................................................. 58 3.1.9 Under-Drainage ....................................................................................................................... 58

3.2 Landscape and Irrigation Management ................................................................................... 59

3.2.1 Irrigation Management ............................................................................................................. 59 3.2.2 Maintenance of Irrigation Systems........................................................................................... 59 3.2.3 Planting Management .............................................................................................................. 59

4.0 Health & Safety .................................................................................................................... 60

4.1 General Guidelines ................................................................................................................. 60 4.2 Reference Documents ............................................................................................................ 60

5.0 References ........................................................................................................................... 62


Volume 4 TSE System Design Page 1 1st Edition June 2005 - Copyright Ashghal

1.0 General

1.1 Introduction

This volume covers the engineering planning and

design of treated sewage effluent (TSE) systems for

irrigation use in the urban environment. TSE may

have other uses, e.g. in certain industrial

applications, but for Qatar, irrigation is likely to be the

primary use. As such, an overview of the broader

issues involved in the use of TSE for irrigation is

covered before discussion of engineering planning

and design of these systems.

1.2 Standards

A full list of standards used in all of the manuals for

design purposes is included in Volume 1, Foreword.

References used in this Volume are also included in

Sections 2.2, 4.2 and at the end of the text.

1.3 Master Planning of Landscape and TSE Irrigation Systems

1.3.1 Landscape Development Master Plan

The following sections deal with the planning and

design of treated sewage effluent (TSE) distribution

networks including pumping stations and reservoirs,

for ultimate use in downstream irrigation systems.

The only purpose of this infrastructure and the related

irrigation installations discussed here, is the supply of

TSE for application to vegetation. Therefore, it is

necessary to provide an overview of the broader

landscape and planning context that the TSE

distribution infrastructure will serve.

Assessing the requirement for amenity landscape,

planning and design are the concern of other

professions. This is undertaken by town planners,

landscape architects and urban designers working

within their own professional fields, following client

requirements and design guidelines that are outside

the scope of a sewerage and drainage manual.

However, the utilities engineers and their teams are

very much concerned with quantity, quality and

applications of irrigation water for these areas, so

that the necessary infrastructure can be provided.

In this respect, knowledge of landscape planning is

necessary for TSE engineers.

A landscape master plan provides a strategic

framework for development within the urban and

surrounding environment. Preparation of a

landscape master plan is a significant step to

ensuring that the finished development will be fit for

purpose. It enables co-ordination of the physical

built environment, with human recreational and

amenity needs, climatic and environmental

considerations, and a broader concept of the urban

landscape structure. It is also one of the most

important inputs in the establishment of irrigation

budgets and will be the basis for planning and

engineering of the irrigation distribution networks

and associated equipment.

1.3.2 Irrigation Budgets

The purpose of establishing irrigation budgets is to

ensure that the available resources of irrigation

water are apportioned so that the needs of future

and existing landscape areas can be satisfied. The

objective is to avoid both shortages and wastage,

so that the water needs of the vegetation can be

assured.

The starting point for setting the irrigation budgets

is to consider the total available quantity of

irrigation water, and also, the Landscape

Development Master Plan that defines the overall

distribution of land use. Division of the Landscape

Development Master Plan into irrigation sectors is

necessary so that budget irrigation quantities can

be allocated to each sector. Irrigation sectors will

not necessarily correspond to town planning

sectors. In case there is already an adequate

existing infrastructure for effluent distribution, this

will help to define a sector’s extent and water

allocation. Hydraulic capacity of the existing

networks affecting the available water flows and

pressures may be constraints on water availability

within a sector, and therefore these need careful

analysis.

The irrigation budgets therefore simply provide a

peak daily irrigation volume for each sector over

time. They may be adjusted from time to time as

necessary within the overall TSE availability, and

according to any hydraulic and storage constraints.


Page 2 Volume 4 TSE System Design 1st Edition June 2005 - Copyright Ashghal

The irrigation budgets may highlight issues related to

supply that will be dealt with by the Irrigation Master

Plan (see section 1.3.3), and they will also provide

essential guidance to the landscape designers for the

quantities and types of vegetation that can be

sustained within each budget sector.

1.3.3 Irrigation Master Plan

The Irrigation Master Plan derives from the

Landscape Development Master Plan and the

irrigation budgets, but needs to address a broader

range of issues concerning irrigation supply. The

objective of the irrigation master plan is to study and

identify specific issues related to the supply and

distribution of irrigation water. It will also make

recommendations, for example regarding future

infrastructure requirements, or matters related to

irrigation water quality (refer to.1.4 below). The

Irrigation Master Plan should also contain a time-

scale or outline programme for execution of any

proposed projects, co-ordinated with expected urban

growth, future effluent availability, and the proposed

implementation of landscape projects.

Examples of typical recommendations that will be

made in the Irrigation Master Plan may include the

following:

• Requirements for new irrigation infrastructure;

• Recommendations for upgrading or

refurbishing of existing effluent distribution

networks, storage reservoirs, pumping

stations etc.;

• Proposals for control and telemetry

installations (e.g. SCADA);

• Proposed measures related to irrigation water

quality (salinity, chemical quality, and

filtration);

• Recommendations related to existing use of

irrigation water, e.g. for improving efficiency,

or upgrading the irrigation systems;

• Operational issues related to existing

irrigation infrastructure.

1.4 Irrigation Water Quality

1.4.1 General

Irrigation water quality is an issue of primary

concern wherever TSE is the source of irrigation

water for public amenity landscape. There are two

main areas of concern. Firstly, the chemical and

biological properties of the irrigation water must be

such that its application on areas of publicly

accessible landscape presents negligible health

risk to members of the public, and in particular

those who by reasons of health or age may be

more susceptible to pathogens or chemical

contaminants. Secondly, the chemical, physical

and biological properties of the irrigation water

should be entirely suitable for plant growth and for

the irrigation system through which the water will

be applied, or at least do not impose undue

constraints on the type of landscaping possible.

1.4.2 Public Health Factors in Effluent Use

The potential risk to public health from wastewater

is generally assessed in terms of biological quality,

expressed as the ratio between biological oxygen

demand and total suspended solids (BOD:SS), and

also measured directly in terms of ‘most probable

number of coliform organisms’. Although there are

no internationally applicable standards for these

parameters, the World Health Organisation (WHO)

has recommended BOD and SS less than 10mg/l

and ‘most probable number of coliform organisms’

not to exceed 100/100ml.

Qatar proposes to adopt a standard of 5:5 for

BOD:SS. This standard would ensure minimal risk

to public health from TSE irrigation water.

However, although the final effluent from Doha

West STW is generally achieving 5:5, the final

effluent from Doha South STW has not been able

to achieve this standard. It may therefore be some

time before this could consistently be achieved in

practice.

Apart from biological impurities, chemical

contaminants in TSE can also affect human health.

The commonest chemical contaminants include

lead, nitrates, and carcinogenic organic

compounds. Since the problem is usually



associated with heavy industry, health issues related

to chemical contamination are less likely to be of

significance where the principal source of TSE is

domestic sewage.

The likelihood of human contact with irrigation water

can not be practically avoided in amenity landscape

areas. There are several possible means by which

pathogenic organisms from irrigation water could be

transferred to humans. The three most likely

methods are as follows:

• Bodily contact with irrigation water or soil;

• Breathing of air that contains fine droplets of

irrigation water;

• Consumption of contaminated food or drinks

sourced from TSE irrigated crops.

Picnicking on grass shortly after it has been irrigated,

or being in the immediate vicinity when sprinkler

systems are in operation are the most likely means

by which pathogens could be ingested. Bacteria may

survive in the soil for two months or even one year in

some cases, although sandy soils and high

temperatures tend to decrease survival times.

Ensuring that lawn sprinkler systems are scheduled

to operate in the early morning hours is a necessary

precaution. Exposure to irrigation water is less likely

with drip irrigation and bubblers as compared to

spray sprinklers.

It should be noted that specific health risk is related

to an individual’s threshold of susceptibility, and that

infants, elderly persons, and those having weakened

immune systems are the most susceptible. Even

with irrigation water of good biological quality, some

degree of health risk cannot be entirely eliminated,

and it is essential that special attention be given to

protecting those members of the public who may be

vulnerable. For this reason, the grounds of hospitals

should be irrigated with potable water, particularly in

those areas accessible to patients. For the same

reason, vegetation within the grounds of nursery

schools and primary schools needs also to be

irrigated with potable water.

1.4.3 Quality of TSE for Landscape Irrigation

Salinity is the single factor most commonly affecting

the suitability of TSE for use as irrigation water. Salt

is poisonous to plants. Even relatively low levels of

salinity can restrict quite severely the range of

plants that may be used, with consequences for the

landscape character and variety of landscape

design options. Furthermore, the problem of salt

accumulation in the soil is exacerbated by the high

water-table and poor drainage in many parts of

Doha.

Qatar proposes to adopt a standard for Total

Dissolved Solids (TDS) not to exceed 2,000mg/l

(equivalent to 3,500µmhos/cm). However, this

level of salinity is still sufficiently high to be

detrimental to many salt-sensitive plant species

and it would be highly beneficial if a lower figure

could be achieved. In fact, irrigation water having

TDS as low as 500-1,000mg/l is harmful to salt-

sensitive plant species. Actual TDS figures for

Doha West STW (for the period 21st – 28th Sept

2003) range from 1,311 to 1,411mg/l. On the other

hand, TDS levels for Doha South STW were rather

higher over this period, ranging from 1,372 to

2,492mg/l. Therefore in order to achieve a target

TDS of better than 2,000mg/l it will be necessary to

address the underlying problem of salinity in the

incoming sewage.

The suitability of TSE for irrigation purposes also

depends upon its chemical properties, including

sodium hazard, usually expressed as sodium

absorption ratio (SAR), and the levels of harmful

ions. SAR is calculated from the ratio of sodium to

calcium and magnesium. Continued use of

irrigation water having a high SAR leads to the

sodium being absorbed, causing the soil to become

hard and compact, and increasingly impervious to

water penetration. Leaching and soil additives,

particularly gypsum, are used to counter these

affects. Sandy soils with a low content of clay

particles are less likely to be affected by high SAR.

Figures for SAR of Doha South TSE are available

from the recent sampling analysis presented by the

Quality and Safety Division. The analysis results

indicate that the SAR values for the TSE from Doha

South are in the range of 4.5 to 5.0, which is 50%

of the acceptable long term limit for irrigation

(please refer to Table 1.4.1).

The effect upon plant growth of the levels of

different chemical constituents in irrigation water is

a complex subject and dependent upon a number

of variable factors. Each plant species has its own

tolerance threshold for each anion or cation, often



varying widely between species of the same genus.

Furthermore, sensitivity depends upon other factors

such as the nature of the soil. The pH and overall

chemical balance of the irrigation water also affect

the availability of different ions such as heavy metal

cations, which become more available to plants at

lower pH, i.e. at higher acidity levels. It can generally

be expected that the levels of heavy metal cations in

TSE from domestic sewage will be below toxic

thresholds.

1.4.4 Recommended TSE Quality for Landscape Irrigation

Table 1.4.1 provides interim recommendations for

TSE water quality criteria to be used for landscape

irrigation in Qatar. Proposed current and future

effluent discharge standards for Doha sewage

treatment works are provided in Table 1.4.2.

Contents of this table should be considered as

temporary standards, which will be modified by the

Environmental Section (ES) within Q&SD during

2004.

1.5 Documentation

Documentation required by the DA to be prepared by

consultants in relation to TSE system design is

described in Volume 1 Section 5.

1.6 Environmental Impact Assessment

The State of Qatar policy on sustainable

development and subsequent environmental

legislation (Law 30)1 requires that an environmental

impact assessment (EIA) process be followed in

planning, designing and implementing TSE system

projects. Consultation with the regulator, SCENR,

the Planning Department, and the Department of

Agriculture and Water Resources, throughout the

process, is a critically important activity.

Initial screening and scoping of potential

environmental impacts should be reviewed by the DA

before submitting to SCENR, the Planning

Department and the Department of Agriculture and

Water Resources.

Guidance on typical content and requirements of

screening, scoping, EIA analysis, reports and data

collection is given in Volume 1, Sections 2.7, 3.7

and 4.7. This guidance should be referred to for

any environmental studies associated with TSE

system projects. Volume 5, Section 1.10 also

provides useful guidance information on the reuse

of treated sewage effluent.

1.7 Building Permit

The requirements for application for building

permits are described fully in Volume 1 Section 4.6.



Table 1.4.1 - Recommended Quality Standards for TSE Irrigation Water in Qatar (Interim)

Parameter Units

Recommended Limit for Irrigation

Remarks Long Term

Short Term

TDS mg/l 500 2000 Lower than the standard of 2000mg/l proposed for Doha - see text above

EC µmho/cm 1500 - As for TDS

PH units 6.0 - 7.0 - Significant indirect effects on plant growth

SAR ratio 10.0 - See text above

BOD (5d @ 20°C)

mg/l 5.0 5.0 According to proposed new standard for Doha

SS mg/l 5.0 5.0 According to proposed new standard for Doha

Total coliforms No/100ml 100 100 Based on WHO recommendation

Ca mg/l - - No recommended limit, toxic to calcifuge plants

Mg mg/l 150.0 ‡ - Minor plant nutrient

Na mg/l 400.0 ‡ - Major component of salinity

K mg/l - - Essential plant nutrient, no recommended limit

Total P mg/l 30.0 ‡ - Essential plant nutrient

N (as NH3) mg/l 1.0 - According to proposed new standard for Doha

N (as NO3) mg/l 50.0 ‡ - Nitrogen is essential plant nutrient

Alkalinity (HCO3 + CO3)

mg/l 200.0 - Affects soil pH

SO4 mg/l 400.0 ‡ - Not toxic to plants

Cl mg/l 650.0 ‡ - Major component of salinity

F mg/l 1.0 * 15.0 * Inactivated by neutral and alkaline soils

Al mg/l 5.0 * 20.0 * Only toxic in very acid soils

As mg/l 0.1 * 2.0 * Toxic to many plants at varying concentrations

B mg/l 0.75 * 2.0 * Essential nutrient, but toxic if too high

Fe mg/l 5.0 * 20.0 * Nutrient but at high levels affects soil chemistry

Cd mg/l 0.01 * 0.05 * Toxic to some plants at low concentrations

Co mg/l 0.05 * 5.0 * Toxic to some plants in acid soils

Be mg/l 0.1 * 0.5 * Toxic to many plants at varying concentrations

Cr mg/l 0.1 * 1.0 * Toxicity to plants is not well established

Cu mg/l 0.2 * 5.0 * Toxic to a number of plants

Cn mg/l 0.05 ‡ 0.1

‡

Mn mg/l 0.02 * 10.0 * Toxic to some plants at low concentrations

Se mg/l 0.02 * 0.02 * Toxic to plants at low concentrations

Pb mg/l 5.0 * 10.0 * Can be toxic to plants at high concentrations

V mg/l 0.1 * 1.0 * Toxic to many plants at low concentrations

Mo mg/l 0.01 * 0.05 * Not normally toxic to plants

Ni mg/l 0.2 * 2.0 * Toxic to some plants in acid soils

Zn mg/l 2.0 * 10.0 * Toxic to many plants at varying concentrations Source: ‡ Based on wastewater quality limits adopted by Sultanate of Oman * USEPA guidelines, cited by Rowe and Abdul-Magid in “Wastewater Reclamation and

Reuse”



Table 1.4.2 - Effluent Discharge Standards Available in Doha

Standard Effluent Criteria Current

Standard Future Standard

Basis of

Compliance

Suspended solids (SS) 5mg/l 5mg/l 90 %ile

Biochemical Oxygen Demand (BOD) 5mg/l 5mg/l 90 %ile

Chemical Oxygen Demand (COD) 50mg/l 50mg/l 90 %ile

Faecal Coliforms (MPN) None Detected /100ml

None Detected /100ml

90 %ile

PH 6-9 6-9 90 %ile

Ammonia (NH3N) 1mg/l 1mg/l 90 %ile

Phosphate (PO4) 1mg/l 1mg/l 90 %ile

Total Nitrogen (N) 10mg/l 5mg/l 50 %ile

Dissolved Oxygen 2mg/l (min) 2mg/l (min) 90 %ile

Chlorine (Free Residual) 0.5 – 1mg/l 0.5 – 1mg/l 90 %ile

Turbidity 2NTU 2NTU 90 %ile

Total Dissolved Solids (TDS) <2,000mg/l <500mg/l 90 %ile

Intestinal Nematodes <1.0 per litre 0.0 95 %ile

Enteric Viruses <1.0 PFU/40 litre <1.0 PFU/40 litre 90 %ile

Giardia <1.0 cysts per 40 litre

<1.0 cysts per 40 litre

90 %ile



2.0 Design of TSE Transmission and Distribution System

2.1 Definitions

A TSE transmission and distribution system

comprises: TSE storage reservoirs at the source;

pumping stations; transmission and distribution

mains; and chambers.

A TSE storage reservoir is a covered reservoir of

relatively large capacity and can be at ground level,

underground or elevated (water towers).

A pumping station is an installation designed to

provide adequate pressure and flow within the

transmission and distribution system. A transmission

main (or trunk main) is used to convey the majority of

the flow from the source, treatment and/or storage

facility to the distribution system.

A transmission main may have a small number of

connections on it, but in general, is intended to

deliver water to the distribution mains where the

majority of distribution points are located. In the Doha

irrigation system, a transmission main is usually a

large diameter pipe of 600mm diameter and above.

Examples of transmission mains in Doha are the

800mm diameter main from Doha West to TSE2 and

the twin 800mm diameter mains from Doha South to

Al Rakhia Farm.

A distribution main is the delivery system to the main

distribution chambers located at certain intervals

along main roads, and giving feed directly to irrigation

systems or to local reservoirs feeding such systems,

if applicable. In the Doha irrigation system, a

distribution main is usually a pipeline of 200mm

diameter and above.

A transmission main or a distribution main can be

either pressurised under gravity or pumped.

2.2 Standards and Sources of Information

In general the TSE transmission and distribution

system should be considered in the same way as any

potable water system and, therefore, the same

standards and guidelines are applicable.

A list of general standards and references

pertaining to design is set out below but is not

limited to:

• British Standards Institution, 1989, BS

8010-1:1989 - Code of practice for

Pipelines, Part 1: Pipelines on land:

general, London BSI.


EN 805:2000, Water supply -

Requirements for systems and

components outside buildings, London,

BSI.


EN 1508:1998, Water supply -

Requirements for systems and

components for the storage of water,

London, BSI.

• Tyson A., and Harrison K, Irrigation for

Lawns and Gardens, Extension

Agricultural Engineers, The University

of Georgia College of Agricultural &

Environmental Sciences.

• Water Authorities Association/Water

Research Centre, 1989, Network

analysis - A code of practice,

Swindon,UK, published by WRC.

• Water Research Centre, 1995, Pipe

materials selection manual - water

supply, 2nd edition, UK, Water

Research Centre.

• Construction Industry Research and

Information Association, 1994, Guide to

the Design of thrust blocks for buried

pressure pipelines, Report 128, London

CIRIA.

• HR Wallingford and DIH Barr, 2000,

Tables for the Hydraulic Design of

Pipes, Sewers and Channels, 7th

Edition, Trowbridge, Wiltshire, UK

Redwood Books.

• T.M. Walski, D.V. Chase, D.A. Savic,

2001, Water Distribution Modelling, 1st

edition, Waterbury USA, Haestad Press

Inc.



• A.C. Twort, D.D. Ratnayaka, M.J. Brandt,

2000, Water Supply, 5th edition, UK, Arnold

and IWA Publishing.

• Washington State Department of Health,

2001,Water System Design Manual,

Washington, State Department of Health.

Standards and manuals pertaining to specific pipe

materials and construction issues are quoted in the

relevant sections of this volume.

2.3 Principles of Design

In general, the Doha Irrigation System is evolving

towards a system of pressurised ring mains, whereby

irrigation water feeds the secondary and tertiary

(application) system directly without recourse to

intermediate storage and/or booster pumping

stations. However, there are cases where local

reservoirs and booster pumping stations would be

necessary. This would mainly be in areas having

specific landscape and irrigation requirements like

golf courses, university campuses, parks and other

amenity areas. In all such cases, it is reasonable to

provide a suitable feed off the distribution system and

leave the downstream arrangements, including local

storage and pumping facilities, to the

owner/developer of the land. Effluent allocation for all

such specific places should be established in

conjunction with: the overall irrigation strategy for the

city; assessment of available resources; and the

irrigation water budget established by the DA in

particular. In order to ensure that only the allocated

amount of TSE is used, the inflow rate should be

monitored by flow meter and controlled by a

motorised valve installed on the inlet to each local

reservoir. All proposed extensions to the irrigation

transmission and distribution system should be

designed in a way that the system provides for the

demand and pressure conditions anticipated at any

given time in all parts of the system.

2.4 Sizing and Flow Estimation

Sizing of irrigation mains should consider a number

of factors including pumping cost, land use, system

demand, friction losses, and flow velocities. These

factors are interrelated and their relative influences in

the selection of optimum piping arrangements should

be recognised. As a whole, transmission and

distribution mains, TSE sources, pumping

facilities, and storage facilities must be

designed so that, in combination, they will

optimize the TSE system.



Hydraulic calculation should be carried out in order to

demonstrate that the system will:

• Satisfy the estimated demand;

• Operate within the required pressure range;

• Operate at acceptable velocities.

Network analysis by a computer–based mathematical

model should be used to analyse the performance of

the existing system and proposed extensions to that

system. Models representing both transmission and

distribution mains are required to assess system

performance under a variety of supply and operating

conditions. A model would include elements

representing physical components of the irrigation

system like pipes, pumps, valves, regulators and

tanks that make up the actual network. The usual

input data for any hydraulic model includes: pipe

diameter and length; friction factor according to the

formula which is applied; node elevation; ground

elevation; pump curve or pump energy if the curve is

unknown; pump speed; tank profiles; upstream and

downstream pressure for regulators; valve status;

and flow coefficients. As an output, the model will

produce predicted flows, velocities, pressures and

head losses, which will indicate the network

performance. The results are then a basis for either

increasing or decreasing pipe diameters, adding new

pipelines or replacing pumps etc.. Hydraulic analysis

and computer models are discussed in Section 2.6.

The latest hydraulic model of the Doha irrigation

system was created using SynerGEE, and that model

should be referred to before starting any further

analysis.

Sizing Procedure

Procedures for sizing distribution and transmission

mains for irrigation systems have been established in

many engineering textbooks, reference books, and

design manuals. There are also many

computer software packages readily available

to aid in the design of complex systems. Apart

from the above mentioned SynerGEE

(Advantica) other reputable software include

InfoWorks (Wallingford Software), InfoWater

(MWH) and WaterCAD (Haestad Methods). It is

expected that the design procedures used for

the irrigation system of Doha will be consistent

with those widely applied and accepted by

professionals world-wide as good engineering

practice.

The sizing procedure shall include the following

steps:

1. Establish demands and flows

2. Assume pipe diameters

3. Carry out hydraulic analysis

4. Correct the assumed pipe diameters,

as necessary

5. Carry out final hydraulic check

Minimum Size

The minimum size for a transmission or

distribution main should be determined by

hydraulic analysis. In general, the minimum

diameter of all distribution mains should not be

less than 200mm internal bore. All sizes are to

be metric sizes. Recommended flow rates,

velocities and corresponding head losses for

different pipe diameters are shown in Tables

2.4.1. and 2.4.2. These examples are for pipes

with an assumed hydraulic roughness factor ks

of 0.15mm and 0.06mm.

Table 2.4.1 - Recommended Flows, Velocities and Resulting Head Losses for Various Pipe Diameters (ks

0.15 mm)

Diameter

(mm)

Flow (l/s) Velocity (m/s) Head loss (m/km)

From To From To From To

200 16 29 0.5 0.9 1.3 4.1

250 29 48 0.6 1.0 1.3 3.5

300 48 72 0.7 1.0 1.3 3.1



400 99 137 0.8 1.1 1.3 2.5

450 137 177 0.9 1.1 1.3 2.2

500 177 252 0.9 1.3 1.3 2.6

600 252 357 0.9 1.3 1.0 2.0

800 524 707 1.0 1.4 1.0 1.8

900 707 900 1.1 1.4 1.0 1.6

1,000 900 1,200 1.1 1.5 0.9 1.6

1,200 1,200 1,800 1.1 1.6 0.7 1.4

Table 2.4.2 - Recommended Flows, Velocities and Resulting Head Losses for Various Pipe Diameters (ks

0.06 mm)

Diameter

(mm)

Flow (l/s) Velocity (m/s) Head loss (m/km)

From To From To From To

200 16 29 0.5 0.9 1.1 3.5

250 29 48 0.6 1.0 1.1 3.0

300 48 72 0.7 1.0 1.2 2.6

400 99 137 0.8 1.1 1.1 2.1

450 137 177 0.9 1.1 1.2 1.9

500 177 252 0.9 1.3 1.1 2.2

600 252 357 0.9 1.3 0.9 1.7

800 524 707 1.0 1.4 0.8 1.5

900 707 900 1.1 1.4 0.8 1.3

1,000 900 1,200 1.1 1.5 0.8 1.4

1,200 1,200 1,800 1.1 1.6 0.5 1.2



Sizing of Gravity Mains

While sizing gravity mains, one must consider the

actual hydraulic gradient and the pipeline profile, and

make sure that the hydraulic gradient does not fall at

any point below the crown of the pipe. In certain

circumstances, the hydraulic gradient may be below

that level. In theory, up to 7m would be acceptable,

but it is recommended not to exceed 2 - 3m at the

critical point, providing that adequate air

release facilities are available to assist in

the air evacuation and pipe self-priming.

Such a gravity main will then work under a

siphon condition. Refer to the attached

Figures 2.4.1 and 2.4.2 from the

“Rationalisation of the TSE system report”2

for examples of land elevation versus

hydraulic grade (HGL).

Figure 2.4.1 – Example of land elevation versus hydraulic grade (HGL) where HGL cuts the land elevation

under a flow of 650L/s due to high losses – not desirable.



Figure 2.4.2 – Example of land elevation versus hydraulic grade (HGL), where HGL lies above the land

elevation under a flow of 550L/s - acceptable.



Peak Demands

The peak demands in an irrigation water system are

directly related to the type of landscape and irrigation

pattern. The irrigation pattern includes the irrigation

timing and irrigation rates. They are both subject to a

seasonal variation, meaning that more irrigation

water will be required in summer than in winter. The

irrigation scheduling should aim to achieve a

reasonably constant demand over the operating cycle

of each irrigation system.

It has been established in the “Rationalisation of the

TSE system report”2 that in the time of the peak

summer demand, the system would work for 12 to 16

hours and that the peak hourly demands should not

exceed 2000-2200l/s. Otherwise, the level of service

and pump efficiency would be compromised. The

maximum flows given above are based on the

assumption that the new pumping and storage

facilities PS TSE1 and PS TSE2, as proposed in the

conceptual design report, are in place.

Distribution pipelines should be able to sufficiently

deliver water to meet “worst case” peak hourly

demands at the required water head.

Minimum Distribution System Pressure

The distribution system should, in general, be able to

provide peak flows at no less than 30m water head

(300kPa), as agreed with the DA in the course of

writing the “Rationalisation of the TSE system report

2”. As various types of sprinklers and drip emitters

require different pressures, the actual requirements

for a given landscape area should be provided by the

designer of the downstream irrigation system. In case

the irrigation water is discharged into a local irrigation

reservoir, then the required pressure would be

governed by the level of the inlet pipe.

Maximum and Minimum Flow Velocity

In normal circumstances it will be desirable to avoid

unduly high or low velocities. A range from 0.5m/s to

2.0m/s under hourly peak demands may be

considered appropriate. However, in special

circumstances, velocities up to 2.5m/s may be

acceptable in the main trunk and distribution

pipelines. For pumping mains, a financial appraisal

should be undertaken to determine the most

economic diameter of pumping main, to minimise the

capital cost and discounted pumping cost. The

resulting velocity will normally lie in the range of

0.8m/s to 1.4m/s. An important consideration is

surge, which becomes more problematic at

higher velocities.

Excess Pressure

The type of pipe used and the pressure

requirements of the system are significant factors

to take into account when designing an irrigation

main. Excessive pressure in a system can lead to

wasted water, and increase the risk of pipe

failure. In general, the pressure in the system

should not exceed 600-700kPa (60-70m water

head).

Surge and Transient Controls

Hydraulic surges and transients (water hammer)

are dependent on a number of factors, including

main size, length, profile, and materials of

construction. Analysis of transient conditions is

discussed in section 2.8.8. Pipe pressure tests

and thrust restraint should be based on the

maximum transient conditions, including an

appropriate factor of safety.

There are a variety of ways to provide surge

control. Methods include:

• Open surge tanks;

• Pressurised surge tanks;

• Surge anticipator valves;

• Vacuum relief valves;

• Regulated air-release valves;

• Optimising main size and alignment;

• Electric soft start/stop and variable speed

drives for pumps;

• Electric interlocks to prevent more than

one pump from starting at the same time;

• Slow opening and closing valves; and

• Increasing the polar moment of inertia of

the rotating pump/motor assembly.

A combination of methods may be necessary and

care must be taken in the design so that the

addition of a protection device does not cause a

secondary water hammer equal to or worse than

the original design could cause.



Reliability of the surge protection facility is important.

Where appropriate, redundancy should be provided

for essential equipment such as vacuum relief valves.

Adequate alarms should be provided on surge tanks

and similar components to give operators early

warning. Consideration should be given to

preventing the pumping system from operating if the

surge protection facilities are not operable.

Surge suppression should always be provided where

modelling predicts negative pressure in excess of the

following:

GRP, cement lined DI -1metre

Fusion bonded epoxy, ceramic epoxy or

polyurethane lined DI -3 metres

HDPE, MDPE -3 metres

2.5 Pipeline Materials

The existing TSE transmission and distribution

system consists mainly of ductile iron (DI), glass

reinforced plastic (GRP), asbestos cement (AC) and

polyvinyl chloride (PVC) pipes. Preferred materials

for new pipelines are DI or polyethylene (PE). PVC

should not be used on account of its susceptibility to

UV damage. It is known that PE is also susceptible to

UV damage, but to a lesser degree, and it is also

more generally robust AC is not permitted to be used

for new pipes on account of health risks.

Due consideration should be given to internal and

external corrosion. Protection from external corrosion

should be employed in areas where corrosive or

contaminated soils are prevalent, or when pipelines

leave the soil environment. This is especially true in

the coastal environment or other harsh environments.

Metal pipes should be evaluated for, and, if

appropriate, be protected against corrosion due to

stray electrical currents in the soil. This is most often

found when such pipes are near, or cross other

pipelines that are protected by impressed current.

The various materials used in the TSE systems are

discussed more fully in Volume 1 Section 4.3.

2.5.1 Ductile Iron Pipes

Ductile iron pipes and fittings up to DN 2000 are

covered under BS EN 5453. Installation of DI pipes is

covered by BS 80104 Section 2.1.

Ductile iron pipes should be protected externally

in accordance with QCS. Internally as a

minimum cement mortar lining should be

provided. Fusion bonded epoxy, ceramic epoxy

and polyurethane are also suitable for internal

protection.

Ductile iron pipes can be considered as semi-

rigid. Bedding design should be in accordance

with the manufacturer’s recommendations.

Ductile iron pipes have flexible joints and require

thrust restraint at bends.

Recommended Use

DI pipes shall, in general, be used for

constructing transmission and distribution mains

of DN 400 up to DN 1600, for underground and

above ground applications. DI pipes smaller than

DN 400 are perfectly acceptable from the

technical point of view, however, may prove to be

less economical than their plastic equivalents. DI

pipes are also recommended for all pumping

stations regardless of the manifold diameter.

2.5.2 Polyethylene Pipes

Polyethylene pipes are covered by BS EN

12201(Draft European Standard)5, WIS 4-37-176

and a comprehensive reference is included in the

Manual for PE Pipe Systems, 2002 edition, by

Water Research Centre and British Plastics

Federation’s Pipes Group7.

The material used for their production shall be in

accordance with QCS. They are classified by

nominal outside diameter and Standard

Dimensional Ratio (SDR),which represents the

ratio between the nominal outside diameter and

the minimum wall thickness (SDR=OD/e). For

pressure applications and Doha climatic

conditions, a minimum of SDR 17 Class PE 100

only shall be considered. The nominal pipe size

range is from DN 90 to DN 1000.

The approved jointing method for PE is fusion

jointing (electrofusion and butt-welding). Fusion

jointing of PE pipes produces a fully restrained

pipeline string and therefore thrust blocks and

anchorages are normally not required. A typical

self bending radius for SDR 17 is 25 times the

pipe OD.



With the safety factor of 1.25 commonly accepted in

the water industry, the maximum continuous pressure

for a 50-year service life, and at 20ºC, is 16 bar for

SDR11 pipes and 10 bar for SDR 17 pipes. Where a

system is to be operated at temperatures in excess of

20ºC, then it must be de-rated in respect of the

maximum operating pressure or service life, or a

combination of both. For Doha conditions, the median

(TSE) temperature of 35ºC has been adopted, and in

order to maintain the service life of 50 years, the

maximum continuous operating pressure has been

reduced to 12.8 bar for SDR 11 pipes and 8 bar for

SDR 17 pipes.

Polyethylene pipes are flexible. They rely on the

bedding and surround for structural support and this

must be designed in accordance with the

manufacturer’s recommendations.

Recommended Use

In general, PE pipes shall be used for transmission

and distribution mains buried in the ground.

Maximum recommended pipe size is 710mm OD.

The determining factor for recommending this

maximum size is the availability of electrofusion

couplings, which not always can be substituted with

but welding. This may change in future thus allowing

larger pipe diameters to be used. A large selection of

HDPE fittings, injection moulded in particular, exists

for pipes of 315mm OD and smaller. For pipes above

450mm OD, the choice is limited and the available

fittings are only segment welded and machined.

PE pipes should not be installed in areas where there

is likely to be ground disturbance in the future as this

could lead to failure of the pipe surround.

2.5.3 GRP Pipes

GRP pipes shall comply with the QCS specification.

The design of the pipe will be undertaken by the pipe

manufacturer in accordance with the particular

requirements and the general specification.

GRP pipes are flexible. They rely on the bedding and

surround for structural support and this must be

designed in accordance with the manufacturer’s

recommendations.

GRP pipes have flexible joints and require thrust

restraint at bends.

Recommended use

GRP pipes are suitable for transmission

mains. They are available in diameters

from 80mm to 2.5m but for TSE should

be considered from 1000mm dia

upwards.

GRP pipes should not be installed in

areas where there is likely to be ground

disturbance in the future as this could

lead to failure of the pipe surround.

GRP pipes are easily damaged by

machinery such as diggers and jack

hammers therefore if future construction

work nearby is envisaged caution should

be exercised in their use.

2.5.4 Asbestos Cement Pipes (Safety Note)

As stated in Volume 1, AC is no longer

acceptable for use in Qatar. However, workers

may encounter existing AC pipes when making

modifications to the system. Wherever this is

likely, the designer must include the handling of

these pipes in the design HARAS, and make not

in the Health and Safety Plan for the project in

order to protect the workers from associated

health risks.

2.6 Hydraulic Analysis

Facilities are usually sized using a hydraulic

analysis to evaluate the design under various

flow regimes. It is expected that a computer

software package will be used for distribution

systems with more than two loops. Manual

calculations are adequate for simpler analyses.

Energy losses, also called head losses, are

generally the result of friction along the pipe walls

and turbulence due to changes in streamlines

through fittings and appurtenances. There are

two head loss equations that are in common use:

Colebrook and Hazen-Williams.



Colebrook-White equation

1 2.51 ks ─── = -2 log (───── + ─────) √ λ Re√ λ 3.71 D

Equation 2.6.1 Re - Reynolds number

ks - roughness coefficient (mm)

λ - Darcy-Weisbach non-dimensional friction factor

D - pipe diameter (m)

For ks values for various pipe materials refer to Table 2.6.1.

Hazen-Williams equation

6.78L HL = ──── (V/C) 1.85 D1.165

Equation 2.6.2 HL - friction loss (m of liquid)

C - coefficient

L - length of pipe (m)

V - average fluid velocity (m/s)

D - pipe diameter (m)

For C values for various pipe materials refer to Table 2.6.2.

First estimates of pipe friction values are

obtained directly from standard tables using all

readily available information on pipe material,

size, age and internal bore condition. These pipe

friction values are refined during the model

calibration process.

Head losses also occur at valves, tees, bends,

and other appurtenances within the piping

system. These losses, called local head losses or

minor head losses, are calculated using the

following equation:

HL = KV2/2g

Equation 2.6.3

For typical values of K coefficient refer to Table

2.6.3.



Table 2.6.1 - Colebrook-White KS-Factors for Various Pipe Materials

Type of Pipe Ks (mm)

Good Normal Poor

Old tuberculated irrigation main

Slight degree of attack 0.6 1.5 3

Moderate degree of attack 1.5 3 6

Appreciable degree of attack 6 15 30

Severe degree of attack 15 30 60

Galvanised iron 0.06 0.15 0.3

Epoxy or polyutherane coated ductile iron 0.03 0.06 0.15

Asbestos cement 0.015 0.03

Spun cement-lined (e.g. cement-lined DI) 0.03 0.1

MDPE or HDPE 0.06

Glass reinforced plastic (GRP) 0.06

PVC (with spigot-socket joints @6-9 metres intervals

0.06

Table 2.6.2 - Hazen Williams C-Factors for Various Pipe Materials

Type of Pipe Pipe diameter(mm)

25 150 300 600 1200

Coated cast iron (smooth and new) 133 138 140 141

30 years old

Slight degree of attack 106 112 117 120

Moderate degree of attack 90 97 102 107

Appreciable degree of attack 70 78 83 89

Severe degree of attack 50 58 66 73

60 years old

Slight degree of attack 97 102 107 112

Moderate degree of attack 79 85 92 96

Appreciable degree of attack 58 66 72 78

Severe degree of attack 39 48 56 62

Galvanised iron (smooth and new) 120 133

Epoxy or polyutherane coated ductile iron 129 142 145 148 148

Coated asbestos cement (smooth and new) 149 150 152

Spun cement-lined (clean) 149 150 152 153

Smooth pipe (including lead, copper, PE and PVC; clean)

140 149 150 152 153



Table 2.6.3 - Local Loss Coefficient for Common Fittings

Type of Fitting K value Entrances

Standard bellmouth 0.1

Pipe flush with entrance 1

Pipe protruding 1.5

Sluice gated or square entrance 1.5

Bends 90˚

Medium radius (R/D=2 or 3) 0.5

Medium radius (mitred) 0.8

Elbow or sharp angled 1.5

Bends 45˚

Medium radius (R/D=2 or 3) 0.25

Medium radius (mitred) 0.4

Elbow or sharp angled 0.75

Tees 90˚

In-line flow 0.4

Branch to line or reverse 1.5

Contraction-sudden

D2/D1=0.8 0.18

D2/D1=0.5 0.37

D2/D1=0.2 0.49

Contraction-conical

D2/D1=0.8 0.05

D2/D1=0.5 0.07

D2/D1=0.2 0.08

Expansion-sudden

D2/D1=0.8 0.16

D2/D1=0.5 0.57

D2/D1=0.2 0.92

Expansion-conical

D2/D1=0.8 0.03

D2/D1=0.5 0.08

D2/D1=0.2 0.13

Gate valve fully open 0.25

Gate valve 3/4 open 1

Gate valve 1/2 open 5.6

Gate valve 1/4 open 24

Butterfly fully open 0.5

Swing non return valve fully open 2.5

Globe valve fully open 10

Angle valve fully open 4.3



Computer Modelling of Irrigation

Networks

The concept of the network model is fundamental to

an irrigation distribution model. The network model

contains all of the various components of the system

and defines how those elements are interconnected.

Network models are comprised of nodes and node

connecting elements (links). There are different types

of nodal elements, including junction nodes where

pipes connect, tank nodes, pump nodes and control

valve nodes. Models use link elements to describe

the pipes connecting these nodes. Also, elements

such as valves, pumps and tanks are sometime

classified as links rather than nodes. The most

fundamental data requirement is to have an accurate

representation of the network topology, which details

what the elements are and how they are

interconnected.

A computer model is not necessarily an exact

representation of all pipes in the distribution system.

For large systems in particular, simplification of the

system (skeleletonisation) may be undertaken.

Methods of reducing the size of the model via

skeletonisation include:

(1) Consider only pipes above a certain size;

(2) Eliminate “tree type” pipe regions in the

system;

(3) Replace series and parallel pipes with

single equivalent pipes; and

(4) Analyse distinct, separate pressure zones

separately.

In all cases, the demands to the regions not modelled

can be shown at nodes (junctions) leading to the

region eliminated. Skeletonisation shall by no means

result from limitations caused by computer hardware

or software. All major modelling packages are

suitable for analysing unlimited number of elements.

There are two basic types of simulation: steady-state

simulation and extended period simulation (EPS).

The former computes the state of the system

assuming that hydraulic demands and boundary

conditions do not change with respect to time, whilst

the latter determines the quasi-dynamic behaviour of

the system over a period of time (a series of steady-

state simulations in which hydraulic demands and

boundary conditions do change with respect to time).

A computer model of the Doha irrigation system was

originally constructed using WATNET software and

then rebuilt using SynerGEE for Water, to suit the

new concept of direct supply eliminating the need for

water towers in the distribution system. The latter

model has not been calibrated as flow and pressure

readings were not available. The type of simulation

performed was a steady-state simulation. A demand

allocation was carried out for each node by assigning

relevant base flow (Q-base) for sprinklers and drip

emitters and applying demand profiles. An

assumption was made that the application system

operates for 12 hrs with drip emitters operating for 12

hrs and sprinklers for 6 hrs. Places having their

discrete irrigation systems, with service reservoirs

and pumping stations, were assumed to be fed in the

off-peak time.

While performing hydraulic analysis it is useful to

check the behaviour of the system by not only

applying fixed demands but also allowing free

discharge at points where water is delivered e.g. at

service reservoirs. That would allow identifying areas

of starvation and proposing appropriate zoning. It is

particularly important in areas of substantial ground

level variation.

Model Calibration

If a hydraulic analysis is to be carried out on an

existing system where values for pipe roughness are

uncertain and/or the location and operation of valves

or pipes in a system are not clear, some adjustments

to a hydraulic model may be necessary. The model

should be calibrated, such that the system pressures

predicted for certain conditions are in general

agreement with field measurements. The calibration

process is necessary if the computer model is

expected to provide accurate and reliable results.

For simulations over extended periods, comparisons

are made between the predicted and observed flow

rates, pressures, and tank water levels.

Deviations between the results of the model

application and the field observations may be caused

by several things, such as:

• Erroneous model parameters (pipe

roughness values and node demand

distribution);

• Erroneous network data (pipe diameters,

lengths, etc.);



• Incorrect network geometry (pipes connected

to the wrong nodes);

• Errors in boundary conditions (incorrect

pressure-regulating valve settings, tank water

levels, pump curves, and so on);

• Errors in historical operating records (pumps

starting and stopping at incorrect times);

• Equipment measurement errors (pressure

gauges not properly calibrated);

• Measurement error (reading the wrong values

from measurement instruments); and

• Field data collection error (e.g. moving too

quickly from one field point to another without

allowing the system to stabilize between

readings).

Elimination of errors will frequently require an

iterative process, especially for modelling larger

systems. Generally, very old and corroded

distribution systems, and water systems with little or

no information, particularly regarding water use, are

the most difficult to calibrate.

The number of nodes at which field measurements of

pressure are made to calibrate the model should be

at least 15% of the number of nodes in the network

model that may be progressively reduced to 10% for

models of 1000 nodes and more. This pressure

monitoring is in addition to field measurements of

flow and pressure at all source and abstraction points

to the system.

Criteria for Model Calibration

Models can be calibrated at one or more snapshot

conditions. For improved results, calibration can be

for a 24-hour simulation period.

The following guidelines (according to the WRc Code

of Practice for Network Analysis8) represent the

acceptable performance criteria against which

modelled flows and pressures should agree with

recorded field data.

Flows

(1) Modelled trunk main flows (where the flow

is more than 10% of the total demand) ±5%

of measured flow.

(2) Modelled trunk main flows (where the flow

is less than 10% of the total demand)

±10% of measured flow.

Pressure

(1) 85% of field test measurement ±0.5m or

±5% of maximum head loss across system

whichever is greater.

(2) 95% of field test measurement ±0.75m or

±7.5% of maximum head loss across

system whichever is greater.

(3) 100% of field test measurement ±2m or

±15% of maximum head loss across

system whichever is greater.

If after detailed calibration, any points still do not

conform to the stated flow and pressure calibration

criteria, they should be reported as anomalies and

investigated.

The elevation of points to be used for field pressure

measurement should be determined by a field

levelling exercise (to within accuracy of ±25mm).

2.7 General Design Considerations

2.7.1 Pipeline Horizontal Alignment

Whenever practical and economic, the preferred

arrangements of ring systems with interconnected

branches should be employed. The use of linear

main arrangements with individual branch mains

should be restricted to simple extensions or

connections. The right-of-way will have to be

established and confirmed by the respective

authorities (refer to Volume 1 Foreword). Alignment

within the road allowance is shown in Standard

Details SR1 and SR2.

In order to minimise head losses, water transmission

pipelines should ideally follow a direct route and have

the minimum number of bends. Pipeline horizontal

alignments are largely constrained by the need to lay

the pipes along allocated service reservations.

Particularly at road interchanges, service

reservations will frequently deviate from the direct

route and additional bends may thus be required.

This is also applicable if avoidance of other



conveyance systems or obstructions is necessary.

Preferred angles for bends are 11º 15’, 22º 30’, 30º,

45º, and 90º.

Where pipelines must be laid around curves or small

changes of direction, the required alignment can be

achieved by angular deflection at joints or, if the pipe

is flexible, by bending the pipe itself. Product

standards, or the manufacturer, shall state the value

of allowable angular deflection at a joint, or pipe

minimum bending radius. The allowable angular

deflection will depend on the type of joint and the

pipe material.

The horizontal distance from foundations and other

pipeline or cable shall be not less than 0.40m in

normal circumstances. At points of congestion, a

distance of at least 0.20m shall be maintained except

where this distance cannot be achieved. In all cases,

suitable measures shall be taken to prevent direct

contact with obstructions. These measures shall be

agreed with the respective operators. There could be

cases where an operator has his own requirements

and those will have to be confirmed during the design

stage.

2.7.2 Pipeline Vertical Alignment

The vertical alignment of transmission pipelines is

determined by a number of factors:

• A minimum depth of cover;

• Avoidance of other buried utilities and

underground structures;

• A maximum depth of cover to limit the need

for ground dewatering;

• The need to pass through road crossings;

• To encourage the release of air liberated

during operation.

To provide protection to the transmission pipelines

and to avoid minor buried utilities, the minimum depth

of cover adopted is generally 1.2m.

Wherever cables and pipelines cross, a clearance of

at least 0.20m shall be maintained. If this is not

possible, measures shall be taken to prevent direct

contact.

The maximum depth of cover has been determined

by the need to pass under existing large utilities, such

as surface water drains. However, to minimise the

need for dewatering, the maximum depth of cover will

be limited to less than 3m wherever possible. This

will not apply to the non-disruptive road crossings

where a minimum cover of approximately 3m to the

sleeve pipe will have to be maintained to avoid

settlement.

High and low points in the pipeline must be created to

encourage air to accumulate and to be released at

the higher points. The minimum recommended

gradients between air release valves and low points

are 1:250 (4mm/m) on descending pipeline sections,

and 1:500 (2mm/m) on ascending pipeline sections.

2.7.3 Internal Pipe Pressures and Restraint of Thrust

Pipeline Design Pressure

In accordance with BS EN 805:20009 design

pressure (DP) is the maximum operating pressure of

the system or of the pressure zone, fixed by the

designer considering future developments, but

excluding surge.

Maximum design pressure (MDP) is the maximum

operating pressure of the system or of the pressure

zone, fixed by the designer considering future

developments, and including surge, where:

• MDP is designated MDPa, when there is a

fixed allowance for surge;

• MDP is designated MDPc, when the surge is

calculated.

For all pipelines, the system test pressure (STP) shall

be calculated from the maximum design pressure

(MDP).

Surge calculated:

STP = MDPc +100 kPa

Equation 2.7.1

Surge non calculated:

STP = MDPa x1.5

Whichever is the least STP = MDPa+500kPa

Equation 2.7.2

The design pressure (DP) of the Doha TSE

transmission and distribution system is 700kPa.

The fixed allowance for surge pressure included in

the MDPa shall not be less than 200kPa. Using this



figure the minimum system test pressure shall be

1350kPa (13.5 bar) and all the pipeline components

like line anchors, thrust blocks and other restraining

structures and joints shall be designed accordingly.

All flanges shall be rated to PN16.

Pipelines shall be designed to withstand a transient

pressure of 80kPa below atmospheric pressure

(approximately 20kPa absolute pressure).

Restraint of Thrust

Restraint shall be provided to prevent pipelines

moving under thrust arising from test and operating

pressures, including an allowance for surge effects.

The pipeline test pressure, being greater than any

operating pressure, will normally determine the thrust

restraint required as described above.

Out-of-balance thrusts, which must be restrained,

arise at bends in the pipelines, but there will also be a

requirement at other thrust points, such as closed

valves and branches, and blank ends. For pipelines

with joints which are not anchored by welded or

bolted flanges, etc, thrust blocks must be used. The

size and shape of a thrust block is decided by; the

force to be restrained, the size and type of the pipe

fitting, and local ground conditions. If adequate space

is not available, construction of piled thrust blocks, or

use of restraint piping systems should be considered.

2.7.4 Air Release

Mains shall be provided with facilities to release air

when the pipeline is being filled and also during

normal operation. On the other hand, it should be

possible to permit the entry of air during draining. At

each high point, a double-orifice air valve with a

separate isolating gate valve shall be installed. The

size of the air valve will normally be from DN 50 to

DN 200, depending on the main diameter, the

predicted flow rate of air, and the configuration of the

system. A general guideline for an air valve selection

is included in Table 2.7.1 below. The spacing of the

air valves should be such that it corresponds to a

maximum pressure drop of 0.3 bar in mains for a flow

rate induced by free flow for a given slope (sudden

break of a main). Reference shall be made to the

appropriate product standards for final valve selection.

Table 2.7.1 - Typical Double Orifice Air Valve

Selection

Pipe Size (mm) Air valve Size DN

(mm)

DN≤250 50, 65

DN 250 to 600 80, 100

DN 600 to 900 150

DN 900 to 1200 200

DN 1400 to 1800 2x200

The air valve assembly shall be installed in a

concrete chamber. For chambers, general

requirements, refer to section 2.7.6.

2.7.5 Pipeline Maintenance – Draining

Appropriate washout facilities, depending upon local

conditions, shall be provided according to operational

requirements for draining and flushing. The size of

the washout shall be related to the volume of water to

be drained, the time available and the capacity of the

receiving watercourse. The discharge diameter

should not normally exceed DN 200.

The wash out assembly will include an invert-level

tee and a gate valve housed in a chamber. The

discharge should be connected to a drainage system.

For chambers, general requirements, refer to item

2.7.6.

2.7.6 Isolation Valves

General Requirements

The location of isolating valves (shut-off valves) shall

be planned to facilitate shut-off in an emergency, for

maintenance, repair, replacement, or additions.

Isolating valves should be installed on all branches,

as close as possible to the through main.

The distance and location of isolation valves should

be fixed according to local conditions. In general, the

intervals between isolation valves should not exceed:

• in trunk mains (transmission mains)- 5km

• in principal distribution mains - 2km

• in secondary distribution mains - 0.5-1km

In general, on mains up to and including DN 600,

gate valves should be used for isolating purposes.

For mains larger than DN 600, butterfly valves should

be considered. Gate valves larger than DN 400 must



be equipped with a by-pass to overcome the problem

of opening a valve against unbalanced heads. It is

also acceptable for the gate valve to be between five-

eighths to three-quarters of the size of the pipeline. In

such cases properly designed tapers should be used

to minimise the head losses.

Unlike butterfly valves, gate valves are not intended

for controlling the rate of flow of water through a pipe.

Valve Operation

For manually operated valves, extension spindles

must be arranged to run in brackets, rigidly attached

to the chamber walls. These extension spindles

should be fabricated to the exact length required to

allow easy operation from the top of the valve

chamber using a standard tee key. Clockwise rotation

of the tee key to close the valve is preferred. Where

frequent opening and closing of a valve is required,

such valves should be fitted with electric actuators.

Valve Chambers

All valves should be placed inside purpose built

chambers. Siting of chambers in carriageways

should be avoided; they should be preferably in the

road verge or in the footway.

Two flexible joints, with a “rocker pipe” should be

provided on either side of the chamber to avoid

damaging pipework in case of differential settlement.

Such joints are not required in the case of PE pipe

which is flexible in itself.

In a stop valve chamber, the valve should be

anchored on the upstream side, having a flange

adapter on the downstream side which permits the

valve to be removed. The chamber construction

should facilitate lifting out the valve.

In cases where non-restrained pipe systems are

used, the chamber must be designed to take the full

thrust when the valve is closed. There should be

sufficient working space and clearances inside valve

chambers, proper access arrangements and gravity

ventilation by employing vent pipes. Those general

requirements are applicable for all other valve

chambers i.e. wash-out chambers, air valve

chambers and other valve chambers.

All pipework within valve chambers should be ductile

iron and the transition from one type of pipe material

to another should be made directly outside the valve

chambers.

Access Covers

Access covers should meet the requirements of BS

EN 12410. In general, the following classes of DI

covers will be applicable:

• CLASS D400 - heavy duty, for streets and

roads;

• CLASS C250 - medium duty, for sidewalks,

gullies, parking areas accessible for lorries;

• CLASS B125 - light duty, for sidewalks,

parking areas only accessible to passenger

cars.

The covers should preferably be medium duty, unless

they are subject to vehicular traffic. Wherever

appropriate, Aluminium covers with locking devices

shall be used, e.g. in grassed areas.

2.7.7 Flow Metering and Remote Sensing

Flow Instruments

For monitoring consumption and checking leakage

and system losses, it is desirable to install permanent

meters on the flows from sources, pumping stations

and reservoirs, and on the flows to zones, direct feed

areas and local reservoirs. In general,

electromagnetic flow meters should be used in the

TSE transmission and distribution system. In some

circumstances, ultrasonic devices may be considered

e.g. where a retrofit is required. Standard

electromagnetic flow meters require pipes to run full

bore and also require a specific straight length of pipe

downstream and upstream of the flow meter. Table

2.7.2 provides a summary of available flow

instruments and their basic parameters.

In general, flow meter locations should facilitate day

to day system monitoring, and network model

calibration, as discussed in section 2.6. Flow meters

outside pumping station buildings, and associated

data loggers, should be housed in suitable,

underground concrete chambers.



Table 2.7.2 - Summary of Available Flow Metering Instruments and their Parameters

Instrument Accuracy Power Supply

Straight Pipe Length Required

Other Features

Magflow +/- 0.2 % External, sizes >500mm.

Battery, sizes

<500 mm

5 pipe diameters upstream

3 pipe diameters

downstream

Can be direct buried

Insertion Magflow

+/- 2%

Battery or loop powered (from data logger)


5 pipe diameters

downstream

Good response on large flow ranges especially good at low flow rates

Ultrasonic (clamp on)

<2%

External


3 pipe diameters

downstream

Not suitable to be installed less than 20 pipe diameters down stream of a pump.

Not suitable to install in

concrete pipes

Ultrasonic (hot tap)

+/- 0.5%

External


3 pipe diameters

downstream

Not suitable to be installed less than 20 pipe diameters down stream of a pump.

Difficult to install in GRP

pipes



Pressure Instruments

Pressure sensing instruments are required in

pumping stations and across transmission and

distribution networks in locations as outlined below:

• On pump suction manifolds;

• On pump delivery manifolds;

• Upstream and downstream of control valves

(PSVs and PRVs);

• At major pipe junctions;

• Along transmission/distribution mains at

approximately 5km intervals.

In general, pressure transducer locations should

facilitate the day to day system monitoring and the

network model calibration as discussed in section

2.6. Pressure tappings outside buildings, and

associated data loggers, should be housed in

suitable concrete chambers. Refer to section 2.7.6.

Level Instruments

Level instruments are required for irrigation water

balancing and storage reservoirs at sources. They

should also be located at local reservoirs fed off the

primary distribution system.

Residual Chlorine

In the TSE main pumping stations, the residual

chlorine level should also be monitored. This can be

achieved by sampling the TSE at the discharge from

the pumping station. The local telemetry or SCADA

system should be programmed to raise an alarm if

the level drops too low. In some main pumping

stations, additional chlorine dosing equipment may

be required to increase the residual chlorine level

before the TSE enters the distribution system. It is

good practice to leave a chlorine dosing connection

point upstream of the residual chlorine monitor so

that if a problem were to arise in the future, a

temporary chlorine dosing plant could be quickly

connected in an emergency.

Salinity Meters

Salinity meters or conductivity meters are required

on the main inlets to the distribution system. These

meters give an output which is directly proportional

to the salinity of the TSE. This will be monitored by a

telemetry system to warn of an increased salt

content, which if left unresolved, could be

detrimental to the growth of plants. This system

would be in addition to any monitoring at the STW

and would be purely for the protection of plants.

2.8 Pumping Installations

2.8.1 Pumping Plant

Pump Types

The most suitable pumps for TSE are centrifugal

pumps as these are the only pumps which will

provide both the head and flow normally required.

Centrifugal pumps are available in a variety of

configurations using the same principle; a centrifugal

pump operates by passing the liquid through a

spinning impeller where energy is added to increase

the pressure and velocity of the liquid.

For high head duties, a pump can be constructed

with multiple impellers on a common shaft. Internal

passages are provided to direct the discharge from

each impeller to the inlet of the next; each impeller

increases the delivery head without increasing the

flow. These pumps are known as multistage pumps.

In a similar manner, two impellers can be arranged

back to back on a common shaft, each with a

separate suction but with both discharging to the

same outlet. The flow from each impeller is

combined, with no increase in head. These pumps

are known as double entry pumps.

Due to the impeller configuration, double entry

pumps have a casing constructed in two parts, split

along the shaft axis.

Large multistage pumps are often constructed in a

similar manner but they can also be constructed with

solid “stage casings” which are assembled along the

shaft, this is the common arrangement for the

smaller pumps. Other considerations include:

• Centrifugal pumps for TSE duties should

have closed impellers with close fitting

suction neck ring seals to minimise

discharge bypass;

• Single inlet pumps should have hydraulic

balancing within the pump to remove end

thrust;



• Large centrifugal pumps should have a

maximum running speed of 1450rpm (4 pole

motor) while smaller low flow pumps

typically have an operating speed of

2900rpm (2 pole motor).

Performance Characteristics

Centrifugal pump performance will be dependant on

both the head and flow, as the head increases the

flow will decrease, and vice-versa.

Each type of centrifugal pump will have a different

performance characteristic according to the design

of the impeller and casing. Works testing of a pump

by accurately measuring the delivery against various

heads will give a series of performance curves

including absorbed power and efficiency.

When selecting any centrifugal pump for a specific

duty the performance curves should be examined

closely for the power consumption and efficiency at

both the designed duty and the operational

extremes.

The selected centrifugal pumps should have a

performance curve as flat as possible in the duty

area with the minimum drop in head as the flow

increases.

NPSH, Vibration, Cavitation and Noise

Net Positive Suction Head (NPSH) is the minimum

total pressure head required in a pump at a

particular flow/head duty. It is normally shown as a

curve on the pump performance sheet.

NPSH is used to check an installation for the risk of

cavitation.

NPSH = Pa – Vp + Hs – Fs

Equation 2.8.1

Where:

Pa = atmospheric pressure at liquid free surface

Vp = vapour pressure of liquid

Hs = height of supply liquid free surface above eye

of pump impeller

Fs = suction entry and friction losses.

In order to avoid cavitation, the NPSH available

should be at least 1m greater than the NPSH

required by the selected pump.

When calculating NPSH, absolute values for

atmospheric and liquid vapour pressures are used.

Cavitation is the formation and collapse of vapour

bubbles in a liquid. Vapour bubbles are formed

when the static pressure at a point within a liquid

falls below the pressure at which the liquid will

vaporise. When the bubbles are subjected to a

higher pressure they collapse, causing local shock

waves. If this happens near a surface, erosion can

occur.

Cavitation will typically occur in the impeller of a

centrifugal pump, where it can cause noise and

vibration, as well as affecting the pump efficiency. If

allowed to persist it can lead to damage to the

pump, or even breaking away of foundations.

Pump Duty Point

Each pump has a performance curve where the flow

is plotted against head.

Each pipework system has a friction curve where

the friction head is plotted against flow.

The system curve is obtained by adding the static

head to the friction losses and plotting the total head

against the flow.

The pump duty point is where the pump

performance curve and the system curve cross. It

shows the flow that a particular pump will deliver

through the pipework system, at a particular total

head at the pump duty level. For examples of pump

and systems curves refer to Figure 2.8.1.

The duty point should be used when considering the

suitability of alternative pumps for a particular duty

by comparing the efficiency and power requirements

for each pump at the duty point.



Figure 2.8.1 – Characteristic Curve for Multiple Pumps



2.8.2 Plant Layout

TSE drywell pumping stations usually take their

suction from a storage tank. They do not need to be

directly attached to a wet sump.

The pumping station layout should be designed to

provide a flow route through the pumps and out to the

TSE distribution system with the minimum number of

bends and changes of direction.

The normal method of operation will be for the

storage tank to be filled at a steady rate, with the TSE

pumps being run for extended periods discharging

either directly to the TSE distribution system, filling

high level storage towers, or both.

For distribution duty, the pumps should be operated

under variable speed control to provide a constant

pressure under variable demands.

For storage tower filling, the pumps should be

operated at a constant speed, selected to fill the

tower at a particular rate.

A flow meter and pressure sensor should be installed

in the discharge manifold to record the flow and

control the pressure.

The pumps will usually be required to operate at

particular times, rather than on storage tank level

control. Level sensors should be installed in the

suction storage tanks to ensure priming, and prevent

loss of suction of the pumps. Level sensors should

also be installed in all storage tanks to avoid over

filling and spillage.

All pumps should preferably have variable frequency

drives and the control system should be designed to

start/stop, ramp up/down, adjust and match the

speeds of all running pumps as required on changing

demand, based on the system pressure.

Fixed speed pumps utilising a smaller jockey pump

and bladder type pressure vessel are an alternative

to the use of variable speed pumps particularly on

smaller systems. It is possible to omit the jockey

pump for off peak network pressurisation duty if the

pressure vessel volume is large enough to ensure the

main pumps do not repeatedly start and stop filling

the vessel under low flow conditions.

The control system should also be able to operate all

pumps at constant speed for tower filling.

Dry well design should incorporate the following

features:

• The pumps should be installed with sufficient

space between them to allow access for

maintenance and repair (minimum of 1m);

• The pumps should be arranged to draw from

and discharge to common manifolds;

• The common suction and discharge

manifolds should be located either side of the

pumps. The suction pipe should be recessed

at a lower level and may require an open

mesh walkway over it at floor level with the

individual pump suction connections rising up

through the covers. This solution is not

practical in all situations, for example

hydraulic considerations such as NPSH

available may require that the suction

pipework be as simple and as straight as

possible. Whatever design is implemented, a

balance must be found between the

competing factors in dry well design. Each

design is different and requires a bespoke

solution;

• The common discharge manifold should be

designed to accommodate a magnetic flow

meter, automatic filters and disinfection

requirements;

• Platforms and walkways should be provided

to permit access to all equipment at a suitable

level for safe operation, maintenance and

repair;

• Craneage should be provided for the removal

of all pumps, and valves 450mm dia and

over.

• Careful thought should also be given to the

shipping route for removing equipment;

• Access to the dry well and machinery should

be by staircase so that tools and equipment

can be carried in and out safely;

• The dry well floor should slope gently towards

one side wall and then to one end where a

sump pump should be installed to keep the

floor as dry as possible;

• The sump pump should be installed in a small

well, large enough to accommodate the pump

and should discharge to the drainage system;



• A high level alarm should be installed in the

dry well to give a warning of flooding before

damage to machinery occurs.

Pump Installation

Double entry pumps have the suction in the centre on

one side of the pump, with the discharge directly

opposite on the other side.

Multistage pumps have the suction and discharge at

the opposite ends of the pump. The suction can be

on the end or the side, the discharge is on the side

but can be in any direction relative to the suction.

Both pumps can be installed with the pump shaft

horizontal or vertical.

The most compact footprint arrangement is for the

pump to be installed with the shaft vertical and the

motor above, this allows the suction to be on one

side with the discharge on the other, but this will

require an upper floor for the motors.

Pumps installed with the shaft horizontal will have a

longer footprint with the motor in the dry well and at

possible risk from flooding. Horizontal pumps are

generally easier to maintain than vertical pumps.

Pumps should generally be installed in a close-

coupled horizontal shaft configuration, unless the

drywell is deep or liable to flooding, when a vertical

installation should be considered. Other

considerations include:

• The pumps should be installed with sufficient

space between them to allow access for

maintenance and repair;

• The pumps should be supplied with a mid-

range impeller, which will meet the design

duty. However, the pump casing should be

sized to accept the maximum sized impeller

for that pump and the motor should be sized

to drive the maximum sized impeller;

• Consideration should be given to fitting

temperature and vibration sensors to each

pump set and connecting them to the station

PLC;

• Pumps and motors installed with a drive shaft

having universal joints should not be installed

directly in line; they should be slightly offset to

provide movement to the universal joints;

• Long drive shafts should have intermediate

support bearings supported from concrete

beams spanning the dry well.

2.8.3 Primary Movers

Electric Motors

Care should be taken in selecting the type of electric

motor, with regard to the characteristics of the driven

load and the starting method. Where motors are to

be used in conjunction with variable frequency drives,

they should be designed for such applications, or

suitably de-rated. The complete drive system should

be matched to ensure compatibility. Other

considerations include:

• All motors should be of the squirrel cage

induction type, suitable for operation with a

415V, 690V or 3.3kV 3-phase, or 50Hz

supply;

• The continuous maximum rating of a motor

should be a minimum of 5% above the

calculated maximum power requirements

under all conditions of operation;

• Consideration should be given to providing

thermistors for temperature protection on all

motors rated above 7.5kW;

• Where the motors are installed vertically they

should be specifically designed for that

purpose with adequately rated end thrust

bearings;

• Motors should be protected to IP55 class F.

Standby Pumping

Standby pumping should normally be provided by

electric motor driven pumps as this allows a greater

degree of control. In the absence of any electrical

power, the use of diesel engine driven pumps should

be considered.

When providing permanently installed diesel driven

pumps where the reservoir is below ground,

consideration should be given to installing the engine

at ground level with a 900 drive gearbox to a vertical

shaft pump installed below:

• Automatic start/stop diesel engines can be

used for standby pumping;

• Permanently installed diesel engines should

be located in a sound proofed enclosure;



• The diesel engine should be fixed speed;

• Pumps installed above the bottom water level

should be fitted with an automatic vacuum

pump for priming.

2.8.4 Variable Speed Drives (VSD)

Variable speed drives are used in applications

requiring speed and torque control. This type of

motor control is required in applications such as

pressurised irrigation networks, where the network

pressure is used as the control variable to modify the

speed of the pumps.

Type of VSD

VSDs convert the incoming fixed frequency 3-phase

AC power supply, into variable voltage and

frequency, to control the speed of the motor.

There are various types of variable speed drive in the

market. The main types can be categorised as

follows:

(1) DC motor drives;

(2) AC drives - frequency control Pulse Width

Modulated (PWM);

(3) AC drives - flux vector control (PWM).

• The construction of the above-mentioned

types varies from one to another according to

the control process required as follows:

a AC drives frequency control

using (PWM)

The speed control of the motor is achieved by

controlling both the voltage and frequency.

The advantage of the AC drive technology over DC

technology is that standard AC motors are less

expensive.

The advantages of AC drive frequency control using

PWM are:

• Low cost;

• No feedback required.

The disadvantages of AC drive frequency control

using PWM are:

• Torque is not controlled;

• Motor status is not considered.

b AC drive flux vector control

using PWM

In this type, the speed and torque are controlled by

the current, voltage, and frequency.

The advantages of the flux vector control are:

• Good torque response;

• Accurate speed control;

• The performance is very close to a DC drive;

• Full torque / zero speed.

The disadvantages of the flux vector control are:

• Feedback required;

• Modulator required;

• High cost.

Selection of VSDs

The selection of the suitable VSD size should be

according to the following criteria:

• Operating voltage (415V, 3.3kV, 6.6kV,11kV);

• Operating frequency (Operation range);

• Motor peak current;

• Ambient temperature (site temperature).

For irrigation pumping applications the most suitable

type of VSD should give both variable torque and

variable speed. In normal applications, AC drives with

PWM are recommended. The manufacturer’s

guidance on the selection of the particular VSD

should be sought for applications above 300kW for

LV applications, and for all sizes of HV application.

HV applications should be avoided wherever

possible.

Example of Control Philosophy with

VSDs

An example of a variable speed pump irrigation

station can be seen in section 2.8.6.



2.8.5 Motor Control Centre (MCC)

The low voltage motor control centre (MCC) panel

forms the link between the electrical loads, such as

motors and actuator valves, and the power

generation source (main authority supply, generator

set).

The design of the MCC should take into

consideration the following points:

• Total Connected Load

The control panel sizing and design needs to

cover the demand of the total load

connected, including the standby load as

well.

• Short Circuit Level

The short circuit level calculation carried out

according to the total connected load and

power source from the local authority

electricity network. Care must be taken in the

design stage to control the fault level. If the

total connected load is too high then the load

to the switchgear can be split into two or

more assemblies to reduce the fault level.

• Type of Co-ordination

Electrical components co-ordination

according to IEC 97-4-111 provides two types

of protection. Manufacturer tests components

such as contactor, circuit breaker, undertaken

together, to confirm what will happen under

short circuit conditions.

According to IEC 947-4-1 the co-ordination

between the electrical components can be

categorised into the following types:

Type -1 co-ordination (personal safety only);

Type -2 co-ordination (personal/components

safety).

• Form of Internal Separation

The form of separation should be according

to BSEN60439-112 or suitable equivalent. The

designer should consider Form-4 in all

designs for high personal safety and

equipment protection.

In case of multi incomer and outgoing

(starters/feeders), Form-4 should be

considered for ease of carrying out

maintenance, without interruption to other

equipment in the case of isolation of a

particular feeder.

• Bus Bar Rating

The bus bar rating should be suitable to carry

the total connected load as mentioned

previously. Consider any future loads, by

increasing the size of the bus bars and also

consider the suitability of extension at both

ends.

• Type of Starter

The designer should consider the following

points when choosing the starter type to be

used. The motor size (KW) will decide

whether a standard starter (direct on line,

DOL, star delta starter, Y/D) or more

advanced type of starter (e.g. soft starter) is

possible. The main issue to consider is the

starting current. The higher the (KW) rating

the more starting current required. The high

starting current has an effect on the system

stability and other equipment installed. The

application of the motor or pumps should be

considered; e.g. for an irrigation system

where the network is always required to be

pressurised, a variable speed drive is often

used to keep the network pressure constant

and available all the time.

• Protection Device

The designer shall categorise the entire load

connected to the switchgear according to the

criticality of its status in the process, and its

effect on operator safety. Some of the

protection types that can be used are as

follows:

1) Short circuit protection

This type of protection is required to protect

the equipment against short circuit which can

be caused by insulation failure/damage, or by

incorrect switching operation. Short circuits

are associated with electrical arcs.



2) Overload protection


the equipment against overload current. This

occurs due to operational over current

occurring for excessive periods of time. If the

equipment (motor/cables) is incorrectly sized,

over current will also raise the (motor

winding/cable) temperature above the

permissible level and shorten its service life.

The task of overload protection is to allow

normal operational overload such as starting

current to flow, but interrupt this flow where

the permissible loading period is exceeded,

such as with a stalled motor.

3) Under/over voltage protection


the equipment against over/under voltage

which is present due to: main power supply

instability (transformer taping change/load

fluctuating); unstable supply from a standby

generator due to a large load connected;

faulty governors or voltage regulators.

Operation with an under-voltage condition will

draw from the supply more current. This over

current will raise the motor winding or cable

temperatures above the permissible level and

shorten the service life of the insulation. The

same will be the case with over-voltage which

will effect the insulation of the motor or cable,

and cause insulation failure. This type of

protection can be applied at the main

incomers of the switchgear by special relay,

to sense the voltage supply and trip the main

incomers if the set limits are exceeded.

4) Phase losses/phase reversal protection


the equipment against phase loss from the

main supply, or phase reversal, which can

happen in the event of main supply

reconnection, or reconnection of the motor

after service. Operation with phase loss or

reversal will raise the motor winding

temperature due to unbalanced current in the

motor winding. In the case of phase reversal,

the motor direction will be reversed, which

will result in equipment damage or faulty

operation (pump vibration, high sound level)

due to the wrong direction of operation. This

type of protection can be applied at the main

incomers of the switchgear or motor feeder

by a special relay to sense the phase status

(direction /availability) and trip the main

incomers/feeder if a fault occurs.

5) Earth leakage protection

This type of protection is required to: protect

the equipment and personnel in the event of

indirect contact; provide additional protection

in the event of single phase direct contact;

give earth fault protection; and protection

against fires resulting from earth fault leakage

current.

This type of protection can be applied at the

switchgear outgoing feeders

(motor/distribution board/other loads) by a

special relay which senses the earth leakage

current through a summation current

transformer. The unbalanced current from the

transformer will release a mechanism that

will trip the breaker if a fault occurs.

6) Motor protection relay (electronic relay)

This type of protection is used to protect the

motor against many faults that can affect the

motor operation and safety. The required

protection type can vary according to the

motor application (critical/normal) and size

(cost considerations). The following type of

protection can be achieved by motor

protection relay:

-Over/Under current;

-Phase losses/unbalance/reversal;

-Ground fault;

-Locked rotor;

-Motor stall.

This type of protection can be applied at the

motor terminals. The fault signal from the

relay will release a mechanism that will trip

the breaker if a fault occurs. Fault indications

will appear on the relay LCD screen or

indication LED, to diagnose the fault type.

• Interlocking Facility



An Interlocking facility is required where more

than one incomer is used in the switchgear.

Some examples are as follows:

1) Supply from two transformers/local

authority supply;

2) Supply from two incomers, one from

transformer/local authority supply and

one from the standby generator(s)

panel;

3) Supply from three incomers, two from

transformers/local authority supply and

one from standby generator(s) panel.

The interlock facility should guarantee the

safety of operation by not allowing, under any

conditions, the connection of two different

incomers to the same bus bar section

(transformer/transformer) or (transformer

/generator), or main bus bars with the bus

coupler closed.

• Accessibility

The panel access for cable termination and

maintenance can be arranged in the following

format:

a) front access (suitable for installation

area with limited space at the back of

the MCC);

b) back access (suitable for installation

area with available space at the back

side of the MCC, minimum 1m);

c) front/back access.

In all cases a minimum of 2m clear space

should be provided in front of the panel.

• Cable Entry

Cable entry to the MCC can be arranged in

the following format:

a) bottom entry (suitable for MCC fixed at

the top of cable/MCC trench);

b) top entry (suitable for MCC fixed in

below ground location with cables such

as feeders and incomers installed at

ground level or above the MCC top level.

Wherever possible bottom access should be

provided with a man entry cable chamber

extending under the entire control room.

2.8.6 Instrumentation and Control

Pressure Sensors

Pressure detection devices can be classified on the

basis of the pressure ranges they can measure, on

the basis of the design principle involved in their

operation, or on the basis of their application. This is

one of the most important instruments for irrigation

networks, which are usually controlled based on

pressure.

Bellows-type Pressure Sensors

Bellows are formed from seamless tubes

hydraulically or mechanically roll-formed. The main

advantages of bellows are their ability to provide

longer strokes and to handle higher forces. When

absolute pressure is to be sensed with bellows

elements, it normally involves two bellows, one for

measuring and the other for reference. The

compensating (reference) element is fully evacuated

and sealed, while the sensing element is connected

to the process. Basically, an increase in process

pressure causes the measuring bellows to extend,

which results in an increase of readout through the

motion balance mechanism.

Diaphragm or Capsule-type Sensors

Among the electronic designs, the strain gauge,

capacitance, potentiometric, resonant wire,

piezoelectric, inductive, reductive, and optical

transducers can all be provided with diaphragm

elements. The full range deflection of a single

diaphragm is usually limited to about 0.002in. and the

amount of deflection varies with the fourth power of

the diameter of the diaphragm. The total deflection

can also be increased by welding several diaphragms

into capsules. Diaphragm materials with good elastic

qualities and with very low temperature coefficients of

elasticity are used. The diaphragm is a flexible disc,

either flat or with concentric corrugations, which is

made from sheet metal of precise dimensions. Some

instruments use the diaphragm as the pressure

sensor; others use it as a component in a capsular

element.



Flow Meter Selection

Magnetic flow meters offer the designer the best

solution for TSE pumped flow. Magnetic-type flow

meters use Faraday’s law of electromagnetic

induction for making a flow measurement. That is,

when a conductor moves through a magnetic field of

given field strength, a voltage level is produced in the

conductor that is dependent on the relative velocity

between the conductor and the field. Faraday

foresaw the practical application of the principle to

flow measurement, because many liquids are

adequate electrical conductors. So these meters

measure the velocity of an electrically conductive

liquid as it cuts the magnetic field produced across

the metering tube. The principal advantages include

no moving components, no pressure loss, and no

wear and tear in components. Magnetic flow meters

should always be installed with full pipe conditions.

Care should be taken during design to provide

sufficient straight run, up-stream and down-stream of

the flow meter in accordance with the manufacturer’s

installation instructions. As a general guideline, 12

pipe diameters of straight pipe on the inlet and 6 pipe

diameters on the outlet will ensure that the flow meter

is able to achieve the specified accuracy. If the

amount of space available is restricted then the

minimum usually accepted by manufactures is inlet

run > 5 pipe diameters and outlet run > 3 pipe

diameters.

Refer to Volume 8 for standard installation details.

The installation should allow for the future removal

and replacement of the flow meter. The

manufacturer’s requirements should take

precedence.

The following International and British Standards are

a good source of information on flow meter selection

and installation, and can be quoted in specifications:

• BS EN ISO 6817: 1997: Measurement of

Conductive Liquid Flow in Closed Conduits13;

• BS 7405: 1991: Guide to Selection and

Application of Flow meters for the

Measurement of Fluid Flow in Closed

Conduits14.

Flow meters should be pressure tested and

calibrated by the manufacturer and certified to a

traceable international standard. As a minimum, the

overall accuracy should be better than ±0.5% of the

flow range. The repeatability of the result should be

within ±0.2%.

In addition to the calibration certificate, the flow meter

manufacturers should provide the following:

(1) Isolated 4-20mA DC and pulse outputs;

(2) Programmable in-built alarm relays for

empty pipe, low and reverse flows;

(3) In-built digital display for flow rate, total and

alarms;

(4) Transmitter enclosure shall be protecteto

IP67;

(5) Calibration and programming kit.

The earthing rings should be included according to

the individual manufacturer’s instructions. The sensor

lining should be neoprene or an equivalent material

of similar or improved properties. In below-ground

flow meter chamber installations, the installed

equipment should be submersible to the maximum

chamber depth.

Control Equipment

PLC

PLC stands for Programmable Logic Controller. The

PLC is a microprocessor-based device which is

programmed to perform certain controlling tasks. The

PLC is the brain of the overall process. It can receive

analogue and digital signals from the process

devices, analyse them and send digital and analogue

signals to control these devices or activate certain

alarms.

PLCs were originally used for controlling purposes.

Almost all PLCs are now equipped with signal

transmitters (i.e. they include some RTU features)

that are capable of transmitting data to the network

operation centre.

A redundant PLC system with hot standby

configuration is highly recommended for critical

applications where uninterrupted control is required.

The power Supply for a PLC system is usually 24Vdc

or 110Vac. In case of power failure, the equipment

should be backed up by a UPS system which can

supply the PLC with up to 8 hours of power

depending on the importance of the process.



The modular type CPU (Central Processing Unit) in

the PLC is capable of: solving application logic;

storing the application program; storing numerical

values related to the application processes and logic;

and interfacing with the I/O systems.

The PLC carries out a significant task which is PID

control. PID (Proportional-Integral-Derivative) control

allows the process control to accurately maintain set-

point by adjusting the control outputs. For example,

pump flow rate set-point is maintained by the

following:

• Proportioning Band: is the area around the

set-point where the controller is actually

controlling the process. The output is at some

level other than 100% or 0%. The band is

generally centred around the set-point (on

single output controls) causing the output to

be at 50% when the set-point and the flow

rate are equal;

• Automatic Reset (Integral): corrects for any

offset (between set-point and process

variable) automatically over time by shifting

the proportioning band. Reset redefines the

output requirements at the set-point until the

process variable (flow rate) and the set-point

are equal;

• Rate (Derivative): Shifts the proportioning

band on a slope change of the process

variable. Rate in effect applies the "brakes" in

an attempt to prevent overshoot (or

undershoot) on process upsets or start-up.

Unlike Reset, Rate operates anywhere within

the range of the instrument. Rate usually has

an adjustable time constant and should be

set much shorter than Reset. The larger the

time constant, the more effect the Rate will

have;

• Modulated Simplex I/O system: is the

preferred solution for safe process since the

duplex (redundant) I/O system is usually

expensive. The modulated simplex I/O

configuration guarantees that any failure of a

single I/O card will not cause the relevant I/O

rack to fail. For instance, if a rack contains

three I/O cards which control three pumps (2

duty, 1 standby), the failure of one card will

cause the whole pumping process to fail. In

Modulated Simplex I/O systems, it will cause

the failure of one pump which will be classed

as the standby pump, and the other two

pumps will continue to run normally.

RTU

RTU stands for Remote Telemetry Unit. This unit

delivers remote information back to network

operation centres. Operations staff can access

remote sites that have RTUs, via a web browser,

SNMP (Simple Network Management Protocol)

Manager, and XML (Extensible Markup Language). If

an ethernet connection is not available, then the

RTU's may be accessed via PSTN (Public Switched

Telephone Network), normal dialup and even SMS

(Short Message Service) messaging.

Earlier generation RTUs were hardwired and

supported limited functionality’s such as data transfer

and alarming. The new generation RTUs are

equipped with a powerful processor which allows the

RTU to control certain instruments/devices, and

receive/transmit analogue and digital I/O

(input/output) signals.

The microprocessor-based RTU has a proven track

record within the water and wastewater industry, a

robust modular construction, and is constructed for

ease of maintenance and repair. These are intelligent

devices capable of handling data collection, logging,

reporting by exception, current data retrieval and

pump sequence control programs.

RTUs equipped with RS232/485 links are

recommended for interconnection to standalone

control systems, standard equipment packages and

PLCs (Programmable Logic Controller). A dedicated

serial port should be provided for connecting a hand

held programming unit or the PC.

The RTU software enables the RTU to process

locally input equipment information before

transmitting it to the master station to reduce

transmission overheads. A report by exception

operation is necessary for cost effective

communication. The report is triggered by change of

state of digital values or analogues reaching

threshold values or varying by specified amounts.

The RTU also reports when polled and when the

memory buffer is full.

SCADA and Telemetry Systems



Supervisory Control and Data Acquisition (SCADA) is

an industrial measurement and control system

consisting of a central host or master (usually called

a master station, master terminal unit or MTU); one

or more field data gathering and control units or

remotes (RTUs); and a collection of standard and/or

custom software used to monitor and control

remotely located field data elements. Contemporary

SCADA systems exhibit predominantly open-loop

control characteristics and utilise predominantly long-

distance communications, although some elements

of closed-loop control and/or short distance

communications may also be present.

Systems similar to SCADA systems are routinely

seen in factories, treatment plants etc. These are

often referred to as Distributed Control Systems

(DCS). They have similar functions to SCADA

systems, but the field data gathering or control units

are usually located within a more confined area.

Communications may be via a local area network

(LAN), and will normally be reliable and high speed.

A DCS system usually employs significant amounts

of closed loop control.

SCADA systems on the other hand generally cover

larger geographic areas, and rely on a variety of

communications systems that are normally less

reliable than a LAN. Closed-loop control in this

situation is less desirable.

The main use of SCADA is to monitor and control

plant or equipment. The control may be automatic, or

initiated by operator commands. The data acquisition

is accomplished firstly by the RTUs scanning the field

inputs connected to the RTU (it may be also called a

PLC - programmable logic controller). This is usually

at a fast rate. The central host will scan the RTUs

(usually at a slower rate). The data is processed to

detect alarm conditions, and if an alarm is present, it

will be displayed on special alarm lists. Data can be

of three main types: Analogue data (i.e. real

numbers) will be trended (i.e. placed in graphs);

Digital data (on/off) may have alarms attached to one

state or the other; and Pulse data (e.g. counting

revolutions of a meter) is normally accumulated or

counted.

The primary interface to the operator is a graphical

display (mimic) which shows a representation of the

plant or equipment in graphical form. Live data is

shown as graphical shapes (foreground) over a static

background. As the data changes in the field, the

foreground is updated, e.g. a valve may be shown as

open or closed. Analogue data can be shown either

as a number, or graphically. The system may have

many such displays, and the operator can select from

the relevant ones at any time.

The SCADA control centre in Doha City is currently

using Intouch Wonderware as the main software for

control and networking between the controlled sites

and the central station.

Control Philosophy

The control philosophy is the way the system will act

to process changes to achieve the objective required.

For the control philosophy to function according to

the client requirements several points should by

taken into account:

• Overall controlling plan. This involves

preparing an overall plan of how the task

required will be achieved. In other words

stating the main tasks which will allow

performance of the general task required;

• Realistic operational function. The sequence

and the functions of the operation should be

realistic and achievable. This means all

process restrictions and conflicts should be

identified and avoided while producing the

control philosophy document;

• Compatibility of products. This is about

verifying that the control philosophy planned

is achievable by existing industrial products;

• Cost effective. The choice of the products

should be cost effective. That means

unnecessary items should be taken out. At

this stage, it is possible to change the control

philosophy slightly if it will decrease the

overall cost of the project, on the condition

that the overall control philosophy will be

unaffected;

• Hazard awareness. When designing the

control philosophy, we should take into

account that a failure in the devices or an

error in the process might appear. In this

process, all possible hazards should be

located and their effect on the control

philosophy should be cleared or at least

minimised.



Example Irrigation Station Control

Philosophy Using VSDs

The main pump control shall be achieved using

variable speed pumps controlled by a PID controller,

usually resident in the PLC or RTU. The set-point

(SP), Proportional (P), Integral (I) and Derivative (D)

terms of the controller should be configurable locally

or be downloaded via the SCADA system. The

process variable (PV) shall be the discharge header

pressure.

Upon receipt of the pump permissive signal, the

control system shall start the duty 1 variable speed

drive and ramp its speed up to the 1 pump operation

set-point (default 70%). A pre-determined

stabilisation period (default 30 seconds) should then

allow the pressure in the discharge header to settle.

The PID controller should then alter the speed of the

pump to control the discharge header pressure to

equal the set-point pressure.

The controller shall continue to modulate the speed

of the variable speed drive based on changes in the

discharge header pressure. If the pressure rises

above the set point the pump speed shall be reduced

and if the pressure falls below the set-point, the pump

speed shall be increased.

When the duty pump reaches full speed and remains

at full speed for a pre-set time (Usually around 120

seconds), the duty 2 pump should be started.

The duty 2 pump should ramp up its speed to the 2

pump operational set-point (usually 75%),

concurrently the duty 1 pump should be controlled to

the same value.

Once both drives have reached the selected speed

they shall be controlled together by the PID

controller. With the speed being increased and

decreased based on changes in the discharge

header pressure.

Similarly in the case of a three duty pump station the

third duty pump shall be started when two pumps are

running and have reached maximum speed for the

pre-set period (around 120 seconds). At this point the

duty 1 and duty 2 pumps shall be ramped down to

the 3 pump operational speed set-point (usually 75%)

and concurrently the third pump ramped up to the

same set-point.

If three pumps are running and their speed has been

reduced to the minimum operating set-point (default

70%) and the controller is still calling for the speed to

be reduced; the first pump to start (the duty 1 pump)

should be stopped. The remaining two pumps should

then be controlled to allow the header pressure to

equal the set-point value.

Similarly, if two pumps are running and their speed

has been reduced to the minimum operating set-point

and the controller is still calling for the speed to be

reduced, the pump that has been running the longest

should be stopped and the remaining pump

controlled until the pressure has reached the set-

point value.

2.8.7 Pump Suction and Delivery Design

Pipework

The pipework installation should incorporate the

following features:

• The pipework should be designed to allow the

pumps to draw from and discharge to

common manifolds;

• The common suction and discharge

manifolds should be located either side of the

pumps. The suction pipe should be recessed

at a lower level and may require an open

mesh walkway over it at floor level with the

individual pump suction connections rising up

through the covers;

• The pipework should be designed with

sufficient flange adapters or bends to allow

easy dismantling and removal of pumps, non-

return valves or other major items of

equipment;

• All flexible couplings will require restraint to

prevent displacement under pressure. The

pipework design should allow the suction and

discharge pipework to and from the pumps to

be completely bolted, with bends to allow

dismantling;

• Each pump should be installed with suction

and discharge isolating valves bolted directly

to the common manifolds which permit

isolation for maintenance, while allowing the

other pumps to continue operating normally;



• Each pump should also be fitted with a

discharge non return valve to prevent reverse

flow through the pump and a suction strainer

to prevent blockage of the impeller passages

by debris;

• Consideration should be given to providing an

isolating valve on the pumping main before

any over-pumping connection, to allow the

pumping station to be fully isolated and the

fixed pipework drained for repair.

Consideration should also be given to

providing a valved connection for draining the

discharge pipework. Suction velocities should

not normally exceed 1.8m/s but should be as

low as practical to improve the NPSH

available (see 2.8.1). Discharge velocities

should not normally exceed 2.5m/s;

• Sumps should be designed in accordance

with the recommendations of the CIRIA guide

‘The hydraulic design of pump sumps and

intakes’15 which gives guidance on sump

design, suction bellmouth clearances and

measures to avoid vortex formation.

Valves

Valves should incorporate the following features:

• Isolation valves for TSE should be of the

double-flanged wedge-gate type with a bolt-

on bonnet. When fully open, the gate should

be withdrawn completely from the flow. The

valve handwheel direction of operation should

be clockwise to close. Station valves should

have metal seats;

• All sluice valves above 500mm bore (300mm

if power actuated) should be provided with

jacking screws;

• Reflux valves for TSE should be of the double

flanged, quick action single door type,

designed to minimise slam on closure by

means of heavy doors weighted as

necessary;

• Reflux valves should be provided with covers

for maintenance without the need to remove

the valve from the pipeline. The covers

should be large enough to permit removal of

the flap and inspection of the seat.

2.8.8 Surge Protection

Surge (or water hammer) is an oscillating pressure

wave generated in a pipeline during changes in the

flow conditions.

There are four common causes of surge in a pipeline:

• pump starting;

• pump stopping/power failure;

• valve action;

• improper operation of surge control devices.

The most likely one of these is the sudden stopping

of all pumps caused by a power failure.

An approximate calculation for a simple pipeline is:

∆∆∆∆P = a x ∆V

g

Equation 2.8.2

Where:

∆P = Pressure change (m)

a = pressure wave velocity (m/s)

∆V = flow velocity change in 1 cycle (m/s)

g = acceleration of gravity (9.81m/s2)

The simple cycle time can be calculated with the

formula:

Cycle time = 2 x pipeline length Wave velocity

Equation 2.8.3

Table 2.8.1 below shows wave velocity in m/s for

pipe materials.

Table 2.8.1 - Indicative Surge Wave Velocity

Values for Selected Pipe Materials

Pipe Material Velocity (m/s)

Ductile Iron 1000 – 1400

Reinforced Concrete 1000 – 1200

Plastics & GRP 300 – 500 NOTE: As the wave velocity is partially dependent on

the physical properties of the pipe, the wave velocity for the particular pipe under consideration must be assessed for each scheme.



If the surge pressure approaches zero or the pipeline

maximum pressure, a full surge analysis should be

carried out.

Surge Suppression Methods

Surge suppression could be achieved using one of

the following devices. The most appropriate device

will depend on the individual circumstances of the

installation:

• Flywheel;

• Pressure vessel with bladder;

• Dip-tube surge vessel;

• Surge tower.

Air valves should not be used as a method of surge

control, but their operation under surge conditions

should be carefully considered.

Flywheels

Flywheels absorb energy on start-up, slowing the rate

of velocity change in the pipeline. In reverse, when

the pump is stopping, the flywheel releases energy

again, slowing the rate of velocity change. Together

these two actions reduce the peak surge pressure.

As the flywheel must be located on the drive shaft it

is not suitable for submersible pumps or close-

coupled pumps. However, they are simple devices

for wet well/dry well pumps and are preferred where

possible.

If submersible pumps have been chosen, a larger

pump running at a slower speed may have the effect

of a flywheel.

Because the flow continues through the pump after

the stop signal, the effect on the stop and start levels

should be carefully considered.

Pressure Vessels

Pressure vessels for surge suppression are tanks

partially filled with a gas (air or nitrogen). Usually the

liquid is contained in a bladder with gas on the

outside to prevent the liquid absorbing the gas or

coming into contact with the inside of the pressure

vessel, and this is the preferred type. The bladder

material should be carefully selected for use in the

conditions experienced in Qatar.

Refilling is usually from a high-pressure cylinder and

care should be taken to avoid over pressurisation of

the bladder. Bladders should not lose pressure in

normal operation, but they can fail, leading to

absorption of the gas into the liquid, and a drop in

pressure.

Vessels without a bladder are charged with air

pressure from an air compressor, either manually or

automatically. There is therefore additional machinery

and an additional maintenance requirement. This

type of surge vessel is not recommended.

On pump start-up, liquid enters the vessel,

compressing the gas until it equals the liquid

pressure. When the pump stops, the gas pressure

forces liquid back out into the pipe system, both

actions slow the rate of pressure change, which

reduces the peak surge pressure.

To dampen oscillations, a non-return valve may be

fitted to the surge vessel outlet pipe, to allow

unrestricted flow into the pipeline, and a bypass

around the NRV fitted with an orifice plate to restrict

the flow back into the vessel.

Dip Tube Surge Vessels

A dip tube surge vessel is pressure vessel, the top

portion forming a compression chamber limited by a

dipping tube with a shut off float valve.

This type of vessel is particularly appropriate for use

on rising mains with flat profiles.

Surge Towers

A surge tower is a vertical tank or pipe fitted into the

pipeline, open to atmosphere and the energy storage

is by the static head of the liquid in the tower.

Surge towers are only practical for systems with

relatively low heads and surge pressures, but can

pose an odour risk.

Due to the design of a surge tower, there is no

routine maintenance required to ensure the surge

tower keeps operating correctly.

It is unlikely that surge towers would be appropriate

for use in Qatar.



Air Valves

Air valves are required on the pumping mains to

release air, but they should not be used as a surge

protection measure.

However, air valves, particularly if fitted with a vented

non-return valve or in-flow check valve, may assist in

surge control, and their operation must be carefully

considered.

Air valves require regular maintenance because if the

air valve does not function correctly, large or negative

surge pressures could result, with consequent

damage to equipment or personnel.

If air is allowed into the rising main on pump stop/trip

through an air valve, the pump control system should

be designed to prevent a restart until the transient

pressures have stabilised.

Control of the pumps is usually by start/stop level

signals, but where surge on start-up may have a

significant effect, the use of ‘soft’ starters should be

considered.

2.8.9 Air Valves

Double orifice type air release valves should be

installed on the pipeline at appropriate points in order

to prevent air pockets from building up.

As a minimum air valves should be provided at the

following locations:

• All high points

• At least every 1000m

The valves shall be capable of handling TSE water at

40°C without any adverse effects and have 316

stainless steel or Ethylene Propylene Diene

Monomer (EPDM) coated float balls.

All air valves should be fitted with an isolating gate

valve.

The manufacturer’s data sheets should be referred to

for the performance data to be included in any surge

analysis.

2.8.10 Filtration

Clean irrigation water is an essential requirement for

trouble-free operation of irrigation systems and for

helping to minimise maintenance commitments. Drip

irrigation in particular requires very clean water if

clogging is to be avoided. This can be achieved by

either providing a very high standard of effluent for

the sewage treatment works (5mg/l SS) or by

provision of filters at the tertiary pumping stations.

The filtration installation needs to suit the specific

requirements of the downstream irrigation systems.

In the case of a system such as that proposed for

Doha comprising pressurised primary transmission

and distribution pipelines feeding the irrigation

systems directly, the filtration system must be

provided at each main pumping station. The

specified filtration must meet the highest filtration

requirements of any of the downstream irrigation

systems and be effective at preventing clogging of

drip emitters, damage to the solenoid valves,

scouring, and wear or damage to the pumps. In

order to satisfy these requirements and provide the

preferred level of protection, the filtration system will

normally comprise the following elements:

a Coarse Filtration

The primary purpose of coarse filtration is to provide

protection to the pumps. From time to time, objects

such as grit, stones and pieces of wood etc. find their

way into the irrigation water and can cause serious

damage to the pumps. It is normal practice to include

a large Y-strainer to ensure that such debris will not

enter the pumps, and to provide the first line of

defence in the overall irrigation filtration.

The Y-strainers will be installed on the suction line

from the reservoir and will have a relatively coarse

screen of typically about 20-mesh, or as necessary to

suit the recommendations of the pump manufacturer.

b Main Pressure Filters

The main pressure filters need to provide filtration

that meets the requirements of the downstream

irrigation system. They must be able to remove

particulates (sand etc.), which will clog drip emitters

and which will also damage the valve seats of

solenoid valves. It is also essential that they are able

to remove biological organisms (especially algae)

that build up and clog drip emitters.

The degree of filtration depends upon the selection of

drip emitters and other application devices, but 150-

mesh (equivalent to about 100 microns) is



recommended as a good specification that would

substantially reduce maintenance problems.

If there is algae growth in a TSE resevoir it can cause

a particular problem with drip irrigation systems.

Algae growth can be prevented by ensuring that light

does not enter the reservoir and also by chlorination.

Algal slime or similar organic matter will readily

squeeze through any type of filtration screen, even of

fine mesh, and it also attaches itself to the filter

screen where it will hold tiny particles that otherwise

would pass through. For these reasons, screen

filters do not provide effective filtration against algae,

and the overall effectiveness of filtration will also be

reduced. The options for irrigation filtration that are

effective at removing algae as well as hard

particulates are either media filters or disc filters.

Selection of the most appropriate solution will depend

upon cost considerations, space availability, pump

characteristics and pumping station configuration.

The main characteristics of these two options are as

follows:

• Media Filters

Media filters work by forcing water through

large vessels containing uniform size crushed

sand or similar medium. The sharp edges of

the medium are able to trap organic matter

such as algae. Media filters are cleaned by a

back-flushing process that lifts and separates

the medium. A small amount of the medium

escapes, and needs to be replenished from

time to time. Media filters are less effective

for removing sand particles because these

are not flushed out during back-flushing.

Media filters are physically large in size and

therefore space availability may be an issue.

It is necessary to place a screen filter on the

outlet to trap the escaping particles of

medium. For optimal operation, media filters

need to be carefully matched to system flow

rates and do not work well with low flows;

• Disc Filters

Disc filters comprise stacks of plastic discs

with a special surface that catches both

inorganic and organic particles as the water is

forced between the discs. They are typically

factory-assembled into multiple batteries.

The back-flushing cycle pushes the discs

apart, loosening them and allowing them to

spin round and release the filtered matter.

They are relatively compact in size but should

be installed indoors, preferably in the

pumping station. Disc filters are well suited to

medium-sized irrigation pumping stations but

there is no technical reason why they should

not be installed in a main centralised pumping

facility.

Irrespective of the type of filtration selected, the

performance of the pump sets must take into account

the head loss through the filtration system. Head

loss through the filters increases with increased flow

as well as with the degree of filtration. The

requirements of the back-flushing cycle also need to

be taken into consideration in the specification of the

pump sets and design of the pumping station.

c Downstream Final Filtration

Although not part of the pumping station installation,

as a final line of defence, a Y-strainer should be

provided at the downstream end of the irrigation

system in each solenoid valve. Refer to section

3.1.1.

2.8.11 Ventilation and Air Conditioning

Ventilation systems should be designed so that in the

event of a fire being detected in any area, all the air

conditioning equipment and ventilation systems are

shut down. All supply and exhaust ventilation louvers

should shut automatically to compartmentalise the

building to restrict the spread of the fire and smoke,

and ensure effective use of automatic fire

extinguishing systems.

The air conditioning system and ventilation fans

should be run together and ventilation fan louvers

should shut, when the fan stops.

Louvers should be sized to keep the air velocity

through them below 0.5m/s.

Air ducts should be designed to ensure the velocity

through them does exceed 6m/s in occupied areas.



Air Conditioning Systems and

Ventilation Capacities

The required air conditioning systems and

ventilation capacities are shown in Tables 2.8.2 and

2.8.3.

Table 2.8.2 - Air Conditioning Systems

Location Air Condition system Electric Switch Gear

Dual Split AC unit system

Control Room Split AC unit system

Table 2.8.3 - Ventilation Capacities Location Approx. air

changes per hour.*

Electric Switchgear Room

1

Pump hall, motor room and control rooms

12

Kitchen and Toilet

12

Electrical Switch Gear Rooms

Electrical switch gear rooms should be completely

isolated from the remainder of the building for the

following reasons:

• The thermal loads are higher than elsewhere in

the building;

• In the event of a fire being detected, the air

conditioning should be switched off to allow the

fire suppression equipment to operate

effectively.

Air Conditioning

Two split AC units working independently

(mechanically and electrically) of each other should

be used to air condition the room, with air diffusers

discharging horizontally towards the panels. Return

air should be sucked back by the split unit, via

receiving air diffusers located at evenly placed

points between the supply air diffusers, and fixed to

the ceiling.

Each split AC unit should be rated at 50% above the

required capacity (i.e. 150% total), so that should

one unit fail, the other unit will provide 75% of the

required air conditioning capacity.

The required thermal load should be calculated on

the basis of peak conditions.

Ventilation

The required quantity of exhaust air should be

removed from electrical switch gear rooms to the

pump room by a fan with an actuated louver.

Air inlet should be by natural supply through a

filtered and actuated louver.

In the event of a fire, the electrically actuated

louvers should be closed to seal electrical switch-

gear rooms during the use of any fire extinguishing

system.

Control Rooms, Kitchens and Toilets

Air Conditioning

A single split AC unit should be provided for air

conditioning the control room. No air conditioning

should be provided for the kitchen or toilet.

The kitchen and toilet areas should be ventilated by

exhausting part of the control room air through them.

Ventilation

Exhaust air in the kitchen and toilet areas should be

discharged outside the building. The fans should be

run continuously for the following reasons:

• Providing the required air changes for the

control room and kitchen;

• Keeping the toilet and kitchen area

ventilated;

• Air louvers should be fitted in the bottom of

kitchen and toilet doors.

Pump Rooms

Ventilation

Air supply should be provided by either two or three

duty fans and one standby fan, depending on the

size of the pump room. The air extracted from any

electrical switch gear rooms should be included in

the air supply calculations.



Exhaust air should be removed by either two or

three duty fans and one standby fan, depending on

the size of the pump room.

The exhaust fans should have approximately 5%

less flow capacity than the supply fans to keep the

building at a slight positive air pressure. This is to

avoid drawing unfiltered dust laden air into the pump

and MCC rooms. This reduces the amount of dust

in the rooms, which can enter electric motors and

switchgear, drastically shortening the equipment life.

Pump rooms should have 10 air changes an hour.

The cable basement should also be ventilated as

part of the pump room ventilation system.

2.8.12 Standby Generation

Before selecting a generator, a list should be

compiled of all electrical loads which the generator

will be required to support. There should be no

diversity factor on the generator loads. Each load

should have its maximum starting load calculated to

determine the largest starting load.

Standby generating sets with varying loads due to

changes in pump numbers or speeds etc. should be

rated for Prime Power (PRP) duty in accordance

with BS 7698/ISO852816, taking into account the

running and starting loads.

Where there is a requirement for continuous running

at high load for extended periods, Continuous

Output (COP) duty rating should be considered.

Limited time running power (LTP) generating sets

should be avoided. LTP generators are unlikely to

have sufficient reserve power to handle the largest

starting load with all other loads connected.

Standby generators should be sized to carry the full

load of all electrical equipment connected to it plus

the largest starting load. Generators for high

starting load installations should be generously

sized.

Electrical loads connected to a standby generator

should include all pumps, compressors, ACUs and

controls essential for the operation of the pumping

station. All other loads should be disconnected and

inhibited.

When loading a generator, it is preferable to connect

the largest load first and the smallest load last, but

the generator must be capable of accepting the

largest starting load last with all other loads

connected.

Standby generators should have a fuel header tank

sized for a minimum of 24 hours running at full load.

A bulk fuel tank with a further 7 days fuel at full load

should also be provided on site.

The header tank size could be reduced if an

automatic replenishment system from the bulk tank

is provided. The replenishment system should

maintain the header tank contents at a level

providing sufficient time for someone to attend the

site in the event of failure.

2.8.13 Maintenance Access and Lifting Gear

Safe access should be provided to all equipment

and local control panels at all times.

Access walkways, platforms and stairs should be

designed so that no dismantling is required for

normal routine maintenance. Vertical access should

be by staircase so that tools and equipment can be

carried in and out safely. Ladder access should be

restricted to infrequent visual inspection points.

Access around equipment for operation should be

installed at a level where all the controls can be

reached and operated easily without excessive

stretching or bending and where all indicators can

be seen.

Access around equipment for maintenance and

repair should be installed at a level where all the

maintenance points can be reached, dismantled and

removed without excessive stretching or bending.

Particular attention should be paid to lifting gear

access and operation where heavy equipment is

involved.

Access below ground to dry wells should be by

staircase so that tools and equipment can be carried

in and out safely.

Permanent access to wet wells and screen

chambers should be provided, using stainless steel

or GRP to just above TWL to allow for cleaning. The

access arrangements should be designed such that

an operator could be rescued from the sump with a

safety harness and man-winch.



When designing access to equipment, careful

thought should be given to shipping routes for

removing equipment to a suitable position for further

work, or for removing from the pumping station

completely. Exit routes for equipment should not be

the same as for personnel access unless there is an

alternative escape route.

When the lifting gear has taken the weight of

equipment and the equipment is released from its

position, the clearance in the shipping route should

be large enough for the equipment to pass through

without rearrangement.

Permanent or temporary lifting facilities should be

provided for equipment that can not be easily lifted.

Consideration should be given to the weight, shape

and position of the item to be lifted. As a guide lifting

facilities should be provided for anything over 25kg.

For long or heavy lifts, gantry cranes should be

powered in all motions. Trolley cranes should

generally be power lift with manual motion, but small

units should be manual on all motions.

The following types of lifting equipment are

available:

• Lifting Eye and Chain Block

Suitable for single straight lifts only inside a building

or dry well. Not suitable for side forces, but may be

used in conjunction with other suitable lifting eyes to

swing a load sideways.

• Davit, Socket and Chain Block

Suitable for most small single lifts i.e. submersible

pumps up to 250kg. Above this, the davit becomes

too heavy to be manhandled.

• Runway Beam, Trolley and Chain Block

Suitable when there are a number of loads in a

straight line, or where a single load must be moved

sideways. For heavy loads or long lifts, the chain

block and trolley should be electrically powered.

• Overhead Gantry Crane

Suitable for installations where there are dispersed

or heavy loads that must be moved in all directions.

• Mobile Crane

Suitable for single heavy loads outdoors which must

be moved in all directions i.e. large submersible

pumps.

Location of lifting equipment

• Lifting equipment should be provided

adjacent to all heavy items that require

lifting;

• Lifting equipment should be positioned to

provide a straight lift of the load and also be

able to lower the load directly to a suitable

setting down position;

• Where lifting through openings in floors, the

lifting gear should be positioned to allow a

direct single lift up through all floors without

moving the lifting point or rearranging the

load.

Controls for Lifting Equipment

• Overhead electric cranes and chain blocks

should be provided with a low voltage

pendant control suspended from a glide

track, independent of the lifting block. The

pendant control should extend to within

500mm of the operating floor, but not touch

the floor;

• Electric chain blocks should be provided with

a low voltage pendant control suspended

from the block. The pendant control should

extend to within 500mm of the operating

floor but not touch the floor;

• Hand operating chains should extend to

within 500mm of the operating floor but not

touch the floor;

• Long travel drive chains should be located to

avoid snagging, and allow the operator safe

passage;

• With the load hook in its highest position, if a

load chain touches the operating floor or any

item of plant, a chain collection box should

be fitted.

2.8.14 Geotechnical Information

Geotechnical investigation must be completed

before any structural design can be undertaken. A

specialised geotechnical engineering firm shall be

employed to design, procure, and supervise the



necessary field works, in-situ and laboratory testing

works.

For storage reservoirs at ground level or overhead

(water towers), bearing capacity and settlement are

prime foundation considerations. For pumping

stations or underground storage reservoirs, bearing

capacity and settlement are of less concern, but

flotation, stability and methods of excavation for

temporary works are major considerations.

The design of geotechnical investigations should

therefore be tailored to suit the type of structures to

be constructed, taking account of the expected

geology in the area concerned. Descriptions of the

regional geology of Qatar are given in Volume 1,

Section 4.2 and Volume 5, Section 1.2.1.

As part of the investigation stage it may be

necessary to drill boreholes and excavate test pits to

determine the nature of the subsurface. Site

investigation (SI) information is essential for the

structural design and to reduce the tender risks.

Prior to deciding what SI is required, an examination

should be made of all existing SI information

available for the site, as well as an understanding of

the general geology of the site. The DA holds a

library of documents on previous projects and this

should be the first source of information.

The number of boreholes to be sunk will be

dependent on the size of the site. A minimum of two

is recommended for a single structure. For large

sites where there are numerous structures,

boreholes at between 50m to 100m centres are

recommended. In cases where existing information

is available, additional boreholes are still likely to be

required in order to provide supplementary

information and confirmation of existing information.

Trial pits should be dug adjacent to any structure

that needs the foundations investigated and at one

or two miscellaneous locations to enable a visual

examination of the subsoil.

All boreholes and trial pits should be logged by a

competent person. The groundwater level should

be recorded. Falling head permeability tests should

be carried out on at least two boreholes.

The following basic tests on the samples should be

carried out in the laboratory:

• Particle size distribution;

• Atterberg limits on fine grained fraction (less

than 425 microns);

• Bulk density;

• Chemical analysis to determine total

sulphate, water soluble chloride and pH (BS

137717, 1990 part 3);

• Uniaxial compressive stress.

Additional laboratory tests are often required to

provide geotechnical design parameters for bearing

capacity, settlement, and stability assessment as

appropriate to the structures.

The field and laboratory works should be undertaken

by an approved site investigation contractor. All

subsurface investigation, sampling, testing and

reporting shall be as required by BS 5930 - Code of

practice for site investigation18 and BS 1377 - Soils

for engineering purposesError! Bookmark not defined..

Reporting requirements are described in Volume 1,

Section 3.1.

2.8.15 Sub- and Superstructure Design

General

The site for the future pumping station should be

carefully considered, bearing in mind the following:

(1) Sufficient area to construct and maintain

the facility, as well as allowing for future

expansion;

(2) Distance to the existing distribution and

transmission system;

(3) Need for new distribution and transmission

pipelines to meet pressure standards;

(4) Existing ground surface elevation and site

drainage;

(5) Site access;

(6) Geotechnical investigations;

(7) Availability of power.

A pumping station usually consists of two main

parts, a substructure below the ground level, on top

of which is a superstructure consisting of a building.

The primary consideration while designing a

pumping station is to accommodate the plant

needed to meet the required duty. This would



include: the type and number of pump sets; their

drives, valves and pipework; power supplies;

method of starting and control; access for

maintenance; and surge protection, if needed. Once

the plant detailed requirements are decided, design

of the pumping station building can proceed.

Substructure

In the case of an irrigation pumping station, the

substructure will usually consist of an underground

compartment to house pumping plant, pipework and

control valves. The size of the superstructure should

be sufficient to house the plant and pipework with an

adequate allowance of free floor space for

maintenance and running repairs. Allowance may

also be required for the installation of future plant. In

general, a cramped layout of plant and pipework is

to be avoided. The floor should fall to a drainage

sump, drained by a dedicated pump or to an

adjacent drainage system, if feasible. Access to the

substructure floor should be in the form of steel or

concrete stairways with landings, if the depth

requires it.

Superstructure

The design and construction of the pumping station

is mainly related to engineering considerations,

however in the case of the building forming the

superstructure, the surrounding amenity has often to

be considered and attention to appearance may

therefore be important. Once the functional

requirements, including the leading dimensions have

been established, the design should become the

responsibility of an architect.

Structural Design

Reinforced concrete shall be used in the

construction of the substructure and is preferred in

the construction of the superstructure. However, if

the pumping station is to be located in an industrial

area, where the surrounding amenity is not so

important, a steel clad structure may be considered

for the superstructure.

The Codes of Practice listed in Table 2.8.4 below

shall be used while preparing structural designs.

Table 2.8.4 - Codes of Practice for use in Structural Designs

Item Standard/Code Description

1 BS 8110 Parts 1, 2 & 3

Structural use of Concrete

2 BS 5950 Part 1

Structural use of steel work in building - code of practice for simple & continuous construction : hot rolled sections

3 BS 5628 Part 1

Code of practice for use of Masonry Part 1 Structural use of unreinforced masonry

4 BS 8004 Foundations 5 BS 6399

Part 1 Part 2 Part 3

Design loading for buildings Code of practice for dead & imposed loads Code of practice for wind loads Code of practice for imposed roof loads

6 BS 4449 Specification for carbon steel bars for reinforcement of concrete

7 BS 2573: Part 1: 1983

Rules for the design of Cranes Part 1: Specification for classification, stress calculations and design criteria for structure

8 BS 8007

Design of concrete structures for retaining aqueous liquids

9 BS 648 Schedule of weights of building materials



2.9 TSE Towers

Water towers are necessary in areas of flat

topography in order to provide sufficient pressure for

delivery into the distribution system. Because of

construction constraints, they provide limited water

storage and do not provide an economical solution.

The designer should aim to produce a structure that

is aesthetically acceptable to the DA and the

planning authorities, bearing in mind that it will

become a landmark in the area it serves. Ancillary

equipment including pipework, ladders,

instrumentation and booster pumps, if required,

should be hidden in the shaft. The accepted

construction materials are concrete and steel. The

optimum depth/diameter ratios should be

determined for each location having regard to the

pumping economy and a need to avoid large

pressure fluctuations in distribution that may be

caused by drawdown or filling in excessively deep

tanks. Typical dimensions adopted for design are

shown in Table 2.9.1. As for any other TSE tank, a

TSE tower should be equipped with inlet, outlet,

overflow/drain pipes, ventilation. There should also

be proper access for maintenance and repair. In

addition, there should be a lightening arrester and

aircraft warning lights in accordance with the civil

aviation authority’s requirements.

Table 2.9.1 - Typical Depth/Diameter Ratios of

Water Towers

Nominal Size (m

3)

Depth of Water (m)

Internal Diameter (m)

1200 7.5 17

2000 9.1 19.4

3000 10.2 22.6

In general, the Doha irrigation system is moving

away from water towers in favour of a pressurised

network fed directly from a central pumping station.

Therefore, it is unlikely that further water towers will

be required.

2.10 TSE Ground Tanks

General

Ground tanks are either elevated reservoirs (located

on a high ground) or low level reservoirs with a

pumping system. Depending on the requirements,

low level reservoirs can be buried, partially buried or

above ground. Reservoirs should mainly be

constructed from reinforced or pre-stressed

concrete. In some circumstances, they may also be

constructed using steel or glass reinforced plastics.

Regardless of the type of construction and materials

used for construction, an irrigation water reservoir

has the following functions:

• To equalise the difference between water

intake and output, and to cover peaks in

demand;

• To maintain the required pressure in the

water distribution system;

• To keep stocks in reserve in case of plant

malfunctions and interruptions in the water

distribution system.

Unlike a potable water service reservoir, an irrigation

water reservoir is not to provide water for fire

fighting, unless specifically required.

The main design criteria are:

• Security of supply and water quality;

• Overall cost of construction, operation and

maintenance;

• Integration into the TSE supply system;

• Town and landscape planning.

Reservoir Shape and Depth

Reservoirs should generally be built with two

compartments so that one can be drained for

maintenance without having to put the whole

reservoir out of service. A reservoir can either be

circular or rectangular in plan. For a two-

compartment rectangular reservoir the most

economical plan shape is when its length (measured

perpendicular to the division wall is) is 1.5 times its

breadth (measured parallel to the division wall).

These proportions may require alteration due to

actual site conditions.



The economic depths for rectangular concrete

reservoirs are listed in Table 2.10.1.

Table 2.10.1 - Economic Depths for Rectangular

Concrete Reservoirs

Size (m3) Depth of Water (m)

Up to 3500 2.5-3.5

3500-15000 3.5-5.0

Over 15000 5.0-7.0

Reservoir Size

In the case of balancing storage, the required size

should be calculated based on peak diurnal

variations in the distribution system, source

production capacity, and the mode of operation

(either continuous pumping for a selected period of

time or by “call-on-demand” through use of reservoir

level control switches). In case of uniform supply the

capacity of a balancing tank should be 25-35% of

the average daily demand.

In order to meet contingencies as well as hourly and

daily variations the recommended volume of storage

is two times the system’s average day demand. If

space is not available this volume can be reduced to

a day’s demand.

Functional Requirements

The following requirements shall be taken into

consideration while designing a reservoir:

• Water circulation;

• Ventilation;

• Prevention of contamination;

• Temperature effects;

• Access and security;

• Inlet and outlet arrangements;

• Overflow;

• Washout.

Stagnant zones shall be minimised. Inlet/outlet

arrangements and baffle walls or curtains shall be

used to achieve proper water circulation.

Ventilation facilities are required to permit air

movement caused by changing water levels. It is

preferred that this is achieved by natural ventilation.

Reservoirs shall be designed to prevent the ingress

of external water and other contaminants.

Although the temperature effect is not as critical as

for potable water storage, thermal insulation

measures may need to be taken for above-ground

reservoirs.

Reservoirs shall be provided with access for routine

visits and repair work. Facilities shall be provided to

permit cleaning of each compartment independently.

Access to the water compartments, control buildings

and all functional equipment shall be designed for

safety, including that of personnel, and for ease of

operation. Openings shall be dimensioned so as to

permit entry for materials and equipment for

cleaning, maintenance and repair.

Inlet, outlet, overflow and washout pipework, the

necessary valves, flow meters and level-measuring

devices shall all be provided for each compartment.

The overflow from each compartment shall be of

adequate dimensions to permit the free escape of

excess water and shall normally allow for discharge

of the maximum inflow capable of being delivered to

the service reservoir. There shall be no isolation

valves on the overflow system. The overflow

arrangements shall not permit the contamination of

the stored water.

Design Life

The design life for properly maintained concrete and

steel storage tanks is typically assumed to be about

50 years. Any other type of storage tank that does

not have the historical longevity of these tanks

needs to be evaluated on a life cycle cost basis

before being considered for use.

Structural Design

Current British practice with regard to concrete

tanks is to follow the procedures set out in BS

800719 for the design of liquid retaining structures by

a method based on limit state philosophy. For steel

tanks BS 2654 - Manufacture of vertical steel welded

storage tanks20, shall be followed.



2.11 Site Facilities

Fencing

Pumping station sites should be fenced off using

either a chain link fence or a boundary wall,

depending on the requirements. Locks should be

provided on all access entries to prevent

unauthorised entry and vandalism. Separate

personnel access should be provided.

Auxiliary Buildings

Auxiliary buildings may include a transformer room,

chlorination room (if required), stores, workshops

and offices. Some of these facilities may be

combined with the main pumping station structure,

depending on circumstances and available space.

Drainage, Sewerage and Water Systems

Each pumping station site should be provided with

separate drainage and sewerage systems. The site

drainage and foul sewage systems should

preferably be connected to external drainage and

sewerage systems, but if those are not available

then consideration should be given to constructing

soakaways and septic tanks. A suitable service

water connection to cater for the staff and other

requirements should also be provided.

External Fire Fighting System

Provision should be made to suit the requirements

stipulated by respective authorities. It is expected

that for the external fire fighting system, potable

water from the mains will be used, therefore suitable

extensions to the mains should be made on which

above ground fire hydrants of DN 100 would be

provided.

Access Roads and Landscape

Treatments

Pumping station sites should be hard landscaped.

Access roads may be paved with asphalt and/or

concrete block paving and footpaths with concrete

pavers. Open areas should be covered with pea

gravel or other suitable material. Trees and other

vegetation should be provided according to the

needs of the pumping station location. All areas

should be sufficiently lit by perimeter lighting and

floodlights.



3.0 Design of Irrigation Systems

3.1 Definition and Scope

Within the context of this manual, irrigation systems

comprise the arrangement of pipe-work, valves and

application devices having the function of supplying

the plants’ irrigation needs, and usually includes

automatic means of control. The intention of a well-

engineered irrigation system is to ensure optimal

plant growth by applying the correct quantity of

water at the right time, and in the right place. The

scope of the irrigation system as discussed herein

includes all pipe-work and components downstream

of the point of connection at the main distribution

chamber.

3.1.1 System Layouts

Layouts for the downstream systems are to be

designed in accordance with recognised best

practice for irrigation system engineering. Principle

design considerations include operational flexibility,

ease of maintenance, and minimising head loss.

Avoiding head loss is especially critical in the case

where the irrigation systems are fed directly from a

pressurised TSE distribution network (refer section

to 2.3 above). An important objective is to ensure

that the best possible pressure is available at the

solenoid valve for the secondary system.

The division of planted areas into irrigation zones

should be logical and balance the needs of

operational flexibility against simplicity and ease of

maintenance, together with hydraulic considerations

of the irrigation mains and sub-mains. Too many

small zones will create additional maintenance with

many solenoid valve installations and electrical

circuits to be maintained. Too few large zones can

reduce operational flexibility and may result in

substantial variations in system flows in the irrigation

mains and sub-mains.

Pipework layouts need to be closely co-ordinated

with the landscape layouts and with other

underground utilities, and as far as possible

positioned clear of obstructions, trees etc. in case

future access to the pipe is required. The irrigation

mains and sub-mains (i.e. the system pipework

upstream of the solenoid valves) should be arranged

to give optimal short and direct routings to the

solenoid valves from the point of connection at the

TSE distribution chamber. For typical irrigation

system arrangements refer to Figures 3.1.1 and

3.1.2.

Solenoid valves will, wherever possible, be arranged

in small groups for ease of operation and

maintenance. Solenoid valve assemblies will be

installed complete with a Y-strainer and an isolating

valve upstream, in the same valve box if space

permits.

The number of tappings from the main TSE

distribution network should be kept to a minimum,

consistent with efficient irrigation system pipework

layouts. Each point of connection needs to be

provided with an isolation valve located in the main

distribution chamber, and a flow meter and pressure

sensor to permit remote monitoring. Distribution

chambers are typically spaced at 200m intervals

along highways.

See also section 3.1.8 below for further issues

relating to system layout.



Figure 3.1.1 – Typical Irrigation Arrangements along Main Highways

Figure 3.1.2 – Typical Irrigation Arrangements for Extensive Landscape Areas



3.1.2 Pipework Materials

Irrigation systems have conventionally used plastic

pipework of PVC-U (unplasticised PVC) to BS 3505

Class 5 (or equivalent) for the irrigation mains and

sub-mains, and either Class 4 or Class 5 for the

lateral pipework (i.e. downstream of the solenoid

valves). Class 4 PVC-U piping is thinner walled and

therefore more liable to cracking or fracture during

construction or after installation, but has a lower

initial cost. BS 3505 has been superseded by BS

EN 1452-2:2000 and the closest equivalents to

Class 5 (or E) and Class 4 (or D) in the new series

are S 6.3 and S 8 respectively.

As an alternative to PVC-U, HDPE (high density

polyethylene) piping is also eminently suitable for

the irrigation mains and sub-mains, having flexibility

and greater physical toughness compared to PVC-

U. LDPE (low density polyethylene) is used for

irrigation drip-lines and the spaghetti tubing.

Plastic pipework of either PVC-U or polyethylene

material has excellent resistance to the chemical

effects of TSE irrigation water, which would be

corrosive to galvanised iron or other metallic piping.

Selection of pipework materials will depend upon

project budget and the design life of the irrigation

system. Therefore in Table 3.1.1 shown below,

alternative recommendations are provided.

Table 3.1.1 - Recommended Pipework Material

Selection for Irrigation

Usage Material Standard

Irrigation mains and sub mains (upstream of solenoid valve)

HDPE or S6.3 PVC-

U

ISO 4427 BS EN 1452

2:2000

Laterals (downstream of solenoid valve)

S6.3 PVC-u or S8 PVC-U

BS EN 1452

2:2000

Drip-lines, spaghetti tubing

LDPE ISO 4427

3.1.3 Pipework Sizing

Irrigation designs are to be submitted with

supporting calculations giving the basis for sizing of

the irrigation pipework. Consideration will be given

to flow, head loss and other relevant considerations.

It is also recommended to take into account possible

or likely future landscape developments within the

area and make appropriate allowance within the

calculations of flow for the irrigation mains in

particular.

Sizing of the irrigation mains and sub-mains should

take account of “worst case” operational flow

conditions where a number of solenoid valves are

open simultaneously, even though this may not be

the intended operating regime. This is not an issue

with the lateral pipework, where the operational flow

will be consistent and dependent upon the number

and type of irrigation application devices. In either

case, maximum flow velocity of 1.5m/sec should not

normally be exceeded, and loss of head should be

kept to a minimum.

3.1.4 Minimum and Maximum Pressures

The designed operating pressure in any irrigation

system will be determined to suit the working

pressure required by the selected application

devices. Modern, heavy-duty, large radius, rotor

sprinklers as used for irrigating large turf areas

would require a pressure of, for example, 3.5 to 6.9

bar for the Rain Bird 8005 model, or 4.1

to 6.9 bar for the Hunter I-90 model.

However, the irrigation requirements of large turf

areas cannot realistically be met from a pressurised

effluent distribution main, and such areas would

need the installation of a local booster pumping

station.

For reliable irrigation system operation, it is essential

that the design working pressure at the application

device should be well within the recommended

range for each device, i.e. in the range of 2.5 to 3.0

bar in order to accommodate normal fluctuations in

the incoming pressure. Pressure losses in the

solenoid valve, other valves, irrigation mains and

sub-mains, Y-strainer and flow meter will be

minimised by careful sizing of components, but will

still amount to 1.0 to 1.5 bar.

It is therefore recommended that the pressure

available at any connection point (tapping) to the

main effluent distribution network should preferably

not be less than 4.0 to 4.5 bar. In case this is not

attainable for particular sections of the network, then

it may be necessary to provide booster pumping

stations for the downstream irrigation systems,



should the proposed irrigation devices required a

greater pressure.

It should be remembered, however, that most of the

town landscape will be watered using direct feeds

from the TSE transmission and distribution system

(via main distribution chambers) and the available

pressure may vary from place to place. The

landscape and irrigation system designers should

take this into consideration while preparing their

designs. In general, the minimum available

pressure in the TSE transmission and distribution

network will be not less than 3 bar (30m water head)

and the maximum available pressure will not exceed

6 bar (60m water head). The DA, or their appointed

consultants, will provide the necessary design

guidance regarding the irrigation water budgets and

available pressure in the network.

Some further examples of typical working pressures

of some common irrigation application devices are

given in Table 3.1.2 below.

Table 3.1.2 - Typical Pressure Requirements for Particular Irrigation Devices

Device Usage Model Pressure (bar)

Large radius rotor

sprinkler

Extensive turf areas Rain Bird 8005

Hunter I-90

3.5 to 6.9

4.1 to 6.9

Spray sprinkler Small turf areas, ground-

covers

Hunter SRS

Rain Bird 1800

Rain Bird 1800-SAM

1.0 to 4.8

1.0 to 4.8

1.7 to 4.8

Bubbler Trees, individual shrubs

etc.

Rain Bird 1400

Rain Bird Xeri-Bubbler

Fitco NCB

1.4 to 6.2

1.0 to 2.0

1.7 to 4.0

Drip emitter Trees, shrubs, ground-

covers etc.

Fitco PCM-6

Rain Bird Xeri-Bug

1.0 to 3.4

1.0 to 3.5

Integrated drip-line Ground-covers, hedges,

shrubs

Rain Bird ADI Dripline

Rhein PC Dripper

0.6 to 4.0

1.0 to 3.5



3.1.5 Irrigation Rates

The water demand of plants is governed by a number

of variable factors, including the climate, soil mix

properties, exposure/shelter, shade, the presence of

other vegetation, reflected heat, and factors particular

to each individual plant species. For the purposes of

this manual, which defines the general parameters

for irrigation system engineering for Qatar, the figures

given in Table 3.1.3 shown below can be used as the

basis for design and system specification, but are not

intended for horticulture reference.

Table 3.1.3 - Guideline Peak Daily Water Demand

for Different Vegetation

Planting Type Water Demand

Date palms 150 litres/tree/day

Ornamental and

shade trees

100-120

litres/tree/day

Drought-tolerant trees 60-80 litres/tree/day

Shrubs (continuous)

(individual)

20 litres/m²/day

12 litres/shrub/day

Flower beds 25-30 litres/m²/day

Ground-cover 10-15 litres/m²/day

Lawn grass 15 litres/m²/day

The irrigation demand of plants in the cooler seasons

is significantly lower. For most types of vegetation,

the winter irrigation regime can be changed to

alternate days, or twice-weekly, to the benefit of the

plants.

3.1.6 Irrigation Equipment

Fitness for purpose will be the basis for selection of

components and materials for the irrigation systems.

The solutions adopted must be properly tailored to

the irrigation needs of Qatar. The primary

requirement is that the irrigation systems should

deliver the plants’ irrigation needs with minimal

wastage and maximum efficiency. Components will

be specified only after making detailed study of all

relevant considerations, which include horticultural

requirements, soil type, water conservation issues,

cost considerations, maintenance and reliability, and

the properties of the irrigation water, including its

degree of filtration, salinity and biological purity.

TSE has usually a larger degree of salinity than

drinking water, and therefore all components of the

irrigation systems need to have excellent corrosion

resistance, and metallic parts should be of

high-grade stainless steel and bronze.

A summary of some key advantages and

disadvantages of different irrigation

application devices is provided in Table

3.1.4 below.



Table 3.1.4 - Comparison of Common Irrigation Devices

Device Type

Advantages Disadvantages

Drip Irrigation Emitters

• Allow the quantity of irrigation water to be accurately applied where needed, according to the plants’ needs

• Wastage from leaching down is minimal

• Losses by evaporation are kept to a minimum

• Reduced likelihood of human exposure when used with treated effluent water

• Easy to install and remove

• Pressure-compensating and multi-outlet models are available, giving flexibility

• Low flows = smaller pipe sizes

• Subject to clogging and thus requiring very clean irrigation water for reliable operation

• Tendency to encourage build-up of salts in the soil especially if the soil is not very free-draining

• Overall, requiring high maintenance and close regular inspection

• The devices are quite susceptible to damage or disturbance

• Relatively costly

Integrated Drip-Line (built-in emitters)

• Allows the quantity of irrigation water to be applied accurately and uniformly, according to the plants’ needs

• Wastage from leaching down is minimal

• Losses by evaporation are kept to a minimum

• Reduced likelihood of human exposure when used with treated effluent water

• Resistant to accidental damage or disturbance

• Pressure-compensating versions are available

• Low maintenance

• Low flows = smaller pipe sizes

• Less suitable where plant spacing is not regular and predictable

• Does not have the inherent flexibility of separate emitters

• Tendency to encourage build-up of salts in the soil, especially if the soil is not very free-draining

• Monitoring requires close inspection

Bubblers • Simple robust devices giving trouble-free low-maintenance operation

• Higher water flow prevents salt build-up

• Gives deep watering that encourages deep rooting

• Operation is very easy to monitor

• Models are available for mounting on pop-ups

• More wastage of water, less efficient than drip systems

• Difficult to ensure that the water is delivered just where it is needed at the root system

• Higher flows = larger pipe sizes

Spray Sprinklers

• Flexible means for irrigating smaller and awkwardly-shaped areas

• Spray cools the air and benefits the surrounding planted areas

• Washing of foliage improves growth and retains a fresh appearance

• Fine spray results in considerable wastage in hot conditions by evaporation

• Needs to be scheduled to operate in early mornings or late evenings

• Moderately high maintenance requirements

• Higher flows = larger pipe sizes

Rotary Sprinklers

• Cost-effective irrigation for larger areas

• Modern models are robust, compact and resistant to damage

• A large area can be covered by fewer sprinklers, reducing maintenance requirements

• Large nozzles are less affected by dirty irrigation water

• Significant wastage in hot conditions by evaporation

• Needs to be scheduled to operate in early mornings or late evenings

• Large radius makes them unsuitable for smaller and awkwardly-shaped areas

• Higher operating pressure requirement

• High flows = large pipe sizes



3.1.7 Control Systems

The available options for irrigation control systems

range from older electro-mechanical controllers and

compact modern solid-state controllers, to

sophisticated and feature-packed centralised

computer-based control systems sold by several of

the leading irrigation equipment companies and

other specialists in the field.

Since the landscape areas will be supplied directly

from a pressurised effluent distribution network and

not from stand-alone local pumping stations and

reservoirs, considerable areas of landscaping will be

effectively served by a single very extensive

irrigation system. It is essential that a means be

provided for centralised monitoring and control of

the usage of irrigation water and the status of all the

various local irrigation systems.

It is necessary that the chosen control system

should have excellent communications features,

able to collect in “real time” the flow and pressure

data from the meters and sensors installed around

the network, and at the points of connection of the

local systems. At the same time it needs to have

flexible irrigation features, especially for water

conservation, and must be able to permit local

control over operation and scheduling at the

individual irrigation systems.

Since the central irrigation control system will be an

off-the-shelf proprietary system such as Rain Bird,

Motorola, or Toro, the features and system

components will be defined by the selected system’s

specification.

3.1.8 Co-ordination of Irrigation and Landscape Design

Irrigation layouts and the landscape design are

clearly intimately related with one another, and the

best results will only be achieved if the concerned

disciplines are working in close co-ordination with

one another as part of one design team.

For example, the irrigation engineer should ensure

that valve boxes and other irrigation equipment such

as controller pedestals and electrical boxes are

located inconspicuously but sited for convenient

access. Valve boxes and the like should not

normally be placed in grass areas or pavements.

Similarly, the landscape architect should heed the

requirements of efficient irrigation in designing the

planting layouts, for example by ensuring that the

outline of grass areas is not creating problems for

obtaining good coverage or avoiding over-spray.

Both disciplines should co-ordinate carefully the

location of irrigation sleeves (for present and future

needs) beneath hard surfaces and structures such

as walls, at the design stage.

It is also important that irrigation and landscape

projects are co-ordinated with TSE transmission and

distribution projects, road projects and building

projects. The concerned parties are the Gardens

Division, Drainage Division, Roads Department,

Building Engineering and their consultants.

The irrigation systems are the responsibility of the

Gardens Division, whilst the TSE transmission and

distribution system up to the main distribution

chamber are the responsibility of the DA.

The works downstream of the main distribution

chambers should be undertaken by specialist

irrigation and landscape consultants/contractors.

3.1.9 Under-Drainage

As a general rule, under-drainage should be

provided beneath all trees and planted areas unless

the natural ground conditions are free draining and

the water table is deep. Although many landscape

plantings appear to thrive without under-drainage,

waterlogged conditions beneath the surface

discourage deep rooting and lead to an increase in

soil salinity.

It is therefore recommended that under-drainage

should be included wherever possible in all new

landscape projects. The main prerequisite is that

there should be a suitable outfall for the under-

drainage network, either into a storm drain or

otherwise by free discharge to the natural

topography.

Under-drains beneath planted areas simply

comprise a rock drainage layer overlaid with

geotextile filter membrane. The water from the

drainage layer is collected by a series of slotted

plastic pipes.



3.2 Landscape and Irrigation Management

3.2.1 Irrigation Management

Irrigation management is concerned with the

effective and sustainable use of available irrigation

resources, for the long-term well-being of the

landscape. It involves planning and monitoring the

usage of irrigation water at a strategic level. The

irrigation budgets and Irrigation Master Plan

discussed in sections 1.3.2 and 1.3.3 are essential

tools for implementing this essential role. The

function of irrigation management will be undertaken

by the Qatari authorities at a departmental level, to

ensure co-ordination between all concerned parties.

3.2.2 Maintenance of Irrigation Systems

Obtaining the best performance from irrigation

systems is essential if efficient use of water is to be

achieved. The effort and funds put into well-

engineered systems, sound specifications and

proper installation will largely be wasted if the

necessary maintenance is not carried out.

Even high quality modern irrigation systems require

constant monitoring and adjustment to give the

optimal performance. Adjustment of drip-lines,

emitters and sprinklers is a day-to-day task

alongside daily landscape maintenance. Servicing

of solenoid valves and other components, and

cleaning of Y-strainers should be carried out as

scheduled maintenance tasks.

A professional and organised approach to system

maintenance is essential for protecting the

substantial initial investments as well as ensuring

trouble-free operation.

3.2.3 Planting Management

Unlike other disciplines, the landscape is dynamic

and in a continuous state of development and

change. This is particularly noticeable in warm

climates such as the Gulf States where irrigated

areas achieve rapid rates of growth and come to

maturity quickly. Although planting management

aims to respect the intended design effect, the

natural result of this process is that the balance of

planting types can change considerably as for

example, trees mature and shade out other planting.

This process will also have an effect upon the

irrigation requirements that may be impossible to

foresee accurately, but implies that flexibility should

be built into the original system designs.



4.0 Health & Safety

4.1 General Guidelines

Under current (2003) legislation, TSE application for

food for human consumption (e.g. salad crops) is

not permitted in Qatar.

Routine Health and Safety considerations for TSE

systems design bear many similarities with foul

sewerage design. There is, however, one major

difference in that the points of application of TSE for

irrigation purposes will be in public areas not under

the control of the DA. TSE is used for landscaping

enhancement in amenity areas, many of which will

be accessible to members of the public.

Exposure to TSE is therefore more likely in such

areas, by a wide cross-section of people. The

general public is less likely to be aware of the health

risks associated with treated effluent than operatives

at sewerage treatment plants. Likewise, the

operational staff that install and maintain the

irrigation systems may also be less likely to be

familiar with the health risks, being remote from the

treatment plant, and more associated with gardening

and landscaping.

For these reasons, it is important that designers give

due consideration to the health of such third parties

when designing TSE systems. It is not possible to

control the ultimate operation of the system at

design stage, however the designer can incorporate

measures to reduce risks. Such measures should

include the following as a minimum:

• Always provide a risk assessment for new

designs, and incorporate Control of

Substances Hazardous to Health (COSHH)

information for TSE into the pre-tender

health and safety plan;

• Provide recommendations for positioning of

irrigation equipment;

• Make recommendations for appropriate

training and certification of all operational

personnel;

• Design appropriate warning signs for public

areas.

The designer should be aware of the more obvious

public health concerns associated with use of TSE.

Untreated sewage can contain many different

pathogenic organisms such as helminths,

nematodes (e.g. ascaris and hookworm), viruses

and bacteria.

It is the policy in Qatar that all sewage is fully treated

and disinfected (generally by chlorination), prior to

discharge. Chlorination will eliminate most of the

pathogens, but some may remain viable. The WHO

publishes guidelines for the safe use of sewage

effluent in agriculture. As stated, Qatari policy is not

to use effluent on food crops; however, the

guidelines would still remain appropriate.

Guidelines for TSE chemical and biological

standards are given in Table 1.4.2 in Section 1.4.

The chlorination dosage is also critical for TSE.

Subsequent to disinfection, the chlorine residual

needs to be maintained in order to prevent

excessive growth of bacteria and other organisms in

the distribution system. This is due to the presence

of nutrients in the effluent being available as growth

factors. Hence, residuals need to be higher than in

potable water systems. However, residuals >5mg/l

will cause plant damage when sprayed direct onto

foliage21.

4.2 Reference Documents

The following is a list of documents that may be of

use to designers when considering health aspects of

TSE systems design.

1. World Health Organisation, 2000, WHO EHC 216

Environmental Health Criteria – Disinfectants and

Disinfectant By products, World Health

Organisation.

This is of relevance where greater detail may be

required in relation to formation of chlorinated

organics and their associated health effects.

2. World Health Organisation, WHO Guidelines for

the Safe Use of Wastewater and Excreta in

Agriculture and Aquaculture, World Health

Organisation.



This gives advice for use relating not only to the

pathogenic content but also a more in depth

discussion on other wastewater content.

3. Blumenthal et al, 2000, Guidelines for the

Microbiological Quality of Treated Wastewater Used

in Agriculture: Recommendations for Revising WHO

Guidelines, World Health Organisation.

This document covers more recent research and

recent literature relating to microbial content.

4. Construction Industry Research and Information

Association, 1997, Special Publication 137: Site

Safety for the Water Industry, London, CIRIA.

This document covers health and safety from a

more general practical aspect.

5. There is also published literature arising from time

to time from the Regional Centre for Environmental

Health Activities (CEHA), a subgroup of WHO,

dealing specifically with issues relating to the

Eastern Mediterranean Countries, having a similar

climate to the Gulf Region. Notes on these

programmes are published on the internet.



5.0 References

1 State of Qatar, 2002, Law No. 30: Environmental

Protection, Qatar, State of Qatar.

2 World Health Organisation, WHO Guidelines for

the Safe Use of Wastewater and Excreta in

Agriculture and Aquaculture, World Health

Organisation.

3 Qatar DD, Rationalisation of the TSE system

report, Qatar.

4 British Standards Institution, 1989, BS EN

545:2002 – Ductile Iron Pipes, Accessories, Fittings

and their joints for Water Pipelines, UK, BSI.

5 British Standards Institution, 1989, BS 8010-

1:1989 - Code of practice for Pipelines, Part 1:

Pipelines on land: general, London BSI.


12201:2002 – Plastic Piping Systems for Water

Supply – Polyethylene(PE), UK, BSI.

7 WIS 4-37-17.

8 Water Research Centre and British Plastics

Federation’s Pipes Group, 2002, Manual for PE Pipe

Systems, by Water Research Centre and British

Plastics Federation’s Pipes Group.

9 Water Research Centre, year, Network analysis -

A code of practice, UK, Water Research Centre.

10 British Standards Institution, 2000, European

Standard BS EN 805:2000, Water supply -

Requirements for systems and components outside

buildings, London, British Standard Institution.


124:1994 – Gully tops and manhole tops for

vehicular and pedestrian areas – design

requirements, type testing, marking, quality control

(AMD 8587), London, BSI.

12 IEC 60947-1,Ed 3.2:1999 Low Voltage

Switchgear and ControlGear. General Rules.

13 British Standards Institution, 1999, BS EN 60439-

1: Low Voltage Switchgear and Controlgear

Assemblies. Type-tested and PartiallyType-Tested

Assemblies, London, BSI.

14 British Standards Institution, 1991, BS EN ISO

6817: 1997: Measurement of conductive liquid flow

in closed conduits. London, BSI.

15 British Standards Institution, 1991, BS 7405:

1991: Guide to selection and application of flow

meters for the measurement of fluid flow in closed

conduits. London, BSI.

16 CIRIA & BHRA (Construction Industry Research

and Information Association, British

Hydromechanics Research Association). 1977. The

hydraulic design of pump sumps and intakes. CIRIA

& BHRA. ISBN: 0-86017-027-6.

17 British Standards Institution, 1993-1999, BS

7698 –Reciprocating Internal Combustion Engine

Driven Alternating Current Generator Sets, UK, BSI.

18 British Standards Institution, 1990, BS1377:

1990 - Methods of test for soils for civil engineering

purposes. London, BSI.

20 British Standards Institution, 1999, BS 5930 -

Code of practice for site investigations, UK BSI.

21 BSI. 1987. BS8007: 1987. Design of concrete

structures for retaining aqueous liquids. London.

British Standards Institution.

22 British Standards Institution, 1989, BS 2654 -

manufacture of vertical steel welded non-

refrigerated storage tanks, UK, BSI.

23 Metcalf and Eddy Inc. (1991). Wastewater

Engineering Treatment, Disposal and Reuse, 4th

edition, UK, Irwin McGraw-Hill.