WS-Chapter3 Print

8/13/2019 WS-Chapter3 Print

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CH-3.0 WATER QUANTITY

Before designing any W/S project, it isrequired to:

1. Determine demand rate

2. Fixing of design period

3. Population forecast at the end of design

period

Wednesday, April 24, 2013 1Chapter-3.0/ water Supply Engineering


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3.1 WATER DEMANDS Necessary to determine the total quantity of water required

for various purposes by the city , while designing the W/S

scheme Suitable water source is find out after total water demand is

determined

Not possible to accurate determination of the actual demand

Certain empirical formula and thumb rule are employed indetermining the water demand, which gives very near to

actual demands

Various types of water demands are

1. Domestic demand 2.Industrial demand

3. Institutional and commercial demand

4. Public demand 5. Fire demand

6. Live stock demand 7. Losses and wastesWednesday, April 24, 2013 2Chapter-3.0/ water Supply Engineering


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3.1 WATER DEMANDS1. DOMESTIC DEMAND:

It is demand of water required in houses for drinking,bathing, cooking, washing and house sanitation etc. it

depends on habits, social status, climatic conditions,

customs and living standards of people

In India: 135 & 200 lpcd for small and large towns

respectively

In developed countries: 200350 lpcd due to high

living standards

WHO standards: minimum 45 lpcd and 100-160 lpcd

for rural and urban areas respectively.



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3.1 WATER DEMANDS1. DOMESTIC DEMAND:

Design practice in Nepal:

25-45 lpcd for rural area (public tap) 65 lpcd for semi-urban area (public and private connection

without sanitation)

100-135 lpcd for urban area (public and private connectionwith sanitation)


Domestic demands Domestic Demands(lpcd) for small towns as per IS:1172-1993

a. Cooking 5

b. Drinking 5

c. Bathing 55

d. Cloths washing 20

e. Utensils washing 10

f. House washing 10

g. Flushing latrines 30

Total 135


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3.1 WATER DEMANDS2. LIVE STOCK DEMAND:

Water required for domestic animals and birds

Generally considered in rural W/S

In Nepal, also considered in urban W/S

20% of domestic demand = livestock demand


Live Stock and Domestic animals demands (lt./animal/day)

India Nepal

a. cows/buffalo 68.25 Department of W/S & sewage

guideline

UNICEF guidelines

b. Dogs 18.2 a. Big animals

(cow/buffalo/horses)

45 a. Horses 35

c. Chickens 0.09 b. Medium animals (dog,

goat, lamb etc)

20 b. cattle/buffalo 40

d. Goat/sheep 13.6 c. Smaller animals (bird,

chickens, duck etc)

20/100 c. pigs, sheep,

goat

10-15

e. horses 45.5 d. chickens 15/100


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3.1 WATER DEMANDS3. INDUSTRIAL DEMAND

Commonly considered in urban areaWater required by factories, paper mill, cloth mill,

breweries, sugar refineries etc.

No relation between industrial demand and

populationWater required in industries mainly depends on

the type of industry in the city

calculation for industrial demand is separately

done Industrial demand = 20-25%of total demand of

the city

Wednesday, April 24, 2013 Chapter-3.0/ water Supply Engineering 6


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3.1 WATER DEMANDS

4. INSTITUTIONAL & COMMERCIAL DEMAND

Universities, institutions, commercial

buildings, commercial centers including

offices, stores, hotels, shopping centers,

health centers, schools, temples, cinemahouses, railway and bus stations, airports etc

45 lpcd is taken

Follows the Indian standards



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Institutional and Commercial demand (India)

S.N Building types consumptions

1.a. Factories with bathroom 45

b. Factories without bathroom 30

2. Hospitals per bed

a. Nos of bed not exceeding 100 no. 340

b. Nos of bed exceeding 100 no. 450

3 Nurse homes and medical quarters 135

4 Hostels 135

5 Offices 45

6 Restaurants ( per seat) 70

7 Hotel ( per bed) 180

8 Cinema, concert halls and theatres (per seat) 15

9 Schools: a) day schools 45

b) boarding schools 135

10 Garden, sports ground 35/m2

11 Animals/ vehicles 45


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Institutional and Commercial demand (Nepal)

S.n Institutions Demands

Urban Rural

A Hospitals/health posts/clinics

i With bed 500 lt/bed/day 325-500 lt/bed/day

ii Without bed 2500 lt/day 1600-2500 lt/day

B Schools

i Boarders 65-135 lpcd 40 -60 lpcd

ii Day schools 10-45 lpcd 6.5-10 lpcd

C Hotels

i With bed 200 lt/bed/day 200 lt/bed/day

ii Without bed 500-1000 lt/day 500-1000 lt/day

D Restaurants/Tea stall 500-1000 lt/day 200-500 lt/day

E Offices

i Unclassified 500-1000 lt/day 325-1000 lt/day

ii Resident 65 lpcd 65 lpcd

iii Non-resident 10 lpcd 10 lpcd


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3.1 WATER DEMANDS5.DEMAND FOR PUBLIC USE or MUNICIPAL DEMAND

Water required for public utility purposes like washing andsprinkling on roads, cleaning of sewers, watering of public

park, garden, fountains etc

5% of total consumption is made for designing of a city


Public water demand

S.N Purpose Water requirement

1 Public parks 1.4 lt./m2/day

2 Street washing 1- 1.5 lt./m2/day

3 Sewer cleaning 4.5 lt./head/day

4 Garden & sports ground 3.5 lt./m2/day


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3.1 WATER DEMANDS6. Fire demand

Water required for fire fighting

Demand is not fixed, difficult to calculate

It is treated as function of population

Fire takes place due to various reasons

Large quantity of water required during firebreakdown to extinguish, so provision is made inwater supply system

fire demand is not considered in Nepal, both rural

and urban areasDifferent empirical relations can be used but, it is

suitable for specific conditions and locations

Cant be used directly for Nepalese conditionWednesday, April 24, 2013 Chapter-3.0/ water Supply Engineering 11


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3.1 WATER DEMANDSEmpirical formula for fire demand

1. Kuchlingsformula: Q = 3182P2. Bustonsformula: Q = 5663P

3. Free mans formula: Q = 1136(P/5+10)

4. Nation Board of Fire Underwriter Formula:Q = 4637P(1-0.01P)

Where, Q=quantity of water in lt./min.

P= population in thousand

5. Indian Water supply Manual(1976) formula

Q=100P where, Q= quantity of water in m3/day

P = population in thousandWednesday, April 24, 2013 Chapter-3.0/ water Supply Engineering 12


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3.1 WATER DEMANDS7. Wastes and Losses

All water from the source does not reach to consumersdue to:

1. Losses due to defective pipe joints, cracked andbroken pipes, faulty valves and fittings

2. Losses due to keep opening the consumer taps andpublic tap, even when they are not using

3. Losses due to unauthorized and illegal connections

Allowance of 15% of total quantity of water is made

Losses in KTM valley 40-50%, losses in metered supply30% and even upto 50% in un-metered supply

Therefore, total demand (t) = demand from(1+2+3+4+5+6+7)



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3.1 PER CAPITA DEMAND or RATE OF DEMAND

total annual average daily consumption

including all demands of water for a person

Per capita demand = Q/(P x 365) lt./day

Where, Q= total quantity of water required by

various purposes for a town in a year in liters

P = population of a town (found after

forecasting) at the end of design period

Per capita demand of a town depends on

various factors like standard of living, no. and

type of commercial places in a town etc.



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3.1 VARIATIONS IN DEMANDS fluctuation of water demand w.r.t time

Per capita demand (annual average daily consumption)is an average consumption of water for a year.

It has been seen that this demand does not remainuniform throughout the year, but it varies from season

to season, even hour to hourMaximum demand at all these variation are expressed

in terms of % of average annual daily consumption(AADC) or Qav

AADC or Qav = P x q where P - population

q - per capita demand

Any maximum demand at variation is expressed interms of % of AADC or Qav



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3.1 VARIATIONS IN DEMANDSA. SEASONAL VARIATION

Water demand is maximum in summer andminimum in winter

Variation may be up to 150% of average demandof year

B. DAILY VARIATIONThis variation depends on the general habits of

people, climatic conditions and character of cityas industrial or commercial or residential

More water demand on holidays compared toother working days

Maximum daily consumption is taken as 180% ofaverage consumptions



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3.1 VARIATIONS IN DEMANDSC. HOURLY DEMAND

Max. in morning and evening while min. inday time and least in night time

In industrial city where both day and night

shift are working, the consumption may bemore in night shift

Hourly variation may rise upto 200% ofaverage daily demand

D. MONTHLY VARIATION

Considered in Nepal

Monthly demand taken as 150% of AADCWednesday, April 24, 2013 Chapter-3.0/ water Supply Engineering 17


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3.2 DESIGN PERIOD Complete W/S project includes huge and costly

constructions such as dams, reservoir, treatment plantsand networks of distribution pipe lines.

These all works cant complete at a time, replacedduring maintenance

For designing and construction, they should havesufficient capacity to meet future demand of the townfor nos. of years

The number of years considered for which the designs

of water works have been done is known as designperiod

Mostly, 22-30 yrs.(generally 25 yr) in urban area, 15-20yrs. in rural area and if dam storage, it may 50 yrs.



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3.2 DESIGN PERIODService year( design year) = survey year + base

period + design period= base year + design period

Survey year:- year in which survey is carried

outBase period:- period of survey, design and

construction. Design period considered afterbase year. Generally 2-3 yr.

Base year:- year in which implementation isdone

Base year = survey year + base periodWednesday, April 24, 2013 Chapter-3.0/ water Supply Engineering 19


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3.3 POPULATION FORECASTINGPopulation of a town depends up on the

various factors like birth, death, migration andannexation

Future population may sharp rise, slowgrowth, stationary condition or even decrease

For prediction of population, development ofother similar towns is studied which havedeveloped under same circumstances

Information of population can be obtainedfrom census of GON(Bureau of statistics orother authorities) and surveys.



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3.3.1 MATHEMATICAL METHOD1. ARITHEMATICAL INCREASE METHOD

Suitable for larger and old cities, practically reachedtheir maximum development

Assumption: population is increasing at constant rate.The rate of change of population with time is constant

i.e. P2- P1= C(t2t1)

The population after n decades can be determined by:

Pn= P + n.C

Where, n = nos. of decades

c = constant determined by average ofincrease of n decades



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3.3.1 MATHEMATICAL METHOD2. GEOMETRICAL INCREASE METHOD

Also known as uniform growth methodSuitable for young and rapidly increasing cities

Commonly used method in Nepal

Assumption: % increase in population fromdecade to decade remains constant

Average % of growth of last few decades isdetermined and will be same for per decade

Where, p = present population

I = average % growth of n decades



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3.3.1 MATHEMATICAL METHOD3. INCREMENTALCAL INCREASE METHOD

It is an improvement of above two methodsFirst, the average increase in population is

determined by arithmetical method and then, tothis the average of the net incremental increase is

added once for each future decade

Where, P = present population

I = average increase per decader = average incremental increase

n = nos. of decades



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3.3.1 MATHEMATICAL METHOD4. DECREASE RATE OF GROWTH

In complete growth of a very old city, early growthtakes place at an increasing rate, but later the growth isat a decreasing rate

Similar to geometrical increase method except thatinstead of constant value of % increase in population

per time unit, the increase in population per unit timeis adopted

Useful for old established cities where population isapproaching saturation limit and rate of growth isshowing downward trend

i. Find net % increase in nth timeIn= In. d

ii. Then population at n time is



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3.3.2 GRAPHICAL METHOD1. SIMPLE GRAPHICAL (GRAPHICAL EXTENSION) METHOD

A curve drawn between population and time fromprevious census data

From the obtained curve pattern, the curve is

smoothly and carefully extended to forecast future

population

From this extended curve, the population at the

end of any decade is approximately determined

It is useful for providing check to the other methods



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3.3.2 GRAPHICAL METHOD2. GRAPHICAL COMPARISION (COMPARATIVE GRAPH) METHOD

Assumption: city under consideration will develop assimilar cities in the past

Method: plotting curves of cities that, one or moredecades ago, had reached the present population of cityunder consideration

Future expected population of town is determined fromthe graph

Curve of expected development of city underconsideration is extended comparing with the othercurves similar to city

Useful for those cities whose level of development issimilar to the other cities



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SIMPLE GRAPHICAL METHOD GRAPHICAL COMPARISION METHOD



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3.4 FACTORS AFFECTING DEMANDS1. CLIMATIC CONDITION

Hotter and dry places required more water than cold

places Sometimes very cold countries required more water due

to wastage

2. SIZE & TYPE OF COMMUNITY Water demand increase with increase of size of town due

to increased public area

3. LIVING STANDARDS OF PEOPLE

Per capita demand of the town increases with livingstandard of people

Use of air conditioners, room coolers, lawns and gardens,flushing of latrines, automatic home appliances etc.



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3.4 FACTORS AFFECTING DEMANDS4. INDUSTRIAL AND COMMERCIAL ACTIVITIES

Industrial demand has no link with population oftown

But , presences of industries in town increasesthe per capita demand of town enormously

Industrial demand is much more than domesticdemand

5. PRESSURE IN THE DISTRIBUTION SYSTEM

Rate of water consumption increases with waterpressure

Water get easily and losses due to leakage,wastages and theft etc.



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3.4 FACTORS AFFECTING DEMANDS6. SYSTEN OF SANITATION

In sewerage system, sewage is carried by water

Per capita demand of town having water carriagesystem will be more than town not using such systems

7. COST OF WATER Cost directly affect the demand

More cost of water- less use of water and viceversa

8. METERING

Use of water meter, lesser is the demand



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3.4 FACTORS AFFECTING DEMANDS9. SYSTEM OF SUPPLY

demand is lesser in intermittent and higher forcontinuous

10. EDUCATION AND AWARENESS

Education and awareness in people changes thebehavior of people in health care than waterdemand which led to use more water

11. AGE OF COMMUNITYOlder and stable communities use less water than

rapidly developing communities



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3.4 FACTORS AFFECTING DEMANDS12. OTHER SOCIO-ECONOMIC FACTORS

i. Public versus private tap stand: lowerdemand in public tap

ii. Affluent(wealthy) versus Subsistence(survival): rich family higher is demand

iii. Habits of people: frequency of washing andbathing habits of people affects in demands

iv. Distance of tapstand: nearer, demand is high

v. Urban versus rural: lower demand in ruralarea due to sanitation system, habit, livingstandards etc.


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WS-Chapter3 Print