Rainwater Ujaveriana Torres 2011

12th International Conference on Urban Drainage, Porto Alegre/Brazil, 11-16 September 2011

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Torres et al. 1

Proposal and assessment of rainwater harvesting scenarios on the

Javeriana University campus, Bogota

Torres A.1*, Estupiñán Perdomo J.L.1, Zapata García H.O.1

1 Grupo de Investigación Ciencia e Ingeniería del Agua y el Ambiente, Facultad de

Ingeniería, Pontificia Universidad Javeriana, Carrera 7 # 40 – 62, sede Bogota,

Colombia *Corresponding author, e-mail [email protected]

ABSTRACT

Globally, rainwater harvesting is becoming more important as a concept that can

support urban sustainable development. The objective of this work was to assess the

infrastructural requirements to use rainwater at the Pontificia Universidad Javeriana

campus in Bogota, through an inventory of water uses, rainfall measurements of the

study area and water quality assessment coupled to pipe hydraulics modeling. The

proposed system allows supplying 14 % of the total use of non-potable water, which

represents savings of 24.174.754 Colombian Pesos (COP) (12.723 USD). Due to a high

initial investment of 694.967.383 COP (365.772 USD), the return of the investment is

assessed as more than 30 years and the proposed rainwater harvesting system therefore

has a low financial viability.

KEYWORDS

Rainwater harvesting, water balance, University Campus, Environmental sustainability

INTRODUCCIÓN

Globally, rainwater harvesting is becoming more important as a concept that can support

urban sustainable development. Nowadays, rainwater in urban areas is principally used

for toilet discharges and irrigation of gardens (Hatt et al., 2004), through technical,

scientific, socioeconomic concepts, associated to sustainable construction processes

(Coombes et al., 2000; Mbugua, 2002). In Latin America, Brazil, Mexico and Chile are

forerunners using this practice for non-potable purposes (Ghisi et al., 2006; May, 2004;

Pachauri, 2008).

With few exceptions, in Colombia rainwater is used for non-potable purposes by

employing handmade tools for water collection, as well as for storage and distribution

processes (Castañeda, 2010; Ramírez, 2009; Sánchez & Caicedo, 2004). This practice

represents high morbimortality risks associated to malaria and other gastrointestinal

ailments. Moreover, in Colombia few research experiences on rainwater harvesting have

been conducted and reported (Castañeda, 2010; Lara Borrero et al., 2007; Suárez et al.,

2006; Torres et al., 2011).

Pontificia Universidad Javeriana’s Campus in Bogota is located at the foothills of the

mountain chain that surrounds Bogota in the east and therefore receives high levels of

precipitation (around 1000 mm/year), which is potentially attractive for planning

2 Rainwater Harvesting on the Javeriana University Campus

rainwater harvesting strategies. Lara Borrero et al. (2007) studied the water resource

availability on the campus with supply and demand balances. Although the conclusions

of that study were enhanced in relation with rainwater availability on the campus,

questions about the water quality and infrastructural demands for a correct rainwater

harvesting were not addressed.

The main objective of the present research is the determination of the infrastructural

requirements in order to fulfill different requirements on the campus by means of

rainwater considering the following criteria: (i) variability on runoff water quality, (ii)

water use on campus, (iii) existing topographical and infrastructural conditions, (iv)

potential collection and storage zones, (v) relationship between supply and demand and

their location on the campus, (vi) economical and environmental benefits, and (vii)

installation and operating costs.

METHODS

The campus of Pontificia Universidad Javeriana in Bogota (PUJB) includes 18 hectares

and almost 200.000 m2 of constructions where academic, administrative, parking areas,

chapels, banks, meeting and other service buildings, as well as sport fields and green

zones can be found (see location of buildings in Figure 1). Every day, approximately

30.000 people enter the campus, whose buildings are up to 70 years old, but mostly

around 40 years and several are recent constructions. The Bogota Water and Sewage

Company (EAAB) provides potable water service to the 46 buildings on campus, which

is accounted by a mean of 16 water flow meters. The variations in consumption were

analyzed, obtaining the historical monthly mean drinking water consumption on

campus.

Figure 1. Location of the buildings on PUJB campus (source: www.javeriana.edu.co)

Water use assessment was realized by means of a field study of the campus, using a site

record form. For each water use, three levels were attributed (minimal, mean and high)

according to consumption scenario analysis. Additionally, variations on water demand

were taken into account using (i) maximum flow rates for water pipes considered, under

the assumption that all the systems are operating simultaneously, (ii) adjusted water

demands using simultaneous demand coefficients for sanitary facilities (Pérez Carmona,

2004) and (iii) evaluation of the system in critical periods by using the augmentation

coefficients proposed by the national Development Ministry (Ministerio de Desarrollo


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Torres et al. 3

Económico, 2000), in order to take into account the behavior regarding a non-expected

increase of the demand (for example growth of campus population).

The analysis of the hydrological supply was executed using the collected inter-monthly

precipitation information between 1936 and 2009 from a rain gauge near the university

campus (San Luis). From this analysis, monthly historic mean values were obtained and

adapted to the campus area. In this way, the mean monthly supply on rainwater was

estimated.

Additionally, the runoff coefficients for the surfaces of the campus were assessed and

different water balances were set up with the aim of examining behaviors related to the

supply and demand of rainwater on campus.

The proposed use scenarios were described as follows: (i) rainwater harvesting for

100% of the university’s uses by means of collecting rainwater on the whole campus

area; (ii) rainwater harvesting for non-potable uses only by means of collecting

rainwater on the whole campus area; (iii) rainwater harvesting for non-potable uses by

means of collecting rainwater on roofs and the soccer field; (iv) rainwater harvesting for

external uses supplying 40 % of the total demand, by means of rainwater collecting on

roofs and the soccer field; (v) rainwater harvesting for external uses supplying 38 % of

the total demand, by means of collecting rainwater on roofs and the soccer field, hard

surfaces and gardens.

The results showed the need of dividing the campus in different potential water

exploitation sub-basins to distribute requirements of infrastructure related to different

uses, especially for the storage facilities. According to the results, two sub-basins were

identified and taking into account the water balance analysis, the supply in each sub-

basin was determined. In accordance with topography and location criteria, zones that

could be supplied with water were identified and this way, the demand in each sub-

basin was determined. The demand values were estimated using a trial and error

methodology for different case scenarios, establishing a definition of storage volumes

for the final scenario, according to water balances assessments based on: (i)

consumption scenarios and expected water quality related; (ii) hydrological supply

based on information from San Luis rain gauge station; (iii) rain-runoff parameters

allowing to transform raw into net hydrological supply.

Different pipe materials (PVC and PE), as well as two options for the topology of the

pipe systems (tree-type and mesh network), were taken into account. The software

WaterCAD (Bentley) was used with the goal of dimensioning a hydraulic infrastructure,

taking into account existing pipes, diameters and optimal pipe materials, accessories and

valves, as well as service levels with respect to pipe pressures and water levels in tanks

and storage facilities. No collecting pipe design was proposed, as our proposal is to use

existing facilities in order to supply rainwater from the storage tanks to the usage areas,

and for this purpose only some modifications of the existing rain water drainage

systems would be necessary.

With the design and definition of all requirements of infrastructure according to their

technical viability, a cost viability study was created, which allowed quantifying the

economical investments needed to implement the rainwater harvesting project.

Moreover, a financial evaluation was realized using tools like Net Present Value (NPV),

Internal Rate of Return (IRR) and Benefit-Cost Ratio (BCR), with the objective of


assessing the economical feasibility, the return periods of the investment and the

economical benefits of the project in comparison to the reduction of water consumption

from the conventional water supply system.

RESULTS AND DISCUSSION

It was established that PUJB uses around 16.651 m3 of water each month and 199.807

m3 yearly. Historically, the water use decreased between 2004 and 2007, but increased

again in 2008 and 2009, so that the use was higher than in 2004. The minimum, mean

and maximal use of water for each building was determined and varied between 134 L/d

(building 35, Figure 1) for the minimal use scenario to 111.751 L/d (buildings 50, 51

and 52, Figure 1) for the maximal use scenario. Additionally, the buildings with highest

(buildings 2, 11, 25, 50-53, 67 and 115, between 14.971 L/d and 78.051 L/d) and lowest

demands (buildings 5, 23 and 35, between 219 L/d and 1.978 L/d) were determined

(consult Figure 1 for locations of the buildings).

With the analysis of water use it was assessed that floor cleaning and irrigation of

external gardens, toilet discharges and cleaning of hard surfaces are the uses with the

highest demands (72 % on the total campus). Likewise, it was also established that the

uses that mainly need potable water are hand washing, laboratory activities, drinking

water, showers and dishwashing, which correspond to only 20 % of the total uses of the

campus.

Moreover, it was observed that the mean monthly water demand on campus varies

substantially and is bimodal. The periods of highest use are the months of academic

activity (February-May and August-November), while use is substantially reduced in

vacation times between semesters (December-January and June-July). The highest use

was registered in September and the lowest in January.

Regarding water supply, the analysis on San Luis rain gauge allowed establishing that

the mean annual precipitation of the zone is 1.007,6 mm.

A preliminary analysis of the different scenarios showed that the first four were

financially not feasible for the following reasons: (i) due to the topography of the

campus, an implementation of an expensive pumping system would be necessary; (ii)

the water storage volumes were excessive (above 4.500 m3), demanding high

investments and space requirements on campus.

For scenario no.5 (rainwater harvesting for external uses supplying 38 % of the total

demand), with the aim of reducing storage tank volumes and taking into account the

topography and existing water pipe distributions, the potential exploitation zones and

placing of the demands, two sub-basins were estimated, defined as Soccer Field and

Baron sub-basins (see Figure 2). As a result of the balances, storage volumes of 912 m3

and 473 m3, were estimated for the sub-basins. The Soccer Field sub-basin would

supply external uses of the lower zone of the campus for irrigation and floor, façade and

hard surface cleaning purposes. The Baron sub-basin would supply water for non-

potable uses at the first three levels of the Engineering Faculty (Building no. 11).


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Torres et al. 5

As a result of the hydraulic analysis, aimed at achieving the service levels demanded by

the national Development Ministry (Ministerio de Desarrollo Económico, 2000) in

terms of pressure (39 kPa), we obtained simple commercial diameters of 2” for most of

the pipes (290 m, representing 41 % of the total length) of 1.5” for intermediate

networks (199 m, 28 %) and 1” for end networks (225 m, 31%) after 12 simulations

using the software WaterCAD (Bentley). A detailed analysis of the Soccer Field sub-

basin allowed to establish that the network of this sub-basin needs to increase the pipes’

diameters significantly in order to distribute the demanded volumes in a better way in

case of an increase in actual water demand.

Figure 2. Location of sub-basins PUJB campus (modified: www.javeriana.edu.co)

The identified collecting pipes of the following types: (i) for Soccer Field sub-basin,

two 8” supplying networks from building 115 were identified; (ii) for the Baron sub-

basin, four 8” supplying networks were identified from the south-western part of the

campus.

Regarding the campus results of runoff water quality obtained in Torres et al. (2009), it

was possible to detect that most of the pollutants are heavy metals, such as iron, lead,

cadmium and mercury, organic matter (BOD5), ammonia, suspended solids and

coliform bacteria. Therefore, treatment processes for both sub-basins were selected as

following: (i) multiple-step filtration systems, (ii) settling systems and (iii) activated

carbon film treatment.

For the proposed Soccer Field sub-basin harvesting system, the estimated budget is

448.200.453 Colombian Pesos (COP) (235.895 USD). For the Baron sub-basin

harvesting system the budget is proposed as 246.776.930 COP (129.878 USD). So, the

total cost for the construction of the exploitation systems would be 694.967.383 COP

(365.772 USD).

http://www.javeriana.edu.co/


Therefore, the total percentage of rainwater use on the university campus would be 14%

of the total water use, reducing the potable water consumption by 2.014.563 COP

(1.060 USD) per month, which would result in total savings of 24.174.754 COP (12.723

USD) per year due to an exploitable rainwater volume of around 28.000 m3 per year.

The following are the financial indicators calculated for the Soccer Field and Baron sub-

basins, respectively: (i) NPV: 6.665.291 COP (3.508 USD) and 10.245.752 COP (5.393

USD); (ii) IRR: 3,52 and 3,68; (iii) BCR: 1,01 and 1,04. An evaluation period of 30

years was established, but, as the indicators do not show feasibility, an additional return

period of 3 years was added. Increasing the projection analysis, it was established that

an equilibrium point was obtained in year 33, when the project would became stable and

profitable.

CONCLUSIONS

The present work consisted in estimating the infrastructural requirements to supply for

rainwater harvesting, several demands at the Pontificia Universidad Javeriana campus in

Bogota were evaluated through an inventory of water uses and studying rainfall

measurements of the zone and runoff water quality assessments coupled with hydraulic

modeling.

Two potential sub-basins were identified for the exploitation of the elevated part of the

campus supplying approximately 14 % of the total water use of the campus: (i) Soccer

Field sub-basin with a storage structure of 912 m3 for external uses in the lower part of

the campus (irrigation and cleaning of façade and hard surfaces) as well as public toilets;

(ii) Baron sub-basin with a storage structure of 473 m3 for non-potable uses in the first

three levels of building 11 (see Figure 1).

Based on 12 hydraulic modeling results, optimal pipe sections (1” to 2”), pipe material

(PVC) and accessories, and required regulation valves were selected, as well as service

levels in terms of pressures in the pipe system and water levels in tanks and storage

structures. In accordance to runoff rainwater quality on university campus (presence of

heavy metal, suspended solids, ammonia and organic matter concentrations), a multiple-

step filtration system was selected in association with an activated carbon film and a

settling process in storage tanks.

Accounting for hydraulic and treatment structures and facilities, the investment required

for implementing the rainwater harvesting system proposed was assessed to

694.967.383 COP (365.772 USD), representing annual savings of 24.174.754 COP

(12.723 USD) due to the reduction of potable water consumption, nevertheless, the

BCR indicator is higher than unity. The return of investment is assessed to more than 30

years, which indicates that the proposed project has a low financial viability.

Nonetheless, in this paper some benefits, such as environmental ones, obtained by

implementing a rainwater harvesting system were not assessed. On the other hand,

solutions proposed were not faced to the campus development policies and impacts on

the construction phase with regard to service coverage were not assessed, either. These

aspects will be studied subsequently, where additionally Sustainable Urban Drainage

Systems (SUDS) will be considered as components of the rainwater harvesting system.


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Torres et al. 7

ACKNOWLEDGEMENT

The authors wish to thank Pontificia Universidad Javeriana Campus Administration and

Bogota Water and Sewage Company (Empresa de Acueducto y Alcantarillado de

Bogota - EAAB) for the information used in this work under collaboration agreement

number 9-07-26100-1060-2008.

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Rainwater Ujaveriana Torres 2011