Rainwater Harvesting in Educational Institution and Residential Area: A Case Study of University of Asia Pacific in Dhaka

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1 Paper ID: WRE International Conference on Recent Innovation in Civil Engineering for Sustainable Development () Department of Civil Engineering DUET - Gazipur, Bangladesh Rainwater Harvesting in Educational Institution and Residential Area: A Case Study of University of Asia Pacific in Dhaka P.C. Sarker 1 *, N. Islam 1 and R.C. Sarker 2 1 University of Asia Pacific, Bangladesh; 2 Swinburne University of Technology, Australia Abstract In recent time, a crisis of water supply takes place around the Dhaka city particularly in the dry season (November to March). Considering the higher growth rate of population in Dhaka city, water crisis will be more acute in the near future unless alternative source of water is found. Groundwater and Surface water (river) cannot meet the demand throughout the year. In this backdrop, rainwater harvesting system can be considered as a sustainable solution. University of Asia Pacific (UAP) city campus located at Green Road near Farmgate, Dhaka, Bangladesh is selected for this case study since rainwater is an alternative source of water because in the period of monsoon (April to October), a huge amount of unused safe, clear and pure rainwater is drained mostly as runoff or through existing drainage system and ultimately reach rivers surrounding Dhaka city. This study shows that rainwater harvesting in UAP City campus will provide significant supplementary support during monsoon season such as collected rainwater from April to October can fulfill up to maximum 66 % of monthly water demand. This harvested water can meet the drinking, washing and sanitation demand. From the econometric point of view, rainwater harvesting in UAP City campus is economically suitable and need 9.5 years to return the installment cost. Keywords: Alternative water resources, rainwater harvesting, rainwater tank 1. Introduction Bangladesh is located between latitude 20 o 34 to 26 o 38 N and longitude 88 o 01 to 92 o 41 E and has tropical monsoon with high rainfall from April to September (125 cm to 500 cm) [1]. The unique geographic location of Bangladesh, with the Indian Ocean to the south, the Himalayas to the North and the prevailing monsoons, has made it one of the wettest countries of the world. The mean annual rainfall of Bangladesh is about 2320mm [2]. Dhaka, the capital of Bangladesh, is the fastest growing mega city in the world. Every year the number of migrants is increasing in the Dhaka city. Dhaka city has been expanding with an annual rate of 3.5 percent following an unsystematic approach to accommodate huge population influx of people. Such urban sprawl exerts immense pressure on the infrastructures of the city. The city inhabitants, therefore, are deprived of basic amenities of urban life where water supply has appeared as the most critical issue. At present, water demand has surpassed the water supply where twenty five percent of the total population of Dhaka city has no direct access to potable water. According to a study conducted by the Institute of Water Modeling (IWM), the groundwater level of the Dhaka city is falling by 3m per year. Moreover, for severe electricity shortage, the option of groundwater withdrawal is also becoming difficult. Groundwater resource of the Dhaka mainly depends on the number of groundwater storage and the volume of annual recharge. Bangladesh receives a healthy amount of rainfall every year. According to Bangladesh National Water Plan Phase- II, "In 1991, Bangladesh receives an annual groundwater of 21 cubic meter [3]. Though the amount is satisfactory but due to an increasing demand of urbanization, the system of groundwater recharge

2 901 has been affected and the amount of surface run-off is increasing. Dhaka Water Supply and Sewerage Authority (DWASA) have faced challenges due to unplanned city development, and have started using surface water besides ground water. DWASA is trying to reduce the scarcity of water but there is still some lacking in water supply. "In 2010, total water demand was 1980 million liter per day (MLD) and the available water was 1700 MLD. Total deficit was 280 MLD. By the year 2020, the predicted water demand will be 2240 MLD and total predicted water availability will be 2125 MLD. Total deficit will be 115 MLD [3]. There exists some system loss in the collection and distribution process which makes it difficult to reduce the deficit only with the ground water and surface water. In Dhaka city the depletion of the ground water table (GWT) has started from a depth of 100m and in some places one needs to dig 300m to reach the main aquifer. The depletion rate varies from area to area. In Mirpur the groundwater level dropped meters between 1991 and 2008 at a rate of 3.2 meter per year. While the decline was 1.1 meter per year in Mohammadpur, it was 2.2 meter per year in Sabujbagh, 0.5 meter per year in Sutrapur, and 0.8 meter per year in Dhaka Cantonment during the same period [3]. The GWT will go down to 120min 2050.Table 1shows the ground water depletion of Dhaka city from 1996 to 2007 which illustrates how this depletion will hamper total water supply network as many operational deep wells may be shut down due to scarcity of water. Considering the declining groundwater level of Dhaka city, it is obvious that other sources of water need to be explored. In many countries, rainwater is used to supplement water supply which is known as 'rainwater harvesting'. Surplus rainwater is also used for groundwater recharge. Even though DWASA has started to use surface water to add to the groundwater supply, it is still not sufficient. The objective of this study focuses on designing and evaluating a rainwater harvesting system for an educational institution University of Asia Pacific (UAP). Table-1. Ground water level depletion situation in Dhaka city (Source: [4]) Year Depletion (m) 2. Study Area And Dataset 2.1. Site Selection This study broadly focuses on application of rainwater harvesting with special focus on educational insinuation. The city campus of University of Asia Pacific (UAP) was considered in this study. The campus is 13 storied building. The total number of beneficiary of the campus is around The location of the campus is 74/A, Green Rd, Dhaka Data Collection Rainfall data To find out the total available rainwater, calculation of the amount of rainfall is necessary. In this study area, there is no particular rain gauge station. So rainfall data from a representative location (recommended by BMD) [5] was collected to estimate the rainwater volume Daily water consumption data of Dhaka city Dhaka is one of the fastest growing cities of the world. So it has a high daily water consumption rate. Water is used for various purposes. From drinking purpose to toilet flushing, water is required. There are several studies focusing on daily demand of Dhaka City. According to Uddin&Baten [3], DWASA has projected water demand as 150 liters per person per day (l/p/d). Empirical evidence shows that

3 Total Monsoon Rainfall (mm) 902 one-third of the city dwellers receive only 40 l/p/d and they have to manage their daily activities with this little amount of water. Only 5.1 percent of total population of Dhaka city receives more than 60 l/p/d. On an average, 42.8 percent of the respondents can receive basic requirement of 50 l/p/d and the rest (57.8 percent) are suffering from water scarcity despite piped connection [3]. Center for Science & Environment also investigates that the daily water consumption rate has estimated 135 l/p/d [6]. These data were adopted in this study as it is very decently broken down Catchment Data In this study, the basic catchment is the roof top of the building. Based on our calculation conducted using the hand measurement, the total roof top area in UAP city campus is ft 2 or 2343 m Data Analysis 3.1. Rainfall Potentiality of rainwater harvesting for an area varies due to the change of rainfall pattern, quantity and quality. To calculate this potentiality, reliable rainfall data is required. For this research, 21 years ( ) of rainfall data of Agargon station was collected from Bangladesh Meteorological Department (BMD). Figure 3.4 shows the monsoon (April to October) rainfall distribution. In monsoon season, the highest rainfall was 2500mm and the lowest was 1000mm. The additional water received during monsoon is a major source of water for rainwater harvesting Year Fig. 1.Distribution of monsoon rainfall (over 21 year s period) (Source: [5]) 3.3. Demand Requirement For water demand calculation and for demand analysis UAP city campus is selected which follow the institutional criteria. According BNBC [6] the water requirement for residential area of restricted facility is 45 liter per capita per day (lpcd).for educational institution, the water requirement is 30lpcd [drinking (5L), sanitation (15L) and washing (10L)] Demand Measurement of UAP City Campus Considering 5,000 capita as total number of beneficiary (Total number of student(4,500), Total number of faculties (350) and Total number of staff(150)), 23days/ month as total number of working days in a month and 8 hours/day as working hour per day, 30L/c/day as daily water demand, Total monthly water consumption of UAP was estimated as 34,50,000 L/month and in 8 hour demand 11,50,000 L/month/8hr Rainwater Harvesting Rainfall data is required to calculate the amount of rainwater that can be harvested from a rooftop area. According to roof top plan of the university, the measured roof area is 2343 square meter (sqm). The average annual rainfall of Dhaka City is 2000 millimeter (mm). The monthly average rainfall data

4 903 based on 21-year period data ( ) is given in Table 2.In the table 2, maximum average rainfall is found in the month of July ( mm). Table 3 shows the monthly demand in 8 hours and harvestable rainwater volume. Table 3shows the water savings percentage in different months throughout the year among which month of July yields maximum of 66%.The distribution of harvested rainwater that can be used in different types of water use such as: drinking, washing and sanitation and ground water recharge. Table-2. Monthly Average Rainfall (mm) in 21 years ( ) (Source: BMD, 2014) Month Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Average Rainfall (mm) ` Table-3. Monthly harvestable water, water demand (in 8 hours) and percentage of water savings Month Harvestable rainwater (L) Demand/8 hrs (L) Demand fulfilled/ Month (%) January February March April May June July August September October November December Water Savings from rainwater harvesting per year and cost return for the UAP city campus. Table 4 shows the economic saving due to installation of a rainwater harvesting system in UAP. Cost return period for UAP city campus has been calculated as 9.5 years that means 9.5 years are required to return the installment cost of water supply (excluding reservoir tank) and GWR. Table-4.Cost savings per year Month Used Water (L) Cost/Liter (BDT) Saving (BDT) January February March April May June July

5 904 August September October November December Total 23, Qualitative Benefit Analysis Traditionally in an urban landscape, rainwater was considered as a burden and the general practice was to get rid of the water from our rooftop and lawn as soon as possible. However, considering the gradual decrease of ground water supply and lack of clean surface water, use of rainwater for household purpose seems to be a viable and effective solution. In the above analysis, we have shown the benefit of using rainwater for UAP. Considering the fact that previously this rainwater was completely unused, this saving in water is quite significant. Besides, rainwater harvesting reduces pressure on the groundwater system. In Dhaka city where 80% of the total water supply comes from groundwater, usage of rainwater reduces the amount of groundwater to be withdrawn by WASA. This also helps to increase the groundwater level of our aquifer system, which is dangerously falling down on an average by 3m annually. During monsoon, flooding in Dhaka city even for a small storm event is a common scenario. Undersized system, lack of drainage infrastructure, significant reduction of receiving water bodies and lack of permeable green spaces are some of the main causes behind the flooding in Dhaka city. To minimize this flooding problem, rainwater harvesting can play a complementary role along with other existing flood reduction measures. If rainwater harvesting is adopted at an educational institution, a cumulative impact will be observed in reducing the flooding potential in Dhaka city. Finally yet importantly, if we think about the cost of a RWH system, it might seem high compared to a conventional pipe system. However, if we consider the installation and maintenance cost and adds the cumulative saving of groundwater to it, the long-term benefit overrides the cost of the system. 5. Conclusion Feasibility of rainwater harvesting systems has been investigated in this study. Performed analysis shows that rainwater harvesting helps water supply system to meet the demand in Dhaka city. During monsoon, it provides safe drinking water, reduces the risk of urban flooding. It also recharges the ground water table and takes pressure off from the overhead supply system. This study has shown that, rainwater harvesting is an energy efficient technology and can be a good solution for environmental sustainability. It also reduces the water bill for the dwellers of the Dhaka city. From this study it can be concluded as follows: Rainwater harvesting system of UAP city campus has been evaluated. Collected rainwater from April to October can fulfill (min.) to 66 % (max.) of monthly water demand. Rainwater harvesting in UAP City campus is economically suitable and requires 9.5 years to return the installment cost of water supply and GWR. Collected rainwater from every month can be used for ground water recharge. 6. Limitations of The Study There are some limitations of our study, those are given below: This study is limited to design only. No pilot project was set up for this project. Existing tank was used for the analysis purposes.

6 905 Educational institution has been adopted for the case study. It is applicable to residential and commercial buildings too. 7. References [1] Islam, M.M., Kabir, MR, Chou, F.N.F., Feasibility study of rainwater harvesting techniques in Bangladesh. Rainwater and Urban Design Conference, Barton (A.C.T.): Engineers Australia, Sydney, 2007 [2] Hossain, M., Islam, A.T.M.A. and Saha, S.K., Floods in Bangladesh-an analysis of their nature and causes In: Floods in Bangladesh Recurrent disaster and people s survival. Universities Research Centre, Dhaka, Bangladesh, pp [3] Uddin&Baten,Water Supply of Dhaka City: Murky Future, The Issue of Access and Inequality, UnnayanOnneshan, 2011 [4] BADC, Bangladesh Agricultural Development Corporation, Ground Water Monitoring Survey Project [5] BMD, Bangladesh Meteorological Department, Agargao, Dhaka, Bangladesh, 2014 [6] CSE, A Water Harvesting Manual For Urban Area Case Study from Delhi, Center for Science and Environment, New Delhi, India, 2010 [7] BNBC, Bangladesh National Building Code, 2010