Rainwater Harvesting Potential of North Western Part of Bangladesh

Abstract

Rainwater harvesting (RWH) is the most traditional and sustainable method, which could be easily used for potable and non-potable, purposes both in residential and commercial buildings. The main emphasis is given on the rainwater harvesting as a source of drinking water. The objective of this research is to study potential of rainwater harvesting system of 6 stations in Northwestern part of Bangladesh. The rainfall data for 37 years of these stations has been analyzed and a field survey has been conducted to gather sufficient data for making design of a reservoir tank. In performing the study, frequency analysis is performed on annual rainfall data from 6 stations of Bangladesh Meteorological Department (BMD). Mass curve analysis is used to determine required storage volumes for every location. Based on statistical analysis of required storage volumes, design curves are developed for estimation of storage tank volumes covering the need for drinking water of different household sizes.

Full text

International Conference on Planning, Architecture and Civil Engineering, 9 - 11 February 2017, Rajshahi
University of Engineering & Technology, Rajshahi, Bangladesh
Rainwater Harvesting Potential of North Western Part of Bangladesh
KEYA ROY1, SHAYLA SHARMIN2, MD. ZINARUL ISLAM3
1Lecturer, Department of Civil Engineering, RUET, Bangladesh (roykeya0944@gmail.com)
2 Department of Civil Engineering, RUET, Bangladesh (shaylasharmin.100016@gmail.com)
3 Department of Civil Engineering, RUET, Bangladesh (zinarul.ruet21@gmail.com)
Abstract
Rainwater harvesting (RWH) is the most traditional and sustainable method, which could be easily used for
potable and non-potable, purposes both in residential and commercial buildings. The main emphasis is given on
the rainwater harvesting as a source of drinking water. The objective of this research is to study potential of
rainwater harvesting system of 6 stations in North-western part of Bangladesh. The rainfall data for 37 years of
these stations has been analyzed and a field survey has been conducted to gather sufficient data for making
design of a reservoir tank. In performing the study, frequency analysis is performed on annual rainfall data from
6 stations of Bangladesh Meteorological Department (BMD). Mass curve analysis is used to determine required
storage volumes for every location. Based on statistical analysis of required storage volumes, design curves are
developed for estimation of storage tank volumes covering the need for drinking water of different household
sizes.
Keywords: Rainwater harvesting, Mass curve, storage volume, cost.
1 Introduction
Bangladesh is located between latitude 200 34′ to 260 38′ N and longitude 880 01′ to 920 41′ E and has tropical
monsoon with high rainfall from April to September (125 cm to 500 cm). In the north and north-western region
of Bangladesh due to heavy extraction of groundwater for irrigation, groundwater depletion continues during
summer and was a main constraint for the development of a dependable water supply system. Groundwater
depletion, water pollution and wetland degradation are causing serious pressure on water supply system in urban
areas (Ahmed, Anwar, & Hossain, 2013). Heavy rainfall is characteristic of Bangladesh causing it to flood every
year. With the exception of the relatively dry western region of Rajshahi, where the annual rainfall is about
1,600 mm (63.0 in), most parts of the country receive at least 2,300 mm (90.6 in) of rainfall per year. A
rainwater based water supply system requires determination of the capacity of the storage tank and catchment
area for rainwater collection in relation to the water requirement, rainwater intensity and distribution. The main
objectives of this study are as follows:
 To develop a feasible rainwater harvesting techniques.
 Determination of the required storage volume for different places (Rajshahi, Bogra, Ishurdi, Dinajpur,
Rangpur, Syedpur)
 Development of the general required storage volume-demand curve for six stations.
 Development of cost-storage volume relationship to examine suitability of the system.

K. Roy, S. Sharmin & Islam
ICPACE 2017
2 Rainwater Harvesting
The method of rainwater harvesting is as far the best possible way to conserve water and awaken the society
towards the importance of water. The method is simple and cost effective too. It is beneficial in the areas, which
faces the scarcity of water. People usually make complaints about the lack of water. During the monsoon lots of
water goes waste into the gutters. And this is when rainwater harvesting proves to be the most effective way to
conserve the water. We can collect the rain water into the tanks and prevent it from flowing into drains and
being wasted. It is practiced on the large scale in the metropolitan cities. In scientific term, rainwater harvesting
refers to collection and storage of rainwater and also other activities aimed at harvesting surface and ground
water, prevention of losses through evaporation of the limited water endowment of physiographic unit as a
watershed (Agarwal and Narain, 1999).
3 Rainwater Catchment Systems
Rainwater catchment systems can be classified according to the type of catchment surface being utilized e.g.
roof, ground and rock catchments.
3.1 Roof Catchment System
This is the most common type of catchment used for harvesting rainwater. The system consists of three main
components: a roof which acts as a catchment surface, a gutter and downpipe, and a tank.
3.2 Ground Catchment System
This is cheaper than roof catchment and is normally employed where suitable roof surface is available. The
main advantage, the availability of large area for water collection. Ground surface is normally not efficient for
collecting rainwater unless covered with cement or some other material to reduce its infiltration capacity. This
may, however, increase the cost of the system.
3.3 Rock Catchment System
This is generally constructed for communal supplies in areas where unjointed massive rock outcrops provide a
suitable catchment surface. The runoff is channeled along stone and cement gutters, constructed on the rock
surface, into reservoirs contained by concrete dams. If the dams lie above the settlements, water can be supplied
to stand posts through a gravity fed pipe network.
As ground catchment systems and rock catchment systems are beyond the scope of this work, they are not
considered further in this thesis. Concentration will be given to the roof catchment system only.
4 Methodology
In performing the job, rainfall data is undertaken from Bangladesh Meteorological Department. The maximum
amount of rainwater was encountered from a roof top;
V= fIA …………………………. (1)
Where V is the amount of harvestable water, A is the catchment area, I is total amount of rainfall, and f is the
runoff coefficient. Surveying was done in a particular area (Terokhadia) of Rajshahi, from where the catchment
areas were found as 800 ft2, 1200 ft2, 1600 ft2 and 1900 ft2. Average household size was found as 6. The system
was designed for meeting water requirements of 6 persons living in the entire building. Total area was about
1200 ft2 per capita water consumption is about 3 lpcd for conservative use.
The method was involved analysis of rainfall data using the mass curve technique. To successful use of this
method required a minimum of 10 years of raw data. It was included tabulating the monthly rainfall (mm),
monthly supply (liters),monthly amount stored (liters) cumulative supply (liters), monthly demand (liters),
monthly amount stored (liters) and total amount stored (liters).
The required tank volume was determined when the table is filled out. The least amount stored during the dry
seasons was subtracted from the largest amount stored during wet season. This difference represents the storage
volume required for that particular year. The difference between the largest and least amount stored in each year
was calculated. The largest difference yields the tank size.

K. Roy, S. Sharmin & Islam
ICPACE 2017
5 Analysis of data
From the analysis of data of rainfall 0f 6 stations for 37 years from 1979 to 2015, it has been found that heavy
rainfall in 6 stations concentrates mostly from April to October.
Figure 1. Average monthly rainfall distribution for Rajshahi (1979-2015)
6 Results & Discussions
Figure 2. Storage volume and household size
relationship for different consumption rates at
Rajshahi (f=0.75, A=1200 ft2)
Figure 3. Storage volume and household size
relationship for different consumption rates at
Rajshahi (f=0.80, A=1200 ft2)
Figure 4. Storage volume and household size
relationship for different consumption rates at
Rajshahi (f=0.85, A=1200 ft2)
Figure 5. Storage volume and household size
relationship for different catchment areas at Rajshahi
(f=0.85; q=3 lpcd)
0
1000
2000
3000
4000
5000
6000
7000
8000
012345678910
St ora ge required (litres)
Hou sehold size (persons)
3 lpcd
4 lpcd
5 lpcd

K. Roy, S. Sharmin & Islam
ICPACE 2017
Figure 6. Storage volume-demand relationship for
different roof areas for Rajshahi
Figure 7. Storage volume-demand relationship for
different roof areas for Bogra
Figure 8. Storage volume-demand relationship for
different roof areas for Ishurdi
Figure 9. Storage volume-demand relationship for
different roof areas for Rangpur
Figure 10. Storage volume-demand relationship for
different roof areas for Dinajpur
Figure 11. Storage volume-demand relationship for
different roof areas for Syedpur

K. Roy, S. Sharmin & Islam
ICPACE 2017
Figure 12. Effect of runoff coefficients (roofs) on storage volume for Rajshahi (q=3 lpcd, A=1200 ft2)
As rainwater harvesting is a new approach for Bangladesh, there is not much data available regarding the
material and construction cost for storage tanks. Moreover costs vary for different types of storage tanks. An
attempt has been made to establish a relationship between cost and storage volume from the table 1.
Table 1. Cost estimation of rainwater collection system
Unit price($)
Total price($)
Structural
Material
Gutters
11 m
0.31
3.41
Pipe (4 inch φ)
16 feet
1.7
27.2
Cup (Holler type)
1 piece
2.5
2.5
T socket
1
0.63
0.63
Tap
1
0.82
0.82
Lock
1
0.19
0.19
Great ball (2 inch)
1
5.63
5.63
L joint
2
0.5
1
Brick(9.5”×4.5”×2.75”)
1262
0.06
75.72
Labor
1
15
15
Annual maintenance
5
5
Total
137.1
*1 US$ = 78.4 Tk.
After all the calculations, a total amount of $138 would be necessary for building and operating whole system.
The table presents the list, unit price and total price of all materials that would be required. Unit price is only
applicable in Bangladesh. Unit price for this proposed system may vary in other countries all over the world.

K. Roy, S. Sharmin & Islam
ICPACE 2017
Figure 13. Cost-storage volume relationship for Bangladesh.
Conclusions
Water demand of Bangladesh with high population density cannot be met solely with municipal water supply
system especially during the dry season. Among all the alternative sources for water supply, rainwater
harvesting has become the most economical solution for the crisis area (Boers and Ben-Asher, 1982).There is
adequate rainfall during the rainy season distributed from April/May to October. In designing a rainwater
harvesting system, the monthly rainfall has more significance than the average yearly rainfall. For storage
volume calculations, rainfall distribution has more effect than the total amount of rainfall. It is also observed that
the required storage volumes calculated by the mass curve analysis for different runoff coefficients do not show
significant differences.
The water quality of rainwater is very high and the stored water quality is also very satisfactory when proper
attention is taken. This water is free from two extreme contaminants i.e., arsenic and fecal coliform (with due
care). The major advantage of the rooftop rainwater harvesting system is that the system is independent and
suitable for scattered settlements. The operation of the rainwater harvesting is easier than any other water supply
system. No specialized skills are necessary to operate the system. The success of the rainwater harvesting
system depends on the interest, enthusiasm and active support of the users. With the application of appropriate
water quality standards, treatment methods, and cross-connection safeguards, rainwater harvesting can be
effectively used in conjunction with public water systems (Rahman, Afreen, 2011).
References
Agarwal and Narain (1999). Rainwater harvesting as an alternative water supply in future. Published in Euro
Journal. Page-133,www.eurojournals.com/ejsr.htm.
Ahmed, M., Anwar, R., & Hossain, M. A. L. I. (2013). Opportunities and limitations in practicing rainwater
harvesting systems in Bangladesh, 2(4), 67–74.
Bangladesh Meteorological Department, Different Climatological Data for the period 1979 to 2015 at 6 stations
of Bangladesh, Dhaka.
Boers, Th.M. and Ben-Asher, J. (1982). A review on rainwater harvesting and Agricultural water management.
Global Publication Ltd., 145-158.
Rahman, Afreen, H. (2011). Potential of Rainwater harvesting in Dhaka city, (March).