INTERNATIONAL JOURNAL OF ENVIRONMENTAL SCIENCES Volume 1, No 7, Copyright 2010 All rights reserved Integrated Publishing Association

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1 INTERNATIONAL JOURNAL OF ENVIRONMENTAL SCIENCES Volume 1, No 7, 11 Copyright All rights reserved Integrated Publishing Association Review article ISSN A pilot scheme for rooftop rainwater harvesting at Centre of Mining Environment, Dhanbad Department of Mining Engineering, Indian Institute of Technology, Kharagpur patrakaditya@gmail.com ABSTRACT Dhanbad is one of the water scarce cities in India. Depending on precipitation intensity, rainwater constitutes a potential source of drinking water. Rainwater harvesting is the technology where surface runoff is effectively collected and stored. Harvested rainwater can then be used for drinking or for ground water recharge. Unless a proper water storage method is adopted, the rainwater harvesting may not be effective. This paper deals with a case study of rain water harvesting method adopted in Dhanbad city of Jharkhand state. Keywords: Rainwater harvesting, water savings, infiltration rate, water requirement, runoff. 1 Introduction The world s single biggest water problem is scarcity (Jury and Vaux 6). Rising population and urbanisation coupled with climate change may reduce urban water supply in developing countries (Murad et al. 7; O Hara and Georgakakos 8; Wheida and Verhoeven 7). The benefits of rainwater harvesting are enormous (Krishna 5).The Groundwater reservoirs get water as a result of recharge by infiltration from rainfall (Precipitation), rivers, canals, irrigation water etc. and loose water due to regeneration in surface water bodies, movement towards down slope of aquifer surface and manmade withdrawals. Such manmade withdrawals are very prominent in mining areas. Rapid industrial development, urbanization and increase in agricultural production have led to freshwater depletion in many parts of the country. Extensive use of advanced pumping techniques has made it possible to extract groundwater from greater depth, making the problem more acute. In this context, rooftop rainwater harvesting can become a popular technique to improve the storage and recharge of water. Proper recharge of harvested water can augment the ground water storage and increase the ground water level (Chandra, 1979). This will also partially meet the demand of drinking water. It would also reduce the wastage of water due to surface run off and has the potential to choke the storm drains (Al Shareef and Abdulla, 9). 2 Study area The study area is Centre of Mining Environment (CME) at Indian School of Mines, located in Dhanbad town (Figure 1). It is situated in Bihar plateau at a height 2 24 m above mean sea level (MSL). Further, the town is situated on very old rocks of the Achaean age. The rocks are generally hard and compact with occasional joints and fractures and weathering on the surface. These are the only characteristics which allow formation of aquifers here. Thus, because of not being located in a sedimentary basin, the region is devoid of thick aquifers. Further, horizontal continuity of aquifers up to a long distance is a rare phenomenon in this area. 3. Design criteria of rainwater harvesting structure Received on March 11 Published on April

2 Structures for rain water harvesting should be designed on the basis of availability of space, availability of runoff, depth to water table & lithology of the area. Two most important components, which need to be evaluated for designing the rainwater harvesting structures, are Hydrogeology of the area including nature and extent of aquifer, soil cover, topography, depth to water levels and chemical quality of ground water. Hydro meteorological characters viz. rainfall duration, general pattern and intensity of rainfall. (Source: Figure 1: Location Map of Study area (Dhanbad Township) International Journal of Environmental Sciences Volume 1 No.7,

3 3.1 Assessment of Runoff The runoff can be assessed by following formula. Runoff = Catchment Area Runoff Coefficient Rainfall Runoff coefficient plays an important role in assessing the runoff availability and it depends upon catchment characteristics. General values are tabulated below (Table 1) which may be utilized for assessing the runoff availability. Table 1: Runoff coefficient of different catchment Types of catchment Roof top Paved area Bare ground Green area Runoff Coefficient Soil Sample Analysis Soil sample analysis is essential for knowing the properties of soil through which the water recharge will take place. Some parameters of soils sample such as infiltration rate, moisture content, bulk density, water holding capacity have been estimated by Standard methods (Maiti, 1). The formulae for assessment of these parameters are summarized in Table 2. Table 2: Soil analysis parameters (Maiti, 1) Sl. No Parameters Formula Reference Infiltration Rate Moisture Content Bulk Density Water Holding Capacity IR = volume of water entering in inner ring(ml) / cross sectional area of the inner ring(cm 2 ) time (hr) MC = loss of moisture/weight of oven dry sample BD = weight of oven dried soil (g) π r 2 h WHC = water / soil Calculation Method of Infiltration Rate Gravitational Method Calculation Method Calculation Method International Journal of Environmental Sciences Volume 1 No.7,

4 4. Results and Discussion 4.1 Infiltration rate The observations of the area are presented in Table 3. The soil infiltration rate of the study area varied from 5.85 cm/hr to 15.6 cm/hr with an average value of 7.83 cm/hr. This indicates that the soil has good porosity and percolation rate. Table 3: Soil Infiltration data near the rain water harvesting (RWH) site at CME Campus Sl. No Time (min) Volume (ml) Time (min) Volume (cm/hr) Results of infiltration measurements can be presented by plotting infiltration rate as well as cumulative infiltration as a function of time (Figure 2). The height of curve shows the maximum rate at which water can soak in to the soil. Figure 2: Infiltration rate at CME rain water harvesting (RWH) Site The moisture content, water holding capacity and bulk density of the soil sample is presented in Table 4. The result indicates that the soil in the study area is good for groundwater recharging. International Journal of Environmental Sciences Volume 1 No.7,

5 Table 4: Results of soil sample analysis Sl. No Parameters Results Moisture content Water holding capacity Bulk density 19.81% 33.% 1.27% 4.2 Proposed rooftop rainwater harvesting scheme The proposed rooftop rainwater harvesting system is a low cost one as proposed by earlier researches (Bhattacharya and Rane, 8). The rainwater pipes are 1 mm diameter and are made of PVC. The areas of rooftop rainwater harvesting system are m 2 (Figure 3). Figure 3: Schematic diagram of proposed rooftop rainwater harvesting structure in CME The scheme provides 3 recharge pits (RP1, RP2 and RP3) of different diameter; such as 3.3 m, 2.45 m, and 2.45 m respectively. While RP1 and RP2 ate the main recharge pits of the study area, RP3 acts as storage for overflow water from RP2. The material used for construction included 2 m thick coarse sand (1.5 mm 2 mm) layer, 1 m thick layer of gravels ( mm) and 1 m thick boulder (75 mm) layer (Figure 4). International Journal of Environmental Sciences Volume 1 No.7,

6 Figure 4: Typical design of recharge pit for rooftop rainwater harvesting (RWH) Recharge pit RP1 Area of the recharge pit = 3.3 m 2 Catchment area for RP1 = m 2 Infiltration rate of the rainwater harvesting site = 7.83 cm/hr = cm/d Runoff = Rooftop area Runoff coefficient Annual rainfall = m m/ year = m 3 / year Recharge rate of water from the recharge pit = Area of the tank Infiltration rate of the area = 8.54 m m/d = m 3 /d Recharge pit RP2 Area of the recharge pit = 2.45 m 2 Catchment area for RP2 = m 2 Infiltration rate of the rainwater harvesting construction site = 7.83 cm/hr = cm/d Runoff = Rooftop area Runoff coefficient Annual rainfall = m / year = m 3 / year Recharge rate of water from the recharge pit = Area of the tank Infiltration rate of the area International Journal of Environmental Sciences Volume 1 No.7,

7 5. Discussion = m m/d = 7.96 m 3 /d The paper describes the results of the pilot study conducted to assess the water harvesting and recharging potential in an urban set up. Dhanbad is a rain scarce city. Therefore it is expected that these figures will improve in the areas where rainfall is adequate and meet part of the water demand of the city. 6. References 1. Aladenola, O. O. and Adeboye, O. B. (). Assessing the potential for rainwater harvesting, Water Resources Management 24(): Abdulla, F. A. and Al Shareefa, A. W. (9). Roof rainwater harvesting systems for household water supply in Jordan, Desalination 243 (1 3): Bhattacharya, A. and Rane, O (3). Harvesting rainwater: catch water where it falls, Centre for Civil Society, ( ; last accessed on 17 May 11). 4. Chandra, S. (1979). Estimation and measurement of recharge to groundwater from rainfall, irrigation and influent seepage. In the Proceedings of International seminar on development and management of groundwater resources, 5 November 1979, School of Hydrology, University of Roorkee. 5. Jury, W. A. and Vaux, H. J., (6). The role of science in solving the world s emerging water problems. Proceedings of National Academy of Science, USA 2: Krishna, H. J., (5). The success of rainwater harvesting in Texas a model for other states. Proceedings of the North American rainwater harvesting conference, Seattle, WA, July 14 16, 5, American Rainwater Catchment System Association. 7. Maiti, S. K. (1). Handbook of Method in Environmental Studies (Volume 2), ABD publishers, Jaipur, India, pp Murad, A. A., Al Nuaimi, H. and Al Hammadi, M., (7). Comprehensive assessment of water resources in the United Arab Emirates (UEA), Water Resources Management 21: Dhanbad city map, accessed during March, 11.. O Hara, J. K. and Georgakakos, K. P., (8). Quantify the urban water supply impacts of climate change, Water Resources Management 22(): International Journal of Environmental Sciences Volume 1 No.7,