ASSESSMENT OF GROUNDWATER POTENTIAL IN JALPAIGURI DISTRICT OF WEST BENGAL

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1 J. Indian Water Journal Resour. Soc. of Indian Vol. 29 Water No. 3, July, Resources 2009 Society Vol. 29 No. 3, July, 2009 ASSESSMENT OF GROUNDWATER POTENTIAL IN JALPAIGURI DISTRICT OF WEST BENGAL A.P. Unde 1, B. C. Mal 1* and V.M.Chowdary 2 ABSTRACT Groundwater potential of Jalpaiguri district of West Bengal was assessed using water balance approach. Groundwater balance equation proposed by Chandra and Saxena (1975) was adopted for the present study. In this approach, different components such as recharge from rainfall, subsurface inflow-outflow, groundwater draft, recharge from canals and streams, seepage to the streams, recharge from irrigation water, evapotranspiration losses and groundwater storage change were considered. Analyzing the data, total usable groundwater in nine blocks of Jalpaiguri District was found to be Mm 3. Different groundwater structures like shallow tubewells, dug wells and deep tubewells are being used to withdraw only Mm 3 of groundwater at present. Therefore, there is ample scope of further utilization of groundwater for irrigating more area. Key words: Groundwater potential, Jalpaiguri district INTRODUCTION In recent years there has been considerable emphasis on integrated management of surface and groundwater resources in irrigation project areas to augment the canal supplies and to increase agricultural productivities as well as to control groundwater depletion, water logging and soil salinity (Rosegrant and Svendsen, 1993; National Water Policy, 2002; Water Technology Centre, 1998)). Thus, judicious management of the water resources of a groundwater basin needs a comprehensive understanding of the total system and its response to recharge. Quantifying recharge to groundwater ( i.e the flux of water reaching the water table from the overlying vadose zone) from rainfall and irrigation is important for developing conjunctive water use plans and designing drainage schemes. Further, it is this quantity, which may in the long term be available for abstraction and is therefore, of prime importance in the assessment of any groundwater resource. The country s average annual rainfall is cm, which when considered over a geographical area of 328 Mha amounts to a total volume of about 400 Mha-m. Of this, utilizable potential is only 67 Mha-m of surface water and 26.5 M ha-m of groundwater (Raghunath, 2000). In general, uneven distribution and irregular timing of 1 Department of Agricultural and Food Engineering, IIT,Kharagapur 2 Regional Remote Sensing Service Centre, IIT campus, Kharagpur *Corresponding Author rainfall occurrence over a given area leads to local water storage or excess at different times. One such example is the occurrence of flood and drought in Jalpaiguri district of West Bengal. An adequate estimate of the availability of groundwater storage in a basin requires water budgeting. Water budgeting helps to evaluate the net available water resources, both surface and subsurface, and to assess the impact of existing water utilization pattern and practices. In India, the Central Groundwater Board provided broad empirical guidelines for estimating various quantities involved in groundwater recharge from different sources on a regional scale (Central Groundwater Board, 1997). Walton (1970) prepared the hydrologic and groundwater budget for three small watersheds in the central Illinois to determine the groundwater recharge variation with time. He reported that the groundwater runoff was 33-70% of the surface runoff. Chandra and Saxena (1975) conducted study of groundwater resources of Ganga- Hindon Doab and estimated recharge from rainfall by different methods. Todd (1980) developed an empirical relationship for estimation of recharge rate in alluvial soil based on the groundwater slope in the range of 0.1 to 10%. Sarma et al. (1983) carried out extensive work on evaluation of groundwater resources of Mahi Right Bank Command Area (MRBC), Gujarat. In this study, subsurface inflow-outflow across the boundary was 34

2 assessed using groundwater balance approach. Further, Sondhi et al. (1989) estimated net groundwater recharge in the MRBC region, Gujarat using the recommendations of the Groundwater Estimation Committee of the Ministry of Irrigation (Central Groundwater Board, 1997) with some modifications based on field observations for estimation of recharge from rainfall, canal systems and groundwater irrigated areas. Ray and Rath (1990) conducted a study for conjunctive use of groundwater in Mahanadi Delta, Orissa. They evaluated the components of groundwater balance equation considering 30% of the water applied in the irrigated field as deep percolation and recharge due to rainfall by infiltration index method. Rao and Chakraborthy (2000) estimated the groundwater recharge and annual water balance in the Sri Ram Sagar Project command area, Andhra Pradesh using the norms suggested by CGWB, Rao (1995) improved the physical basis of the estimation of recharge by using a distributed soil water balance model to calculate percolation losses and a vertical groundwater flow model for seepage losses from canals. But the models were used only for a limited arbitrarily chosen location and their results were extrapolated for the area. Chowdary, et al., (2003) developed a generalized integrated framework for assessment of groundwater resources in large canal irrigation project areas with varying soil, weather, crop and water use conditions. The integrated framework consists of Basic Simulation Units (BSU) derived for the project area by overlaying rainfall, soil, water use, and administrative unit maps using GIS, simulation models; canal flow model, soil water balance model and groundwater flow model. Pawar (1996) carried out study on investigation of groundwater potential to find out the future prospects of groundwater development in two blocks of Jalpaiguri District and feasible alternatives to utilize available groundwater economically. He showed that recharge to groundwater from rainfall is about 19.5% to 24.6%. In Jalpaiguri district, less than 20% of the cropped area is provided with irrigation through minor irrigation projects. These projects include river lift irrigation schemes, diversion from perennial streams or groundwater utilization through deep tubewells, shallow tubewells or pump dug wells. Though, a large number of vegetable crops, pulses and oil seeds are grown during the winter season, but for want of irrigation, either a large area remains fallow during the non-monsoon months or the yield is very low. Hence, for planning of proper groundwater utilization, it is necessary to estimate the total groundwater recharge and the actual volume of water available annually for utilization. The water balance study taken up to evaluate the different components of groundwater recharge in the district and to suggest the safe volume of groundwater withdrawal is presented in this paper. Study area The study was undertaken in Jalpaiguri district of West Bengal having an area of 6245 sq. km. consisting of 9 blocks (administrative units) and lies within the latitude of 26 o 16 to 27 o N and longitude of 88 o 25 to 89 o 25 E. The study area is bordered by Bhutan and Darjeeling in the North, Assam in the east, Cooch Bihar district and Bangladesh in the south, Siliguri and Darjeeling in the west (Figure 1). The study area is fringed on the northern side by sub-himalayan ranges and these ranges gradually slopes downward and merge with the alluvial plains of the Ganga-Brahmaputra river systems in the south. The maximum elevation of the study area is about 600 m above msl and the minimum elevation is about 60 m above msl towards south. The sub mountain tract towards north which is formed of deposits of turbulent streams emerging from the hills is locally called as Bhabar or Bhabar belt, while gently Figure 1 Location map of the study area 35

3 sloping alluvial terrain towards the south is called as Terai. The southern part is more flat with wide valley intersected by some rivers, like Teesta, Torsha and Jaldhaka. The total average annual rainfall of the area is about 4000 mm, 84% of which falls during June to September months. The soils are alluvial and predominantly coarse. As a consequence, the water retention capacity is low, resulting in quick depletion of soil moisture during dry weather condition. The main crops are aman paddy (kharif), wheat (winter) and jute (pre-kharif). METHODOLOGY The groundwater balance equation proposed by Chandra and Saxena (1975) was adopted for assessment of groundwater resources. The equation can be written as, R r + R c + R i + I = S e + O + ET g +T p + S (1) where, R r, R c, R i = recharge from rainfall, canal and irrigation water respectively, I, O = sub-surface inflow and out flow, S e = seepage to the streams, ET g = evapotranspiration from groundwater, T p = groundwater draft and S = change in groundwater storage. Assessment of groundwater balance components Recharge from rainfall Recharge from the rainfall was computed using the empirical formula suggested by Chandra and Saxena (1975) and is given as follows: R = (P 40.64) 0.5 (2) where, R = recharge to the groundwater, cm and P = precipitation, cm. In the present study, recharge was estimated using the five years monthly rainfall data of different raingauge stations collected from the office of the Joint Director of Agriculture, Jalpaiguri. Sub-surface inflow-outflow Subsurface inflow-outflow was estimated by flownet analysis. Pre-monsoon and post- monsoon water table contour maps of the study area and transmissivity (T) values were used in the estimation of sub-surface inflow and outflow. Transmissivity (T) values were determined for different blocks of the study area from the analysis of pumping test data conducted by the State Water Investigation Department (SWID) (Unde, 1997). Darcy s Law was used for the calculation of subsurface inflow-outflow. Q = T i L (3) where, Q = flow across the boundary, m 3 /day, T = transmissivity of the aquifer, m 2 /day, i = hydraulic gradient and L = length across which flow takes place, m. Groundwater draft The details of the groundwater extraction structures, i.e. hand tube wells (HTW), pump dug wells (PDW), shallow tube wells (STW) and deep tube wells (DTW) were collected for the study area (Table 1) (Principal Agricultural Officer, 1992). Annual groundwater draft was estimated using the number of groundwater extraction structures and average number of operating hours per year. Table 1 Details of groundwater Structures in nine blocks of Jalpaiguri district of West Bengal Name of Block HTW PDW STW DTW Jalpaiguri Rajganj Maynaguri Dhupguri Mal Matiali Nil Nil Nagrakata Nil 55 2 Nil Falakata Madarihat Nil Discharge (m 3 /h) Annual operating hrs HTW - Hand pump Tube Wells, PDW - Pump Dug wells, STW- Shallow Tube Wells, DTW- Deep Tube Wells. Source: State water Investigaton Department, West Bengal Recharge from canals/streams The deep percolation losses from canal was considered as 8% of the total water available (CGWB, 1984). Seepage to the streams The lean period discharges flowing through the streams of the district were measured using the areavelocity method during June 1996 and this discharge was considered to be the uniform seepage flow from the groundwater throughout the year. 36

4 Recharge from irrigation water The recharge from the field due to canal irrigation was considered to be 35% of the total water applied (Baweja, 1979). In case of well irrigation, deep percolation was considered as 30% of water applied from the wells (i.e. groundwater draft). Total water applied to the field was computed by considering cropping pattern and gross water requirement of the crop. Evapotranspiration losses from groundwater Evapotranspiration data were collected from the Sub-Divisional Agricultural Officer of the district. Evapotranspiration from the groundwater in the forest and plantation area was considered to be 60% of the total evapotranspiration from the study area. This component of the groundwater balance is very difficult to evaluate. But this assumption is based on the fact that average effective root zone depth is 8 m for trees and 40% of the water is extracted from the top 25% root zone which generally lies above the water table. This is mainly from the soil moisture. Remaining 60% of water is extracted through the bottom part of the root zone, which lies within the water table. Groundwater storage change Change in the groundwater storage was estimated by the following relationship, S = h x A x Y (4) where, S = change in groundwater storage, h = water table fluctuation, A = area under consideration and Y = specific yield of the formation. Table 2 Hydrogeological parameters in different blocks of Jalpaiguri district of WB Block Aquifer type Average Thickness of Aquifer (m) Jalpaiguri Medium to coarse sand Average Transmissivity (m 2 /day) with gravel Rajganj 1 -do Maynaguri 1 -do Dhupguri 1 -do Falakata 1 -do Mal 2 -do Matiali 2 -do Nagrakata 2 -do Madarihat 2 -do Southern terai belt 2 Northern bhaber belt Source: State Water Investigation Department, West Bengal in bhabar belt are having low transmissivity values in the range of 155 to 412 m 2 /day. On the basis of depth to water table data recorded through piezometers, it was noticed that in the central and southern part of the district water table is within 4.5 m below the ground level whereas, in northern part water level is more than 4.5 m below ground level during pre-monsoon season. The post-monsoon groundwater table level in the district is within 3 m below ground level. It was also observed that during monsoon, water table fluctuates between 1 to 2 m in southern part and 2 to 4 m in northern part. Annual water balance of the study area was carried out and presented in Table 3. The table shows that percentage of rainfall recharge to the groundwater is in the range of to percent and usable groundwater balance is in the range of 6.38 to million cubic meters. Overall percentage of groundwater RESULTS AND DISCUSSION From the hydrogeological parameters of the study area (Table 2), (Unde, 1997) it is clear that the study area has two distinct aquifer patterns (Figure 2). The southern terai belt is having good aquifer under water table as well as confined conditions and any groundwater extraction structures like shallow tubewell, dug well or deep tubewell can be used in this belt. Whereas, in northern part of bhabar belt, water table aquifer is poor and confined aquifer is considerably deep. Therefore, water extraction is possible through deep tubewells or large diameter dugwells from the northern belt. Blocks located in the terai belt have higher transmissivity ranging from 910 to 1046 m 2 /day whereas, the aquifer Good ground water prospect, suitable for any types of well, water table within centritugal limit. Limited ground water prospect, water table aquifer very rare, deep tube wells, dug wells suitable hu SCALE Figure 2 Aquifer pattern in the Jalpauguri district of WB 37

5 utilization in the district is in the range of 6 to 18 percent only with an average of 12.6 percent. However, it is clearly indicated from Table 1 that the available groundwater structures are also being underutilized. Different groundwater structures, especially, privately owned structures namely, the shallow tubewells and pump dug wells are grossly underutilized. They are being used only for 450 to 500 hours annually. Irrigation is required from these wells at least for 6 months from November to April. If used properly, they can be used for about 1200 hours annually and groundwater drafts from the existing structures including government owned deep tubewells can be easily doubled. The reason for gross under-utilization of private tubewells is that the farmers are irrigating only their small land holding located around the well and not sharing or selling water to other farmers. Moreover, if the command area is increased conveyance loss in the unlined irrigation channel is increased considerably. Lining a part of the channel may help to increase the command area. In nine blocks of Jalpaiguri district, total usable groundwater potential is million cubic meters. If double the J. Indian Water Resour. Soc. Vol. 29 No. 3, July, 2009 Table 3. Annual water balance of the study area (Mm 3 ) of Jalpaiguri district of WB GW balance Block Blocks of Jalpaiguri of Jalpaigudi district district components Jalpaiguri Rajganj Mayanguri Dhupguri Mal Matiali Nagrakata Falkata Madarihat Inputs, Mm 3 Recharge from rainfall Recharge from well irrigation Recharge from canal/surface irrigation Seepage from canal/streams Sub-surface inflow Total Input Outputs, Mm 3 Sub-surface outflow Seepage to the streams Evapotranspiration from groundwater Total natural output Groundwater Balance Usable groundwater (70% of balance) Groundwater Draft Net Groundwater Resources to be Developed amount of present volume is withdrawn, the volume utilized will be million cubic meters. Even after that huge quantity of water ( Mm 3 ) will remain unutilized. For utilizing this balance quantity of water, about 7500 shallow tubewells, same number of dugwells and 650 deep wells can be constructed with 1200 hours of operation per annum. CONCLUSIONS The net recharge to groundwater from different sources was quantified to determine the available groundwater potential in the area. The available annual groundwater potential was estimated to be million cubic meters, which is about 7.9 times the existing level of groundwater development. Overall, Jalpaiguri district is having two distinct aquifer patterns. Southern terai belt is having good groundwater prospect compared to the northern bhabar belt where the shallow water table aquifer is rare and only large diameter dugwells or deep tubewells can be constructed to utilize the groundwater. The aquifer in the southern belt is having higher transmissibility as compared to the northern belt. 38

6 Groundwater utilization of the district is in the range of 6 to 18% with an average of 12.6% which indicates an underutilization of the existing groundwater resource and structures. By proper utilization, existing groundwater draft can easily be doubled. For extracting the balance water, about more shallow tubewells/dug wells and 650 deep tubewells are required to be constructed. Thus, sufficient scope exists for further development of groundwater resources in the study area. REFERENCES 1. Baweja, B.K Hydrological set up of India and status of work of Central Groundwater Board. Lecture delivered at UNESCO regional training course at N.G.R.I., Hydrabad. 2. Central Groundwater Board, Groundwater Resource Estimation Methodology Report of the Groundwater Estimation Committee, Ministry of Water Resources, Govt. of India, New Delhi. 3. Central Groundwater Board, Groundwater Resource Estimation Methodology. Report of the Groundwater Resource Estimation Committee, Ministry of Water Resources, Government of India, New Delhi, India, 100pp. 4. Chandra, S and Saxena, R.S Water Balance Study for Estimation of groundwater resources, Irrigation and Power Journal, CPIB, New Delhi 32(4): Chowdary, V.M., N.H.Rao., Sarma, P.B.S GIS based decision support system for groundwater assessment in large irrigation project areas. Agricultural Water Management.62: National Water Policy, Ministry of Water Resources, Govt. of India, New Delhi, India. 7. Pawar, D.D Investigations on groundwater potential and its management: A case study. Unpublished M. Tech Thesis. IIT, Kharagpur. 8. Principal Agricultural Officer, Jalpaiguri Report on annual plan of Jalpaiguri district. 9. Raghunath, H.M Hydrology, principles, analysis and design. New age international (P) limited, publishers. pp Rao, K.V Decision support system for conjunctive use in irrigation projects. Unpublished Ph.D thesis. Division of Agricultural Engineering. Indian Agricultural Research Institute. New Delhi. 11. Rao, V.V. and Chakraborti., Water balance study and conjunctive water use planning in an irrigation canal command area: a remote sensing perspective. Int. J. Remote Sensing. 21(17): Ray, S.K. and Rath, D.P Conjunctive use of groundwater in Mahanadi Delta. Proceedings of the CPIB, New Delhi. 1: 252: Rosegrant,M.W. and Svendsen,M Asian food production in the 1990s irrigation investment and management policy, Food Policy, Feb 1993, Sarma, P.S., Sondhi, S.K. and Rao, N.H Groundwater management and development in MRBC area, Resources analysis and plan for efficient water management, A case study of Mahi Right Bank Command Area, Gujrat, W.T.C., IARI, New Delhi. 15. Sondhi, S.K., Rao, N.H., and Sarma, P.B.S., assessment of groundwater potential for conjunctive water use in a large irrigation project in India. Journal of Hydrology, 107: Todd, D. K Groundwater Hydrology. John Wiley and Sons, New York. 17. Unde, A. P An unpublished M.Tech. thesis, IIT Kharagpur. 18. Walton, W. C Groundwater Resources Evaluation. Mc Graw Hill Book Company, New York. 19. Water Technology Centre Development of guidelines for sustainable water management in irrigation projects including conjunctive use of canal water and groundwater, in, Contributions to Water Science and Technology, IARI, New Delhi,