Hydrogeologic assessment and groundwater reserve evaluation in northwestern parts of Dun valley aquifers of Chitwan, inner Terai

The Chitwan Valley is one of the largest Dun Valleys in the Himalayan foothills of Nepal. Dun gravels perhaps deposited in the late Pleistocene to very early Holocene about 22,000-7000 yr. B.P. Chitwan Dun Valley is underlain by Dun fan gravels or Dun gravels which form unconfined to semiconfined or leaky confined aquifers. The study area, situated in the NW part of the valley occupies an area of 70.8 km 2 .The hydrogeological situation in the study area is inferred from drilling data of Ground Water Resources Development Board (GWRDB), Agriculture Development Project Janakpur (ADPJ) and several private drilling companies .The Chitwan Dun Valley constitutes a closed groundwater system in the Siwalik Zone of Nepal Himalaya. The study area reveals the existence of two definite groundwater sub-basin each having its own hydraulic system and is a part of single large regional groundwater basin. Annual potential evapotranspiration (PET) calculated at Rampur (station no 0902) for five-year period (1990-1995) is 1.68 mm/day. Annual precipitation data recorded at Rampur is 2214 mm. Area of recharge is 70.8 km 2 and estimation of total groundwater storage(reserve) is 87.31 MCM per year, and dynamic reserve or annual potential recharge is estimated as 48.60 MCM per year. doi: 10.3126/bdg.v12i0.2249 Bulletin of the Department of Geology, Vol. 12, 2009, pp. 43-54