The fluvio lacustrine deposits of the Kathmandu Valley, Nepal are divided into four zones in terms of aquifer distribution. Deep confined aquifer in the south, GRI, medium depth interbedded aquifer, GRIT, shallow unconfined aquifer in the north, GRIII and an unconfined aquifer of thin sand and gravel deposit widely distributed on the surfaces of the terraces and other locations.
Surface sediment deposits of fine to medium grain size referred to as surface gravel deposits, supply considerable quantity of water for residents of the valley through“Dharas”(stone spouts) and wells at superficial depths. The discharge is reported to double during monsoon period. General quality of water from these sources is considered good with some exceptions.
For some years now, underground water source is believed to contribute about 40% of the city water supply. This is aggregated even further by pumping of the water in the private household with overdrafting going on for sometime. This overdrafting can be observed from the declining trend of the water levels in the tube wells. The total dynamic reserve of the valley is 12,730 m³/day. The average amount of infiltration from the rainfall is 17.2%.
The discharge from“Dharas”adds to 1380 m₃/day. Hence if the ground water is properly managed, overdrafting may not be necessary. Multipurpose projects specially in the northern zone should help induce artificial recharge. Otherwise, Kathmandu may face a potential disaster in the near future.