Kathmandu Valley Multidisciplinary Project

Abstract

Globally, growing demand for fresh water and declining water availability puts significant pressure on water resources. Due to rapid urbanization and insufficient water resource planning and waste water management, the Kathmandu Valley (Valley) is facing both a water quantity and quality crisis. Annually, groundwater extractions in the Valley significantly exceed recharge rates, resulting in a serious groundwater table declines. While streams often constitute an important linkage between surface water and groundwater systems, from both a quantity and quality perspective, understanding stream-aquifer interactions in the Valley are limited. To improve this understanding, we performed topographic surveys of water levels, and measured water quality, in streams and adjacent hand dug wells (shallow aquifer) in three watersheds (total of 16 stream-well pairs) during 2018 pre-monsoon (April and May) and eight watersheds (including the same three from pre-monsoon; total of 35 stream-well pairs) during 2018 post-monsoon (September and October). In pre-monsoon, we found 88 % of water levels in wells lower than adjacent streams with an average of -0.82 m, indicating a loss of stream water to the aquifer. However, in post-monsoon 69 % of wells had water levels higher than adjacent streams with an average water level difference of 0.44 m, indicating that monsoon rainfall recharged the shallow aquifer, causing streams to transition from losing to gaining. No recurring trend in water level difference was seen longitudinally from upstream to downstream. Our results indicate statistically significant correlations between electrical conductivity, ammonia, chloride, hardness, and alkalinity measured in streams and adjacent wells. Both stream and groundwater quality of adjacent wells depletes longitudinally from upstream to downstream. In order to prevent further deterioration of groundwater resources, stream-aquifer interactions should be taken into account for sustainable water resource management. Further research is essential to quantify the groundwater flow, and to investigate the long-term trends and reversibility of the problem. Our findings highlight the importance of managing streams and aquifers as a single integrated resource, from both a water quantity and quality perspective. For example, improper waste management in the Valley’s streams is having a clear and negative impact on the shallow aquifer. The population of Kathmandu will become increasingly dependent on the government for water supply, potentially increasing the cost of living.