Abstract
Interconnection between river water and groundwater plays an important role in maintaining water quantity and quality in hydrological systems. Furthermore, the exact interconnection is often difficult to observe and measure. This study attempts to explain river and shallow groundwater interconnection in urbanized areas of the Kathmandu Valley, Nepal. Isotopic (δD and δ18O) and chemical analyses were performed on river and groundwater samples, and the results were analyzed using statistical methods to identify areas of interconnection between river water and groundwater. Higher concentrations and positive strong correlations of Na+ with K+, NH4+-N, Cl−, HCO3−, and PO4−-P, and a change of water type from Ca-HCO3 during the wet season to Na-K-HCO3 during the dry season indicate higher contamination in river water during the dry season. Hierarchical cluster analysis was used in grouping water samples into clusters on the basis of isotopic and chemical (Na+ and Cl−) composition. Grouping of river and groundwater samples in one–one clusters from wet and dry seasons shows the presence of interconnection, indicating the contribution of river water in recharging shallow groundwater. These results imply that shallow groundwater found near rivers is chemically contaminated by polluted river water through bank infiltration, in both wet and dry seasons.
Highlights
Interconnection of river water and groundwater is a process of exchange between waters located on the river channel with those in the rocks/sediments under the surface
DO was high in river water during the wet season and abruptly decreased below the value measured in groundwater during the dry season (Table 1)
Slight deviations of isotopic compositions from global meteoric water line (GMWL) with a lower slope may suggest the possibility of evaporation in river water during the dry season
Summary
Interconnection of river water and groundwater is a process of exchange between waters located on the river channel with those in the rocks/sediments under the surface. The exchange rate of water is controlled by hydraulic conductivities of the river channel and aquifer sediments; the relative stage of the river channel and nearby groundwater level; and geometry of the river channel within the alluvial plain [1,2]. Interconnection of river water and groundwater depends on the distance from a river channel, the geological conditions, and climatic factors [4]. Understanding of groundwater and surface water interconnection is very important to develop effective water resource management and policy as it can change the water quality and quantity of both water systems [5,6].
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