Identifying Groundwater and River Water Interconnections Using Hydrochemistry, Stable Isotopes, and Statistical Methods in Hanumante River, Kathmandu Valley, Central Nepal

• Main Authors: Ramita Bajracharya, Takashi Nakamura, Subesh Ghimire, Bijay Man Shakya, Naresh Kazi Tamrakar
• Format: Article
• Language: English
• Published: MDPI AG 2020-05-01
• Series: Water
• Subjects: stable isotopes; chemical ions; hierarchical cluster analysis; groundwater-river water interconnection; Hanumante River
• Online Access: https://www.mdpi.com/2073-4441/12/6/1524

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.