A review of groundwater-surface water interaction studies in India

Worldwide, highly populated countries are experiencing an imbalance between the supply and demand of water. India is one such example which has only 4% of the world's water resources and a population of more than 1.3 billion. Its water demand is expected to rise by more than 75% in the upcoming decades due to fast population growth and expansion of irrigated agriculture, industrialisation and urbanisation. The consequences of this increased demand are already visible such as water quality deterioration near urban centres, water table lowering in the North-Western region, and seawater intrusion in coastal areas due to aquifer over-exploitation. The occurrence of erratic and unreliable rainfall in the past few years has further aggravated the situation. In such a scenario, information on groundwater-surface water (GW-SW) interaction processes is helpful for the conservation and management of water resources. Therefore, this study thoroughly reviews the interaction phenomenon occurring in Indian waters. It covers the interaction in natural and artificially-constructed environments, methods for exchange flux quantification, conceptual applications, and challenges in accomplishing these investigations. Rivers/streams, canals or seawater were considered as SW components in the majority of the studies, with the main focus on the Ganga River basin in the case of river-aquifer systems. However, most of the investigations were site-specific without providing a generalised perspective, and in many cases, the interaction was not considered in totality. Also, certain critical sites have not received the attention of the scientific and research community. These are dam reservoirs and wetlands in the Himalayas, eco-sensitive areas in North-Eastern India, submarine GW discharge sites at islands, and desertic and karstic terrains. On a regional scale, very few research articles are available for India's Western and Central regions. Accordingly, all such regions need to be explored in the upcoming studies. In the context of flux quantification methodology, modern techniques like geophysical methods and fully coupled numerical models were used fewer times than conventional techniques such as isotopic, hydrochemical and hydrological analyses. Therefore, extensive data collection and modern methods are recommended to study complex systems and obtain more accurate information. Further, the government sector seems reluctant to recognise this concept since, in various reports, complete information is unavailable for the interaction mechanism, and only some aspects of the phenomenon have been considered. Additionally, there are anomalies in the GW recharge estimation from non-rainfall sources. Hence, we suggest an institutional framework that allows the stakeholders to undertake detailed investigations for any interaction setup and frame an appropriate strategy for handling the country's water issues.