A quantitative study of changing groundwater-surface water interactions of a large reservoir due to impoundment based on hydrochemistry and isotope characteristics

Abstract

Xiluodu Reservoir is the third-largest dam worldwide constructed in 2012. Significant changes in the hydrogeological conditions and regional groundwater-surface water (GW-SW) interactions associated since the dam impoundment in 2012 contributed to the river valley contraction (RVC). In this study, various factors that influence hydrochemistry and isotopic characteristics of GW-SW distribution interactions along with their migration patterns are extensively discussed. Based on these studies, the saturation index (SI) of different minerals during the GW-SW interaction in different periods was quantified considering the ion activity. The confined limestone GW and phreatic basalt GW are dominating GW in the dam site that play a predominant role in the regional GW-SW interactions. The impoundment strengthened the water–rock interaction and promoted the dissolution of minerals in limestone and basalt, contributing to an increase in the SI of different minerals in SW and GW. The primary recharge source for the limestone GW is Lake water; however, the secondary basalt GW recharge shifts from Ditch water to Reservoir water. The comprehensive studies summarized in this paper lays a foundation for rigorous understanding of the RVC mechanism that can be extended to other large reservoir projects in the world.