PNNL

Abstract

The hydrologic flows across the river-aquifer interface play an important role in groundwater dynamics and biogeochemical reactions within the subsurface; however, little is known about the effects of river-aquifer interactions on land surface processes. In this study, we developed a fully coupled three-dimensional (3-D) land surface and subsurface model to investigate how river-aquifer interactions modulate surface water budgets in a semiarid watershed at a high resolution (~1 km) that accounts for high-frequency hydrologic exchange flow conditions. Our results show that the spatiotemporal dynamics of river-aquifer interactions are highly heterogeneous, driven mainly by river-stage fluctuations. Adding 6.64×106 m3 yr-1 of water over the watershed from the river to groundwater owing to the lateral flow, river-aquifer interactions led to an increase in soil evaporation and transpiration supplied by higher soil moisture content, particularly in deeper subsurface. In a hypothetic future scenarios where a 5-m rise in river stage was assumed, the hydrologic flow exchange rates were intensified, resulting in higher surface water and energy fluxes over the entire watershed. Overall, lateral flow induced by river-aquifer exchanges leads to an increase in evapotranspiration of ~75% in the historical period and of ~83% in the hypothetical future scenario. Our study indicates that river-aquifer interactions fundamentally alter the water balance and hydrological cycle of the riparian zone, and demonstrates the potential of our coupled model as an effective tool for understanding river-aquifer-land surface interactions.