Development of an alpine hydrological model considering the recharge of stream water to alluvial plain aquifers

Abstract

The recharge of stream water to alluvial plain aquifers is of significant importance for alpine hydrology, yet it has not been adequately represented in hydrological models, limiting the reliability of hydrological simulation and future projection. This study developed a watershed model that can simulate this process with moderate complexity. A parsimonious method was proposed to calculate the stream water recharge fluxes into aquifers at the mountain front area, relying on the storage dynamics of alluvial plain groundwater. The inter-subbasin groundwater movement in seasonally frozen ground areas was also simulated to represent the connectivity of aquifers. A small headwater catchment in the northeastern Qinghai-Tibet Plateau was selected to validate the model. The simulation results indicated that the developed model can well reproduce multi-faceted observations, such as soil temperature profiles, the groundwater dynamics at different locations, streamflow at the catchment outlet, and the contributions of groundwater. In this case study, approximately 75 % of stream water from the permafrost areas infiltrated into alluvial plain aquifers in the seasonally frozen ground areas, and then gradually released to river, maintaining base flow during dry periods. This process buffers the movement of water from glacier and permafrost to the catchment outlet, and may delay the impact of global warming on discharge at the catchment outlet. The model developed in this study provides a reliable tool for assessing the effects of climate change on hydrological processes in alpine watersheds.