The effect of stream discharge on hyporheic exchange

Abstract

Streambedmorphology, streamflow dynamics, and the heterogeneity of streambed sediments critically controls the interaction between surfacewater andgroundwater. The present study investigated the impact of different flowregimes on hyporheic exchange in a boreal streamin northern Sweden using experimental and numerical approaches. Low-, base-, and high-flow discharges were simulated by regulating the streamflow upstreamin the study area, and temperature was used as the natural tracer to monitor the impact of the different flow discharges on hyporheic exchange fluxes in stretches of stream featuring gaining and losing conditions. A numerical model was developed using geomorphological and hydrological properties of the stream and was then used to perform a detailed analysis of the subsurface water flow. Additionally, the impact of heterogeneity in sediment permeability on hyporheic exchange fluxes was investigated. Both the experimental and modelling results show that temporally increasing flowresulted in a larger (deeper) extent of the hyporheic zone aswell as longer hyporheic flow residence times. However, the result of the numerical analysis is strongly controlled by heterogeneity in sediment permeability. In particular, for homogeneous sediments, the fragmentation of upwelling length substantially varies with streamflow dynamics due to the contribution of deeper fluxes.