Regional groundwater funneling within the hyporheic zone

Groundwater-surface water interaction controls the exchange of contaminants, solutes and energy between aquifers and surface water resources. In particular, groundwater contamination and solute transport time is prolonged due to the impact induced by hyporheic fluxes within the streambed sediment. The retention of contaminants and solutes in streambed sediment influence the ecology and biodiversity of hyporheic zone. In this research, a numerical groundwater model was developed and supported with hydrologic and hydrogeological observations of the Krycklan catchment, Sweden, to investigate the impacts of hyporheic flows on the regional groundwater flow direction and discharge areas at the groundwater-surface water interface along stream networks. The applied method involved a multiscale modelling framework where the regional groundwater and hyporheic flows were analyzed via numerical modelling and exact solutions, respectively; and then superimposed to obtain the subsurface flow field. The regional groundwater flow was analyzed in presence and absence of the hyporheic flow and significant changes in groundwater flow trajectories and size of discharge areas were found upon adding the hyporheic flow fields. In particular, the upward groundwater flow was strongly contracted near the streambed surface due to the impact of hyporheic flow, which led to groundwater funneling and an acceleration of groundwater discharge velocities into streams. Consequently, the size of groundwater coherent discharge areas were substantially reduced leading to significantly fragmentation of groundwater discharge zones due to the impact of hyporheic fluxes.