Lateral inflow into the hyporheic zone tested by a laboratory model

Abstract

Groundwater and river water with a different composition interact and exchange in the hyporheic zone. The study of hyporheic zone and its impact on water quality has re- cently received growing interest because of its role in nutrients and pollutants interac- 5 tions between rivers and the aquifer. In this research our main purpose is to identify the physical processes and characteristics needed for a numerical model, which include the unsaturated recharge zone, the aquifer and the river bed. In order to investigate such lateral groundwater inflow process, a laboratory J-shaped column experiment was designed. This study determined the transport parameters of the J-shaped col- 10 umn by fitting an analytical solution of the convective-dispersion equation on individual segments to the observed resident breakthrough curves, and by inverse modelling on the entire flow domain for every flux. The obtained transport parameters relation was tested by numerical simulation using HYDRUS 2D/3D. Four steady-state flux conditions (i.e. 0.5cm hr−1, 1cmhr−1, 1.5cmhr−1 and 15 2cmhr−1) were applied, transport parameters including pore water velocity and disper- sivity were determined for both unsaturated and saturated sections along the column. Results showed that under saturated conditions the dispersivity was fairly constant and independent of the flux. In contrast, dispersivity under unsaturated conditions was flux dependent and increased at lower flux. For our porous medium the dispersion 20 coefficient related best to the quotient of the pore water velocity divided by the water content. A simulation model of the hyporheic exchange of the water and dissolved materials should take this into account.