Integral Flow Modelling Approach for Surface Water-Groundwater Interactions along a Rippled Streambed

Tabea Broecker,Katharina Teuber,Gunnar Nützmann,Vahid Sobhi Gollo,Jörg Lewandowski,Reinhard Hinkelmann

doi:10.3390/w11071517

Abstract

Exchange processes of surface and groundwater are important for the management of water quantity and quality as well as for the ecological functioning. In contrast to most numerical simulations using coupled models to investigate these processes, we present a novel integral formulation for the sediment-water-interface. The computational fluid dynamics (CFD) model OpenFOAM was used to solve an extended version of the three-dimensional Navier–Stokes equations which is also applicable in non-Darcy-flow layers. Simulations were conducted to determine the influence of ripple morphologies and surface hydraulics on the flow processes within the hyporheic zone for a sandy and for a gravel sediment. In- and outflowing exchange fluxes along a ripple were determined for each case. The results indicate that larger grain size diameters, as well as ripple distances, increased hyporheic exchange fluxes significantly. For higher ripple dimensions, no clear relationship to hyporheic exchange was found. Larger ripple lengths decreased the hyporheic exchange fluxes due to less turbulence between the ripples. For all cases with sand, non-Darcy-flow was observed at an upper layer of the ripple, whereas for gravel non-Darcy-flow was recognized nearly down to the bottom boundary. Moreover, the sediment grain sizes influenced also the surface water flow significantly.

Highlights

Hyporheic exchange—the exchange of stream and shallow subsurface water—is controlled by pressure gradients along the streambed surface and subsurface groundwater gradients
In contrast to Broecker et al [35], the present study examines both free surface flow and subsurface flow
The aim of the present study is to evaluate the impact of ripple dimensions, lengths, spacing and surface velocity on flow dynamics within the hyporheic zone using a new integral model

Summary

Introduction

Hyporheic exchange—the exchange of stream and shallow subsurface water—is controlled by pressure gradients along the streambed surface and subsurface groundwater gradients. A decrease of the groundwater level, in turn, impacts surface water infiltration up to a maximum where groundwater and surface water are disconnected. This condition is achieved when the clogging layer does not cross the top of the capillary zone above the water table [12]. The flowing fluid encounters an uneven surface on the permeable streambed, which results in an irregular pattern in the pressure along that surface and induces hyporheic exchange [11,12,13]

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