Author(s): Tabea Broecker, Katharina Teuber, Vahid Sobhi Gollo, Reinhard Hinkelmann, Gunnar Nützmann, Reinhard Hinkelmann, Gunnar Nützmann, Jörg Lewandowski

Linked Author(s): Reinhard Hinkelmann, Reinhard Hinkelmann

Keywords: Hyporheic exchange; Computational Fluid Dynamics (CFD); OpenFOAM; Ripples;

Abstract: The hyporheic zone as the transition zone between surface water in streams and groundwater is a key area for the ecological functioning of running waters. Quantities of hyporheic exchange fluxes can help to better understand hydrological, chemical and biological processes at the stream-aquifer interface. This paper presents hyporheic exchange fluxes based on a novel integral modelling approach for the hyporheic zone using the computational fluid dynamics (CFD) model OpenFOAM. Most applications are based on one‐way sequential coupled schemes of groundwater and surface water flow. The integral model uses an extended version of the Navier-Stokes equations for the whole domain and accounts for feedbacks from subsurface flow into the surface water domain and vice versa. For the validation of the integral solver, analytical and numerical solutions for seepages through two dams with varying geometries and varying ambient water levels were compared with numerical simulations using the integral flow model. A good agreement was achieved for both test cases. Hyporheic exchange fluxes through immobile ripples with varying morphologies were investigated for different surface hydraulics with high resolution simulations. Turbulent two-phase flow (water and air) was considered to depict water level fluctuations, which influence pressure distributions and consequently can have a high impact on hyporheic exchange fluxes. Simulation results indicated that higher flowrates in surface water as well as distances between the ripples increase hyporheic exchange fluxes. Decreasing ripple sizes reduced hyporheic exchange fluxes and bigger grain sizes enlarged the exchange fluxes drastically.

DOI: https://doi.org/10.3850/38WC092019-0407

Year: 2019