An integral approach for flow and transport modelling at the surface water-groundwater interface
2 Ecohydrology Department, Leibniz-Institute of Freshwater Ecology and Inland Fisheries, Berlin, Germany,
3.5 in Grundwasser-Oberflächenwasser-Interaktionen - vom Flussabschnitt zum Einzugsgebiet
27.03.2020, 11:45-12:00, Telemann-Saal
Exchange processes of ground- and surface water 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 which solves an extended version of the Navier-Stokes equations. The solver allows us to simultaneously simulate surface and subsurface flow and transport with one system of equations to get a deeper understanding of the present processes at the interface. In contrast to many other coupled models, the solver is also capable to model non-Darcy flow.
For all the simulations we used the computational fluid dynamics (CFD) model OpenFOAM. In a first step we present flow processes within the hyporheic zone, the transition zone between surface water in streams and groundwater. Pressure and velocity distributions as well as quantities of hyporheic exchange fluxes were investigated at a rippled streambed with varying ripple morphologies and surface hydraulics. 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 flow rates in surface water, bigger sediment grain sizes as well as distances between the ripples increase hyporheic exchange fluxes. Larger ripple lengths decreased the hyporheic exchange fluxes, while for higher ripple dimensions no clear relationship was found. For all cases, non-Darcy flow areas were recognized, especially at the upper layer of the sediment.
In a next step, we included a transport equation into our integral solver and verified the solver by comparing model results to analytical one- and two-dimensional solutions for initial and permanent tracer injections. A good agreement between the calculated and analytical results was obtained. Currently, we compare laboratory tracer distributions at a rippled streambed for gaining and losing streamflow with results calculated with the integral model. Moreover, we simulate the pumping activity of chironomid larvae in U-shaped burrows inducing flow and transport in lake sediments. Here, we compare our integral approach to a coupled approach to discuss advantages and disadvantages of the integral model.
(not included in abstract, for further reading about the project):
Broecker,T., Schaper,J., El-athman,F., Gillefalk,M., Hilt,S. & Hinkelmann,R. (2017a): Surface water - groundwater interactions. IAHR World Congress 2017, Kuala Lumpur, Malaysia
Broecker,T., Teuber,K., Elsesser,W. & Hinkelmann,R. (2017b): Multiphase modelling of hydrosystems using OpenFOAM. SimHydro 2017: 3D two-phase flows (experiments and modelling) 2017, Sophia Antipolis, book chapter: Advances in Hydroinformatics, SimHydro 2017- Choosing the Right Model in Applied Hydraulics p.1013-1029
Broecker,T., Teuber,K., Sobhi Gollo,V., Lewandowski,J.,Nützmann,G. & Hinkelmann,R. (2019a): Quantifying hyporheic exchange fluxes through ripples with an integral flow model, 38th IAHR World Cngress, Sep 1-6, Panama City, Panama
Broecker,T.; Teuber,K.; Sobhi Gollo,V.; Nützmann,G.; Lewandowski,J. & Hinkelmann,R. (2019b): Integral flow modelling approach for surface water-groundwater interactions along a rippled streambed. Journal: Water
Fox,A., Boano,F. & Arnon,S. (2014): Impact of Losing and Gaining Streamflow Conditions on Hyporheic Exchange Fluxes Induced by Dune-Shaped Bed Forms. Water Resources Research 50, No. 3, 1895–1907
Oxtoby,O.F., Heyns,J.A. & Suliman,R. (2013): A Finite-Volume Solver for Two-Fluid Flow in Heterogeneous Porous Media Based on OpenFOAM. Open Source CFD International Conference, Hamburg
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