Author(s): Finn Amann; Jorg Lewandowski; Reinhard Hinkelmann

Linked Author(s): Reinhard Hinkelmann

Keywords: Surface water-porewater interactions; Hyporheic zone; Integral model; Navier-stokes; OpenFOAM

Abstract: The interaction between surface water and porewater across the sediment surface is a key determinant of the hyporheic zone's ability to support a healthy river ecosystem. At the hyporheic zone scale, advective pumping is a predominant factor influencing interfacial flux and is often induced by surface water flow around large roughness elements. In this study, an intergral modelling approach was employed to investigate the physical drivers of this exchange. The used multiphase solver is suitable for non-Darcy flow regimes, as it solves a modified version of the Navier-Stokes equations to simulate flow through the porous medium, rather than relying on Darcy's law as most other models do. Three test cases were created to examine the influence of varying water depths on cobble induced surface water-porewater interactions for a gravel sediment. The findings show that shallower water depths promote greater hyporheic exchange. Results also suggest that advective pumping is sensitive to even slight changes in the Froude number and a minor deformation of the water surface, which leads to higher flow velocities near the cobble. This emphasises the importance of free- surface modelling in the context ofsurface water-porewater interactions. Additionally, a qualitative comparison between the integral model and a coupled model was conducted. While variations were expected, as simulation parameters and model approaches were different, the results showed good qualitative agreement.

DOI: https://doi.org/10.3850/978-90-833476-1-5_iahr40wc-p1302-cd

Year: 2023