The 24th IAHR-APD Congress (24th IAHR-APD Congress)

107 / 2024-02-01 17:52:12

Numerical simulations of transverse hyporheic flow in a compound channel under the influences of bed sediment heterogeneity

Transverse hyporheic exchang,numerical simulation,secondary flow,heterogeneity,compound channel

The permeability heterogeneity of riverbed sediment alters flow paths, interfacial fluxes, and the spatial configuration of interfacial exchange zone (IEZ) in riverbeds. Previous researches on transverse hyporheic exchange in compound rivers primarily concentrated on processes driven by riverbed morphology under homogeneous conditions, while ignoring the impacts of riverbed heterogeneity. A one-way sequential coupling model was employed to examine the transverse hyporheic flow under the combined effects of bedform and bed heterogeneity in a conceptual compound channel. Two scenarios were considered: one with layered bedforms and the other with equivalent homogeneous bedforms. The analysis focused on the hyporheic exchange area, interfacial flux through the sediment-water interface (SWI) and mean residence time. The results show the numerical model exhibits good performance and effectively represents the transverse hyporheic flow patterns in the vicinity of the SWI. In both homogeneous and heterogeneous cases, an IEZ may still form in the cross-section of compound channels. The flux, depth, and mean residence time of IEZ increases, decreases and decreases with bank slope angles, respectively. Results also indicate that bed heterogeneity can potentially influence transverse hyporheic flow through changes in IEZ flux, depth, and mean residence time. As the heterogeneity increased, the IEZ area (or depth) becomes much smaller but accompanied by larger IEZ flux. Compared with the IEZ flux, the IEZ depth is more sensitive to bed heterogeneities. Heterogeneity significantly reduces the IEZ depth but only slightly alters the IEZ flux relative to homogeneous bedforms, resulting in a shorter mean residence time for water within the IEZ.