Author(s): Nairu Wang; Lei Huang; Huai Chen; Jiaming Liu; Lijun Zhu
Linked Author(s): Lei Huang
Keywords: Compound channels; Transverse hyporheic flow; Numerical modeling; Secondary flow; Sediment heterogeneity
Abstract: The permeability heterogeneity of riverbed sediment significantly changes the spatial configuration, flow paths, and interfacial fluxes of the hyporheic zone (HZ) in riverbeds. Previous research on transverse hyporheic flow in compound rivers has primarily focused on processes driven by riverbed morphology under homogeneous conditions, often ignoring the effects of permeability heterogeneity. In this study, a one-way sequential coupling model was used to examine the transverse hyporheic flow under the effects of layered heterogeneity in a conceptual compound channel. Both a layered bedform with a low-permeability layer and an equivalent homogeneous bedform were considered. The results demonstrate that the numerical model performs well and effectively represents the transverse hyporheic flow patterns through the HZ. Hyporheic zones can still form in the cross-section of compound channels in the presence of layered heterogeneity. However, the low-permeability layer tends to hinder the development of HZ by decreasing its lateral and vertical spatial scales. Notably, low-velocity zones in semi-circular or quarter-circular shapes form within the low-permeability layers. Compared to the exchange flux, the size of HZ is more sensitive to permeability heterogeneity. A larger hydraulic conductivity contrast decreases the IEZ depth (or area), accompanied by reduced interfacial fluxes through the HZ. As the relative thickness of HZ layers increases, the exchange depth (or area) of HZ becomes significantly smaller, while the exchange flux increases slightly.
Year: 2024