2004), Hyporheic exchange with heterogeneous streambeds: Laboratory experiments and modeling

[1] Hyporheic exchange is generally analyzed with the assumption of a homogeneous hyporheic zone. In reality, streambed sediments have a heterogeneous structure, and this natural heterogeneity produces spatially variable interfacial fluxes and complex hyporheic exchange patterns. To assess the basic effects of sediment structure on hyporheic exchange, we performed salt and dye injection experiments in a recirculating laboratory flume with two heterogeneous sediment beds characterized by negative-exponential correlated random hydraulic conductivity fields. Dye injections showed that the hyporheic flow structure was controlled by the spatial relationship of bed forms to high- and low-permeability regions of the streambed. As no existing model could represent these effects, we developed a new finite element model to calculate the pore water flow field resulting from the interaction of the bed form-induced boundary head distribution and the heterogeneous sediment structure. A numerical particle-tracking approach was then used to assess the resulting hyporheic exchange. The combined flow-transport model did an excellent job of predicting the complex hyporheic flow pathways in the heterogeneous bed and the net hyporheic exchange up to t 30 hours. Th