Bedform-induced hyporheic exchange: impact of porous medium permeability

Stream and pore waters continuously interact and mix within streambeds due to spatial and temporal variations in channel characteristics. This mixing is termed hyporheic exchange and the zone where groundwater and stream water are mixing is called the hyporheic zone, which can greatly affect water quality in both surface and subsurface water systems. The paper presents some results of a numerical study carried out to investigate the influence of porous medium permeability on hyporheic exchange. Laminar flow in the water column above triangular bedforms and Darcian flow in the underlying permeable sediments were considered. Numerical simulations were carried out in steady-state conditions for a range of bedforms height-based Reynolds number ReH from 6 to 4442 for three different values of the permeability of the porous medium. Moreover, numerical simulations were performed in the range of ReH from 178 to 4455 using a porous medium with permeability decreasing with the depth. First, numerical results confirmed the close relationship between the characteristics of the separation region downstream the bedform crest and those of the hyporheic zone. Second, numerical results highlighted the influence of the permeability on the development of the hyporheic zone.