A numerical study of the lateral hyporheic flow about a channels confluence

Stream and pore waters continuously interact and mix within streambeds due to spatial and temporal variations in channel characteristics. This mixing is termed as hyporheic exchange and the zone where groundwater and stream water are mixing is called hyporheic zone, which can greatly affect water quality is both surface and subsurface water systems. Typical examples of hyporheic fluxes are those under bedforms, intra-meander or across point bar deposits, while the lateral and vertical hyporheic exchanges about a riverine confluence was almost never investigated. The paper presents some results of a numerical study carried out to investigate the basic features of the lateral hyporheic exchanges about the confluence of two channels. A 2D triangular geometry was used. Laminar flow in the channels and Darcian flow in the porous medium between them were considered. The simulations highlighted the role of the confluence planform and velocity ratio between the channels in controlling both the direction and the magnitude of the lateral hyporheic exchange.