Hydrologic control of spatial patterns of suspended sediment concentration at a stream confluence

A conceptual model of the relationship between incoming hydraulic conditions and spatial patterns of suspended sediment at a stream confluence is evaluated using suspended-sediment data collected at a small stream confluence in east-central Illinois, USA. Patterns of normalized sediment concentrations at a cross-section near the exit of the confluence are a function of the ratios of momentum flux and mean sediment concentration in the upstream channels. These patterns reflect a shift in the location of the shear layer toward the outer bank as momentum ratio increases. Appreciable cross-channel mixing occurs within a distance of four channel widths downstream from the confluence. These findings suggest that confluence hydrodynamics may have important effects on the dispersal of dissolved or suspended substances in headwater areas of channel networks.