Bed-load transport on transverse slope.I

Bed-load particles tend to move downslope in response to gravity and downstream in response to fluid drag. The effect of gravity becomes particularly important when the downslope gravitational force has a component normal to the streamwise direction. Such phenomena as bank erosion, bed topography in river bends, sediment sorting, and stream braiding are strongly influenced by transverse bed-load transport under the influence of gravity. Here, the problem is analyzed from a consideration of the dynamics of saltating grains. Simultaneous solution of the streamwise and transverse equations of motion for a grain saltating on a transversely tilting bed of moderate slope allows a determination of mean particle trajectory. This mean trajectory, while predominately directed in the streamwise direction, includes a transverse downslope component as well. The results are used to determine a relation for the ratio of transverse to streamwise bed-load transport. This ratio increases with increasing transverse slope and decreases with increasing streamwise shear stress. The relation is compared with observations as well as existing relations obtained from simpler considerations.