Upper boundary conditions for overland flow.

A laboratory experiment is done to learn more about the influence of upstream boundary conditions on the hydraulics of overland flow under rainfall. The experiment is done on an impermeable plane 1-m wide, with a rainfall simulator that generates a uniformly distributed and time-invariant geometrical rainfall pattern over a length L measured along the plane (from x=O to x=L; x=O is defined as the upslope limit of the applied rainfall). Results show the importance of considering upstream boundary conditions, for gentle slopes, other than the most frequently used h(O,t)=O for t≥O, where h(x, t) is the flow depth as a function of position x and time t. The observed nonzero water depth at x=O and the consequent increase of water depth over the surface radically change the overland flow process over the slope