Rill erosion begins with the concentration of surface runoff on depressions of soil surface, evolving into the formation of channels or ravine, increasing soil degradation by water erosion. The objectives of this study were to evaluate the hydraulic conditions of the water flow in rills and characterize the water flow regime, and to measure the induced changes in the geometry of the preestablished rills. An experiment was conducted in which outflows of 17.5; 47.0; 60.0; 77.0 and 110.0 L min-1 were applied for 20 min to preformed rills in a Cambissolo Háplico, in Serra Talhada, Pernambuco. The deepening of the rills was dominant at the beginning of the tests. From the moment the rill reached the undisturbed soil, the erosive process, i.e., the action of shear stress, was characterized mainly by the widening of the rill, wearing off the bases of the rill sidewalls. The action of the concentrated water flow in the experimental rills produced flow regimes in the range of supercritical transition, confirming the occurrence of rill erosion. The shear stress at the rill base provoked by the flow facilitated the wearing off of the sidewalls.
water erosion; hydraulic flow; flow regimes
