Effect of soil stratification on the development and migration of headcuts in upland concentrated flows

Abstract

Experiments were conducted to examine the effect of vertical stratification in soil erodibility on the development and migration of steady state headcut scour holes in upland concentrated flows typical of agricultural fields. Packed soil beds with a preformed step were subjected to identical simulated rainstorms and clear‐water overland flow rates, which resulted in predictable, actively migrating headcut scour holes with nearly identical characteristics. When an erosion‐resistant layer was incorporated into the packed soil bed at a depth that exceeded this expected plunge pool scour depth, the erosion and hydraulic processes of the migrating headcuts remained unchanged. When the erosion‐resistant layer was placed so as to intersect this potential headcut scour depth, the erosivity of the reattached wall jet was unable to erode this layer, and the depth of scour, the nappe entry angle, and sediment efflux all were reduced inversely proportional to the relative depth of the resistant layer. These data were successfully predicted using modified jet impingement theory for headcut scour holes and demonstrate further the effects of soil management and tillage practices on total soil losses from agricultural fields.