Effects of freshly incorporated straw residue on rill erosion and hydraulics

Rill hydraulics (and hence, flow detachment) are modified by the presence of incorporated vegetation residue. Typically, water flow in the rill is retarded due to the extra shear stress generated by the residue. The main objective of this study was to develop an approach to predict soil detachment by rill flow in the presence of freshly incorporated vegetation residue that is compatible with our current understanding of rill hydraulics and requires no additional information on rill geometry. Laboratory experiments were carried out to collect a dataset on rill flow detachment on surfaces with incorporated straw that was compatible with existing dataset on bare soils (Giménez and Govers, 2001). Interaction between bed roughness and flow hydraulics in eroding rills. Water Resources Research, Vol. 37 No. 3, 791–799).We found that effective unit length shear force, Γe, is well related to soil detachment when incorporated residue is present. The determination of Γe is based on the recalculation of the wetted cross-section area for a given flow velocity and slope, a hypothetical wetted cross-section area is estimated using empirical relationships defined for rills formed in bare soils. This procedure was also successfully applied to data from former field experiments. The procedure allows estimating erosion rates when flow characteristics (velocity and hydraulic radius) are known. However, the prediction of these flow characteristics remains uncertain.