Modelling interrill sediment delivery

Shallow surface runoff is a primary transport agent for interrill sediment delivery. Runoff, rainfall intensity, and slope interactively affect interrill erosion. We hypothesized that the inclusion of a runoff factor in an interrill erosion model can reduce the dependence of the interrill soil erodibility (K-i) on soil infiltration characteristics as well as improve model predictability. A complete factorial rainfall simulation experiment with two soils (Cecil sandy foam, a clayey, kaolinitic, thermic Typic Kanhapludult, and Dyke clay, a clayey, mixed, mesic Typic Rhodudult), four rainfall intensities, four slopes, and two replicates was conducted under prewetted conditions to measure runoff and sediment delivery rates. Tap water with electrical conductivity <0.2 dS m(-1) was used in all the runs. Rainfall intensity I, unit discharge q, slope S, soil type, and their interactions significantly affected sediment delivery per unit area (D-i). Sediment delivery had the greatest correlation (r = 0.68) with unit discharge; however, neither discharge nor rainfall alone adequately predicted sediment delivery. The equation D-i = K(i)Iq(1/2)S(2/3) was proposed. The linear intensity term (1) represents detachment of soil by raindrop impact and enhancement of transport capacity of sheet flow, while the product of q(1/2)S(2/3) describes sediment transport hr sheet flow, Validation with independent data showed that the model predicted soil erodibilities well, The mean r(2) for four validation soils was 0.93 when the proposed model was fitted to validation data to predict interrill erodibility (K-i), The better estimation of K-i indicates that interrill erosion processes were adequately described by the model.