Technical Abstract: Wind-driven rain (WDR) experiments were conducted to evaluate interrill component of the Water Erosion Prediction Project (WEPP) model with two-dimensional experimental set-up in wind tunnel. Synchronized wind and rain simulations were applied to soil surfaces on windward and leeward slopes of 7, 15 and 20%. Since WDR fall trajectory varied with differences in horizontal wind velocity, both magnitude of raindrop normal and lateral stresses on flow changed and a vector field was established at impact-flow boundary and differentially directed lateral jets of raindrop splashes with respect to downward flows occurred. To account for these differences, a vector approach with kinetic energy fluxes of raindrop splashes and flow were used instead of vector-free parameters of intensity and interrill runoff. When compared with original WEPP approach, these replacements resulted in greater correlations when predicting sediment rates, and using all experimental data the model coefficients of determination (r2) were 0.63 and 0.96, respectively.