This study evaluates the performance of the RUNOFF01 model for simulating Hortonian overland flow under conditions where the entire watershed contributes to runoff, rendering scale effects negligible. The model was validated against three distinct datasets: (1) rainfall simulator experiments on a loam soil with various surface treatments (gravel, corrugations, and chemical amendments), (2) flume experiments on sandy loam and silty clay soils under different slopes and rainfall intensities, and (3) data from a 4.83-hectare agricultural catchment. Statistical analysis, using normalized root mean square error (NRMSE 0.96), and F-tests, demonstrated strong agreement between simulated and measured runoff across all scenarios. The results confirm that for slope lengths under ~ 350 m and extended rainfall duration—common in arid-region micro-catchments—the time to equilibrium (tₑ) is rapidly achieved, and the model accurately predicts runoff volume using key inputs like rainfall intensity, infiltration rate, and slope. The RUNOFF01 model can be used as a reliable tool for designing water harvesting systems and soil conservation strategies in ungauged agricultural basins.
Shabani et al. (Mon,) studied this question.