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This study was conducted in Barangay Badiangan, Ajuy, Iloilo City, Philippines (11°10'N, 122°58'E) to determine the effects of rainfall intensity and other rainfall-derived parameters on the directional components of splash erosion in hillslopes. There are five experimental setups with slope angles ranging from 0% to 48% were tested under natural rainfall conditions using a modified splash collector. The data collected shows that kinetic energy, slope, and rainfall intensity have shown significant effects on splash erosion. The models obtained using regression analysis are Qdet = 0.0093 (KE0.80) and Qtrans = 0.060(KE0.107) (S0.700) (I20 0.700). The model equation performance has been validated using the Standard Error of Estimates with values of 12 and 9.4 for splash detachment and splash transport, respectively. The constants used for kinetic energy in detachment and slope in transport align with the research by Quansah (1981) for sandy soil, which is similar (the characteristics) to the soil at our research site. Additionally, rainfall intensity, especially with a 20-min duration, generated the best model as it yielded the lowest SEE value for all cases. [ABSTRACT FROM AUTHOR]

The Curve Number (CN) method has been widely used for estimating runoff from rainfall. However, some uncertainties in the method have been recognized by various researchers all over the world. One of which is the NRCSassumed initial abstraction ratio (Ia/S) of 0.20. In this study, the Ia/S for the upper catchment area of Sawaga River in Bukidnon was determined using event analysis of different rainfall events with a total precipitation depth ranging from 21.50 to 57.90 mm. The resulting representative values of Ia/S and CN are 0.03 and 62.3, respectively. Evaluating the runoff prediction performance of both the original NRCS (Qesti0.20) and locally derived parameter values (Qesti0.03), Qesti0.03 had a lower error rate with a Standard Error of 2.2639 compared to Qesti0.20's 2.6760. For accuracy in predicting runoff, Qesti0.03 also showed better performance with a Nash-Sutcliffe Efficiency of 0.7854 versus 0.6942 for Qesti0.20, and its Percent Bias was lower at 2.6410 compared to 36.4201 for Qesti0.20. Both methods had very good coefficients of determination, with Qesti0.20 at 0.8459 and Qesti0.03 at 0.8343. Overall, Qesti0.03 proved to be more reliable and effective for accurate runoff prediction in this watershed. These findings suggest that the CN method, with certain adjustments on Ia/S and CN, is appropriate for the direct runoff estimation in the upper Sawaga watershed, Bukidnon. [ABSTRACT FROM AUTHOR]