Increasing surface impermeability influences peak discharge with the Snyder method in the Ngadipiro sub-watershed of the Bengawan Solo watershed

Abstract

This research was conducted to determine the effect of increasing soil impermeability in the Ngadipiro Sub-watershed on Cp and Ct numbers in 2015 and 2021. The measured unit hydrograph is used as a reference in calculating the Synder synthetic unit hydrograph method. Test the validation of the two methods using the correlation coefficient. The results of this study showed an increase in tightness in the form of an increased runoff coefficient from 0.26 in 2015 to 0.34 in 2021. This increase in tightness is also in line with the increase in peak discharge using the Measured unit hydrograph in 2015 of 73.3757 m3/s and 2021 of 139.1005 m3/s. The results obtained using the Snyder method obtained peak discharges in 2015 and 2021 of 75.10 m3/s and 148.89 m3/s. The results of the correlation test between the two methods obtained very strong correlation results with a 2015 R-value of 0.96 and a 2021 R-value of 0.92. The non-physical parameters of the watershed, namely Ct and Cp, were optimal in the Ngadipiro Sub-watershed in 2015, the Ct value was 2.2 and the Cp value was 0.9, while in 2021 the Ct value obtained was 1.3 and the Cp value was 1.1.