Pendugaan Debit Puncak Menggunakan Model Rasional dan SCSCN (Soil Conservation Service-Curve Number); Studi Kasus di Sub-sub DAS Keyang, Slahung, dan Tempuran; Sub DAS Kali Madiun, DAS Solo

Abstract

Flooding can occur as a result of an increase in the amount and velocity of run-off exceeds the capacity of drainage channels. In addition, floods can occur as a result when drainage channel capacity is reduced, so the amount and velocity of run-off exceeds the capacity whendrainage channels. The decreasing of dranaige channel capacity can occur because of the superficiality of the river due to sedimentation from erosion in the upstream, blockage by garbage or constriction by the accumulation in water bodies. The increasing of amount and velocity of run-off caused by extreme rainfall and changes in land us that causes land clearing and soil compaction. The amount and velocity of run-off that causes the maximum peak discharge (Qp) is important to be known, because it has potential to cause flooding. Peak discharge as important information fordesign of flood control is generally estimated by using the rational model and model of Soil Conervation Service-Curve Number (SCS-CN). To know the validity of both models by using available data in Sub-sub Watershed of Keyang, Slahung and Tampuran (KST), the models are tested by comparing the esimated and obsered Qp. Estimated Qp by using rational model with the peak discharge data in 2009 (39.10 mm precipitation) is 30.82% greater than observed Qp, while the result by using SCS-CN model is 113.87% greater. Estimted Qp by using rational model with maximum rainfall data in 2009 (45.97 mm) is 4,074.74% greater than observed Qp, while the result by using SCS-CN model is 18.06% smaller than observed Qp. The coefficient run-off that calculated by using the rational model is greater (0.375) than calculation by direct observational data (0.34).