Perbandingan Perkiraan Debit Banjir Rancangan Menggunakan Data Hujan dan Debit di DAS Kaliwadas Kab. Pekalongan, Jawa Tengah

Design flood discharge is one of the important parameters in the management of water resources, especially water resources utilization structures and water damage control structures. This parameter serves to determine the dimensions and capacity of the planned water structures. As an important reference, this design flood discharge must be carefully determined so that the planned building is effective and financially functional and economically efficient. This study aims to determine the design flood discharge using rainfall data which will be recommended as a reference for the design of a micro-hydro power plant building in Kaliwadas River, Pekalongan Regency, Central Java Province. The results of the analysis based on rainfall data are compared with estimates using discharge data to determine deviations resulting from the use of rainfall data. Frequency analysis is applied to both types of rainfall and maximum daily discharge data. Chi-Square and Kolmogorov-Smirnov tests were performed to test four distribution methods: Normal, Normal Log, Pearson Log III and Gumbel. Transformation of design rainfall into design discharge is done using the Snyder Synthetic Unit Hydrograph Method, by first optimizing the hydrograph parameter. The analysis shows that the design flood discharge using rainfall data is relatively lower than using discharge data with an average deviation of more than 15%. This deviation is expected to occur when the transformation of rainfall into discharge is influenced by various very complex parameters, especially changes in land cover and rainfall distribution that have not been fully accommodated. However, for watersheds with very limited discharge data, the use of rain data can be an option for establishing a design flood discharge.