Analisis Debit Banjir Rancangan Menggunakan Metode Nakayasu (Studi Kasus Di Perumahan Gauri Akratama)

Batu City, located in East Java, Indonesia, about 15 km southwest of Malang, is known as a popular tourism city. The rapid development of new tourist destinations has increased the resident population, leading to extensive housing and villa developments. Gauri Akratama Housing in Batu City is one of the residential areas that continues to grow along with the increasing population. As the housing area expands, the growth of impervious surfaces such as roads, sidewalks, and buildings reduces natural rainwater infiltration areas, potentially causing serious drainage problems, including flooding, soil erosion, and groundwater pollution. This study aims to determine the design flood discharge and to analyze the influence of the design discharge on the shape and characteristics of the hydrograph curve for 5 year and 20 year return periods. Design flood discharge calculation was carried out after obtaining the design rainfall using the Polygon Thiessen method and Log Pearson Type III distribution. The resulting design rainfall was tested using the Smirnov–Kolmogorov test. Rainfall values that passed the test were then processed using the Mononobe rainfall intensity method and hourly effective rainfall. The analysis method used was the Nakayasu synthetic unit hydrograph (HSS Nakayasu) to obtain the design flood discharge for the specified return periods The results show that the design flood discharge in Gauri Akratama Housing, Batu City, for a 5-year return period is 352.88 m³/s, and for a 20-year return period is 417.16 m³/s. The design discharge influences the shape and characteristics of the hydrograph, which exhibits a near-normal distribution with a peak occurring at the second hour, with a peak ordinate of 6.882.