Analisis Hidrograf Satuan Sintetik Nakayasu Untuk Perancangan Dimensi Saluran Drainase (Studi Kasus Jl. Ketintang Surabaya)

The drainage channel located on Jalan Ketintang, Gayungan District, Surabaya, East Java, is influenced by geographical conditions, vulnerable to damage due to landslides and flooding. Along with the presence of quite high rainfall during the wet months (October - January), the problem of inundation in the form of flooding always arises in the area. To minimize flooding, it is necessary to repair the channel (capacity) periodically at certain periods. In the period of August - December 2022, channel repairs were carried out by installing a fabricated rectangular channel using U/DITCH 150/150. The purpose of this thesis is to determine the value of the design flood discharge (Q) and obtain the value of the channel dimensions that can accommodate the design flood discharge at a return period of 5 years and 10 years. The analysis in this thesis is in the form of obtaining rainfall data at 3 (three) rainfall stations, namely Perak 1, Perak 2 and Juanda rainfall stations, rainfall data using 2008 – 2022 (15 years) data, calculation of planned discharge using the Log Pearson Type III method, rainfall data testing using the Smirnov Kolmogorof, rainfall intensity using the Mononobe model, and calculation of designed flood discharge using the Nakayasu Synthetic Unit Hydrograph. The results of the analysis show that the design flood discharge obtained is 17.1 m3⁄s (10-year return period) and the dimensions of the planned channel are a square channel measuring 1,325 m x 1,325 m. This is in accordance with the capacity of the 150/150 U/Ditch channel installed along 945 meters which can minimize the occurrence of inundation/flooding/overflow of channels in the area because the channel has been repaired and the capacity is enlarged