Flood management analysis in the Ngasinan River, Trenggalek Regency, Indonesia

Abstract

Flood event occurs during the rainy season when water volume increases because rainwater flows through the water channel; due to water volume being larger than the water channel capacity, this event can cause flood inundation through residential areas. The Ngasinan catchment at Trenggalek Regency experienced a flood event that affected thousands of lives in October 2022, to reduce the impact of future floods, this study objective carried out recommendation plans for flood management in the Ngasinan River. The Ngasinan catchment hydrology, maximum annual rainfall from 230.0 mm to 585.0 mm, flood discharge design for the Ngasinan river (river length 21.73 km as main river drainage) are Q25 = 318.64 m3/s, Q100 = 394.96 m3/s. Hydraulic simulation using flood discharge design Q25 -Q100 showed that flood occurs in Ngasinan River sections especially those without embankments or at lower river elevations and cross-sections. Recommendation plans for the Ngasinan River flood management are river normalization, river embankment repairs, residential drainage system, and construction of dams/reservoirs/retarding basins, expected to restore the river’s storage capacity due to sedimentation and destructive flood discharge also to reduce flood discharge, protect river channel banks against flood discharge, and prevent overtopping water into nearby land.