Estimating Flood Inundation Depth Along the Arterial Road Based on the Rainfall Intensity

This study identifies the rainfall intensity that causes the flood along the arterial road connecting Malang to Surabaya, East Java, Indonesia, estimates flood occurrences based on the recorded rainfall data, and proposes the normalization of the side ditch to reduce flood occurrences. The Nakayasu synthetic unit hydrograph was used to analyze the runoff discharge, and the Hydrologic Engineering Center’s River Analysis System software was used to analyze the water level profile of the side ditch. The regression method was used to determine the relationship between the rainfall intensity and inundation depth along the arterial road. Analysis results show that floods occur if the rainfall intensity is ≥1.01 year return period. To estimate the flood inundation depth, simple linear regression was conducted herein. Furthermore, it was observed that flood occurrences can be avoided by normalizing the side ditch cross section with a fully rectangular shape having a channel bottom elevation equal to the existing elevation.