Rainfall-runoff modelling for flash floods in urban areas of Ban Phai city, Khon Kaen Province

Abstract

Flash floods in urban areas are natural disasters that frequently happen due to the rapid urbanization. Generally, flash floods are caused by severe rainfall. These phenomena usually occur within a few hours of excessive rainfall, leaving extremely short time for warning. As a result, they can cause loss of life and destroy properties. The flash flood event occurred in Ban Phai city located in the Huai Jik basin during 31 August 2019 was studied. This study was a challenging task because there was no a stream gauge in the study area. The main objective of this study was to create a rainfall-runoff model for estimating the flood peaks and lag time. To set up the model, QGIS, open source software, was used to estimate model parameters from digital elevation model, land use maps, and soil maps. For model calibration, observed hourly rainfall data were converted by the rainfall-runoff model to simulated runoff. This simulated runoff was compared with the estimated runoff at the outlet of the Huai Jik basin, which was based on operation rule curves of the Kang La Wa reservoir. The results showed that the rainfall-runoff model was able to simulate the flood peak and lag time, which were considered to be acceptable. For further studies, rainfall analysis and design will be taken into account of rainfall-runoff modelling in order to provide several potential flash flood scenarios. These may provide a useful support to an early flood warning system.