Flow Estimation using Hec-Ras Model A Case Study of Lam Takong River Basin

Abstract

Lam Takong River Basin is an important basin for Nakhon Ratchasima province, because it is a large river basin that flows through both the agricultural and economic areas in many districts throughout the province. In 2010, there was a flood that damaged in several areas around the Basin caused from drainage system of the Lam Takong Dam. It resulted in high water levels in the Lam Takong Dam and overflows. Another factor contributing to this is several consecutive days of heavy rain which caused surface runoffs and floodplains in many areas. The objective of this research is to analyze the drainage potential of Lam Takong and assess the flooding area caused by overflows from the Lam Takong banks at the return periods of 5, 10, 25, 50 and 100 years respectively using HEC-RAS model. This study used Manning's roughness coefficient (n) of 0.0415 for both sides of the banks and of the channel. The calibration and validation of model was performed in comparison with the data from 2011 and 2014 models. Calibration results showed the coefficient of Determination (R2) of 0.860, the Nash-Sutcliffe coefficient of efficiency (NSE) value of 0.850, the validation values (R2) were 0.645 and the NSE value was 0.626. The study of potential drainage found that the maximum flow rate for each surface area of the flow ranged from 33.38 to 37.74 m3/s. The maximum water level for each surface area ranged from 177.94 to 246.07 m. MSL. In addition, the average maximum flow rate of 35.50 m3/s was for the analysis of flood areas, under constant flow conditions it was found that the flooding area caused by overflows at the return periods of 5, 10, 25, 50 and 100 years were 107.928, 120.596, 133.299, 140.726 and 147.878 km2, respectively.