The Application of HEC-HMS and HEC-RAS Mathematical Models for Study of Flood Mitigation in Cha-Uat, Nakhon Si Thammarat

Abstract

This article presents flooding simulation and flooding alleviation measures of Cha-Uat Municipality, Cha-Uat District, Nakhon Si Thammarat. HEC-HMS and HEC-RAS were applied to determine runoff and simulate flooding events in the study area. The results of the HEC-HMS model’s calibration (2005) and verification (2000) gave correlation coefficients (r) of 0.95 and 0.82, respectively. The results of the HEC-RAS model’s calibration (2005) and verification (2000) using recorded water levels at Cha-Uat municipality bridge gave errors of water levels of 0.15 m and 0.23 m, respectively. The results of flooding simulation found that there was no flooding at Cha-Uat Municipality for 2 years return periods, but the areas out of Cha-Uat Municipality were flooded at approximately of 0.5-1.0 m. Considering 5, 10 and 25 years return periods, Cha-Uat Municipality was flooded at approximately of 1.0-2.0 m. and up to 2-3 m for 50 and 100 years return periods. We proposed flooding alleviation measures by construction of a floodway at Kangkao channel in order to drain water before entering the area of Cha-Uat Municipality. By doing this, flood peak decreased by 90 m3/s for a 5 year return period.

Keywords

• mathematial model
• hec-hms
• hec-ras
• flow rate