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

Abstract

This article presents flooding simulation and flooding alleviation measure 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 study area. The results of HEC-HMS model’s calibration (2005) and verification (2000) gave correlation coefficient (r) of 0.95 and 0.82, respectively. And the results of HEC-RAS model’s calibration (2005) and verification (2000) using recorded water levels at Cha-Uat municipality bridge gave the error of water levels of 0.15 m and 0.23 m, respectively. The results of flooding simulation were found that there was no flooding at Cha-Uat Municipality for 2 yrs return periods, but the areas out of Cha-Uat Municipality were flooded at approximately of 0.5-1.0 m. Considerating of 5, 10 and 25 yrs return periods, Cha-Uat Municipality were flooded at approximately of 1.0-2.0 m. and up to 2-3 m for 50 and 100 yrs return periods. We proposed flooding alleviation measure by construction of floodway at Kangkao channel in order to drain water before entering area of Cha-Uat Municipality. By doing this, it could cut flood peak of 90 m³/s for 5 yrs return period.