Hydrodynamic Analysis and Overbank Flow Risk Assessment of the Phetchaburi River using MIKE-11 Model

Abstract

The Phetchaburi River Basin in Phetchaburi Province has experienced recurring floods in areas downstream of the Phet Dam. This study aims to analyze the hydrodynamic conditions and identify flood-risk areas along the Phetchaburi River using the MIKE-11 hydrodynamic model. The model was employed to simulate river flow along the 53.68-kilometer river reach from streamflow gauging station B.10 (Downstream Phet Dam,
Tha Yang District) to Bang Tabun Bay in Ban Laem District. The model utilizes river cross-sections surveyed in 2020. Model calibration was performed using water level data from 2022-2024, yielding Manning's roughness coefficients ranging from 0.03 to 0.07. Model validation was performed using water level data from 2020-2022. The calibration and validation results at gauging stations B.15 and B.16 showed satisfactory R², RMSE, and NSE values. The validated model was then applied to analyze the river capacity and minimum water depths at various locations. Results showed that channel capacity analysis identified critical sections between kilometers 20+001 and 30+000 in Mueang Phetchaburi District, where the discharge capacity drops to 82.16 cubic meters per second, and when compared with the minimum water depths data during that period, it was found that at the cross-section at kilometers 28+971, located in Nong Sano Subdistrict, Mueang Phetchaburi District, the lowest water level was 1.92 meters. This cross-section falls within the range where the water level is below 2.00 meters., indicating a high potential for overbank flow in this area. This finding corresponds with flood monitoring reports from the Department of Disaster Prevention and Mitigation during the November 2021 flood event. The analysis reveals that this section has limited flow capacity, which could lead to overbank flow during flood events. Further studies on channel capacity improvement and related river mechanics factors are recommended to serve as a guideline for preparedness and effective flood mitigation in the Phetchaburi River area.