Hydrodynamics MIKE11 Model for Flooding Assessment in the Pho-Phraya Field

Abstract

Diversion of flooding to a detention field is one of the importance measures for mitigation on inundation risk due to upstream floods in the Chao Phraya Basin. The present study therefore develops the hydrodynamic MIKE11 model for assessment of depth and area of flooding as a result of the diversion. The MIKE11 model is widely accepted in practice as a flood model in a river. In this research, we further improve the model ability to evaluate flooding situation in a detention field by assuming imaginary hydraulic structures to distribute flood excesses of actual canal network over the field area obtained from the digital elevation model (DEM). The improved MIKE11 model is then developed for describing the flood in the Pho-Phraya field. The development uses the flood data between 2016 and 2017 for model calibration and validation respectively. Development results can be divided into 2 cases: (1) flooding in the canal network and (2) spilling over the canals. For the first case, the model adopts coefficient of roughness from 0.025to 0.035. Itcould estimate upstream water level at the Pho-Phraya gate that is reasonably accurate, as compared with an appropriate observation. The coefficient of determination R² ranges from 0.72 to 0.83 while the root mean square error (RMSE) is between 0.15 and 0.23 m. Secondly, considering the roughness coefficient of 0.045-0.05, the flooding depths (0.9-1.2 m) of the model agree with corresponding data satisfactorily. In addition, the results obtained have suggested that the concept used in the improved model could be applied to the other flooding detention field.