Towards an Automated Floodway Optimizer for HEC-RAS

In the United States, one component of the detailed flood study is to outline the floodway. In floodway boundary determination, encroachment is applied at every cross section to where the rise in water surface is kept just below an allowable threshold while preserving the same flow state as in the floodplain model. Determination of optimal floodway boundaries can be tedious and time consuming if done manually. However, good floodway boundaries provide valuable information to regulating agencies and engineers aiding them in decision making, planning and management of floodplain development activities. This study introduces the automated floodway optimizer for HEC-RAS (AFORAS). AFORAS uses the standard HEC-RAS hydraulic model and the isolated-speciation-based particle swarm optimization (ISPSO) algorithm to produce reach-wide optimal floodway boundaries. The proposed method was developed to automate the determination of optimal floodway boundaries such that the resulting floodway will occupy minimal footprint area without violating user-specified hydraulic constraints. Preliminary simulations show that, once setup, AFORAS was able to produce optimal floodways without user intervention. The model was also observed to be robust and capable of handling cases with different boundary conditions. AFORAS shows promise as a tool for automating the floodway for practical use. In addition, the model was designed to tightly couple with the standard HEC-RAS hydraulic model and, therefore, can be a useful tool for the floodplain modeling community as well as regulating agencies.