Monolithic Multiphysics Simulation of Compound Flooding

Abstract

When heavy rainfall, riverine flooding, and coastal storm surge coincide catastrophic flood conditions can occur, a process referred to as compound flooding. Many studies investigating the effects of compound flooding have relied on discrete models that simulate flooding processes separately. Consequently, they fail to mechanistically account for the complex interactions of multiple flood processes and the resulting impact on hazard estimates. We implemented the Adaptive Hydraulics Modeling System (AdH) that fully couples two-dimensional (2-D) shallow-water equations (SWEs) and 2-D diffusive wave equations (DWEs) to conduct monolithic simulations of compound flooding and quantify its impacts on water levels relative to Hurricane Harvey. The SWE simulated coastal storm surge and riverine flow while the DWE simulated overland flow. Spatially and temporally variable rain rates and wind effects within the model resolved heterogenic storm characteristics. A dense network of gage observations and surveyed high-water marks indicated the model’s ability to simulate the magnitude and timing of water levels. A comparison against benchmark flood extents indicated similar spatial inundation patterns. Model results revealed a transition zone, where multiple flood processes interact, that extends for almost 40 km along Buffalo Bayou highlighting the extensive impacts of compound flooding and the need to account for interacting physical phenomena with a fully coupled model. The results demonstrate the ability of this model and methodology to mechanistically account for the interactions of multiple flood processes with a 2-D hydrodynamic model.