PNNL

Abstract

Floodwater can mobilize and redistribute large volumes of sediment from upland to downstream urban areas, threatening infrastructure, water quality, and ecosystem health. However, existing modeling approaches often fail to capture sediment dynamics in urban floodplains due to the lack of integration between upland hydrological processes and riverine sediment transport. This study introduces a novel integrated modeling framework that couples the Energy Exascale Earth System Model (E3SM) land component, which simulates runoff and hillslope erosion, with TELEMAC-GAIA, a two-dimensional hydrodynamic and sediment transport model. This framework enables the fully distributed, process-based simulation of high-resolution (as fine as 30 m) sediment dynamics from hillslopes to floodplains. Applied to a highly urbanized watershed in Houston during Hurricane Harvey, this framework effectively captured hydrologic responses of flood depth, key sediment dynamics such as sediment transport and deposition processes, and reproduced spatial deposition patterns consistent with LiDAR-derived data. Based on the simulation, we estimate that 8.0 million cubic meters of sediment were deposited along major stream channels, floodplains and flood-control reservoirs, corresponding to an estimated dredging cost of $581 million. This study provides a valuable tool for the holistic analysis of sediment dynamics, particularly sediment deposition-induced damage, during extreme urban floods. More broadly, it highlights the importance of integrating physically based hydrological processes for urban flooding and sediment research.