Investigation into the Impacts of Land Subsidence on Flood Inundation during Hurricane Harvey in Brays Bayou, Texas

Over an area of 44,000 square kilometers in 45 states of U.S. had been impacted by land subsidence reported by the National Research Council back in 1980s. Among all the affected areas, the Houston-Galveston area experiences land subsidence as early as 1900s. Over the past two decades, many studies have found that flooding could be related to land subsidence. To gain a better understanding of the impacts from land subsidence on flood inundation, the authors conduct a research on flooding characteristics in the Brays Bayou watershed of Texas using a hydrodynamic/hydraulic 2D model. Hurricane Harvey is selected in this study for its catastrophic flooding in Texas. The model is first calibrated using observed stage hydrographs from four (4) stream gauges and then validated using ninety-nine (99) highwater marks. Ten (10) flood inundation scenarios with different land elevation conditions from multiple years (1900, 1930, 1945, 1960, 1970, 1980, 1990, 2000, 2010 and 2017) are simulated to investigate the change of flood characteristics due to land subsidence. Then the simulation results from the scenarios are visualized, quantified, and further analyzed in upstream, mid-stream and downstream sections of the watershed. The results indicate that while land subsidence has trivial influence on flood inundation area throughout the simulated years with only 0.05 square kilometers increasing from 1930 to 2017, it does have obvious impact on flood depth and flow velocity. The results show that flood depth difference reaches to its climax between 1970 to 1980, which is in accordance with the place where land subsidence rate is the highest in the same period. This research provides insights of the impact of land subsidence on different aspects of flooding, which also enlightens for further work in other watersheds.