Characterizing the hydraulic interactions of hurricane storm surge and rainfall–runoff for the Houston–Galveston region

Abstract

Planning of traditional coastal flood risk management strategies are largely predicated on storm surge protection against extreme hurricanes, i.e. storm surge. However, (1) hurricane storm surge and (2) hurricane rainfall–runoff are not mutually exclusive flood hazards. Little research has emphasized the need for quantifying and characterizing the joint hydraulic processes between hurricane storm surge and rainfall–runoff during real events for enhancing effective flood risk mitigation. In this regard, an improved hydrological and hydrodynamic modeling framework has been developed for the Houston Ship Channel (HSC) and Galveston Bay to serve as a quantitative testbed for evaluating coupled hurricane storm surge and rainfall–runoff. Modularity within the modeling framework allows for landfall shifting of historical hurricane tracks, wind fields, and corresponding rainfall patterns to serve as numerical model inputs, as well as providing an expanded dataset of storm events. Distributed hydrologic and unsteady hydraulic analyses of upstream rainfall–runoff and storm surge are conducted for hurricanes Katrina (2005), Ike (2008), and Isaac (2012) under three synthetically shifted landfall locations near the HSC and Galveston Bay regions. For the modeled scenarios, results show that peak flows from storm surge easily dominate those of rainfall–runoff, but that rainfall–runoff can constitute more than half of the total flood volume draining towards the HSC. Most modeled scenarios reveal less than 24h of separation between peak surge and peak rainfall–runoff. In the same way that storm surge is sensitive to hurricane landfall location and angle of approach, so are spatial rainfall distributions and associated inland runoff processes, due to wide topological variations in coastal watershed boundaries. Analysis of coastal flood mitigation is extended with the dynamic modeling of a proposed storm surge barrier system at the HSC, with its performance quantified under the given hurricanes. The surge barrier system is demonstrated to be hydraulically feasible for all scenarios, with maximum water surface elevation reductions ranging between 0.63m and 3.28m. However, accurate storm surge and riverine flood forecasting methods will be critical for achieving optimal gate and barrier operations.