Floodproof Galveston: A multidisciplinary project on flood risk and exploration of effective mitigation measures for the City of Galveston

In the past, Galveston Island has suffered from several tropical storms and hurricanes. Some of them have had a tremendous impact on the City of Galveston and its inhabitants. Two recent hurricanes, Ike (2008) and Harvey (2017), caused significant damage and struck the city in different manners. While Hurricane Ike brought about high wind speeds and surge, Hurricane Harvey deposited extreme amounts of precipitation over the island.There is a high probability that the City of Galveston will be struck again by a major hurricane. Hence, research is needed on mitigation measures that reduce the flood vulnerability of Galveston. More specifically, the simultaneous occurrence of surge and extreme precipitation is worth investigating, as currently little is known about the synergy between these aspects.This report elaborates on how the risk of flooding in the City of Galveston can be mitigated, considering the influences of extreme pluvial, coastal and compound flooding.In order to provide adequate mitigation measures, a vulnerability analysis is performed on the City of Galveston using hydraulic modelling software. Furthermore, a stakeholder and system analysis is done for all relevant stakeholders. Their respective interests, influence and interactions are mapped in a power-interest diagram and tube model. In addition, three residential stakeholder focus sessions were organized which provided valuable validation of the model and evaluation criteria for designs.The flood vulnerability of the City of Galveston is not merely limited to a single area. Vulnerability maps and an inventory of critical infrastructure show that Galveston has various bottlenecks scattered around the city. A crucial result of the analysis was that flood risk issues in Galveston can be divided into two aspects: nuisance flooding by regularly occurring precipitation and flooding due to hurricanes. This distinction is reflected in the proposed mitigation measures, as they require a fundamentally different approach. While damage caused by nuisance flooding can be fully prevented with the proposed measures, damage resulting from hurricanes can at best be mitigated.A comprehensive plan containing preliminary measures for both flooding scenarios is proposed for the City of Galveston. As part of this integrated plan, thirteen projects are defined which are elaborated in this report. Proposed measures to prevent damage originating from nuisance flooding include retention and infiltration of stormwater, discharge by pumps and raising frontier roads. Measures that mitigate damage due to hurricanes include breakwaters, retractable barriers and shelters for vertical evacuation.The authors recommend that more stakeholders are actively involved in interactive design sessions to make the plan more inclusive. Furthermore, for more accurate designs a probabilistic approach is preferred to the deterministic approach used in this report. In addition, more work is needed to elaborate on the design proposals as presented in this report.MDP26