Langan Offers Diverse Strategies to Help
Clients Mitigate Flood Risk
Following Hurricane Katrina in 2005 and Superstorm Sandy in 2012, the public developed a heightened awareness of the effects of storm surge and sea level rise (SLR). As storms become more extreme and ocean surface heights continue to increase due to climate change, normal tides and storm surge flood elevations will also continue to rise. In response, municipalities and land owners are developing flood risk reduction strategies for individual sites, while cities around the world have installed massive retractable gates that provide storm surge protection.
Yet when it comes to resiliency planning, one solution does not fit all. Langan works closely with clients on flood risk reduction strategies, providing advisory services and designing flood risk mitigations that respond to the unique requirements, characteristics, and environmental conditions of each site. Some of the solutions we consider include:
In September 2005, the Natural Resources Defense Council issued a paper titled After Katrina: New Solutions for Safe Communities and a Secure Energy Future, which pointed out that Louisiana’s barrier islands and coastal wetlands had traditionally provided a buffer against storm surges. For areas like the massive coastal wetlands of Louisiana, this solution provides many ecological benefits and mitigates flooding. However, it is important to note that a small wetland at an individual site cannot prevent upland flooding from coastal waters.
Elevating a site is an effective solution in any area. Yet it is important to consider the potential drainage, access, traffic, and utility issues that may arise because of elevation differences with neighboring properties and streets. Additionally, many waterfront properties are supported by structures that need to be reinforced or reconstructed to bear the load imposed by additional fill.
SLR will eventually cause water bodies to cover drainage outfalls during storms and ultimately under normal conditions. Some cities located on flat, reclaimed land are already experiencing high-tide or “sunny day” flooding, including Miami, Charleston, Savannah, Norfolk, Annapolis, and parts of Boston and New York. The short-term solution is to install backflow preventers that stop incoming water while allowing the upland to drain. In the longer term, outfalls (and potentially the entire upland) must be raised or upland water must be pumped out through submerged outfalls.
Walls can be erected on a site’s perimeter to prevent the infiltration of flood waters, typically with movable gates that allow for upland circulation under non-flood conditions. With this approach, soil characteristics must be analyzed to ensure flood waters do not pass under the wall. If they do, below-grade cut-off walls must be installed (which can be difficult in areas with underground utilities). New York City implemented this solution earlier this year, successfully installing the first 42-foot-long, 10-foot-high gate of the larger 2.4-mile East Side Coastal Resiliency project.
Regardless of a site’s environmental characteristics and potential flood risks, it is important to engage an expert who is knowledgeable about the options available and understands the opportunities – and limitations – of each project. Langan’s expertise in flood mitigation and waterfront structure design allows us to provide clients with appropriate, cost-effective, resilient solutions for present and future conditions.