Jul 232014

A new report from the National Research Council of the National Academies of Sciences and Engineering calls for a national coastal risk assessment in order "to identify coastal areas that face the greatest threats and are high priorities for risk-reduction efforts." (report page with links)

From report, page 63

"There is a misalignment of risk, reward, resources, and responsibility related to coastal risk management, which has led to inefficiencies and inappropriate incentives that ultimately increase coastal risk,” said Richard A. Luettich Jr., professor of marine sciences at the University of North Carolina, Chapel Hill, and chair of the committee that wrote the report. “There is a crucial need for collaboration among federal agencies and between the federal government and the states, as well as policy changes that will help us evolve from a nation that is primarily reactive to coastal disasters into one that invests wisely in risk reduction and resilience,” he said.

Also from the press release:

"Coastal risk management strategies can include built or natural infrastructure to reduce flood hazards and wave damage in at-risk areas as well as steps to move people and property out of harm’s way.  Structural strategies to reduce storm-related hazards include seawalls, levees, flood walls, and storm-surge barriers, as well as beach nourishment, dune building, and restoration or expansion of natural habitats.  Conversely, elevating existing structures, relocation, and land-use planning to deter future development in high-hazard areas can reduce the number of people or buildings at risk.  The committee found that in the past, most risk reduction projects have focused on fortification, with few efforts to limit redevelopment in high-risk areas and steer development toward safer, lower-risk areas."

Though not specified in the news release, the report says wetlands can be helpful in mitigating flood hazards. "Numerous designs and strategies can be used to mitigate coastal risk associated with severe storms.  These include measures to reduce the hazard, such as seawalls, breakwaters, and levees; natural and nature-based features, including wetlands, natural and replenished dunes, and mangrove forests; and strategies to reduce the consequences of an event, such as land-use planning, floodproofing, and relocation."  (emphasis added)


"Conservation or restoration of ecosystem features such as salt marshes, mangroves, coral reefs, and oyster reefs provides substantial ecological benefits and some level of risk reduction against coastal storms, but the risk reduction benefits remain poorly quantified." (page 4)

"The presence of natural features, such as barrier islands, vegetated dunes, coastal wetlands, mangrove forests, and reefs, may reduce coastal storm hazards by attenuating wave energy and storm surge and possibly stabilizing sediment. However, the effectiveness of these features depends on the specific characteristics of the storm and the features themselves." (page 26)

"Dunes serve as a physical barrier blocking storm surge, although their longevity depends on the adjacent beach slope, the sediment characteristics, the height and width of the dune, and the extent of dune vegetation. Coastal wetland vegetation and the land it helps retain may reduce the rate of storm surge advancement and extent (Wamsley et al., 2010). " (page 27)

"Levees fundamentally change flow conditions above and below the structure. Even when water is allowed to flow through gates in levees, salinity values and the flux of nutrients can be modified to a point that entirely different biological communities develop on either side of the structure and fish migration patterns are altered. Construction of new levees without provision for natural water exchange results in the elimination of wetlands. Levees also prevent the delivery of waterborne sediment to formerly inundated areas, contributing to subsidence and reducing the potential to keep pace with sea level rise." (page 70)

"Levees in the coastal environment have little direct environmental value, but there is increasing interest in modifying the design of coastal risk reduction features to increase ecological functions and reduce the overall impacts (Day et al., 2000). The “rich levee” concept (Dijkman, 2007) proposes to increase biodiversity within wide coastal levees (as used in the Netherlands) by providing diverse habitats within the structural design, including vegetated shore-parallel ridges and carefully selected armoring material that could provide habitat for diverse flora and fauna." (page 7

Other reports