Reducing coastal risk

With so many living on the coastal edge, how can society reduce the inevitable risks of living near the shore? Beach nourishment is seen by an increasing number of coastal communities as an alternative to forcing people to move from the coasts, even though many replenished beaches have lasted only a few years rather than decades; for most locations, this strategy cannot work in the long term. Armoring the beach with seawalls can stabilize the shore, but the monetary and aesthetic costs are very high and do not protect the beaches currently enjoyed by oceanfront properties. Structures of the sort that protect Galveston (see Figure 10.3) will increasingly be needed. This seawall was built following the disastrous 1900 hurricane and has served the city well, but the entire sandy beach has been lost.

By contrast, the Coastal Zone Management (CZM) Program offers states an incentive to better manage beachfront development. Unfortunately, best management practices have rarely been exercised (Leatherman and White, 2005),

1938 1957

Figure 10.2 Wetlands loss at Blackwater, Maryland, since 1938, from aerial photographs Source: IHRC.

1972 1988

Figure 10.2 Wetlands loss at Blackwater, Maryland, since 1938, from aerial photographs Source: IHRC.

and unless such management efforts include provisions for building levees around especially valuable regions or facilities and for ultimate retreat from the coastline, this approach has limited potential to work in a cost-effective manner.

With adequate steps to ensure coastal protection not yet taken, most of the burden of sustaining vulnerable (and increasingly damaged) coastal communities

Figure 10.3 The Galveston seawall has protected buildings and coastal infrastructure at the expense of the beach

Source: IHRC.

has fallen on the Federal Emergency Management Agency (FEMA) and its National Flood Insurance Program (NFIP). FEMA has taken an important step towards protecting coastal property by providing incentives to build new structures above the projected elevation of storm surges and to strengthen existing structures against windstorm damage. However, there has been no direct consideration of horizontal shoreline movement, specifically coastal erosion, nor planning to accommodate the accelerating pace of sea level rise and the likelihood of more intense storms (with their higher winds and larger storm surges). The lack of coordinated federal programs and policies is abundantly evident as the coastal building boom continues.

The flooding and destruction caused by storm surges are well known. Accurately predicting surge height and extent are critical for evacuation decisions. The National Weather Service's SLOSH model has served the country well for several decades, but it is now outdated and new models, such as AdCIRC, which was developed for the US Army Corps of Engineers, and the Coastal and Estuarine Storm

Time (CEST) model, which is being developed by the International Hurricane Research Center (IHRC) at Florida International University, are coming on line. The CEST model incorporates high-resolution Light Detection and Ranging (LIDAR) data that are gathered by an airborne LIDAR (laser) profiler, which can determine coastal elevations to an accuracy of a few centimeters. CEST also uses a 50 m grid size and a new overland flooding algorithm to provide superior results compared to the SLOSH model.

In advance of Hurricane Katrina's landfall, a 30 ft storm surge at Bay St Louis, Mississippi was predicted by the IHRC research team (see Figure 10.4 and Plate 15). The CEST model proved to be highly accurate as field measurements2 confirmed the extremely high surge height and landward penetration. Katrina surpassed the previous storm surge record of 22.4 ft generated by Hurricane Camille in 1969 at Pass Christian, Mississippi.

The IHRC CEST model is presently undergoing further development with the goal of becoming a real-time forecast model for use by NOAA's National Hurricane Center and FEMA, perhaps along with other models of storm surge

Figure 10.4 Storm surge height forecast from IHRC's CEST model for Hurricane Katrina (see Plate 18 for color version)

Source: IHRC.

height to produce a suite of forecasts, as is done for hurricane track and intensity. These advances will save lives during hurricanes while also allowing better mapping of coastal vulnerabilities and planning of the adaptations necessary to be prepared for increasingly severe coastal storms and rising sea level.

Continue reading here: New technology to improve coastal resilience

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