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The Coast to Come Coastal Erosion, Storm Surges, and Flooding Accelerated Erosion As oceans rise, the pounding of waves and storm surge will almost certainly cause barrier islands, bluffs, and spits to erode more quickly. The result will be land loss. Erosion, of course, is a natural process that has been driven by relatively slow rates of sea-level rise over the last thousands of years. However, historically unprecedented future sea-level rise will accelerate the processes of erosion. Higher storm surges and waves can more easily overwash barrier islands and breach them, damaging highways, homes, and potentially forming new inlets across entire barriers. Coastal Floods Higher sea levels also mean storm surges will more easily reach low-lying areas. Scientists have already observed that low-lying regions are flooding more often during storm surges and spring tides as a result of 20th century sea-level rise. More intense rainfall from hurricanes and other storms (which is predicted as a consequence of climate change) could further increase the risk for coastal flooding. Erosion also increases the odds of flooding by removing the protection of dunes, beaches, and wetlands, and by moving the shoreline closer to existing properties. Vulnerable Regions Though coastal erosion will increase as sea level rises and the exact manner and rates cannot be predicted, certain trends can. Scientists project that it is virtually certain that midAtlantic bluffs, headlands, spits, and barrier islands will erode more quickly in response to future sealevel rise. As estuaries and lagoons deepen as sea level rises, they may become sinks for sediment from shore, cutting off the supply to barrier islands and increasing the potential for erosion and shoreline retreat. Vulnerable Regions (cont’d) Wetlands are also at risk from increasing erosion. Those that are fed with sediment from land may be able to withstand the erosive effects of climate change. But those whose sediment source has been blocked up or lost will suffer losses from erosion, further increasing the danger of storm surge in these area. If the oceans rise between 0.7 and 2.3 ft (0.2 to 0.7 m) in the next century, it's also likely that some barrier islands in the Atlantic region may cross an erosive threshold where they will either move landward, shrink, or break up suddenly. Vulnerable Regions (cont’d) Barrier islands formed in response to slow sea level rise rates. When an un-predetermined erosive limit is reached, a beach, barrier island, or other feature suddenly becomes unstable and experiences tremendous and irreversible changes. Narrow, low-elevation barriers will be most at risk. Chandeleur Islands The effects of accelerated sea level rise and potential threshold crossing could be already occurring on the Chandeleur Islands of Louisiana, where subsidence of the Mississippi Delta from oil extraction and delta compaction have led to unusually large sea level rise. Many major storms over the last decade and little input of island-building material from land have also contributed to the increase. The Chandeleur Islands are a north-south oriented chain of low-lying islands located approximately 100 kilometers east of the city of New Orleans, Louisiana. Chandeleur Islands (cont’d) The 45-mi (72 km) long chain of the Chandeleur Islands suffered greatly during Hurricane Katrina in 2005, in which a storm surge 13 ft (4m) high overtopped the islands and eroded 85% of the islands' sand. The Chandeleur Islands were mapped in the late 1980s and at that time calculated to last another 250 to 300 years based on erosion rates from 1850 to present. Studies of the island since Hurricane Katrina seem to indicate some sort of tipping point has been crossed and natural processes will not be able to rebuild the barrier.