Coastal Change Hazards: Hurricanes and Extreme Storms

Storm-Impact Scale

Inundation Regime

Inundation Regime Net onshore transport order 1,000 meters

If the storm surge is high and the elevation of the barrier island is low, the barrier can become completely subaqueous. Sand is transported landward over the island an order of magnitude farther than typical overwash of the overwash regime.

Catastrophic Impacts of the Inundation Regime

On August 29, 2005, Hurricane Katrina made landfall as a category-3 storm over the Mississippi Delta in Louisiana. This strong storm approached the coast with category-4 strength winds, building large waves and record-levels of storm surge. Aerial video, still photography, and laser altimetry surveys of post-storm beach conditions were collected August 31 and September 1, 2005. Comparisons of post-storm data with earlier surveys were used to show the nature, magnitude, and spatial variability of coastal changes such as beach erosion, overwash deposition, and island breaching.

Louisiana's Chandeleur Islands are an undeveloped, north-south oriented chain of barriers located approximately 110 km east of the city of New Orleans and 70 km east of Katrina's path. These low-lying barrier islands were totally stripped of sand, heavily fragmented by large waves and storm surge, and completely inundated during the storm.

Pre- (A) and post-storm (B) photography reveal the dramatic changes that occurred along the entire stretch of islands. This loss of sand and marsh is quantified using lidar topographic surveys (C and D). The elevation difference (E) between the two surveys reveal erosion over the entire island. This is in contrast to the erosion/accretion patterns typical of the overwash regime, in which a barrier island slowly migrates inland. This extreme coastal change may lead to long-term, permanent changes in the barrier island morphology and may affect its future resilience in storms. [larger version]

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