Storm Overwash and the Knickpoint Effect: Northwest Florida Coast, USA.

Storm overwash is a critical issue in coastal management efforts to mitigate damage to infrastructure. This paper contributes to those efforts by documenting the findings of a field survey at the Perdido Key, Florida, section of Gulf Islands National Seashore following the landfall of tropical cyclone Isidore in September 2002. The poststorm survey of overwash sites detected scouring along the northern edge of an access road that faced away from the Gulf of Mexico and the oncoming storm surge. Most sites experienced removal of minor amounts of sand and roadbed material, which left the edge of the overlying asphalt road surface unsupported. However, more severe scouring at one site caused the overlying asphalt road surface to fracture and collapse. An extreme example of this process was observed following the landfall of Hurricane Opal at Pensacola Beach, Florida, in 1995. The scouring process and its effects were consistent with a process recognized in fluvial systems as knickpoint development. Related scouring processes known as hydraulic jump and dam overtopping are also discussed. Coastal management options for mitigating this problem include reducing overwash and increasing resistance to scour. Methods to protect dams from overtopping offer potential solutions to this problem. An alternative solution is proposed that would offer protection against minor overwash events; however, it is unlikely that any of the methods discussed herein would be highly effective against an extreme event like Hurricane Opal. [ABSTRACT FROM AUTHOR]