Storm surge

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Graphic illustrating storm surge.

A storm surge is an onshore rush of water associated with a low pressure weather system, typically a tropical cyclone. Storm surge is caused primarily by high winds pushing on the ocean's surface. The wind causes the water to pile up higher than the ordinary sea level. Low pressure at the center of a weather system also has a small secondary effect, as can the bathymetry of the body of water. It is this combined effect of low pressure and persistent wind over a shallow water body which is the most common cause of storm surge flooding problems.

Storm surges are particularly damaging when they occur at the time of a high tide, combining the effects of the surge and the tide. This increases the difficulty of predicting the magnitude of a storm surge since it requires weather forecasts to be accurate to within a few hours.

The most extreme storm surge events occur as a result of extreme weather systems, such as tropical cyclones, but storm surges can also be produced by less powerful storms.

The highest storm surge ever recorded was produced by the 1899 Cyclone Mahina, which caused a 13 meters (43 feet) storm surge at Bathurst Bay, Australia. In the United States, the greatest recorded storm surge was generated by 2005's Hurricane Katrina, which produced a storm surge 9 meters (30 feet) high in the town of Bay St. Louis, Mississippi, and in the surrounding coastal counties. The worst storm surge, in terms of loss of life, was the 1970 Bhola cyclone and in general the Bay of Bengal is particularly prone to tidal surges.

Contents

1 Hurricane storm surge; potential for disaster
2 Mechanics of the storm surge
3 Storm surge barriers
4 See also
5 External Links
6 References

Hurricane storm surge; potential for disaster

Nine out of ten people who die in hurricanes are killed by storm surges. The Galveston Hurricane of 1900, a category 4 hurricane that struck Galveston, Texas on 8 September, drove a devastating surge ashore; between 6,000 and 12,000 lives were lost, making it the deadliest natural disaster ever to strike the United States (Hebert, 1990). The second deadliest natural disaster in the U.S. was the storm surge from Lake Okeechobee in the 1928 Okeechobee Hurricane which swept across the Florida Peninsula during the night of September 16. The lake surged over its southern bank, virtually wiping out the settlements on its south shore. The estimated death toll was over 2500; many of the bodies were never found. Only two years earlier, a storm surge from the Great Miami Hurricane of September 1926 broke through the small earthen dike rimming the lake's western shore, killing 150 people at Moore Haven (Will, 1978).

In the Bay of Bengal area, the "storm surge capital of the world", 142 moderate to severe storm surge events are on record from 1582 to 1991. These surges, some in excess of eight meters (26 ft.), have killed hundreds of thousands of people, primarily in Bangladesh (Murty and Flather, 1994). The Caribbean Islands have endured many devastating surges as well.

[Data on Bangladesh disasters] from NIRAPAD disaster response organisation.

Mechanics of the storm surge

At least five processes can be involved in altering tide levels during storms. These include the pressure effect, the direct wind effect, the effect of the earth's rotation, the effect of waves, and the rainfall effect (Harris, 1963). The pressure effects of a tropical cyclone will cause the water level in the open ocean to rise in regions of low pressure and fall in regions of high pressure. Wind stresses cause a phenomenon referred to as "wind set-up", which is the tendency for water levels to increase at the downwind shore, and to decrease at the upwind shore. This effect is inversely proportional to depth (Harris, 1963). Wind set-up on an open coast will be driven into bays in the same way as the astronomical tide. Surge and wave heights on shore are affected by the configuration and bathymetry of the ocean bottom. A narrow shelf, or one that drops steeply from the shoreline and subsequently produces deep water in close proximity to the shoreline tends to produce a lower surge, but a higher and more powerful wave. This situation is seen along the southeast coast of Florida. The edge of the Floridian Plateau, where the water depths reach 91 meters (300 feet), lies just 3 km offshore of Palm Beach, Florida; just 7 km offshore, the depth plunges to over 180 meters (Lane, 1980). The 180 meter (600-foot) depth contour followed southward from Palm Beach County lies more than 30 km to the east of the upper Keys.

Conversely, coastlines such as those along the Gulf of Mexico coast from Texas to Florida, have long, gently sloping shelves and shallow water depths. On the Gulf side of Florida, the edge of the Floridian Plateau lies more than 160 km offshore of Marco Island in Collier County. Florida Bay, lying between the Florida Keys and the mainland, is also very shallow; depths typically vary between 0.3 and 2 meters (Lane, 1981). These areas are subject to higher storm surges, but smaller waves. This difference is because in deeper water, a surge can be dispersed down and away from the hurricane. However, upon entering a shallow, gently sloping shelf, the surge can not be dispersed away, but is driven ashore by the wind stresses of the hurricane.

Topography of the land surface is another important element in storm surge extent. Areas where the land lies less than a few meters above sea level are at particular risk from storm surge inundation.

Storm surge barriers

A prophylactic method introduced after the North Sea Flood of 1953 is the construction of dams and storm surge barriers. They are open and allow free passage but close when the land is under threat of a storm surge. Major storm surge barriers are the Oosterscheldekering and Maeslantkering in the Netherlands which are part of the Delta Works project.

External Links

["The 1953 English East Coast Floods"]
[DeltaWorks.Org] North Sea Flood of 1953, includes images, video and animations.
[DeltaWorks.Org] DeltaWorks Project, approx. 15 dams and barriers against tidal storm surges

References

Anthes, R.A., 1982. Tropical Cyclones; Their Evolution, Structure and Effects, Meteorological Monographs,19(41), Ephrata, PA., 208 p.
Cotton, W.R., 1990. Storms. Fort Collins, Colorado: *ASTeR Press, 158 p.
Dunn, G.E. and Miller, B., 1964. Atlantic Hurricanes. Baton Rouge: Louisiana State University Press, 377 p.
Finkl, C.W. Jnr., 1994, Disaster Mitigation in the South Atlantic Coastal Zone (SACZ): A Prodrome for Mapping Hazards and Coastal Land Systems Using the Example of Urban subtropical Southeastern Florida. In: Finkl, C.W., Jnr. (ed.), Coastal Hazards: Perception, Susceptibility and Mitigation. Journal of Coastal Research, Special Issue No. 12, 339-366.
Florida Department of Community Affairs, Division of Emergency Management, 1995. Lake Okeechobee Storm Surge Atlas for 17.5' & 21. 5' Lake Elevations. Southwest Florida Regional Planning Council, Ft. Myers, Florida. var. pag.
Gornitz, V.; Daniels, R.C.; White, T.W., and Birdwell, K.R., 1994. The development of a coastal risk assessment database: Vulnerability to sea level rise in the U.S. southeast. Journal of Coastal Research, Special Issue No. 12, 327-338.
Harris, D.L., 1963. Characteristics of the Hurricane Storm Surge, Technical Paper No. 48, United States Weather Bureau, Washington, D.C., 139 p.
Hebert, P.J. and Case, R.A, 1990. The Deadliest, Costliest, and Most Intense United States Hurricanes of This Century (and other Frequently Requested Hurricane Facts), NOAA Technical Memorandum NWS NHC 31, Miami, Florida, 33 p.
Hebert, P.J.; Jerrell, J.; and Mayfield, M., 1995. The Deadliest, Costliest, and Most Intense United States Hurricanes of This Century (and other Frequently Requested Hurricane Facts), NOAA Technical Memorandum NWS NHC 31,Coral Gables, Fla., In: Tait, Lawrence, (Ed.) Hurricanes...Different Faces In Different Places, (proceedings) 17th Annual National Hurricane Conference, Atlantic City, N.J., 10-50.
Jarvinen, B.R. and Lawrence, M.B., 1985. An evaluation of the SLOSH storm-surge model. Bulletin American Meteorological Society 66(11) 1408-1411.
Jelesnianski, C.P., 1972. SPLASH (Special Program To List Amplitudes of Surges From Hurricanes) I. Landfall Storms, NOAA Technical Memorandum NWS TDL-46. National Weather Service Systems Development Office, Silver Spring, Maryland, 56 p.
Jelesnianski, Chester P., Jye Chen and Wilson A. Shaffer, 1992. SLOSH: Sea, Lake, and Overland Surges from Hurricanes, NOAA Technical Report NWS 48. National Weather Service, Silver Spring, Maryland, 71 p.
Lane, 1981. Environmental Geology Series, West Palm Beach Sheet; Map Series 101. Florida Bureau of Geology, Tallahassee, 1 sheet.
Murty, T.S. and Flather, R.A., 1994, Impact of Storm Surges in the Bay of Bengal. In: Finkl, C.W., Jnr. (ed.), Coastal Hazards: Perception, Susceptibility and Mitigation. Journal of Coastal Research, Special Issue No. 12, 149-161.
National Oceanic and Atmospheric Administration, National Weather Service, 1993. "Hurricane!" A Familiarization Booklet, NOAA PA 91001, 36 p.
Newman, C.J.; Jarvinen, B.; and McAdie, C., 1993. Tropical Cyclones of the North Atlantic Ocean, 1871-1992, National Climatic Data Center, Ashville, N.C. and National Hurricane Center, Coral Gables, Florida, 193 p.
Sheets, R.C., 1995. Stormy Weather, In: Tait, Lawrence, (Ed.) Hurricanes... Different Faces In Different Places, (Proceedings) 17th Annual National Hurricane Conference, Atlantic City, N.J. 52-62.
Simpson, R.H., 1971. A Proposed Scale for Ranking Hurricanes by Intensity. Minutes of the Eighth NOAA, NWS Hurricane Conference, Miami, Florida.
Tannenhill, I.R., 1956. Hurricanes, Princeton University Press, Princeton, New Jersey, 308 p.
Will, L.E., 1978. Okeechobee Hurricane; Killer Storms in the Everglades, Glades Historical Society, Belle Glade, Florida, 204 p.