Coastal Storms And Storm Surges

Coastal areas affected by cyclones and hurricanes are prone to flooding by storm surges associated with these storms. storm surges, formed by water pushed ahead of storms, typically move on land as exceptionally high tides in front of these severe ocean storms. storm surges are one of the major, most unpredictable hazards to people living along coastlines.

When hurricanes, cyclones, or extratropical lows (also known as coastal storms and northeasters) form, they rotate and the low pressure at the centers of the storms raises the water several to several tens of feet (<1-10 m). This extra water moves ahead of the storms as a storm surge that represents an additional height of water above the normal tidal range. The wind from the storms adds further height to the storm surge, with the total height of the storm surge being determined by the length, duration, and direction of wind, plus how low the pressure gets in the center of the storm. The most destructive storm surges are those that strike low-lying communities at high tide, as the effects of the storm surge and the regular astronomical tides are cumulative.

Like many natural catastrophic events it is possible to predict the statistical probability of a storm surge of a specific height hitting a section of coastline in a specific time interval. If the height of the storm surge is plotted on a semilogarithmic plot, with the height in a linear interval and the frequency (in years) on a logarithmic scale, then a linear slope results. This means that statistically some coastal communities can plan for storm surges of certain height to occur about once in a specified interval, typically calculated as every 50, 100, 300, or 500 years, although there is no way to predict when the actual storm surges will occur. This is a long-term statistical average; one, two, three, or more 500-year events may occur over a relatively short period, but over a long time, the events average out to once every 500 years.

During some hurricanes and coastal storms the greatest destruction and largest number of deaths are associated with inundation by the storm surge. The waters can rise and cover large regions, staying high for many hours during intense storms, drowning victims in low-lying areas, and continuously pounding structures with the waves that move in on top of the storm surges.

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