Responding to Changes in Sea Level Engineering Implications (1987) / Chapter Skim
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4 Affected Hydrodynamic Processes
4 Affected Hydrodynamic Processes
Pages 34-39
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From page 34... ...
STORM SURGE Storm surges, the flooding induced by wind stresses and the barometric pressure reduction associated with hurricanes, tropical storms, and northeasters, will be modified by sea level rise mostly in areas of very mild onshore slopes. With higher sea levels the larger expanse of shallow water will result in increased storm surge elevations compared to areas of steep offshore slopes, because the surge heights are proportional to both the length and the inverse slope of the offshore bottom.
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From page 35... ...
This reduction in surge height for a uniform depth offshore profile is proportional to the ratio of the change In sea level to the mitial water depth. As an example, if the return periods of storm surges resulting in water levels of 3 and 4 m are 50 and 100 years, then to a first approx~nation, a sea level rise of 1 m would result in an increase in frequency of the 4 m surge level from 100 years to 50 years.
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From page 36... ...
The predicted sea level rise will be manifested ~ two different ways the change in surge elevation and the change in wave heights felt at the shoreline. The present methodology used by FEMA Is to determine the wave heights at the shoreline based on a breaking condition; that is, the shoreline wave height is 78 percent of the water depth at the flooded shoreline.
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From page 37... ...
The change in prism due to inundation can be shown to be related to the per~rneter (or shoreline length) C of the bay and the relative sea level rise S: rim Trcs ~ — where Tr is the tide range and ~ ~ an average shoreline slope.
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From page 38... ...
From this equation, larger water depths decrease the size of F and hence decrease the amount of wave height reduction due to friction. This effect becomes more ~rnportant for wider continental shelves.
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From page 39... ...
For the same values as in the last example: AH = 0.15 m 1' or a 7.5 percent increase In wind-generated wave height as a result of the movement of the offshore region due to sea level rise. The effects of reduced wave damping and augmented wave generation would be combined in an approximate linear manner.
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