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Engineering Geology

Engineering Geology - geomuseu

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E n g i n e e r i n g G e o l o g y<br />

Figure 3.40<br />

Flooded polder at St Philipsand, The Netherlands, January 1953.<br />

along the shoreline that is above the normal seasonally adjusted high-tide level. Low pressure<br />

and driving winds during a storm may lead to marine inundation of low-lying coastal<br />

areas, particularly if they coincide with high spring tides. This is especially the case when<br />

the coast is unprotected. Floods may be frequent, as well as extensive where flood plains are<br />

wide and the coastal area is flat. Coastal areas that have been reclaimed from the sea and<br />

are below high-tide level are vulnerable if coastal defences are breached (Fig. 3.40). Storm<br />

surge risk is often associated with a particular season. The height and location of storm<br />

damage along a coast over a period of time, when analyzed, provides some idea of the maximum<br />

likely elevation of surge effects. The seriousness of the damage caused by storm surge<br />

tends to be related to the height and velocity of water movement.<br />

Factors that influence storm surges include the intensity in the fall in atmospheric pressure,<br />

the length of water over which the wind blows, the storm motion and offshore topography.<br />

Obviously, the principal factor influencing storm surge is the intensity of the causative<br />

storm, the speed of the wind piling up the sea against the coastline. For instance, threshold<br />

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