2.2 Coastal flooding

The following are the most important types of coastal floods:
– Storm Surge Floods   
Often the hurricanes or the storm are in the sea. As a result, large waves are formed battering the coast and causing floods.
Storm surges commonly occur with coastal storms caused by massive low-pressure systems with cyclonic flows that are typical of tropical cyclones and severe winterstorms.
Factors influencing Storm surge intensity are: wind velosity, storm surge height, coastal shape, nature of coast and human activity.
Storm surges are controlled by four factors:
– The more intense storms have higher wind speeds which drive greater amounts of water across the shallow continental shelf, thereby increasing the volume and elevation of water pushed up against the coast. In areas with mild slopes and shallow depths, the resulting flooding can reach great heights.
– The low barometric pressure experienced during coastal storms can cause the water surface to rise, increasing the height of storm surges.
– Storms landfalling during peak astronomical tides have higher surge heights.
– Coastal shoreline configurations with concave features or narrowing bays create a resonance within the area as a result of the winds forcing in water, elevating the surface of the water higher than experienced along adjacent areas of open coast.

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– Estuarine floods 
They are floods caused by the combination of strong winds and high tide. 
This type of floods is typical for the Tropical and Equatorial belts and especially for islands e.g. Filipinas. With the change in climate they start manifesting themselves with increased intensity. Such floods in combination with other kind of floods like river ones can affect large areas within a short space of time.
– Floods caused by powerful pressing wind at the mouth of rivers, as a result of which water is retained in the river and the river water level rises.
– Floods resulting from tsunamis which are large seismic sea waves, impulsively generated by shallow – focus or high magnitude earthquakes which can cause disastrous flloding in coastal areas (Fig.2.2 a).
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Fig.2.2. Coastal flood triggered by Fukushima (Japan) quake M = 9.0 on 11 March 2011

Given that Coastal floods happen continuously in one and same region for most cases, they can be predicted precisely.

Usually the coastal floods are a combination of some of the above-mentioned floods including the river floods.
It is obligatory to elaborate and implement proper national and regional policies as well as national and regional plans to reduce the losses caused by floods.