13.5: C.5- Interpretation
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Maps also may provide direct information about coastal processes like wind and wave directions and heavy breaking of waves. Many other phenomena can be derived by interpreting the coastal forms on the map: a spit indicates the direction of the longshore transport, and thus the dominant wave direction, and river sediment transport is shown by the presence of shoals and bars. If the map shows only a long straight sandy shore, you can say little about wave/wind direction and intensity. Only when there is some kind of interruption to this shore is it possible to determine the prevailing wave/wind direction and possible sediment transport. For example at a river mouth one may find out whether the river is dominant or the sea. The magnitude and direction of longshore sediment transport and river sediment transport may be deduced. Another example is formed by protruding rocks or artificial features like groynes or breakwaters on a sandy coast. Here also one may find indications of the presence of longshore sediment transport (magnitude and direction) and so the wind/wave direction. Detached obstacles (rocks, or detached breakwaters) may give even more exact information about wave direction. In the sheltered side sediment tends to settle. So the position of the shoals indicate the sheltered side and so the wave direction.
If dredged channels are present, it is clear that sediments have to be removed on a more or less regular basis. The location of the dumping grounds of dredged material gives sometimes an indication of the dredging method that is commonly used.
In large sandy areas, the bottom contours also indicate possible current patterns. Places with great depths probably indicate areas where the current will be concentrated. Shallow areas indicate low current velocities.