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    Coastal Processes


    The coast is the zone between land and sea. The action of waves and sea, constantly change the form and shape of the coast. Coastal and shelf processes include wind, waves, currents, climates and tides. This processes influence the distribution of salinity, sediments, and water borne particles that shape the coast, seabed, water quality and distribution of marine life within the water body.

    There are five main processes which cause coastal erosion. This include hydraulic action, attrition, abrasion, corrasion, corrosion/solution.
    Hydraulic action is the action of waves and flowing water in the removal of rocks and sediment from a coastline. In other words, it means that the coastal erosion is carried out by water and waves.
    Attrition is the breaking down of rocks into smaller particles as a result of collision with one another. In other words, the water brought into the coast consists just more than water. It also contains rocks, sediments and particles which collide with rocks already present at the coastline, breaking them into smaller and smoother units or particles.

    Abrasion is the sand-paper action of particles rubbing against the coastline. This sand-paper action actually causes corrasion. This two are very similar and are classified together by some sources. Flowing water may contain rocks, sand and sediments which may rub against the floor of the coastline. This ‘rubbing’ action, causes a sand-paper effect on the coast which causes wearing on the surface. Simply put, corrasion is the wearing away of the coastline by abrasion.

    Water flowing to the coastline may contain chemicals which can react with other chemicals at the coast. This reaction causes a solution which is more or less, a homogenous mixture of the constituent chemicals, resulting in a gradual and eventual deterioration and breakdown of the coast.

    Wave action is the dominant mechanism in both erosion and deposition along coastlines.
    Waves are powerful due to their pounding action but are also very selective in etching out rock weaknesses and controlling sediment deposition.
    The largest and most powerful waves are those which have travelled furthest, i.e. have the greatest fetch.
    Large storm waves are powerful and destructive.

    Tidal surges cause damage when waves reach new heights; they occur on high spring tides, aided by strong onshore winds and low atmospheric pressure, as in the North Sea, 1953, and at Bangladesh, 1970.


    Coastal erosion occurs often by wave action at beach level. This creates a wave notch, which advances, leaving a wave cut platform, and undercutting the cliffs – which retreat by a sequence of rock falls (or larger landslides in weak material).

    Selective wave erosion of strong rock cliffs etches out faults, joints and weaknesses to form sea caves, arches and inlets which retreat between headlands and sea stacks.

    Coastal equilibrium produces slowly eroding headlands between bays where soft rocks are protected by beach deposition.

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