Coasts Geography

Deposition and transportation

The ebb and flow of the tides create depositional landforms, such as narrow spits, offshore bars and tombolos, cuspate forelands, and sand dunes. Sediment from muddy rivers and streams maintains the process of coastal construction. There are four main processes involved in the transportation of the sediment:

The transportation of sediment along the shore is known as longshore drift or littoral drift.

Erosion

The constant pounding of waves wears away at the base of cliffs, forging platforms and making chunks of rock crumble into the sea. This is known as mass movement. The solid rock eventually breaks away, and the waves scoop out the weaker clays left behind, creating a bay or cove. Headlands are formed where the coastline gives way on either side. This leaves stacks and stumps.

The waves erode the coast in a number of ways:

Weathering

Along with the marine forces, sub-aerial processes (land-based) help to alter the coast. These can be broken down into weathering, the gradual breaking down of rocks in situ, to mass movement, which is the movement of material downslope through gravity.

Coastal systems

The steady supply of building material via what is known as the coastal system (it has inputs, outputs, stores, and transfers) to the littoral zone (the area of shoreline from the sea to the land) is how this ever-changing coastal landscape is achieved. The coastline can be classified according to its formation process (primary and secondary) as a result of sea-level changes (submergent and emergent) or as a result of plate activity (primary and secondary).

The coast can be steep cliffed (rocky coastline) to relatively flat (coastal plain) depending on if the waves are high or low energy. The geological structure has a massive influence on the morphology (for example, strata, the different layering of rocks) and erosion rates of a coast.

Structure

Rapid coastal erosion is caused by geological factors such as lithology (soft rock type, weak cohesive bonds, and porous rocks) and geological structure combined with marine factors that quickly remove collapsed sediment, allowing erosion to restart.

Long-term sea-level changes occur as a result of a complex interplay of eustatic (the rise and fall of the sea levels which are influenced by the ice age), tectonic (where the land sinks or rises because of changes at tectonic plates boundaries), and isostatic changes (these refer to changes in the level of the land which is also influenced by the ice age).

Coastal Management and Engineering

Coastal management (such as hard and soft engineering) disrupts the sediment cells. Human activity, such as the construction of major dams or dredging along the coastline, interrupts the operation of the sediment cell. This can increase rates of coastal recession. Economic and social issues arise where the coast has eroded (on the U.K. Holderness coastline, a holiday park lost over 400 holiday homes through coastal retreat).

Fig. 1 - Groynes at Mundesley in Norfolk, UK. This is a hard engineering method in coastal management.

Coastal flooding

Coastal flooding is largely a natural event. However, human influences on the coastal environment can exacerbate this. Engineered protection structures along the coast, such as a seawall, alter the natural processes of the beach, often leading to erosion on an adjacent stretch of the coast which also increases the risk of flooding. Sea level changes and the extreme weather caused by climate change have increased the intensity and occurrences of coastal flooding.

Fig. 2 - Flood gate on Chesil Beach in Dorset, UK.