Scarps

Coastal Erosion features known as Scarps, are defined as almost vertical sea-facing walls, cut into sandy beaches or cliffs. Examples of Scarps have been seen recently at Hemsby Gap, where a 10 ft drop was cut into the beach and at Crantock Beach in Cornwall, where a 20 ft drop has been cut into the cliff.

Scarp creation can be described as the sudden action of high-energy waves scouring into sand. Contributory factors to this powerful action, describe an interplay between waves, sediment, and beach morphology, (the shape of the beach).

Regarding hydrodynamic (wave) processes, on the night the Scarp was created at Hemsby Gap, a high tide of 3.322 metres, with a surge residual of 0.619 metres was recorded at nearby Lowestoft at 12:30 am on the 25^th of February 2023. Data originates from the National Tidal and Sea Level Facility, provided by the British Oceanographic Data Centre and funded by the Environment Agency.

Considering sea state in perhaps an elevated, agitated form, it is thought that, not surprisingly, Destructive Waves possess the greatest ability to cause coastal erosion, as they possess a stronger Backwash, (the movement of waves back down to the sea). A process called Wave runup is described as the extra height a breaking wave achieves as it travels up the shore before resistance with the beach surface and the effect of gravity reduce its power. It is thought the height of a sand berm, influences the peak of a Scarp, whilst the raised toe of the Scarp is determined by the height of maximum Wave runup.

In a Collison Regime, Wave Runup strikes the face and the toe of the dune and cuts into the sand, shifting sediment out to sea, forming a Scarp.

There is some debate about whether summer waves cause Scarps and winter waves destroy them, as their height and energy tend to overtop and inundate sandy berms. Other views state higher winter waves usually cut back Californian beaches with significant amounts of sand removed from beaches.

Sediment and wave type, combine to influence beach shape in the following ways. Scarps are more likely to form on steeply sloping beaches, as it is thought forceful wave systems tend to produce beaches with uniform sediment sizes, with the predominant type being larger sediments. Sediment size also relates to beach slope, with a steep profile enabling larger sediment sizes to be flung further up the beach by higher waves.

On beaches with steep slopes, waves are better able to reach the edge of a dune or berm increasing the ability of aggressive wave action to cut into the beach. The Backwash of a wave also retreats down a beach with stronger force on steep sloping beaches. As wave action strips sediment from a beach, its lower section is reduced in height, as the top section of beach keeps its original level.

This discussion looked at Scarps, the creation in dynamic storm situations of near-vertical cuts in sandy beaches, cliffs or dunes, that can reach 10-20 ft in size. As a coastal erosion feature on a beach, Scarps can pose a serious hazard, and can take years to disappear. However, in the case of Hemsby, installation of flood defence mechanisms has corrected the destructive formation of the 10 ft Scarp. It will be useful to observe as the rock revetment settles to become part of the beach, and takes its place in the high-energy, tide and surge environment of the North Sea.