Beach Erosion and Protection Questions and Answers

Answer: C

Correct answer: a logarithmic spiral or parabolic bay shape relationship

A bay in static equilibrium takes a curved form in which the shoreline everywhere meets the dominant wave crests at the same angle, so no net longshore transport occurs. The logarithmic spiral and the parabolic bay shape equation are the two standard descriptions, both fitted to the wave approach direction and the position of the updrift control point. They are the design tool for artificial headland schemes.

Answer: D

The first two are correct and underlie headland control design. The third is contradicted by the observation that bay orientation follows the dominant wave approach closely. Bay orientation is a reliable indicator of that direction.

Answer: A

Static equilibrium means the planform has adjusted so that no net transport occurs. Dynamic equilibrium by contrast requires a continuing supply to maintain the shape. The distinction decides whether a scheme will hold.

Answer: B

Distinguishing these is central to assessing whether a headland scheme will hold. A bay assumed static that is in fact dynamic will erode once the supply is interrupted. Diagnosing the condition correctly is essential.

Answer: C

The berm is placed shallower than the closure depth so that waves can rework it. It also attenuates waves while it lasts, giving a second benefit to the frontage behind. Maintenance dredgings can be used productively this way.

Answer: D

Both are true and the reason gives both effects, and this makes it an attractive use for maintenance dredgings. Placement depth determines whether the feeding benefit is realised at all. Too deep a placement wastes the opportunity entirely.

Answer: A

Correct answer: True

The depth of closure marks the seaward limit of measurable profile change, so material placed beyond it lies outside the zone the waves rework and will not migrate landward on any useful timescale. Nearshore berms are placed deliberately just landward of that depth for exactly this reason: shallow enough to feed the beach, deep enough that the dredger need not come inshore.

Answer: B

Correct answer: aims to stop undercutting rather than to retain a beach

A cliff retreats because waves remove material from its base and oversteepen it, so toe protection is aimed at the marine cause of failure. Beach protection is aimed at holding sediment on the frontage. The two are related, since a wide beach protects a cliff toe naturally, but the objective is different and so is the measure of success.

Answer: C

Both are true and the reason gives the limitation, and drainage works are often needed as well. A toe structure addresses only one of the several causes of cliff failure. Drainage often matters as much as toe protection.

Answer: D

Correct answer: 1 and 2 only

Statements 1 and 2 correctly identify the two causes and their remedies. Statement 3 is the important qualification: cliffs also fail from within, through groundwater raising pore pressures, weathering of the face, and material standing at an unstable angle. A cliff can therefore continue to retreat behind a perfectly sound revetment, and stabilisation generally requires drainage and slope works as well as toe protection.