Coastal Processes and Morphology Questions and Answers

Answer: C

Correct answer: intertidal habitat is trapped between rising sea level and a fixed defence

The intertidal zone would normally migrate landward as sea level rises, but a seawall or embankment prevents it, so the habitat is squeezed between the advancing water and the fixed line and progressively lost. Since such habitats are generally designated, the loss must be compensated - which is a large part of why managed realignment schemes are undertaken.

Answer: D

Correct answer: Both A and R are true, and R is the correct explanation of A

Both are true and the reason describes coastal squeeze. A saltmarsh survives sea level rise by moving landward, and a defence at its back removes that possibility, so the marsh narrows and eventually disappears - taking with it the wave attenuation it provided to the defence itself. The defence therefore destroys part of its own protection, which is one of the strongest arguments for realignment.

Answer: A

Vegetation and shallow water together dissipate a large proportion of the incident energy. Loss of the marsh therefore increases the design loading on the structure behind. Foreshore level is a design parameter for a wall.

Answer: B

Sediment accumulates on the updrift side and the supply beyond the field is reduced. The problem is displaced rather than solved, which is the classic objection to groyne schemes. The drift must go somewhere once it is intercepted.

Answer: C

Both are true and the reason gives the mechanism, and the effect may appear some distance away. Sediment cell thinking exists largely to anticipate consequences of this kind. Effects can appear kilometres from the works.

Answer: D

Correct answer: 2 - 4 - 1 - 3

The order runs from least to most intervention. Do nothing and monitor involves no works at all. Managed realignment moves the defence line landward, working with the processes rather than against them. Nourishment adds sediment and must be repeated, which is a continuing intervention. Hard defence structures are the most interventionist, fixing the line permanently and altering the processes themselves.

Answer: A

Correct answer: adds sediment to the system rather than resisting the waves

Nourishment addresses the cause - a sediment deficit - while a hard structure addresses the symptom by resisting the waves. That is its distinctive merit, and it also means it works with the natural processes rather than interrupting them. It certainly does not prevent erosion permanently: the placed sand moves as any sand does, so it must be renourished, and the interval is set by the sediment budget it was designed against.

Answer: B

The first two are correct and describe the approach honestly. The third is not the case, and the whole life cost of repeated renourishment is central to any appraisal. Comparisons against hard defence must use whole life cost.

Answer: C

Finer material than the native sand is winnowed away rapidly and the fill fails. An overfill ratio is applied to allow for the losses expected from the finer fraction. Borrow material is characterised carefully before use.

Answer: D

Both are true and the reason gives the failure mode, and an overfill ratio is used to compensate. Slightly coarser material generally performs better than the native sand itself. Slightly coarser fill remains on the profile longer.