Beach Erosion and Protection Questions and Answers

Answer: C

Both are true and the reason gives the cause, and this initial adjustment is not a failure. Distinguishing profile adjustment from genuine loss is essential when judging performance. Early apparent loss is often adjustment rather than failure.

Answer: D

Correct answer: True

Sand placed on a beach is dumped at a slope steeper than the waves will tolerate, so the first months redistribute it seaward into the profile the wave climate demands. Volume measured above the waterline falls sharply and the scheme looks to be failing, but the material is still in the active profile and still protecting the frontage. Judging a nourishment before that adjustment is complete is the commonest error in assessing one.

Answer: A

The interval depends on the loss rate and on the volume placed initially. Whole life cost appraisal must include every anticipated renourishment campaign. A single placement is not the whole cost. Discounted future campaigns can dominate the total.

Answer: B

Comparing a single nourishment against a permanent structure is a misleading comparison. Discounting future campaigns is the standard way of placing them on a common footing. Discount rate strongly affects the comparison.

Answer: C

Both are true and the reason gives the non-monetary argument, and amenity has real economic value. Tourism and recreation are frequently the largest benefits in the appraisal. Amenity is a genuine economic benefit, not a soft one.

Answer: D

Correct answer: accelerates the lowering of the beach in front of it

A wall reflects wave energy instead of letting the beach absorb it, and the reflected waves and the scouring flow at the toe carry sediment away. The beach in front therefore steepens and lowers, which exposes the wall to larger waves and to toe undermining - a process that feeds itself. The wall does its own job, protecting the land behind, but it does nothing for the beach and often hastens its loss.

Answer: A

Both are true and the reason gives the mechanism, and toe protection is provided for this reason. Toe scour is the commonest single cause of seawall failure. Toe protection is not an optional extra. Scour undermines the foundation the wall stands on.

Answer: B

The first two are correct and are the standard objection to reflective walls. The third is the opposite of what is observed, since beach lowering in front is the usual outcome. Reflection and beach level are inversely related.

Answer: C

Correct answer: dissipates rather than reflects much of the incident energy

A rough, permeable slope breaks the wave and lets water percolate into the armour, turning much of the energy into turbulence and friction within the layer. A vertical face returns most of it seaward, and it is that reflected energy, interacting with the incoming waves, that sets up the scouring flow at the toe. Less reflection means less scour, which is the principal hydraulic argument for a sloping revetment.

Answer: D

Correct answer: A-2, B-4, C-1, D-3

Each structure has one primary purpose. A seawall protects the land immediately behind it. A groyne intercepts longshore drift so that a beach builds on its updrift side. A detached breakwater sits offshore and reduces the wave energy reaching the shore in its lee. A revetment armours a slope - of a cliff, an embankment or a dune - against direct wave attack.