Design of a coastal structure for climate change normally allows for
Answer: C
Guidance specifies allowances that vary by region and by the period considered. Adaptability, such as the ability to raise a crest later, is increasingly built into the design. Allowances vary by region and by the period considered.
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Assertion (A): Adaptive design is increasingly preferred for coastal structures.
Reason (R): Future sea level rise is uncertain, so provision to raise the structure later is valuable.
Answer: D
Correct answer: Both A and R are true, and R is the correct explanation of A
Both are true and the reason gives the argument. Sea level rise over a hundred year design life is uncertain by a factor of two or more, so designing now for the upper estimate wastes money if it does not occur, and designing for the lower one fails if it does. An adaptive design provides for the crest to be raised or the section widened later - a wider foundation, a crown wall that can be extended - at modest present cost.
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Consider the following statements about climate adaptation in structure design.
1. A sea level allowance is added over the design life.
2. Adaptive designs allow later raising at modest cost.
3. Designing immediately for the worst case is always cheapest.
Answer: A
Correct answer: 1 and 2 only
Statements 1 and 2 describe current practice: an allowance for sea level rise over the design life is added to the design water level, and adaptive provision allows later raising cheaply. Statement 3 is wrong - building immediately for the worst plausible case commits money now against a rise that may not occur, and discounting alone usually makes the staged approach the cheaper of the two.
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All of the following are inputs to a coastal structure design EXCEPT
Answer: B
Correct answer: the number of visitors expected at the site each year
Visitor numbers may bear on the amenity case for a scheme and on the tolerable overtopping discharge if people stand behind the crest, but they are not an engineering input to the structure itself. The design proceeds from the wave height at the toe, the extreme water level for the chosen return period, and the geotechnical properties of the bed, which between them fix the armour, the crest level and the foundation.
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The single most important input to a rubble mound design is generally
Answer: C
Armour mass varies with the cube of it, so every other input is secondary by comparison. Establishing it reliably is worth a disproportionate share of the whole design effort. A cube law rewards precision in this one input.
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