State whether the following is true or false.
Construction of a dam on a river can cause erosion at the coast many kilometres away.
Answer: C
The dam traps sediment that would otherwise have reached the shore. Deltas and beaches downdrift of the river mouth then erode as the supply is cut off. The effect appears far from the dam itself. Sediment starvation travels the whole length of the river.
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Assertion (A): Damming a river is a common indirect cause of coastal erosion.
Reason (R): The reservoir traps the sediment load that formerly nourished the shoreline.
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 mechanism. A dam traps the sediment the river was carrying to the coast, so the beaches downdrift of the river mouth lose an input they had depended on for centuries and begin to erode - often decades later and many kilometres away, which is why the connection is so easily missed. The Nile delta after the Aswan High Dam is the classic case.
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A spit is a depositional landform that
Answer: A
Drift carries sediment past a change of coastal direction and deposits it in deeper quieter water. A recurved distal end is common where refracted waves wrap around the tip. The hook records the wave directions at the distal end.
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Match each depositional landform with its description.
List I
A. Spit
B. Tombolo
C. Bar
D. Cuspate foreland
List II
1. a ridge across the mouth of a bay
2. a ridge extending from land into open water
3. a triangular projection built by two drift directions
4. a bar joining an island to the mainland
Answer: B
All four are built by longshore drift depositing where the transport capacity falls. The shape depends on the local geometry and on the directions from which waves arrive. All four are products of the same drift process.
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A tombolo forms where
Answer: C
The island shelters the water behind it, so drift converges and deposits in the lee. Detached breakwaters can produce exactly the same feature artificially. The shelter is what causes the deposition. Design and natural formation share one mechanism.
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Assertion (A): A detached breakwater can create a tombolo behind it.
Reason (R): It shelters the water in its lee so that drift converges and deposits.
Answer: D
Both are true and the reason gives the mechanism, and this is sometimes the design intention. Where the deposit stops short of the structure a salient forms instead. Gap width and distance offshore control which forms.
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Consider the following statements about detached breakwaters.
1. A salient forms where deposition does not reach the structure.
2. A tombolo forms where deposition connects to the structure.
3. A tombolo allows drift to continue past unimpeded.
Answer: A
The first two are correct and distinguish the two outcomes. The third is wrong, since a tombolo blocks the drift entirely and starves the coast downdrift. A salient allows some drift to pass. The two outcomes differ greatly in their downdrift effect.
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Wave cut platforms are formed by
Answer: B
Undercutting at the notch causes collapse and the cliff retreats landward. The platform left behind widens until wave energy reaching the cliff foot becomes too small to continue the process. The platform is the record of the cliff's former positions.
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Assertion (A): Cliff retreat slows as the wave cut platform widens.
Reason (R): The wider platform dissipates more wave energy before it reaches the cliff foot.
Answer: C
Both are true and the reason gives the negative feedback, and the system tends towards an equilibrium width. Sea level rise renews the attack by allowing waves to reach the cliff again. Rising level resets the equilibrium the platform reached.
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Arrange the stages of cliff retreat by wave attack in order.
1. debris at the foot is removed by wave action
2. waves cut a notch at the base of the cliff
3. the notch is cut again into the fresh cliff face
4. the overhang becomes unstable and collapses
Answer: D
Correct answer: 2 - 4 - 1 - 3
The cycle repeats. Waves cut a notch at the base of the cliff; the overhang above it eventually becomes unstable and collapses; the debris protects the foot until wave action removes it; and the notch is then cut afresh into the newly exposed face. Cliff retreat is therefore episodic rather than continuous, and the debris apron is what determines how long the pause between collapses lasts.
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