Coastal Processes and Morphology Questions and Answers

Answer: A

Correct answer: causing waves to break offshore and dissipate their energy

A reef crest forces waves to break well seaward of the shore, so most of their energy is dissipated in turbulence over the reef flat and only a small fraction reaches the beach. Reefs are estimated to remove the great majority of incident wave energy, which is why their degradation shows up directly as erosion behind them.

Answer: B

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 living reef grows upward and keeps its crest at the depth where waves break; a degraded or dead reef flattens and deepens, so waves pass over it without breaking and arrive at the shore with far more energy. Bleaching and acidification therefore translate directly into a coastal defence problem for the communities behind the reef.

Answer: C

Correct answer: a vertical concrete revetment

A concrete revetment is engineered hard defence. The other three are natural systems that attenuate wave energy: a saltmarsh foreshore dissipating it in the vegetation and shallow water, a vegetated dune ridge acting as a sediment reserve and a barrier to overwash, and a fringing reef forcing the waves to break offshore.

Answer: D

Strong tidal currents overturn the water column and remove the vertical salinity gradient. A salt wedge estuary at the other extreme has a sharp interface with fresh water flowing above. Tidal energy relative to river flow decides the type.

Answer: A

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

Estuaries are classified by how far the fresh and salt water mix. A salt wedge estuary has strong river flow and weak tides, so a sharp interface persists with salt water wedging beneath. A partially mixed estuary has stronger tides and active mixing across a weaker gradient. A well mixed estuary is vertically uniform in salinity. An inverse estuary, in an arid climate, loses so much water to evaporation that salinity increases landward.

Answer: B

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. Clay particles carry a surface charge that keeps them apart in fresh water; saline water screens that charge and lets them stick together into flocs, whose settling velocity is many times that of the individual particles. They therefore drop out where the fresh and salt water meet, forming the turbidity maximum and the mud shoals that make estuarine navigation channels so expensive to maintain.

Answer: C

Flocculation and residual circulation together trap sediment in this zone. Its position migrates with the tide and with the river discharge. Its position is not fixed in space. Dredging strategy must account for that movement.

Answer: D

Correct answer: True

The dissolved ions in seawater compress the electrical double layer around each clay particle, reducing the repulsion that kept them dispersed, so collisions result in adhesion and flocs form. Even quite low salinities are enough. It is the reason fine sediment that travelled hundreds of kilometres in suspension settles within a few kilometres of the salt intrusion.

Answer: A

A shorter and stronger flood than ebb tends to import sediment and infill the estuary. Understanding the asymmetry is essential to predicting siltation in ports and channels. Asymmetry decides the direction of net transport.

Answer: B

Both are true and the reason gives the mechanism, and dredging and reclamation can shift an estuary into this state. The change is often unintended and is difficult to reverse. Channel deepening can tip the balance towards import.