Answers to homework

Homework: O Level N2006 P2 Q5

(i) State the differences between destructive and constructive waves. [3]

Most of you did not hae linking words in your answers as you wrote about constructive waves and then you wrote about destructive waves. You should use linking words eg whereas, in comparison. Some of you also uses the weak point such as writing about the wave energy that is high or low. You could have described that in terms of weight height and length.

Sample answers

1. Wave height and length + Gradient of slope

Constructive waves are small low waves with long wave lengths and low heights, they are usually found in places with a gentle coastal slope. On the other hand, destructive waves are large high waves with short wave lengths and a greater wave height, they are commonly found in steep coastal slopes.

2. Wave frequency

Constructive waves occur at a lower frequency of 6-8 breaks per min as compared with  the destructive waves of 10-14 breaks per min.

3. Swash (deposition) and backwash (erosion)

The constructive wave has a more powerful swash than BW which leads to sand being deposited onto the coast and building beaches.  Whereas destructive waves have greater erosive power which enables them to erode the coast with their more powerful BW.

(ii) Explain how constructive waves may form beaches. [3]

Swash and BW

- The more powerful swash than BW forms a beach when deposition occurs. The BW is weak as energy is spent overcoming friction with the beach. The powerful swash merely spills over when it breaks.

Deposition of sediments

- Materials are carried up and deposited more than they are removed due to a stronger swash than BW

- Due to low energy from constructive wave,  deposition from eroded headlands, rivers and neighbouring coasts are not washed away but deposited to form the beach over time.