The table below gives results from a coastal fieldwork enquiry at two sites near Durban, South Africa. Fig. 1 shows students using a pebbleometer to measure...
Question 1 Report
The table below gives results from a coastal fieldwork enquiry at two sites near Durban, South Africa. Fig. 1 shows students using a pebbleometer to measure the long axis of pebbles. At each site, they selected 20 pebbles at random from the strandline. The class wanted to test whether transport along the beach affects the shape and size of sediment.
| Site | Distance from river mouth (km) | Mean pebble length (cm) | Mean roundness score, 1-5 |
|---|---|---|---|
| A | 0.2 | 6.4 | 2 |
| B | 3.8 | 3.7 | 4 |
(a) State the mean roundness score at site B. [1]
(b) Describe the change in mean pebble length between sites A and B. [1]
(c) Explain why pebbles may become more rounded during transport. [2]
Table 1 gives data collected by a school group on two beaches in Pembrokeshire, Wales. Fig. 1 shows the beach profile equipment used. Students measured the angle of the beach using two ranging poles, a tape measure and a clinometer. Both beaches were surveyed at low tide on the same day, so that the method was comparable.
| Beach | Mean beach gradient (degrees) | Mean sediment size (mm) |
|---|---|---|
| Harbour Cove | 4 | 1.2 |
| Ridge Bay | 10 | 8.5 |
(a) State which beach has the steeper gradient. [1]
(b) State the sediment size at Harbour Cove. [1]
(c) Suggest why Ridge Bay has a steeper beach profile. [2]
Answer Details
Pebble transport
(a) The mean roundness score at site B is 4. [1]
(b) Mean pebble length decreases from 6.4 cm at site A to 3.7 cm at site B. [1]
(c) During transport, pebbles collide with each other and with the beach. Attrition and abrasion wear away sharp edges, making the pebbles smoother and more rounded. [2]
Beach profiles
(a) Ridge Bay has the steeper gradient, at 10 degrees. [1]
(b) Harbour Cove has mean sediment size 1.2 mm. [1]
(c) Ridge Bay has larger, coarser sediment. Water infiltrates more easily through coarse sediment, reducing backwash. More material is therefore deposited on the beach, allowing a steeper profile to develop. [2]
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