1(a) The diagram shows differences in the speed of flow of water in a river channel along a straight part of a river’s course (Click to see a bigger picture)
(i) Describe and explain the differences in the speed of flow
A) from the river bank to the middle of the river channel at the surface (from X to Y) [5]
B) from the surface of the river channel to the river bed near the middle of the river (from Y to Z) [4]
(ii) Explain how the speed of flow in a meander channel might differ from that shown in the diagram above and state the resulting features at the meander sides. [6]
(ii) Explain how the speed of flow in a meander channel might differ from that shown in the diagram above and state the resulting features at the meander sides. [6]
1b. Figs A and B show a section of coastline before coastal defences were built and after coastal defences were built.
(i) Describe the coastal section shown in Fig A and explain how it was affected by natural processes. [4]
(ii) Evaluate the success of the coastal defences shown along this section of the coastline as shown in Fig B. [6]
Suggested Answers
Suggested Answers
1(a) The diagram shows differences in the speed of flow of water in a river channel along a straight part of a river’s course.
(i) Describe and explain the differences in the speed of flow
A) from the river bank to the middle of the river channel at the surface (from X to Y) [5]
1. the speed of flow is slowest at the river bank (X)
2. because of friction with the sides
3. the speed of flow becomes faster towards the
middle of the channel (Y)
4. because the channel at the centre is deep
5. so there is less friction
B) from the surface of the river channel to the river bed near the middle of the river (from Y to Z) [4]
1. at Y, which is near the surface of the middle of the
channel, the river flow is fastest
2. as there is no friction
3. on approaching the river bed at Z, the river speed
slows down
4. because there is increasing friction with the river bed
(ii) Explain how the speed of flow in a meander channel might differ from that shown in the diagram above and state the resulting features at the meander sides. [6]
1. in a meander channel, the river bends
2. as the river water flows downstream and round a bend, the
force and hence speed of flow is greatest at the concave
bank (outer bank)
3. this will give rise to river cliffs
4. the force of water is furthest from the convex bank so the
speed of flow is slowest at the convex bank (inner bank)
5. this will give rise to slip-off slopes
6. hence the fastest flow is at the concave bank of a
meander and not in the centre as shown in the diagram above
(i) Describe the coastal section shown in Fig A and explain how it was affected by natural processes. [4]
1. in fig A, a landslip has taken place
2. this is because the land has poor drainage due to the layer
of clay
3. the water cannot drain through the layer of clay and so
collects in the soil
4. eventually the weight of the water-logged soil causes it to
slump down
(ii) Evaluate the success of the coastal defences shown along this section of the coastline as shown in Fig B. [6]
Level 1 (briefly describes at least two measures taken without evaluation) 1-2m
- drain is constructed at the point where the layer of clay starts
- steel barrier is placed mid-way up the cliff
- trench filled with rocks is carved out at the foot of the cliff
- concrete posts are placed at the foot of the cliff
- wooden barriers (groynes) are laid at the shoreline
Level 2 (describes at least two in greater detail and attempts to evaluate) 3-4m
- drain is constructed at the point where the layer of clay starts so that it can drain off the water and the soil will not be water-logged
- steel barrier is placed mid-way up the cliff to hold the land back and prevent it from slipping
- trench filled with rocks is carved out at the foot of the cliff so that even if the land slips, the trench will contain it and the rocks will prevent the soil from slipping further (rocks provide resistance)
- concrete posts placed at the foot of the hill hold the soil in place as the posts have to be driven into the soil so they are a stabilizing force
- wooden barriers (groynes) laid at the shoreline slow down erosion from longshore drift so the soil at the bottom of the cliff is not washed away and this will prevent weakening of the base of the cliff
Level 3 (considers broader picture) 5-6m
- the coastal defences are strong and should hold the cliff in place
- but if rainfall is too heavy, there might be some landslip still as gravel and sand are small and loosely-held so they may just be washed down the cliff face, thus causing erosion and slumping
No comments:
Post a Comment