Questions
1a) Drainage patterns refer to the way in which rivers and its tributaries are arranged. With the aid of labelled sketch diagrams, describe 2 different drainage patterns. (4)
1b) Figure 1.1 shows an aerial view of a river in its course. Using labelled sketch diagrams, explain the river development that is likely to take place at point X. (6)
1c)
i. Figure 1.2 shows the top view of a riverbed seen through the water surface. State the name of the erosional feature on the riverbed. (1)
ii. Which type(s) of erosion could have caused the formation of this feature? Justify your answers. (6)
1d) Many rivers in Monsoon Asia experience differences in seasonal water level. What effects might these differences in water level have upon the work of rivers and human
settlements near rivers? (8)
Answer Scheme
1a) Drainage patterns refer to the way in which rivers and its tributaries are arranged. With the aid of labelled sketch diagrams, describe 2 different drainage patterns. (4)
Suggested Answer
Dendritic: This drainage pattern looks like the branches of a tree. It is a common drainage pattern in a basin where there is only one type of rock, and where erosion takes place evenly.
Trellis: This drainage pattern resembles a fence built around a garden. It is a common drainage pattern in a basin where resistant rocks alternate with less resistant rocks.
Radial: This drainage pattern resembles the spokes of a wheel. It occurs where rivers flow outwards and downhill in all directions from the crater of a volcano.
Marking Scheme
Give 1 mark for stating 2 different drainage patterns.
Give a maximum of 1 mark each for accurate drawing of each pattern (maximum of 2 marks here).
Give another mark if there is an explanation of where the drainage pattern commonly occurs.
1b) Figure 1.1 shows an aerial view of a river in its course. Using labelled sketch diagrams, explain the river development that is likely to take place at point X. (6)
Suggested Answer
Point X lies in between two concave banks of a meander that has undergone prolonged erosion such that the neck between the two concave banks is very sharp, narrow and pronounced.
Figure A Figure B
Figure A: Constant erosion of the concave banks and deposition on the convex banks causes the area between two adjacent concave banks to become sharp and pronounced.
Figure B: With continued erosion and deposition, the neck of land between two adjacent concave banks becomes even narrower.
Figure C Figure D
Figure C: Over time, deposition along the convex banks begins to cut the river from the meander. The river then flows straight through the channel.
Figure D: Eventually, the meander that is cut off becomes an oxbow lake.
Marking Scheme
Give 1 mark for stating that the meander will eventually form into an ox-bow lake.
Give a maximum of 2 marks for diagrams that are clearly drawn and annotated.
Give a maximum of 2 marks for clear explanation of ox-bow lake formation without any use of technical terms like sharp and pronounced concave banks, continued deposition on convex banks etc.
Give a maximum of 3 marks for clear explanation of ox-bow lake with appropriate use of technical terms.
1c)
iii. Figure 1.2 shows the top view of a riverbed seen through the water surface. State the name of the erosional feature on the riverbed. (1)
Answer: Potholes
iv. Which type(s) of erosion could have caused the formation of this feature? Justify your answer(s). (6)
Suggested Answer
a) State the type of erosion: corrasion/abrasion
b) Define corrasion/abrasion
i. The grinding of rocks carried by the river against the riverbed and the sides of the river channel
c) Explain why it is corrosion/abrasion and not other types of erosion that caused the formation of the potholes.
i. The riverbed is made up of rocks that are of different hardness. When rock fragments carried by the river in corrosion scrape and knock against softer rocks, potholes form there. Harder rock is more resistant to corrosion but is also susceptible to corrosion over time.
ii. Potholes form due to the grinding and scraping motion that occurs in corrosion and cannot form during attrition, solution or by hydraulic action alone. (Refer to Figure A)
Figure A
d) Explain how attrition, solution and/or hydraulic action can accentuate the formation of potholes
i. When the potholes get larger, they undermine the adjoining harder rocks which are then attacked by other forms of river erosion
ii. Hydraulic action: Swirling movement of water can cause potholes to enlarge. (Refer to Figure B)
iii. Solution: By the process of solution, certain material in the potholes may dissolve which then causes weaknesses in the structure thus making it susceptible to further corrasion and hydraulic action.
Figure B
Marking Scheme
Give 1 mark for stating that corrasion/abrasion causes the formation of potholes and 1 mark for defining corrasion/abrasion accurately.
Give a maximum of 2 marks for an explanation as to why it is corrasion and not other types of erosion.
Give 1 mark for stating that other forms of erosion can cause further erosion of potholes.
Give 1 mark for clear explanation on how other types of erosion can enlarge potholes.
1d) Many rivers in Monsoon Asia experience differences in seasonal water level. What effects might these differences in water level have upon the work of rivers and human
settlements near rivers? (8)
Suggested Answer
a) Effects on the work of rivers
(Compare and contrast between effects during high water level and low water level)
i. Higher erosive power of rivers during high water level
ii. River load increases and is transported
iii. As a results, rivers deposit more silt along its course
iv. Lower erosive power of rivers during low water level
v. River load decreases but is still transported
vi. However, deposition is much less then during high water level season.
b) Effects on human settlements near the river
(Compare negative and positive effects during both high and low water levels)
i. Negative effects
a. Flooding which causes loss and damage of property, lives and livestock
b. Crops are flooded and therefore wasted.
c. Accumulation of sediment in lower courses of the river that raise river bed and cause flooding
d. Low water levels do not allow the overflowing of alluvial material onto floodplains. As a result, fertility of floodplain dwindles.
ii. Positive effects
a. Deposition of alluvial material on floodplains during flooding makes plain fertile ground
b. Crops can be harvested during season of low water level
The above points are examples of points that are acceptable. Reward any other acceptable answers.
A full answer does not need to include all the above points, but it should refer to the effects on the work of rivers during both seasons. Positive and negative effects on human settlements near the river both seasons should also be included.
The question does not ask for examples, therefore it is possible to gain maximum marks without quoting examples.
Candidates at each level will show the following characteristics.
Level 1 (0 – 3 marks)
One or two general statements on the effects seasonal water levels have on the work of rivers and human settlements.
Effects are linked to either high water level or low water level, not necessarily both.
No comparison is made between the effects during high and low water level.
No usage of technical terms like higher/lower erosive power, accumulation of sediment et
Only refers to either positive or negative effect, not both.
Level 2 (4 – 6 marks)
At least 3 statements made on the effects seasonal water levels have on the work of rivers and human settlements.
Effects are linked to both high and low water levels.
Comparison is made between effects at high and low water levels.
Some technical terms are used.
Both positive and negative effects are mentioned.
Level 3 (7 – 8 marks)
Comparison is made between effects of seasonal water level on the work of rivers and human settlements.
Technical terms are used to convey meaning effectively.
Positive and negative effects on the work of rivers clearly explained.
Positive and negative effects on human settlements near rivers clearly explained.
Explained that some initially negative effects can become positive effects later e.g. flooding as a negative effect but when flood ceases, floodplain is abundant with deposited alluvium conducive for farming.
Mention that people living near rivers have to take into account the work of rivers and seasonal water levels before deciding on what they can or cannot do during a particular season.
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