DSE Geography Practice Paper: River Landforms And Flood Management (12 Questions, 100 Marks, 75 Minutes)

DSE Geography Practice Paper: River Landforms and Flood Management (12 questions, 100 marks, 75 minutes)

2026-11-03

DSE Geography: Rivers and Flood Management

DSE Geography practice paper on river landforms and flood management: 12 questions, 100 marks, 75 minutes, with full answers, marking points and data-response tasks.

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Paper details　Level: S6 | Subject: Geography | Time: 75 minutes | Marks: 100 | Questions: 12

Section A: River discharge and data calculations (Questions 1-4, 24 marks)

Answer all questions. In calculations, write down the formula, substitute values and give units.

#	Question	Answer and marking notes
1	A gauging station records a river width of 12.0 m, mean depth 2.5 m and mean velocity 1.6 m s-1. (a) Calculate the cross-sectional area. (b) Calculate the discharge in m3 s-1. (6 marks)	Answer: (a) Area = 12.0 × 2.5 = 30.0 m2. (b) Discharge = 30.0 × 1.6 = 48.0 m3 s-1. Marking: formula 2, substitution and units 2, correct answer 2.
2	A catchment of 240 km2 receives 80 mm of rain in 24 hours. (a) Calculate the total rainfall volume in m3. (b) If 65% of the rain becomes runoff, calculate the runoff volume in million m3. (6 marks)	Answer: (a) 240 km2 = 240 000 000 m2 and 80 mm = 0.080 m, so volume = 240 000 000 × 0.080 = 19 200 000 m3. (b) Runoff = 0.65 × 19 200 000 = 12 480 000 m3, that is 12.48 million m3. Marking: unit conversion 2, multiplication 2, percentage and expression 2.
3	A city had 45 000 people in 15 km2 in 2015 and 54 000 people in the same area in 2025. (a) Calculate the 2015 population density. (b) Calculate the population growth rate from 2015 to 2025. (6 marks)	Answer: (a) 45 000 ÷ 15 = 3 000 people per km2. (b) (54 000 − 45 000) ÷ 45 000 × 100% = 20.0%. Marking: formula 2, value 2, units and percentage sign 2.
4	A map has a scale of 1:25 000. (a) Two points are 6.4 cm apart on the map; find the real distance in km. (b) A river reach is 9.2 cm long on the map; find its real length in km. (c) Explain how the same river would appear if the scale changed to 1:50 000. (6 marks)	Answer: (a) 6.4 × 25 000 = 160 000 cm = 1.6 km. (b) 9.2 × 25 000 = 230 000 cm = 2.3 km. (c) The scale denominator doubles, so the same river is drawn at half the map length, from 9.2 cm to 4.6 cm. Marking: 2 marks each; part (c) must state that doubling the denominator halves the map distance.

Section B: Flood management and river landforms (Questions 5-8, 32 marks)

Write explanations in complete sentences and name the relevant landform or hydrological process.

#	Question	Answer and marking notes
5	Explain how a detention basin reduces downstream peak discharge during a storm, and state two factors that must be considered in its design or siting. (8 marks)	Answer: A detention basin stores upstream flow during a storm, cutting the peak and delaying its arrival downstream, so channels do not exceed design capacity; water is released at a controlled rate afterwards. Two factors: siting needs enough low-lying land close to the peak source; capacity must be sized for the storm volume of a chosen return period (for example the 1 in 50 year event), with spillway and desilting provision. Marking: peak reduction and delay 3, siting 2, capacity or return period 2, spillway or maintenance 1.
6	Compare the hydrological response of the same land before and after urbanisation: runoff was 25% of rainfall on greenfield and rose to 65% after paving. (a) Calculate the change in runoff in percentage points. (b) Explain the changes in infiltration, evapotranspiration and lag time. (8 marks)	Answer: (a) 65% − 25% = 40 percentage points. (b) After paving, infiltration falls and evapotranspiration falls, so most rain becomes surface runoff; overland flow is faster, so lag time shortens and the peak rises. Marking: (a) 2; (b) infiltration, evapotranspiration, runoff and lag time 1.5 each.
7	Describe the formation and development of a meander, and explain how an oxbow lake is produced. (8 marks)	Answer: Flow is faster on the outer bank, so erosion is stronger there and an undercut bank forms; flow is slower on the inner bank, so sediment is deposited as a slip-off slope. The outer bank retreats and the inner bank advances, so the bend grows. When a flood cuts through the narrow neck, the channel straightens and the abandoned bend is sealed at both ends, forming an oxbow lake. Marking: outer bank erosion 3, inner deposition 2, bend growth 1, cut-off and sealing 2.
8	Compare hard engineering (embankments, channelisation) with soft engineering (floodplain restoration) for flood control, giving one advantage and one limitation of each. (8 marks)	Answer: Hard engineering (embankments, channelisation) raises the flood standard quickly and protects existing urban areas, but capital and maintenance costs are high and risk may be transferred downstream while river habitats are damaged. Soft engineering (floodplain restoration, allowing the channel to move) costs less, brings ecological benefits and aids groundwater recharge, but needs large areas of land and gives weaker short-term protection. Marking: 3 for each approach (advantage and limitation), 2 for comparison and trade-off.

Section C: Essays and strategy evaluation (Questions 9-12, 44 marks)

Answer essay questions in points and support each argument with data or examples.

#	Question	Answer and marking notes
9	What conditions are needed for a delta to form? Discuss sediment supply, coastal energy and crustal stability. (11 marks)	Answer: Sediment supply must be plentiful so that the river can carry a large suspended load to the mouth; wave and tidal energy at the coast must be weak, allowing sediment to settle; the coast must be tectonically stable or subsiding slowly so that deposits can accumulate. All three are needed for a classic delta; with strong waves or rapid uplift the load is removed and beaches or cliffs form instead. Marking: 3 per condition with mechanism, 2 for the contrasting case or examples.
10	How does climate change alter the hydrological cycle in Hong Kong and nearby regions? Discuss rainfall intensity, evapotranspiration and groundwater recharge. (11 marks)	Answer: Rainfall intensity rises and short intense storms become more frequent, so peaks are higher and flashier; higher temperatures raise evapotranspiration and lower soil moisture, adding pressure on agriculture and reservoir supply; sea level rise and saltwater intrusion reduce recharge to coastal aquifers and degrade groundwater quality. The overall effect is a wider gap between wet and dry seasons, so drainage and supply design standards must be raised. Marking: 3 per aspect, 2 for the integrated effect.
11	Explain how erosion, transport and deposition change an upland V-shaped valley into a wide alluvial plain. (11 marks)	Answer: In the upper course the steep gradient gives high velocity and dominant vertical erosion, cutting a V-shaped valley; in the middle course the gradient eases, lateral erosion dominates, the valley widens and meanders appear; in the lower course velocity falls, competence drops and sediment is deposited on the bed and floodplain, building a flat alluvial plain. The whole sequence is driven by the balance of erosion, transport and deposition as gradient changes. Marking: 3 per stage, 2 for the mechanism linking them.
12	In one basin, peak discharge rose by 20% between 1990 and 2020 while impervious cover rose from 18% to 42%. Evaluate three flood management strategies and state which should be the first priority, with reasons. (11 marks)	Answer: Impervious cover rose from 18% to 42%, an increase of 24 percentage points, while peak discharge rose by 20%, so urbanisation is the main driver. Three strategies: (1) build detention basins and flood meadows upstream to cut and delay the peak; (2) use permeable paving and rain gardens in the city to restore infiltration; (3) add flood warning and land-use zoning downstream to limit development in high-risk zones. Strategy (1) should come first because it removes a large share of peak volume at source, gives the best cost-benefit and works alongside (2). Marking: use of data 2, each strategy 2, priority and reason 3.

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