Secondary 3 Geography Physical Geography Quiz

Secondary 3 Geography Quiz - Physical Geography (Answer Key)

Total Marks: 40

Section A: Multiple Choice Questions (10 marks)

1. B — Hydraulic action is the force of water hitting against river banks and forcing air into cracks, causing the rock to weaken and break apart.
Marking note: A describes abrasion, C describes solution, D describes attrition.

2. A — V-shaped valleys are formed by vertical erosion in the upper course where the river has high energy and steep gradient.
Marking note: Middle course has lateral erosion forming meanders; lower course has deposition forming floodplains/deltas.

3. D — The fastest flow (thalweg) is found at the outer bank (cut bank) just below the water surface due to helical flow. The outer bank is deeper and experiences maximum erosive force.
Marking note: Inner bank has slower flow and deposition (slip-off slope). Centre surface is not the maximum velocity zone.

4. A — An ox-bow lake forms when a meander loop is cut off during a flood event when the river breaks through the narrow neck of the meander.
Marking note: Floodplain is the flat valley floor; levees are raised banks; delta forms at river mouth.

5. A — Hydraulic radius = Cross-sectional area ÷ Wetted perimeter. It measures channel efficiency; larger radius = more efficient flow.
Marking note: This is a standard formula in fluvial geography.

6. C — Urbanisation increases impermeable surfaces (concrete, asphalt), reducing infiltration and increasing surface runoff, leading to shorter lag time and higher peak discharge.
Marking note: A, B, and D all reduce flood risk by increasing infiltration or slowing runoff.

7. B — Lag time is the time interval between peak rainfall and peak discharge on a storm hydrograph. It indicates basin response speed.
Marking note: A describes rising limb start; C describes falling limb duration; D is storm duration.

8. B — Longshore drift moves sediment along the coast at an angle (due to prevailing wind), and when the coastline changes direction, sediment continues straight, forming a spit.
Marking note: Hydraulic action and abrasion are erosion processes; solution is chemical weathering.

9. B — Constructive waves: low frequency (6-8/min), long wavelength, gentle slope, strong swash > weak backwash, leading to net deposition.
Marking note: Destructive waves are high frequency, steep, strong backwash.

10. B — Wave orthogonals converge on headlands due to wave refraction, concentrating wave energy there. In bays, orthogonals diverge, dissipating energy.
Marking note: This explains why headlands erode (cliffs, stacks) while bays deposit (beaches).

Section B: Structured Questions (18 marks)

11.
(a) Vertical erosion (or downcutting) [1]
Accept: Downward erosion, vertical corrosion.

(b) Gradient decreases because:

• The river approaches base level (usually sea level), the lowest level to which it can erode. [1]
• As gradient decreases, vertical erosion slows and lateral erosion becomes dominant, widening the valley. [1]
  Marking note: Must link to base level concept and shift from vertical to lateral erosion.

(c) Meander — Formed by lateral erosion on outer banks (cut banks) and deposition on inner banks (slip-off slopes), causing the channel to develop sinuous bends. Helical flow transports eroded material from outer to inner bank. [1]
Accept: Interlocking spurs (upper course), but meander is the classic middle course landform. Must include process for the mark.

12.
(a) Hydraulic radius = Cross-sectional area ÷ Wetted perimeter

Site A: 1.28 m² ÷ 4.0 m = 0.32 m [1]
Site B: 79.8 m² ÷ 34.1 m = 2.34 m (accept 2.3–2.35 m) [1]

Marking note: Correct formula + correct calculation for each site. Units (m) required.

(b) Two reasons why velocity increases from Site A to Site B:

1. Hydraulic radius increases (0.32 m → 2.34 m), meaning less water is in contact with the channel bed/banks relative to volume, reducing friction and allowing faster flow. [1]
2. Bedload size decreases (15 cm → 0.3 cm) and angularity decreases (angular → rounded), reducing bed roughness and turbulence, further reducing friction. [1]
3. Channel shape becomes more efficient (wider, deeper, smoother), reducing wetted perimeter relative to area. [1]

Marking note: Any two valid points with data reference. Must explain mechanism (friction reduction), not just state data.

13.
(a) Alternating layers of resistant (hard) and less resistant (soft) rock horizontally or near-horizontally bedded. [1]
Accept: Cap rock overlying softer rock; differential resistance.

(b) Undercutting occurs because:

• Hydraulic action and abrasion are most intense at the base of the waterfall where the plunge pool forms. [1]
• The less resistant rock beneath the cap rock erodes faster, creating an overhang. [1]
  Marking note: Must mention processes and differential erosion.

(c) As undercutting continues, the overhanging cap rock collapses under gravity. The waterfall retreats upstream, leaving a steep-sided gorge behind. [1]
Marking note: Key sequence: undercutting → collapse → retreat → gorge.

14. Two ways urbanisation affects the storm hydrograph:

1. Reduced lag time — Impermeable surfaces (roads, roofs) prevent infiltration, increasing surface runoff. Water reaches the river faster via storm drains, steepening the rising limb and shortening lag time. [2]
2. Higher peak discharge — Rapid runoff concentration increases the volume of water reaching the channel in a short time, raising peak discharge and increasing flood risk. The falling limb may also be steeper as water drains quickly. [2]

Marking note: 1 mark for identifying change (lag time/peak discharge), 1 mark for explaining mechanism (impermeable surfaces, drainage, runoff). Must use hydrograph terminology.

15.
(a) Longshore drift (or littoral drift) [1]

(b) The hooked end forms because:

• A secondary wind/wave direction (often from a different quadrant) curves the spit tip landward. [1]
• Wave refraction around the spit end causes sediment to be deposited in a curved shape. [1]
  Marking note: Must mention change in wind/wave direction or refraction.

(c) Conditions for spit formation (vs. barrier beach):

• Change in coastline direction (e.g., river estuary, headland) where longshore drift continues straight into open water instead of following the coast. [1]
• Relatively shallow, sheltered water (e.g., behind a headland or in an estuary) allowing sediment accumulation above water level, often with a river outlet preventing the spit from joining the opposite shore. [1]
  Marking note: Barrier beaches form parallel to coast with no major interruption; spits require a coastline break and often a river current maintaining the opening.

Section C: Extended Response Questions (12 marks)

16. Named river example: Singapore River / Mississippi River / Yangtze River / Rhine River / any valid example.

Marking descriptors (6 marks):

Sample Level 3 response (Singapore River):
The Singapore River was heavily polluted and prone to flooding in the 1970s. Management strategies included:

1. Channelisation — The river was widened, deepened, and lined with concrete, increasing channel capacity and hydraulic radius, reducing friction and allowing faster conveyance of floodwater.
2. Marina Barrage — Completed in 2008, it acts as a tidal barrier and creates a freshwater reservoir. During heavy rain, gates open to release water at low tide; during high tide, gates close to prevent seawater backflow.
3. ABC Waters Programme — Afforestation and bio-retention swales in catchment areas increase infiltration, reduce surface runoff, and lengthen lag time.

Evaluation: Channelisation is effective for rapid drainage but destroys natural habitats. Marina Barrage provides flood control and water supply but is costly. ABC Waters is sustainable and enhances biodiversity but requires land and long-term maintenance.

Marking note: Credit other valid strategies (levees, flood relief channels, afforestation, floodplain zoning, dams). Must evaluate, not just describe.

17.
(a) Two differences from the diagram:

1. Wave morphology: Constructive waves have low height (~0.5 m) and long wavelength (~100 m); destructive waves have high height (~2 m) and short wavelength (~20 m). [1]
2. Swash/backwash balance: Constructive waves have strong swash > weak backwash (net deposition); destructive waves have weak swash < strong backwash (net erosion). [1]
   Accept: Wave period (constructive ~10 s, destructive ~5 s); wave frequency; beach profile change (berm vs. erosion).

(b) Wave refraction affects energy distribution:

• As waves approach an irregular coastline (headlands and bays), the part of the wave front in shallower water slows down due to friction with the seabed, while the part in deeper water continues at speed. [1]
• This causes wave fronts to bend (refract), becoming parallel to the coastline. Wave orthogonals converge on headlands, concentrating wave energy → erosion (cliffs, wave-cut platforms, caves, arches, stacks). [1]
• In bays, wave orthogonals diverge, dissipating energy → deposition (beaches, spits, tombolos). [1]
  Marking note: Must explain mechanism (differential speed → bending → convergence/divergence) and link to erosion/deposition.

18. Formation of a stack from a headland (sequence):

1. Headland projects into the sea, exposed to high wave energy due to wave refraction concentrating orthogonals. [1]
2. Hydraulic action and abrasion exploit lines of weakness (joints, faults, bedding planes) in the cliff face, forming a cave. [1]
3. Cave enlarges and cuts through the headland (especially if weakness runs through), forming an arch. [1]
4. Weathering (freeze-thaw, salt crystallisation, biological) and erosion widen the arch; the roof becomes unstable and collapses under gravity. [1]
5. The seaward portion of the headland is left isolated as a stack (vertical column of rock). [1]
6. Continued erosion at the base of the stack forms a wave-cut notch; the stack eventually collapses, leaving a stump. [1]

Marking note: 1 mark per stage in correct sequence. Must name processes (hydraulic action, abrasion, weathering) and landforms (cave, arch, stack, stump). Diagrammatic description accepted.

19.
(a) Temperature is uniformly high throughout the year (~27°C) with a very small annual range (1–2°C). No distinct seasons. [1]

(b) High year-round rainfall because:

• Equatorial location → Sun overhead year-round → consistently high temperatures → high evaporation and evapotranspiration from dense vegetation. [1]
• Convectional rainfall — Intense heating causes rapid uplift of warm, moist air → cooling → condensation → cumulonimbus clouds → heavy afternoon thunderstorms almost daily. [1]
• Intertropical Convergence Zone (ITCZ) — Convergence of trade winds forces air to rise, enhancing uplift and rainfall. The ITCZ remains near the equator year-round, so no dry season. [1]
  Marking note: Must link high temp → evaporation → convection → rain. Mention ITCZ for full marks.

20. Named tropical rainforest: Amazon Rainforest / Borneo Rainforest / Congo Basin / any valid example.

Marking descriptors (6 marks):

Sample Level 3 response (Amazon Rainforest):
Causes of deforestation:

1. Cattle ranching (~80% of cleared land) — Large areas cleared for pasture; Brazil is the world's largest beef exporter.
2. Soybean plantations — Driven by global demand for animal feed; often follows logging roads.
3. Logging (legal/illegal) — Selective logging opens canopy, dries forest, increases fire risk; roads enable further encroachment.
4. Infrastructure — Trans-Amazonian Highway, Belo Monte Dam fragment habitat and enable access.

Sustainable management strategy: Selective logging with Reduced Impact Logging (RIL) guidelines

• Only mature trees of commercial species are felled (e.g., 1–2 trees/ha), maintaining canopy cover and biodiversity.
• Skid trails planned to minimise soil compaction and damage to residual trees.
• Rotation cycles (25–35 years) allow forest recovery.
• Certification (FSC) ensures market access for sustainable timber.

Evaluation:
Pros: Maintains forest structure, carbon storage, biodiversity; provides income; reduces waste.
Cons: Requires strict enforcement; illegal logging persists; RIL more costly than conventional; may not prevent conversion to agriculture if land value higher.

Alternative strategies accepted: Ecotourism (e.g., Yasuni, Ecuador), Protected areas (e.g., Jaú National Park), Agroforestry, REDD+ (payment for ecosystem services), Indigenous land rights recognition.

Marking note: Must evaluate (pros/cons), not just describe. Link to named rainforest essential for Level 3.