This set mixes the five skills in rivers and drainage: river processes, cross-sections, landform sequences, hydrographs and flood evidence. All numbers are invented for practice.
Work in order from easy to harder, with a calculator and a pencil. Cover the answers until you have written your own. The statistics and distribution explorer and food-web and energy-flow explorer help you check working, and the mistake log is the place to record slips.
Questions
Q1 (easy). Name the process: (a) pebbles carried by the river scrape the bed; (b) stones collide and become smaller and rounder; (c) water forced into cracks loosens rock.
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(a) Abrasion. (b) Attrition. (c) Hydraulic action.
Q2. Name the transport process for each: (a) boulders rolled along the bed in a flood; (b) sand bouncing in short hops; (c) fine clay carried within the water.
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(a) Traction. (b) Saltation. (c) Suspension.
Q3. A channel is 5 m wide. Depths at 1 m intervals from one bank are 0, 0.6, 1.0, 0.8, 0.4, 0 (metres). Find the cross-sectional area.
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Strips: (0 + 0.6) ÷ 2 = 0.3; (0.6 + 1.0) ÷ 2 = 0.8; (1.0 + 0.8) ÷ 2 = 0.9; (0.8 + 0.4) ÷ 2 = 0.6; (0.4 + 0) ÷ 2 = 0.2. Total = 0.3 + 0.8 + 0.9 + 0.6 + 0.2 = 2.8 m².
Check: middle depths 0.6 + 1.0 + 0.8 + 0.4 = 2.8, ends 0, times 1 m gives 2.8 m².
Q4. The mean velocity in the channel in Q3 is 0.5 m/s. Find discharge.
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Q = A × v = 2.8 × 0.5 = 1.4 m³/s.
Q5. A river carries 9 m³/s through a section of area 6 m². Find the mean velocity.
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v = Q ÷ A = 9 ÷ 6 = 1.5 m/s.
Q6. The channel in Q3 has a wetted perimeter of 5.6 m. A second channel has the same area but a wetted perimeter of 7.0 m. Which is more efficient?
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First: 2.8 ÷ 5.6 = 0.5 m. Second: 2.8 ÷ 7.0 = 0.4 m. The first channel is more efficient, as its hydraulic radius is higher and there is less contact with the bed and banks, so less friction.
Q7. A long profile has these points: 0 km at 600 m, 20 km at 200 m, 80 km at 50 m. Find the gradient of each section and say which is steeper.
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0 to 20 km: fall 400 m over 20 km = 20 m per km. 20 to 80 km: fall 150 m over 60 km = 2.5 m per km.
The first section is steeper, which fits strong vertical erosion near the source. Check: 400 + 150 = 550 = 600 − 50.
Q8. Put in order from source to mouth: oxbow lake, delta, V-shaped valley, meander. Explain how the oxbow lake forms.
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V-shaped valley, meander, oxbow lake, delta.
A meander grows through erosion on the outside of the bend and deposition on the inside. The neck narrows until a flood cuts through it. Deposition then seals off the old loop, which becomes an oxbow lake.
Q9. Peak rainfall is at 08:00. Peak discharge is 24 m³/s at 11:30. Baseflow is 3 m³/s. Find the lag time and the rise above baseflow.
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Lag = 11:30 − 08:00 = 3 hours 30 minutes. Rise = 24 − 3 = 21 m³/s.
Q10. Catchment A has a lag of 1 hour and a peak of 40 m³/s. Catchment B has a lag of 4 hours and a peak of 15 m³/s. Suggest which has more impermeable ground, and state a limit on your answer.
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Catchment A is more consistent with impermeable ground, because rain reaches the river sooner and the peak is higher. The limit is that the graph alone cannot prove it: slope, soil wetness and rainfall amount could also differ.
Q11 (harder). A report says a wetland restoration lowered flood heights. Three floods before averaged 5.2 m (5.2, 4.8, 5.6). Two floods after averaged 4.5 m (4.4, 4.6). Find the percentage fall and evaluate the claim.
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Check: 15.6 ÷ 3 = 5.2 and 9.0 ÷ 2 = 4.5. The fall is 0.7 m, so 0.7 ÷ 5.2 ≈ 0.135, which is about 13%.
The data are consistent with a lower flood height. The claim is only partly supported: there are just two events after the work, and the storms may not have been the same size. We would need rainfall for each event and a longer record.
If you got these wrong
- Q1 or Q2 wrong: revisit erosion, transport and deposition, especially abrasion versus attrition.
- Q3 to Q6 wrong: revisit interpreting a channel cross-section. Check you added strips and did not use maximum depth times width.
- Q7 or Q8 wrong: revisit tracing a landform sequence. Write fall divided by distance, and place a meander before an oxbow lake.
- Q9 or Q10 wrong: revisit reading a hydrograph with time lag. Lag is a difference between two times, and your wording should be “consistent with”.
- Q11 wrong: revisit evaluating a flood-related claim. Name the limits of the evidence before you conclude.
If the same step keeps going wrong, a teacher in online one-to-one Geography tuition can find the cause and fix it with you.