Rivers and Coastal Management
What this domain tests
Rivers and coastal management questions test your understanding of drainage basins, flood hydrographs, erosion and deposition, coastal processes and management strategies. You must interpret graphs and maps and justify management choices with costs and benefits.
Core rules and concepts
- A flood hydrograph shows rainfall and discharge over time; lag time is the gap between peak rainfall and peak discharge.
- Urbanisation increases impermeable surfaces and drains, reducing infiltration and lag time while raising peak discharge.
- Coastal erosion is caused by hydraulic action, abrasion and solution; longshore drift moves sediment along the coast in the direction of the dominant swash.
- Hard engineering (sea walls, groynes, dams) is expensive and can shift problems; soft engineering (beach nourishment, managed retreat, afforestation) works with natural processes.
Worked example
Rainfall peaks at 13:00 and river discharge peaks at 19:30. Lag time = 19:30 − 13:00 = 6.5 hours. If the same catchment were urbanised, expect a shorter lag, perhaps 2–3 hours, and a higher, steeper peak because water reaches the channel quickly. Reasoning: identify the two peaks, subtract the earlier from the later, and then link land-use change to infiltration and channel flow.
Traps that cost marks
Do not measure lag from the start of rainfall; use the peaks. Do not say urbanisation increases infiltration. Do not describe a groyne as a soft engineering option. Do not ignore the difference between river discharge (cumecs) and rainfall (mm).