A drainage density study recorded that a sandstone area receiving 900 mm of annual rainfall had a drainage density of 2.5 km per km2, while a limestone area receiving the same 900 mm of annual rainfall had a much lower drainage density of only 1.5 km per km2. Despite receiving identical rainfall, why does the limestone area have a lower drainage density than the sandstone area?

Limestone is permeable, so rainwater infiltrates through joints and solution features instead of forming surface streams.

Two river basins receive exactly the same annual rainfall, yet one produces a much higher peak discharge after storms than the other. Which basin characteristic best explains this difference?

Impermeable underlying rock in the high-discharge basin, which generates more surface runoff and a higher peak discharge.

A Level Geography

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