Paper 1 · Fluvial Geomorphology
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?
AThick vegetation cover in the high-discharge basin, which intercepts less rainfall than expected and therefore speeds up the movement of water into the channel below.
BImpermeable underlying rock in the high-discharge basin, which generates more surface runoff and a higher peak discharge.
CA gentle valley-floor gradient near the river mouth in the high-discharge basin.
DA higher total annual rainfall falling on the high-discharge basin than on the other basin.
Explanation: With rainfall held equal, basin characteristics such as rock permeability determine how much rainfall becomes surface runoff: impermeable rock sheds water quickly into the channel, producing a higher and faster peak discharge. Vegetation cover actually intercepts rainfall and increases infiltration, reducing runoff rather than speeding it up; valley-floor gradient near the mouth affects channel flow, not how much runoff a storm generates; and the question already states rainfall is identical in both basins, ruling out the fourth option.
Derived from ZIMSEC Geography Paper 1, November 2003, Q5
