Paper 3 · June 2023 · GIS: georeferencing, digitising and measurement
The Esigodini sheet shows shallow open valleys, few perennial channels and long stretches of higher ground with almost no channels at all, giving a low to moderate drainage density. What best explains this?
AA permeable, deeply weathered granite regolith that takes water in as throughflow, combined with gentle relief and a strongly seasonal rainfall regime.
BAn exceptionally high annual rainfall total, which has eroded the smaller channels away and left only the largest valleys visible.
CRecent glacial scour, which stripped the established drainage lines from the higher ground and left channels surviving only in the sheltered valley bottoms where the moving ice could not reach them.
DAn impermeable clay subsoil across the sheet, which sheds almost all rainfall as surface flow within minutes of it landing.
Explanation
Deeply weathered granite lets rainfall infiltrate and move as throughflow instead of cutting surface channels, and gentle relief gives little energy for incision. Seasonal rainfall leaves most channels dry outside summer. An impermeable subsoil would raise drainage density, not lower it.
Derived from ZIMSEC Advanced Level Geography 6037/3 Paper 3 Practical Test, June 2023 session, Q3