Theory question 307
Rivers and River Landforms(a) List three processes of river erosion. (b) Outline four characteristics of each of the following sections of a river valley: (i) upper course; (ii) middle course; (iii) lower course.
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(a) Hydraulic action; corrasion (abrasion); attrition; solution (corrosion).
(b)(i) Upper course: steep gradient; fast flow; mainly vertical (downward) erosion; narrow, steep-sided V-shaped valley; interlocking spurs; waterfalls, rapids, potholes and gorges; small volume; large boulders.
(ii) Middle course: gentler gradient; lateral erosion widens the valley; larger volume from tributaries; meanders begin; river cliffs and slip-off slopes; some deposition; wider, open V-shaped valley with small floodplain.
(iii) Lower course: very gentle gradient; slow flow; deposition is the main work; wide flat floodplain; large meanders and ox-bow lakes; levees; braided channels; delta or estuary at the mouth; largest volume and fine load.
Four points for each course.