The action of water in arid regions
299
Various factors can be recognized that control the intensity of erosion on desert slopes.
The effect of slope was analyzed by Abrahams and Parsons (1991 b) in a simulated rainfall
study at three experimental stations with distinct lithology and vegetation. At slope angles
below 12 ~ the run-off increased very slowly and sediment production increased with slope
due to the gravitational component (Figure 13.16). If the slopes were greater than 12 ~ runoff decreased rapidly, by a value that increased with slope. This reduction compensated for
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Figure 13.16. Curves fitted to graphs of (a) sediment yield and (b) run-off coefficient against gradient for
three sets of experiments denoted by E~, E2, and E3 at Walnut Gulch, Arizona. Experiments E~ and E2 were
conducted on plots underlain by Quaternary alluvium, with the ground vegetation being clipped for E] but
not for E2. Experiment E3 was performed on plots underlain by the Bisbee Formation (after Abrahams and
Parson ( 1991 b )).