Influence of rainfall direction on erosivity and soil loss

Abstract

A study was carried out to determine the directional impact of rainfall on erosivity and soil loss in the Kabete area of Nairobi. This was done by employing three major fields of data collection : (1) Wind monitoring using a wind recorder. (2) Rainfall monitoring using a rain recorder and three sets of raingauges, each set consisting of five gauges facing different directions and (3) Runoff and soil loss monitoring on twenty-four microplots of size 1x2m and oriented to face four different compass directions. The four compass directions used were NE, SE, NW and SW. The following erosivity indices: ElalI30' EusdaI30' E1a1 and AI30 were the best indices found to describe runoff erosion in the Kabete area. There was no significant difference in their ability to describe runoff erosion. Hence any of the four can be used for this region. Rainfall dominantly from westerly directions was found to have a significant directional effect over that of easterly and even vertical rainfall. This observation makes inclined gauges really better to use for erosivity predictions than vertical gauges. Slopes facing westerly directions suffered more soil loss, thus were more prone to damage than those facing easterly directions. Conservation planning should focus more attention to westerly facing slopes in this region.