The influence of vegetation on the water resources of the Naro Moru river catchment.

Abstract

The effects of vegetation on water resources was studied for the upper forest, lower forest and footzone of the Naro Moru catchment on the western slopes of Mount Kenya during November 1991 to June 1992. Climatic parameters on a daily basis and soil water content were monitored for different vegetation systems using a neutron probe at approximately one-week intervals. Vegetation types included Tussock grass and alpine vegetation in the upper levels, mixed bamboo forest, dry montane forest and cypress plantations below that, natural open forest and small holder crops such as potato in the footzone, and open Acacia grassland on the savannah. The results show that there were significant differences between the zones for climatic water availability, soil water storage and vegetation water use. Differences in soil water storage and vegetation water use were more pronounced in the lower forest and the footzone than in the upper forest. In the lower forest, the cypress plantations used the greatest amount of water while the potato crop used the least. The cypress plantation had lower soil water levels and higher water requirements compared to the natural vegetation. In the upper and lower forest, surplus water drained into deep percolation and/or surface runoff, especially in the wet season. In wet periods the potatoes were at risk of damage from surface runoff and soil erosion.