EFFECT OF RAINFALL INTENSITY ON SPLASH AND WASH EROSION OF SOME SOILS AT ALEMAYA, ETHIOPIA
FEKADU, Y.
Abstract
Accelerated erosion by water is a serious problem
in Alemaya -watershed and in many other ecologically sensitive parts of Ethiopia.
The major causes of soil erosion and overall land degradation are inappropriate
crop and land management practices. Soil erosion is determined by rainfall erosivity
and soil erodibility. Field plots are often used to measure a wide range of
effects such as rainfall, soil type and erosion. However, field experiments
depend on natural rainfall, which is unpredictable. A rainfall simulator experiment
was thus conducted using a spinning disc simulator that enables representative
kinetic energy to be achieved at a wide range of intensities. In this study,
an assessment of the effect of rainfall intensity on splash and wash erosion
was made on five soils sampled along a toposequence in Lake Alemaya watershed.
The soils were subjected to simulated rainstorms rangingfrom 42.4 to 125.4mmlhr.
The highest splash loss was observed in Soil 1 followed by Soil S. The least
splash loss was that of Soil 2 and 3 under all the rainfall intensities. The
results of the wash erosion showed that the amount of wash material increased
with rainfall intensity for all the soils. Soil 1 and 2 produced the highest
wash loss for the rainfall intensities 125.4 and 102.3 mm/hr. High amount of
wash loss clearly showed that Soil 1 and Soil 2 would benefit from erosion control
measures. Wash loss decreased by about 80 to 90%for the 60 and 48.8mm.Ihr intensities
as compared to the average wash loss of all the soils for the higher intensities.
Simple regression analysis was also carried out relating splash and wash loss
to rainfall intensity, which could be a useful tool for predicting erosion and
conservation planning.
Key words:
rainfall simulator, rainfall intensity, splash loss,
wash loss