Journal of Food, Agriculture and Environment

Spatial analysis and semi-quantitative modeling of specific sediment yield in six catchments of the central rift valley of Ethiopia

Author(s):

Derege Tsegaye Meshesha ^1*, Atsushi Tsunekawa ¹, Mitsuru Tsubo ¹, Nigussie Haregeweyn ^{1, 2}

Recieved Date: 2011-06-07, Accepted Date: 2011-09-26

Abstract:

The Central Rift Valley (CRV) of Ethiopia is one of the most environmentally susceptible areas in the country. Most of the lowland is arid or semiarid, and droughts occur recurrently. Soil erosion in the highlands surrounding the Ethiopian Central Rift Valley is causing serious land degradation and siltation problems in the local lakes of the valley. Measured specific sediment yield (SSY) that ranges from 214 to 611 t km^-2 yr^-1 for six catchments in the rift valley show that there exists a serious sedimentation problem for lakes in the region. Although accurate predictions of SSY are needed to plan and implement policies to mitigate these problems, so far there is little reliable data on sediment yield and no adaptable model to predict (SSY) has yet been developed for the region. We used field observations and a previously developed factorial scoring model (FSM) that calculates SSY as a function of topography, vegetation cover, gully morphology, lithology and catchment shape to determine which of these factors have the greatest effect on SSY in the region; we found that gully morphology is the primary factor that controls SSY, followed in order of decreasing importance by catchment shape, topography, vegetation cover and lithology. We then modified the model by adding a climate factor to account for the effect of rainfall on SSY in the Central Rift Valley. We found that both calibrated models that used modified factors of FSM and our modified version that included climate provided reasonably good statistical correlation between observed and predicted SSY during calibration and validation. However, because of significant differences in rainfall among the six catchments, the version that included the climate factor provided better estimates of SSY (ME = 0.82, RRMSE = 0.13) than the model that used the original FSM factors (ME = 0.77, RRMSE = 0.15).

Keywords:

Ethiopia, specific sediment yield, soil erosion, factorial scoring model, catchment, central rift valley, gully, calibration, validation

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Journal: Journal of Food, Agriculture and Environment
Year: 2011
Volume: 9
Issue: 3&4
Category: Environment
Pages: 784-792

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