Soil erosion risk assessment in the Chaleleka wetland watershed, Central Rift Valley of Ethiopia
Wolka et al. Environmental Systems Research
Soil erosion risk assessment in the Chaleleka wetland watershed, Central Rift Valley of Ethiopia
Kebede Wolka 0
Habitamu Tadesse 0
Efrem Garedew 1
Fantaw Yimer 0
0 Hawassa University, Wondo Genet College of Forestry and Natural Resources, School of Natural Resources and Environmental Studies , P.O.Box 128, Shashemene , Ethiopia
1 Hawassa University, Wondo Genet College of Forestry and Natural Resources, School of Forestry , P.O.Box 128, Shashemene , Ethiopia
Background: Increased flooding and newly formed rills and gullies were observed in the Cheleleka wetland watershed, over the past three to five years. These events are due to problems related to land use changes and are adversely affecting land productivity. This study was conducted to quantify, analyze and map soil erosion risk areas using the Revised Universal Soil Loss Equation. Results: Only 13.6 percent of the study area has a soil loss value less than 10 ton per hectare per year with the remaining area experiencing a higher soil loss value. A large area, 53.6 percent of the watershed, is under severe to extremely severe soil loss (>45 ton per hectare per year). Another 17.3 percent of the study area has annual soil loss of 20-45 ton per hectare. Conclusion: A significantly large area of the Cheleleka wetland watershed has non-tolerable soil erosion that threatens annual crop production, land productivity, and hydrological functioning of the area. From the conservation perspective, a large proportion of the watershed needs immediate watershed management intervention.
Conservation priority; Land use change; Topography; Soil erosion
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Background
Soil erosion is a natural geological phenomenon resulting
from the removal of soil particles by water or wind (Gitas
et al. 2009). This natural process can be accelerated by
human activities creating soil loss that exceeds the soil
formation rate in a given area. Human activities that
change land use from a comparatively higher form of
permanent vegetation cover, to a state of lesser vegetation
cover, have increased soil erosion (Cebecauer and
Hofierka 2008).
Several studies in Ethiopia have revealed that soil
erosion has become an alarming problem (Wagayehu and
Drake (2003); Admasu (2005); Bewket and Teferi (2009);
Haile and Fetene (2012)) and it is the major factor
affecting the sustainability of agricultural production.
The leading factors causing erosion include: increased
population pressure resulting in forest/woodland
clearance for wood and smallholding agriculture; traditional
agricultural practices; and declining land productivity.
In the Cheleleka wetland watershed, large expansions
of new land uses were made mostly through the
displacement of the original forests and pasture land.
For example, using remote sensing and Geographic
Information System (GIS) methods, Gessesse (2007),
estimated an alarming 82% forest decline in the area when
comparing 1972 forest cover to 2000. In many cases, this
conversion occurred without evaluating the land use
capacity, thus exposing the new cultivated fields to a
high level of degradation. Moreover, the erosion and
sedimentation processes disrupt the hydrological balance
in the study watershed. In contrast to other lakes in the
Rift Valley of Ethiopia, the level of Lake Hawassa has
been increasing while the Cheleleka wetland is
unfortunately drying up. Thus the increasing discharge from the
wetland through the TikurWuha River is partially
related to the activities of erosion and the sedimentation
processes in the Cheleleka watershed (Gessesse 2007;
Tenalem et al. (2007); Kebede et al. (2014)).
Increased flood and erosion risks were investigated as
part of the field work for this study (Figure 1). Medo,
Burara, and Gotu-Onoma akebeles were found to be
victims of erosion and flooding which damaged large areas
of cropland, forming new rills and gullies, and damaged
Figure 1 Partial view of the study site (ashows erosion site and b shows topography).
ditches along concrete and asphalt roads. Recently, the
watershed stream discharge has increased, causing
flooding (Kebede et al. 2014). Therefore, the extent and
spatial pattern of the watersheds soil erosion needs to
be assessed. This will assist the identification of erosion
susceptible areas for planning and implementation of a
watershed-based soil and water conservation plan. No
soil erosion susceptibility analysis and map were
available for this watershed. This highly populated,
socioeconomically, and hydrological relevant rural watershed,
supplying significant water resources to watershed
residents and other towns outside the watershed, is in need
of assessment and management.
A relevant approach needs to be followed in
estimating the spatial variation of soil erosion. In various
corners of the globe, scientists apply related approaches and
models for estimating soil erosion and related processes.
For instance, the Hairsine-Rose model and hysteresis has
been (...truncated)