Assessing the Impact of Watershed Development Programs on Soil Erosion and Biomass Production Using Remote Sensing and GIS: The Case of Yezat Watershed, West Gojam Zone of Amhara Region, Ethiopia
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Date
2016-06
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Addis Ababa Universty
Abstract
Environmental problems are alarming all over the world. Land degradation, environmental
and social problems associated with its use, calls for adopting appropriate policy measures
and practical actions for the best land management practices. Integrated Watershed
Development Program (IWSDP) was implemented for reducing soil erosion, improving
water resources and reestablishing vegetation under the Sustainable land management (SLM)
program. Consequently, this study was conducted in Yezat watershed with the objective of
determining the trends and changes of soil erosion, vegetation cover and land-use/landcover(
LULC) that has changed during pre and post treatment periods (2001−2010 to
2010−2015) and evaluating the impact of watershed development program using remote
sensing and Geographical information system(GIS) approach. The study was carried out time
series satellite imageries (Landsat ETM+ 2001, TM 2010, and OLI 2015) together with other
ancillary data covering the watershed. The satellite image was classified into different landuse/
land-cover categories using supervised classification by maximum likelihood algorithm.
They were also classified into different biomass levels using Normalized Difference
Vegetation Index (NDVI) analysis. Revised Universal Soil Loss Equation (RUSLE)
modeling is applied in a GIS environment to quantify the potential soil erosion risk. The
modeling is carried out for the years 2001, 2010, and 2015, and is based on Landsat satellite
imageries, rainfall, soil and DEM data. The results reveal significant modification and
conversion of land-use/land-cover of the watershed. A significant portion of the watershed
was continuously under intensively grass land, wood land and homesteads. The area covered
with grassland, woodland and homesteads were increased by 610.69 ha (4%), 101.69 ha
(0.67%) and 126.6 ha (0.83%) while cultivated land and shrub/bush land where decreased by
323.43(0.02%) and 515.44ha (3.41%), respectively during post treatment period
(2010−2015). The estimated woody biomass considerably decreased during the period
2001−2010 (pre treatment) while in 2010 −2015 (post treatment), significant increase in the
woody biomass area was observed. Based on the result, vegetation cover was decreased
during pre treatment periods (2001−2010) which account for 91.1% of the land area. From
2010 −2015 (post-treatment) period, 88% of the land area was changed to increasing trend.
The increasing of NDVI indicates better ground cover vegetation condition. The result
derived from the estimated annual soil loss rate has shown the mean annual soil losses are
7.2 tons ha-1 yr-1 in 2001, 7.7 tons ha-1yr-1in 2010 and 4.8 tons ha-1yr-1in 2015. The study
further shows that IWSDP decreased soil erosion, reduced sedimentation and run off, and
rehabilitation of degraded lands. This study reconfirms the importance of IWSDP as a key to
improve the status and utilization of watershed resources in response to sustainable land
management interventions and sustainable livelihood. Thus, remotely sensed data using
advanced techniques such as remote sensing and Geographic information system (GIS) can
be useful to guide decision making process in evaluating the impact of IWDP on trends of
soil erosion and biomass production.
Keywords: Biomass, watershed, GIS, NDVI, LULC, Remote Sensing, RUSLE, Soil erosion
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Keywords
Biomass, Watershed, GIS, NDVI, LULC, Remote Sensing, RUSLE, Soil erosion