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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Addis Ababa Universty


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



Biomass, Watershed, GIS, NDVI, LULC, Remote Sensing, RUSLE, Soil erosion