Sediment Yield Assessment and Mitigation Measures in Finchaa Watershed, Ethiopia *Megersa Kebede Leta Dr. Ankit Chakravarti Faculty of Civil and Environmental Engineering Faculty of Civil and Environmental Engineering Jimma Institute of Technology, JIT Jimma Institute of Technology, JIT Jimma, Oromia, Ethiopia Jimma, Oromia, Ethiopia Abstract - The effects of land use land cover changes and improper management systems have played a significant role in causing high soil erosion rates, sediment transport and affects life expectancy of the reservoir and have an impact on the water balance of the catchment.This study investigates sediment yield to changes in land use, land cover and mitigation measure practices at Finchaa watershed, Ethiopia.The input data used for this study were Digital Elevation Model, land use land cover map, soil map and data, and weather data. As the measured data was not available on sediment yield, only the simulated data has been used to identify the impact of value on some measure of simulated sediment output. Model calibration and uncertainty analysis were performed with sequential uncertainty fitting (SUFI-2) that is linked with SWAT. The results of the land use and land cover change analysis identified those farmlands agricultural land use class has expanded. Performance of the model for both calibration and validation watershed were found to be reasonably good for calibration and validation respectively. Various land use mitigation measures were further evaluated based on economic analysis as adaptation options to mitigate the land use land cover change impacts and appropriate soil conservation measures based on suitable afforestation techniques can prove influential in mitigating the risk of soil erosion in this Finchaa watershed. Keywords: Finchaa watershed, Mitigation measures, Sediment yield, SWAT Model 1. INTRODUCTION Land use change is the main causes for soil degradation and could significantly change the sediment yield availability. Land cover change is a primary concern in watershed management as it may also lead to increased flooding, soil degradation and decreased recharge of aquifers. The land use and land cover change occurrence is increasingly rapid, and that can have adverse impacts and implications at local, regional, and global environments [1]. Deforestation which has converse effects to afforestation, significantly affects the characteristics of stream flow [2]. Forests are thought to make rain, augment low flows, reduce floods, improve soil erosion, reduce amount of sediment in the reservoir and sterilize water. Therefore, such changes of land use and land cover may have impacts on the sediment yield to reservoirs during the wet and dry months. The major sources of sediments may be from other human activities such as road construction, poorly constructed and maintained terraces, and runoff from cultivated land or bank erosion [3]. The overland flow of watershed also affects the land use land cover, it also depends upon the rainfall runoff charecteristics like intensity, slop of watershed and duration of rainfall [23, 24]. Soil erosion is largely determined by the absence of protective land cover, whereas sediment export to rivers is determined by on site sediment production and connectivity of sediment sources and rivers [4]. All reservoirs formed by dams on natural water courses are subject to some degree of sediment inflow and deposition. The reservoir sedimentation is a complex process that varies with the watershed amount of sediment production, rate of sediment transportation and mode of deposition in watershed. Sediment is fragmental material, primarily formed by the physical and chemical breakdown of rocks from the earth’s crust. Sediment yield refers to the amount of sediment exported by a basin over a period of time and also it is the amount of eroded sediment discharged by a stream at any given point; it is the total amount of fluvial sediment exported by the watershed tributary to a measurement point and is the parameter of primary concern in reservoir studies. Sediment export is also a function of land use, since the sediment transport capacity is different for different types of land cover. Sediment yield is dependent on factors of soil erosion (mainly rainfall, soil condition, land use, topography) and the capacity of transportation. Sediment is deposited between the source and the stream cross section whenever the transport capacity of runoff water is insufficient to sustain transport. Reservoir sedimentation is a phenomenon that also has positive impacts to water usage systems particularly to the downstream river. The Reservoir sediment deposition is a indication of watershed erosion and deposition in the watershed processes which can be controlled by different processes such as terrain form, soil type, surface cover, drainage networks and rainfall- related environmental attributes [5]. In order to increase the life expectancy of the reservoir and to best achieve the purpose for which the reservoir has been constructed, reducing sediment inflow and removing sediment from the reservoir are substantial activities. In Ethiopia accelerated sedimentation in reservoirs providing hydroelectric power and irrigation water has resulted in loss of these intended services.Therefore, the aim of this study was to evaluate the effects of sedimentation and to develop the adaptation options to mitigate the adverse impacts of sediment on the reservoir. International Journal of Engineering Research & Technology (IJERT) ISSN: 2278-0181 http://www.ijert.org IJERTV6IS080106 (This work is licensed under a Creative Commons Attribution 4.0 International License.) Published by : www.ijert.org Vol. 6 Issue 08, August - 2017 220