Abstract
In the watershed, sediment yield spatially and temporarily variable due to the factors for instance land use land cover, type of soil, rainfall distribution, topography and management practices. The main objective of this study was to evaluate spatial and temporal variability of sediment yield on Bilate watershed using Soil and Water Assessment Tool (SWAT) model. Simulation carried out using meteorological and spatial data by dividing watershed in to 23 sub basins with 174 Hydrologic Response Units (HRUs). Model calibration period (2001-2010) and validation period (2011-2015) performed for monthly flow and sediment data using Sequential Uncertainty Fitting (SUFI-2) within SWAT Calibration of Uncertainty Program (SWAT-CUP). Model performance efficiency checked by coefficient of determination (R2), Nash-Sutcliffe model efficiency (ENS), and observation Standard Deviation Ratio (RSR) and percent bias (PBIAS) indicating good performance of model evaluation. From 23 sub basins, 11 were categorized from moderate to very high (10-26 ton/ha/year) sediment yielding sub basins and selected for sediment management scenarios. Scenarios result showed that average annual sediment yield reduction at entire watershed level after application of grassed waterway, filter strips, terracing and contouring were 54.45%, 30.13%, 63.26% and 59.56% respectively. Also, at treated sub basins level 68.04%, 38.41%, 80.58% and 77.42% of sediment reduction revealed after application of grassed waterway, filter strips, terracing and contouring respectively. It concluded that sediment yield reduction applying terracing was more effective than other conservation measures for affected sub basins.
Highlights
Poor land use practices, inappropriate management systems and deforestation have play a major role causing soil erosion; land degradation, desertification and sedimentation problems in the watershed [1]
Sediment spatial variability analysis used for identification of sediment prone areas in the catchment and sediment yield reduction is possible by providing soil conservation measures [5]
Average annual rainfall ranges from 1280-1339mm, 1061-1616mm and 769-956mm at upper, middle and lower part of the Bilate watershed respectively [11]
Summary
Inappropriate management systems and deforestation have play a major role causing soil erosion; land degradation, desertification and sedimentation problems in the watershed [1]. Sediment yield has strong correlation with soil type, land use/cover and slope of the watershed [2]. Effects of soil erosion in watershed especially on cultivated land are reduction of cultivable soil depth, loss of soil fertility and decrease of productivity, which may lead potentially widespread food shortages [3]. In its broader sense, considered an attempt to reduce nutrient damages, surface-run-off and sediment yield from watershed and to safeguard sustainable agricultural production [4]. Inclusive understanding of hydrological processes in watershed considered as a precondition for effective land and watershed management. Spatial variaility of sediment yield evaluation carried out with semi-distributed models for instance SWAT and pixel-based model such as WATEM/SEDEM [8, 9]
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