Spatial Distribution Of Sediment Yield Research Articles

Impacts of sustainable management on the spatial distributions of erosion susceptibility and probable sediment yield in a mixed-forested watershed

Forest management practices play multifaceted roles in enhancing the geophysical properties that affect raindrop erosion in the watershed, and consequently, sediment deposition in the reservoir. The current work attempts to integrate empirical and physically-based modeling approaches to quantify the impacts of forest conservation on erosion risk and potential sediment accumulation in the mixed-forested Ogouchi Dam watershed in Japan. The reliability of the empirical model for estimating the total erodibility coefficient (TEr), as a function of various forest properties, was evaluated by applying the mathematical expression to multiple forest conditions and comparing the values to field-measured soil erosion rates. The spatial distribution of the empirically derived values showed that about 25.8% of the Government-managed forests and 45.1% of the private forests have higher risks of raindrop splash erosion compared to natural forests. The TEr value in each small Government-divided forest land (less than 5 ha) was then corresponded to the MUSLE management practice factor (MUSLE P) input in each hydrologic response unit (HRU) in the Soil and Water Assessment Tool (SWAT) model to create a sediment yield distribution map and to predict the amounts of sediment accumulation for different management scenarios. The spatial distribution of sediment yield for the base condition showed that 20.9% of the Government-managed forests and 61.6% of the private forests have higher probable amounts of sediment yield relative to the value simulated in the natural forest. A maximum cumulative sediment reduction of about 14.4% is likely attainable upon the complete control of the Government in the entire planted forest area. Overall, this study effectively utilized the field survey datasets to develop a robust empirical model for quantifying erosion risk and was able to couple the results to a GIS-based model that predicts the amounts of sediment yield under varying environmental conditions.

Prioritization of Susceptible Watershed to Sediment Yield and Evaluation of Best Management Practice: A Case Study of Awata River, Southern Ethiopia

Soil erosion is currently a global problem that causes land degradation and long-lasting challenges in Ethiopia. Sediment yield is influenced by the watershed characteristics such as land cover, soil class, and slope, which are considered the drivers of soil erosion in the basin. The middle Awata watershed is highly susceptible to soil erosion due to its topographical features. This study is therefore aimed at estimating sediment yield, examining its spatial distribution, and evaluating the selected Best Management Practices (BMPs) to reduce soil erosion-prone areas at downstream. The model simulation was done by dividing the total watershed area of 1912 km2 into 37 subbasins and 294 hydrologic response units (HRUs) for 31 years (1988–2018). The model’s uncertainty evaluation was carried out on monthly basis using the Sequential Uncertainty Fitting (SUFI-2) algorithm. The performance of the model was evaluated by statistical parameters that gave R2 = 0.76, NSE = 0.75, RSR = 0.51, and PBIAS = 5.6% for calibration and R2 = 0.75, NSE = 0.74, RSR = 0.51, and PBIAS = 2.7% for validation of streamflow. Meanwhile, sediment yield in the watershed was also simulated with R2 = 0.69, NES = 0.66, RSR = 0.58, and PBIAS = 3.7% for calibration and R2 = 0.67, NES = 0.65, RSR = 0.61, and PBIAS = 5.6% for validation of sediment distribution. The simulated annual average sediment yield was 34.543 × 103 ton/year at the outlet of the middle Awata watershed. The developed spatial distribution of sediment yield identified the first twelve upstream subwatersheds as being soil erosion-prone areas. Following an evaluation of the four selected BMPs, it was determined that parallel terracing is the most recommended method for soil erosion reduction option in all critical subbasins found in the watershed.

Developing a DEM and Elucidating through SWAT to Conserve Soil in Kulfo Watershed of Rift Valley Basin, Ethiopia

Due to uninterrupted erosion and transportation, huge volume of sediments carried away by streams and rivers are finally deposited on the meanders, lakes, and reservoirs when the velocity of the surface water flow decreases. Kulfo River in the southern part of Ethiopia faces a challenge due to massive deposit of sediments. Hydrometeorological and spatial data of Kulfo watershed from the observed stream flow data series near Kulfo bridge and four meteorological station data were used to assess the depositional environment of Kulfo watershed. The data length covers the period from 2000 to 2019. Geomorphic parameters of the watershed were developed by using a 30m × 30m digital elevation model (DEM). The spatial distribution of sediment yield of the study area was estimated using SWAT, the soil and water assessment tool. Scenarios were developed to assess the effectiveness of watershed management interventions provided at the watershed and critical subwatershed level. The model genuinely replicated the observed discharge and sediment with an overall performance of 0.75 as measured by NSE. Twenty-one subbasins were created, and the observed average sediment yield was calculated as 11.9 ton/ha/y. The observed average sediment yield reduction at the hotspot subwatershed level postapplication of contouring, filter strip, terracing, and strip cropping were 40.79%, 57.94%, 66.02%, and 62.93%, respectively. By intricately analyzing, it can be referred that terracing is the best conservation measure to be incorporated into the affected subbasins.

The Hypsometric Integral Based on Digital Elevation Model for the Area West of Lvliang Mountains in Loess Plateau, Shanxi, China

A hypsometric integral (HI) is a topographical index with important geomorphological meaning. It can both describe the development state of the watershed and reflect the strength of activity in the geological structure. Based on this index, the integral curve method was used to analyze the HI characteristics of watersheds in the region west of the Lvliang Mountains on the Loess Plateau of Shanxi Province, China, in combination with 30-m resolution Shuttle Radar Topography Mission data. In order to accurately characterize erosion development within the watershed, the HI characteristics of each topographic feature object in the watershed were comprehensively analyzed. The results of HI scale effects show that HI was not strongly dependent on the spatial resolution of Digital Elevation Model (DEM) data, but had some scale dependence on the stable area of the watershed. The spatial distribution of the HI shows that the HI values of the watersheds in the southern loess residual tableland were the largest, and the degree of erosion was the weakest; the HI values of the watersheds in the north-central part of the loess hilly-gully region were relatively small, and the degree of erosion was stronger. This result is consistent with the results of the spatial distribution of sediment yield in literatures. The reasons for the spatial distribution of the HI were analyzed in terms of geological formations and climatic environments. The results show that for the study area, tectonic activity, formation lithology, rainfall, and agrotype were not the main factors affecting the HI values. The structure of the paleotopography and erosion cutting due to the uplift of the Lvliang Mountains and later water erosion controlled the spatial distribution state of HI. Thus, for the study area, the HI value cannot reflect the strength of tectonic activity. The combination of topographic feature object method and the HI index further quantified the erosion development state of the watershed.

The Use of Artificial Neural Network and Advanced Statistics to Model Sediment Yield on a Large Scale: Example of Morocco

Morocco ranks among countries with the greatest achievements in the field of dams in Africa but is affected by the sedimentation phenomenon due to soil erosion in upstreams. The assessment of Sediment Yield (SY) and Suspended Sediment Yield (SSY) remains a challenging global issue, especially in Morocco, characterized by a great diversity of morphological, climatic, and vegetation cover. The main objective of this paper was to perform advanced statistics and artificial neural networks (ANN) in order to understand the spatial distribution of sediment yield and the factors most controlling it, including factors of the RUSLE model (Revised Universal Soil Loss Equation). In order to produce a model able to assess SY, we collected and analyzed extensive data of most variables that can be affecting SY using 42 catchments of the biggest and important dams of Morocco. Statistical analysis of the studied watersheds shows that SY is mainly related to the watershed area and the length of the drainage network. On the other hand, the SSY is higher in watersheds where gully erosion is abundant and lower in areas with no soil horizon. The SSY is mainly related to the altitude, aridity index, sand fraction, and drainage network length. In front of the complexity of preserving this phenomenon, the ANN was applied and gave very good satisfactory results in predicting the SSY (NSE=0.93, R2=0.93).

Multi-site calibration of SWAT for the spatial distribution of sediment yield, Middle Awash Dam watershed, Ethiopia

Multi-site calibration of sediment yield has a significant effect on evaluating the spatial distribution of sediment yield of watershed and reservoirs sedimentation. Multi-site calibration was conducted at three gauging stations of the Proposed Middle Awash Dam watershed. The sequential Uncertainty fitting (SUFI-2) calibration uncertainty program (SWAT-CUP) has been used to calibrate and validate flow and sediment parameters using monthly flow and sediment rate observed data. P-factor and R-factor measured model calibration and uncertainty where the P-factor recorded 0.56-0.86/0.54-0.77 and R-factor 0.52-0.93/0.68-0.84 values respectively during the calibration and validation period for the three gauging stations. Model result showed the performance model was excellent during the calibration period with the coefficient of determination R2=0.78-0.82, Nash-Sutcliffe Efficiency ENS=0.77-0.79, Observation Standard Deviation Ratio RSR=0.44-0.48 and percent bias PBIAS=-13.3 to +14.3. Following the calibration process, the model estimated mean annual spatial distribution of sediment yield 7.23 ton/ha/yr at the outlet. Sediment yields spatial distribution showed that among the 19 sub-watersheds ranked based on their sediment yield contributions, eight sub-watersheds have a slope greater than 5%, which is relatively steeper and contributed average annual sediment yields of 16 ton/ha/yr. The temporal variability hydrograph showed 70.8 % of yearly sediment yield in the study area during the rainy season. The study results informed to development of watershed management strategies to minimize the sediment problems in the entire watershed. Keywords : Hydrological modelling, Middle Awash Dam, sediment yield, spatial distribution, SWAT model

Sediment Yield Estimation and Effect of Management Options on Sediment Yield of Kesem Dam Watershed, Awash Basin, Ethiopia

Assessing sediment yield and identifying hotspot areas play a significant role for watershed management. Watershed models can be used for such processes. Therefore, this study aims to develop watershed model and estimate sediment yield, including mapping the spatial distribution of sediment yield for the Kesem Dam watershed (Ethiopia), which had experienced intensive agricultural activities and high sediment loadings problems. The study also aims to evaluate the effect of implementing management options on sediment reduction especially in high sediment yielding areas. The most widely used Soil and Water Assessment Tool (SWAT) model was used for sediment yield modeling and management options implementation. We developed the SWAT model of the Kesem Dam watershed for the period 1994-2010 based on available geo-spatial and hydro-meteorological data of the watershed. Using observed streamflow and sediment yield data of the watershed, the model was calibrated for the period 2000-2006 and validated for the period 2007-2010. Parameters used for the model calibration were identified based on sensitivity analysis. The performance of the model was evaluated by coefficient of determinations (R2), Nash-Sutcliffe efficiency (NSE), and percent bias (PBIAS). SWAT adequately reproduced the observed daily flows and sediment loads temporal evolution with R2 and NSE ≥ 0.7 and PBIAS < 15% both for the calibration and validation periods. The mean annual sediment yield of the watershed was 11.43 t/ha/yr. The model also identified areas with the highest sediment yields of 24 to 29 ton/ha/yr, indicating the suitability of the model to implement and assess the impacts of management options. However, treating those areas with different sediment management options reduced the annual average sediment yield by 80% under vegetative filter strips. These findings can be used as inputs for reducing sediment loadings to the Kesem dam watershed and implementing sustainable watershed management of the watershed and other similar areas.

A new simple approach to assess sediment yield at a large scale with high landscape diversity: an example of Morocco

Sedimentation of dams and soil erosion remain a worldwide issue, this is especially true in countries characterized by great environmental diversity where their assessment remains a serious difficult issue. Morocco ranks among countries with the greatest achievements in the dams field in Africa, characterized by a great climate, vegetation cover and morphological diversity. The objective of this study was to identify the spatial distribution of Sediment Yield (SY) and Area-Specific Sediment Yield (SSY) on the country scale and to present a new simple approach by exploiting the statistical tool to assess their controlling factors. We collected and analyzed environmental data of 42 catchments of the biggest and most important dams of the country of Morocco. The adopted statistical methodology reveals that Moroccan catchments can be subdivided into 5 categories (depending on climate, morphology and vegetation cover conditions) in which SY is most related to the catchment area and drainage network length, while SSY is mostly related to the soil organic carbon stock, rainfall and clay fraction. Our approach provides important new insights regarding modelling catchment scale sediments dynamic to asses SY and SSY in different regions around the world, especially in large scale and where there is a great environmental diversity.

Assessing sediment yield in Kalaya gauged watershed (Northern Morocco) using GIS and SWAT model

An efficient design for erosion-control structures of any watershed in the world is entrusted with the delicate forecasting of sediment yields. These outlook yields are usually inferred by extrapolations from past observations. Because runoff, as the transporting vehicle, is more closely correlated with sediment yields than any other variable. So, calibration as well as validation of process-based hydrological models are two major processes while estimating the sediment yield in watershed. The actual survey is fulfilled with the aim of developing a trustworthy hydrologic model simulating stream flow discharge and sediment concentration with least uncertainty among the parameters picked out for calibration so as to verify the effect of the scenarios on the spatial distribution of sediment yield (sediments transported from sub-basins to the main channel during the step of time). Soil and Water Assessment Tool (SWAT, version 2012) model integrated with Geographic Information System (GIS, version 10.1) was used to simulate the stream flow and sediment concentration of Kalaya catchment situated in north of Morocco for the period from 1971 to 1993. Model calibration and validation were performed for monthly time periods using Sequential Uncertainty Fitting 2 (SUFI-2, version 2) within SWAT-CUP using 16 parameters. Our calibration outputs for monthly simulation for the period from 1976 to 1984 showed a good model performance for flow rates with NSE and PBIAS values of 0.76 and −11.80, respectively; also a good model performance for sediment concentration with NSE and PBIAS values of 0.69 and 7.12, respectively. Nonetheless, during validation period (1985–1993) for monthly time step, the NSE and PBIAS values were 0.67 and −14.44, respectively for flow rates and these statistical values were 0.70 and 15.51, respectively for sediment concentration; which also means a good model performance for both. Following calibration, the inclusive effect of each parameter used was ranked using global sensitivity function in SWAT-CUP. From our analysis, the effective hydraulic conductivity in main channel alluvium (CH_K2), USLE support practice factor (USLE_P) and manning's "n" value for the main channel (CH_N2) were found to be the most sensitive parameters during different iterations with different number of simulation but with the same inputs. The least sensitive parameter were found to be different in either cases unlike the most sensitive parameters. As a result, the global evaluated soil erosion rate in the study area varied from 20 to 120t/ha/yr. It was summarized that the entire knowledge of the hydrologic processes happens within the watershed and the consciousness about acceptable meaningful range of the parameters is crucial while developing reliable hydrologic model.

RUSLE and SDR Model Based Sediment Yield Assessment in a GIS and Remote Sensing Environment; A Case Study of Koga Watershed, Upper Blue Nile Basin, Ethiopia

Soil erosion and the subsequent sedimentation are the major watershed problems in Ethiopia. Removal of top fertile soil, siltation of Koga irrigation reservoir, clogging of irrigation canal by sediment and reduction of irrigated land are the major threat of Koga watershed. Hence, this study was attempted to assess and map the spatial distribution of sediment yield of Koga watershed in a GIS and remote sensing environment. Sediment yield is dependent on factors of soil erosion such as rainfall erosivity, soil erodibilty, land use land cover (C and P) and topography (LS) and sediment delivery ratio of the drainage basin to the total amount of sediment yield by sheet and channel erosion. RUSLE framed with GIS and Remote sensing technique was therefore employed to assess the amount of soil loss existed in KW. Main stream channel slope based sediment delivery ratio analysis was also carried out. Soil map (1:250,000), Aster DEM (30 × 30 m), Thematic Mapper (TM) image (30 m × 30 m) of the year 2013, thirteen years (2000-2013) rainfall records from four rain gauge stations and topographic map (1:50,000) were the major data used. The estimated mean annual SY delivered to the out let of KW was found to be 25 t ha-1year-1. Most critical sediment source areas are situated in the steepest upper part of the watershed due to very high computed soil loss and sediment delivery ratio in this part. It could be therefore difficult to attain the intended goal of Koga irrigation reservoir positioned at lower part of the watershed. Sustainable land management practices have to be conducted in the upper part of the watershed by taking each stream order as a management unit to increase the storage capacity, and/or lessen the transportation capacity of the watershed. Proper drainage construction and stream bank stabilization via vegetative cover have to widely implement to safely dispose the eroded sediment.

Downslope runoff and erosion response of typical engineered landform to variable inflow rate patterns from upslope

Downslope wash-scour erosion driven by upslope inflow from compacted platform plays an important role in the acceleration of water and soil loss from engineered landforms. To explore the quantitative effects of variable upslope runoff on downslope runoff and erosion, a typical abandoned spoil deposit derived from the construction of Shenfu Expressway was selected to conduct a set of field runoff scouring experiments on steep slope (72.7 %). Four types of upslope inflow rate patterns including constant inflow rate pattern and earlier, intermediately, as well as later peak inflow rate patterns were designed dependent on different rainfall patterns and the timing for peak inflow rate (total inflow amount was kept constant). Thus, the downslope runoff and erosion response of the selected abandoned spoil deposit under variable upslope inflow conditions were investigated, and the results reveal that: (i) Maximum peak runoff intensity and the timing for the maxima were greatly impacted by upslope inflow rate patterns; however, little impact was exerted on total surface runoff; total runoff from the inflow events with earlier, later, and intermediately peak inflow rate increased by 20.6, 11.7, and 8.5 % in comparison with that from the uniform inflow event. (ii) Runoff events induced by variable inflow rate patterns altered the sediment-yielding process as well as the spatial distribution of sediment yield in the downslope direction, and thus produced more soil loss. Total soil loss from inflow events with earlier, later, and intermediately peak inflow rate increased by 79.7, 78.2, and 14.2 %, respectively, in comparison with that from the uniform inflow event. Statistically, sediment yield from designated control section decreased as a negative exponential function of slope length downslope. (iii) Among the selected runoff erosivity factors, runoff depth, unit runoff erosivity, and stream power are effective indicators for predicting the area-specific sediment yield from individual upslope inflow events, regardless of inflow rate pattern. (iv) Area-specific sediment yield performs remarkable power function correlation with unit runoff erosivity; the unit runoff erosivity can represent the variation in runoff erosion dynamics from individual inflow events, regardless of upslope inflow rate patterns. The results may provide evidence for soil erosion degree assessment, erosion model construction in drastically disturbed areas, as well as the prevention of newly arising water and soil loss from engineered landforms.

Modelling spatial distribution of surface runoff and sediment yield in a Chinese river basin without continuous sediment monitoring

In numerous river basins, continuous data are available for streamflow, but not for sediment transport, soil erosion and sediment yield. Our study shows an approach to assess the spatial distribution of surface runoff and sediment yield in a data-scarce Chinese river basin. Specific objectives of this study were (a) to use the process-based, ecohydrological model SWAT and to parameterize it by fixing as many parameters as possible in advance using field observations, measured data and literature; (b) to calculate streamflow and suspended sediment at the basin outlet as well as surface runoff and sediment yield in each sub-basin using SWAT; and (c) to validate and check the credibility of our simulated results using published literature on land use and associated land management. Our modelling results show a spatial distribution of sediment yield between all 50 sub-basins (0 to 7 t ha-1 year-1) with highest amounts predicted for cabbage cultivation (37.5 t ha-1 year-1) and only low values for forest (0.2 t ha-1 year-1). Previous studies used for validation purposes approve our findings.Editor Z.W. Kundzewicz; Guest editor V. Krysanova

Estimating Sediment Yield from Upland and Channel Erosion at A Watershed Scale Using SWAT

Sediment discharge is one of the main water quality concerns in integrated watershed management. A proper identification of sediment sources is therefore important to the success of watershed conservation programs. Since water quality monitoring data collected at the mouth of the watershed alone are typically not sufficient for identifying key sediment sources distributed in the watershed, hydrologic models can be applied to prioritize Best Management Practices (BMPs) implementation for sediment control in a watershed. In this paper, the Soil and Water Assessment Tool (SWAT) is applied to the South Tobacco Creek (STC) watershed in Canada to identify sediment sources and to estimate the spatial distribution of sediment yield from both upland and channel erosion processes. The model is calibrated and validated against observed flow and sediment data measured at fourteen edge-of-field and mainstream stations based on 20 years of land management data. Modeling results show that approximately 60 and 40 % of the sediment discharge at the mouth of the watershed are originated from channel erosion and upland erosion respectively. A high spatial and temporal variation of sediment yield is found in the watershed depending on climate, topography, land use, and soil conditions. These findings will be helpful for understanding the runoff and erosion processes and evaluating the cost-effectiveness of soil and water conservation programs at a watershed scale.

Dynamic processes of soil erosion by runoff on engineered landforms derived from expressway construction: A case study of typical steep spoil heap

Soil erosion on newly engineered landforms severely threatens the ecological security of construction sites and their surrounding areas. A field scouring-erosion experiment was conducted on a typical spoil heap along the Shenmu–Fugu Expressway in China to investigate the processes of soil erosion by simulated runoff. A 2.5×12m2 runoff plot with 72.7% gradient was established on the spoil heap. Clean water was applied at the top of the plot with five different inflow rates of 0.167×10−3, 0.25×10−3, 0.33×10−3, 0.417×10−3 and 0.5×10−3m3/s to simulate surface runoff processes. The variation of sediment concentration was greatly influenced by gravitational erosion which occurred at the critical inflow rates ranging from approximately 0.33×10−3 to 0.417×10−3m3/s. The process of sediment yield on the spoil heap, in terms of sediment transport rate, was characterized by three stages: abruption, fluctuation and stabilization. The spatial distribution of sediment yield in different slope segments at different inflow rates showed two trends: steady decreasing and drastically fluctuated decreasing. The flow over the spoil heap belonged to supercritical flow and the critical inflow rate controlling the transformation from transitional flow to turbulent flow for rill flow was between 0.33×10−3 and 0.417×10−3m3/s. Statistically, power, exponential and logarithmic-linear equations can be used to describe the interrelations of main hydraulic parameters including flow velocity, Reynolds Number, Froude Number and Darcy–Weisbach roughness coefficient. The three forms of equations were also appropriate for describing sediment concentration in relation to the hydraulic parameters mentioned. Slope length was more significant than inflow rate in affecting hydraulic parameters, which showed an exponential relation with the increase in distance from the top of the plot for all the parameters except Reynolds Number. Stream power was the best hydrodynamic parameter to simulate the changing trend of soil detachment rate. As for different control equations, mechanic parameters and energy parameters had some relative advantages in depicting the dynamic processes of sheet erosion and rill erosion, respectively.

Physically-based distributed soil erosion and sediment yield model (DREAM) for simulating individual storm events

A relatively simple process-oriented, physically-based distributed (PBD) hydrological model, the distributed runoff and erosion assessment model (DREAM), is described, and a validation study conducted in the semi-forested watershed of Pathri Rao, in the Garhwal Himalayas, India, is reported. DREAM takes account of watershed heterogeneity as reflected by land use, soil type, topography and rainfall, measured in the field or estimated through remote sensing, and generates estimates of runoff and sediment yield in spatial and temporal domains. The model is based on simultaneous solution of flow dynamics, based on kinematic wave theory, followed by solution of soil erosion dynamics. As the storm rainfall proceeds, the process of overland flow generation is dependent on the interception storage and infiltration rates. The components of the soil erosion model have been modified to provide better prediction of sediment flow rates and sediment yields. The validation study conducted to test the performance of the model in simulating soil erosion and sediment yield during different storm events monitored in the study watershed showed that the model outputs are satisfactory. Details of a sensitivity analysis, model calibration and the statistical evaluation of the results obtained are also presented and discussed. It is noteworthy that the distributed nature of the model combined with the use of geographical information system (GIS) techniques permits the computation and representation of the spatial distribution of sediment yield for simulated storm events, and a map of the spatial distribution of sediment yield for a simulated storm event is presented to highlight this capability. Citation Ramsankaran, R., Kothyari, U.C., Ghosh, S.K., Malcherek, A., and Murugesan, K., 2013. Physically-based distributed soil erosion and sediment yield model (DREAM) for simulating individual storm events. Hydrological Sciences Journal, 58 (4), 872–891.

토사유출량의 공간분포 산정결과 평가를 위한 RUSLE와 LISEM의 비교

Various models have been developed for the estimation of spatial distribution of sediment yield. However, they often generate distinct results because of differences in their development purposes and calculation processes. Therefore, it is challenging to verify the simulation result without ground measurements of spatially varying sediment fluxes. Here, we postulate that applying multiple models to a same watershed and checking whether they provide similar spatial distributions can be an indirect method of evaluating the performance of the models. To test this idea, we apply two models of LISEM and GIS-based RUSLE for a small watershed in Gyeonggi-do, South Korea, where actual sediment yield was measured at the outlet. Two models result in similar spatial patterns in the distribution of sediments yield. LISEM results show more evenly distributed sediment yield. This difference is partly due to the difference in model structures and due to the ranges of parameters chosen between the two models. Compared to RUSLE, there are limited references for model parameter values of LISEM in Korean practices. Helped by physically-based model structure, LISEM is expected to simulate sediment yield in a more reasonable manner, compared to RUSLE, once the appropriate ranges of model parameters are suggested in the future.

SWAT based runoff and sediment yield modelling: a case study of the Gumera watershed in the Blue Nile basin

Land degradation caused by soil erosion (sheet and rill erosion) and soil fertility decline is a serious threat in the Ethiopian highlands, especially in the Gumara watershed. In this study the SWAT (Soil and Water Assessment Tool) model was applied to the Gumara watershed to predict sediment yield and runoff, to establish the spatial distribution of sediment yield and to test the potential of watershed management measures to reduce sediment loadings from hotspot areas. The model was calibrated using five years of flow and sediment records and validated using data for the next three years. Out of 30 SWAT sub-basins, 18 sub-watersheds (72%) were identified as erosion prone areas contributing to a mean annual sediment load ranging from 11 to 22 t ha−1 yr−1. The model was used to evaluate the potential of vegetation filter strips of various widths to reduce sediment production from critical micro watersheds. The installation of vegetation filter strips on vulnerable land was shown to result in a 58 to 74% reduction in sediment yield for strip widths of 5m and 10m respectively.