Average Annual Sediment Yield Research Articles

Modeling the sediment yield and estimating the best management practices in the Seybouse basin, Northeastern Algeria.

Identifying vulnerable areas to erosion within the watershed and implementing best management practices (BMPs) are crucial steps in mitigating watershed degradation by minimizing sediment yields. The present study evaluates and identifies the BMPs in the Seybouse basin, northeastern Algeria, using the Soil and Water Assessment Tool (SWAT) model. After successful calibration and validation, the model demonstrated a satisfactory ability to simulate monthly discharge and sediment. Then, the calibrated model was employed to evaluate the efficacy of diverse management practices in sediment control. In the SWAT, three soil and conservation practices, as well as vegetated filter strips (VFSs), grade stabilization structures (GSSs), and terracing were evaluated. The average annual sediment yield in the Seybouse watershed is determined to be 14.43 t/ha year, constituting 71% of the total soil loss. VFS demonstrated a sediment reduction of 37.30%, GSS 20.40%, and terracing 42.30%. Among these strategies, terracing results in the greatest reduction, followed by VFS. The results of this study area can be useful for informed decision-making regarding optimal watershed management strategies.

Sediment yield assessment and suggesting mitigation measures—A case study of Deme watershed, Omo‐Gibe Basin, Ethiopia

AbstractSoil erosion is a big challenge of natural resource development in Ethiopia due to the high expansion of agricultural activity and poor land‐use management. Deme watershed is one of the watersheds found in the Omo‐Gibe Basin, Ethiopia with soil erosion problems. It covers 1284.4 km2. The Soil and Water Assessment Tool (SWAT) integrated with ArcGIS was used to assess the sediment yield of the Deme watershed and develop mitigation measures for soil erosion. The purpose of this study was to assess the sediment yield and provide mitigation measures for the Deme watershed. Ground Control Point (GCP) data collection and field observation were conducted for land‐use land cover classification. The performance of the model was evaluated by coefficient of determination (R2), Nash Sutcliffe simulation efficiency (NSE), and percent bias (PBIAS). SWAT adequately reproduced the observed daily flows and sediment loads temporal evolution with R2 and NSE ≥ .7 and PBIAS < 15% both for the calibration and validation periods. The sediment‐rating curve measured an annual average suspended sediment yield of 12.79 tons per hectare per year, whereas the SWAT model predicted an annual average sediment yield of 14.35 tons per hectare per year. The spatial distribution map of sediment showed that 9 out of 17 sub‐watersheds generate a higher amount of sediment yield (15.1–45 tons/h/year) and are found to be erosion‐prone areas. For proper management of watershed terracing, filter strips, contouring, and reforestation scenarios were developed. Each scenario reduces the sediment yield by 74.29%, 58.34%, 47.78%, and 69.76%, respectively. The proper combination of these scenarios resulted in a 90% reduction in sediment yield. Policymakers and land‐use planners of different organization will benefit from this research by implementing soil and water conservation mechanisms and practices that strengthen and mitigate the natural systems of Deme watershed.

Predicting runoff and sediment yields using soil and water assessment tool (SWAT) model in the Jemma Subbasin of Upper Blue Nile, Central Ethiopia

The Jemma Subbasin (JS) has a major soil erosion problem emanating from deforestation, overgrazing, and agricultural expansion, including farming of unproductive fringed lands and steep slope terrains. This study was conducted to assess runoff and estimate the subsequent sediment yields in the JS using the Soil and Water Assessment Tool (SWAT) model. The overall efficiency of the SWAT model to accurately estimate the sediment yields in the JS was evaluated by the values of its calibration (R2 = 0.66) and validation (R2 = 0.63), respectively. The findings of the SWAT model revealed that barren land was not only the most susceptible land use type to soil erosion, but also had the highest sediment loads followed by agricultural and grazing lands. In particular, the highest soil erosion coupled with significant sediment yields is attributed to the crop-growing period particularly in the months of July and August in which the cultivated lands were extremely vulnerable to soil erosion resulting from heavy rainfall. Consequently, sediment yields were all significantly greater in the agricultural fields of the lower, middle, and upper parts of the subbasin. This is because those agricultural lands were mainly composed of undulated and moderately steep slope terrains so that they had the highest soil erosion values. However, due to the dense vegetation cover and the associated root density, forestlands were the least erosion vulnerable land use type which in turn resulted in minimal soil loss. Furthermore, the SWAT model showed that the maximum upland sediment yield was estimated to be 3,685.14 tons/ha whereas the average upland annual sediment yield was predicted to be 78.1 tons/ha; however, the sediment yield can be doubled due to climate projection scenario. As a result of the effective implementation of cover (c) and conservation practice (p), the SWAT model predicted that the sediment yields can be reduced by 44.28 % and 35.92 % for RCP8.5 and RCP4.5, respectively. Effective designing and executing of proper soil and water management measures are crucial in the study subbasin so as to minimize the serious soil erosion challenges that can be accelerated by climate and land use land cover (LULC) changes for the long-term sustainability of the degraded landscape of the JS which is categorized by subsistence farming.

Evaluating the impact of land use and land cover changes on sediment yield dynamics in the upper Awash basin, Ethiopia the case of Koka reservoir

Land Use and Land Cover changes (LULC) are the driving forces to change the hydrological response of the watershed. In this study, the Quantum Geography Information System Interference Soil and Water Assessment Tool Plus (QSWAT-PLUS) model was applied to evaluate the effects of LULC on sediment load at the Upper Awash River Basin (UARB) which are causing sedimentation problems in Koka reservoir. The LULC data for 2005, 2010, and 2015 were obtained from historical satellite images using Earth Resources Observation and Science (ERDAS) 2014. The classification of LULC changes showed that the agricultural practice, and the settlement land both increased by 6.7 % and 6.3 %, respectively. In contrast, the forest area, woodland, shrubland, and water bodies decreased by 5.47 %,0.93 %,0.96 %, and 1.34 % from 2000 to 2015 respectively. The model evaluation results were satisfactory for the three LULC scenarios. The average annual surface runoff volume for the 2005 LULC data was 182.2 mm, which increased to 193.29 mm in 2010 and 205.3 mm in 2015. Similarly, the average annual sediment yield that would enter to the Koka reservoir under the 2005, 2010, and 2015 LULC scenarios were 26.03 t/ha/yr, 26.34 t/ha/yr, and 28.33 t/ha/yr respectively. In general, streamflow, surface runoff, and sediment output increased by 4.55 %, 12.68 %, and 8.84 %, respectively due to the rapid change of LULC from 2000 to 2015. Temporarily, the sediment load at the upstream side of the Koka Dam watershed was 60.8 % during the wet season. The southwest direction of the watershed was identified as the primary erosion-prone area. Based on the simulation results, the filter strip, contour, and terraces reduced the watershed sediment yield by up to 60 %, 65 %, and 80 %, respectively. Therefore, the selected best management practices are highly effective in reducing silt along the entire upstream side of the Koka Dam watershed.

A Predictive Model For Quantifying The Combined Effect Of Land Use Change And Climatic Variability On Sedimentation In Malaba Sub Catchment

Over the previous years, sedimentation in Malaba sub catchment has become a major problem, this research aimed at using SWAT as a predictive model to assess the impacts of historical and future climate change and land use changes on sedimentation in Malaba sub catchment. Two variables rainfall and temperature were considered under climate change. Four scenarios were modeled in SWAT during this study, the first scenario focused on historical sedimentation in the catchment, land use data of 2000 and weather data of 1990 to 2005 was used to simulate flow and sediment yield in the catchment. The second scenario focused on the current sediment yield in the catchment where land use data of 2020 and weather data of 2003 to 2020 was used to simulate the sediment yield and flow. Calibration and validation was done using SWAT CUP software. The calibrated and validated model was then used to further simulate two future scenarios. The two future scenarios used projected land use data and projected weather data. Land use data was projected using Clerk Labs Terr set software while weather data was projected using the Statistical Downscaling Model (SDSM). The third scenario considered projected land use data of 2035 and projected weather data of 2020 to 2035 to simulate flow and sediment yield of 2023 to 2035. The forth scenario considered projected land use data of 2050 and projected weather data of 2033 to 2050 to simulate catchment flow and sediment yield of 2036 to 2050. The results obtained from climate change analysis indicated un even changes, rainfall over the catchment is expected to increase, maximum temperature is expected to increase, minimum temperature is expected to reduce. Land use change results after comparison between the historical land use and projected land use indicated that from 2020 to 2050 cropland and built up area will increase while forests and water bodies will reduce. Average annual Sediment yield of 1993 to 2020 is expected to generally increase from 4975.4 tons/km2/year to an average annual sediment yield of 5525.6 tons/km2/year from 2023 to 2050. Therefore, mitigation measures should be adopted to ensure sustainable management of the catchment. Some of the recommendations made in this research are; Government through NEMA should put restrictions on cultivation close to the river banks, encourage planting trees within the catchment, bare lands within the catchment should be converted to other sustainable land uses. The study findings of this research shall be relevant for planning, design and management of reservoirs, dams, irrigation systems and sustainability of eco systems in the catchment.

Assessing hydrological and water quality responses to dynamic landuse change at watershed scale in Mississippi

The hydrology and water quality modeling in a watershed are affected by land use land cover (LULC) input. This study differs from numerous LULC change studies by introducing multi-year LULC input in a single simulation of Soil and Water Assessment Tool (SWAT) model. The proposed approach highlighted the outperformance of the model with dynamic LULC input (DM) over static LULC input (SM) based on the magnitude and direction of the hydrological responses. The difference between DM and SM outputs allowed for studying effects of historical LULC change. Additionally, agricultural management operation inputs enabled more realistic simulation of runoff, sediments, total nitrogen (TN), and total phosphorus (TP). The SM used static landuse data layers for 2009, and DM used landuse data layers for 2009, 2015, and 2018 to represent changes in LULC distribution over time. The expansion of agricultural land (0.9%) and forest cover (0.5%), as well as the reduction of grassland, water, and barren areas (1.4%), were the significant LULC changes from 2009 to 2018. Even though the expansion of forest cover was identified from 2009 to 2015, a declining trend was observed from 2015 to 2018. The agricultural land cover increased consistently from 2009 to 2018. The expansion of agricultural land increased average annual surface runoff, sediment yield, TN, and TP loads by 1.3%, 5.4%, 5.8%, and 5.9% respectively at watershed scale as determined by DM model simulation results. At sub-watershed scale, agricultural land expansion increased runoff, sediment, TN, and TP loads by up to 5%, 16%, 15%, and 15% respectively whereas, the expansion of forest cover resulted in reduction in same parameters by up to 5%, 15%, 23%, and 26% respectively. In general, the study determined that the integration of dynamic LULC and agricultural operations in SWAT allows a more accurate representation of agricultural watersheds for hydrological and water quality analysis.

Spatial-temporal evolution of sediment transport in the upper Yangtze River Basin considering the cumulative impacts of mega reservoirs

The intensive construction of large dams in the upper Yangtze River Basin (UYRB) has formed large-scale cascade reservoirs and obviously altered the flow regime and sediment transport of the basin. However, few studies have quantitatively described the cumulative impact of these reservoirs on sediment interception. In this study, a flow and sediment transport model that fully considers the operation processes of 24 mega reservoirs in the UYRB was established, and the spatial and temporal variations in sedimentation from 2011 to 2080 were elucidated, assuming repeated series of daily input flow discharge and sediment concentration during 2011–2020 and monthly water operation levels of 24 reservoirs during 2018–2021 as boundary conditions. The results showed an annual average sedimentation of more than 300 Mt in the UYRB during 2011–2060, which falls to 270 Mt in the period 2061–2080, and more than 80% of the sedimentation occurs in the flood season. Nearly 80% of the total sedimentation during 2010–2080 was observed in the mainstream reservoirs, especially the four mega reservoirs in the lower Jinsha River and the Three Gorges Reservoir (TGR), which accounted for 31.9% and 22.7% of the total sedimentation, respectively. The proportion of sedimentation in mainstream reservoirs will further increase with increasing operation periods. Most reservoirs in the UYRB will not reach sedimentation equilibrium by 2080, except for reservoirs in the Min River Basin. The ratio of siltation capacity to average annual sediment yield determines the percentage of residual siltation capacity of each reservoir. The operation of the cascade reservoirs in 2013–2020 had no more immediate impact on the middle and lower Yangtze River than that in 2003–2012, when the TGR started impoundment. However, the joint operation of these cascade reservoirs has changed the spatial distribution of sedimentation in the UYRB, and will lead to prolonged impacts on downstream channel erosion.

Comparative analysis of discharge and sediment flux from two contiguous glacierized basins of Central Himalaya, India

In the present study, suspended sediment load (SSL), sediment yield and erosion rates in Pindari Glacier basin (PGB) and Kafni Glacier basin (KGB) have been estimated using daily discharge and suspended sediment concentration (SSC) data for three ablation seasons (2017-2019). For this, one meteorological observatory and two gauging sites have been established at Dwali (confluence point), and water samples have been collected twice in a day for high flow period (July to September) and daily for lean period (May, June and October). An area-velocity method and stage-discharge relationship has been established to convert water level into discharge (m3 s-1). For estimating SSC (mg/l), collected water samples have been filtered, dried, analysed and confirmed with an automatic suspended solid indicator. Further, SSL, sediment yield and erosion rates have been computed using SSC data. The results reveal that mean annual discharge in PGB (35.06 m3s-1) has been found approximately 1.7 times higher than KGB (20.47 m3s-1). The average SSC and SSL in PGB have been observed about 396.07mg/l and 1928.34 tonnes, and in KGB, it is about 359.67mg/l and 1040.26 tonnes, respectively. The SSC and SSL have followed the pattern of discharge. A significant correlation of SSC and SSL has been found with discharge in both the glacierized basins (p < 0.01). Interestingly, average annual sediment yield in PGB (3196.53 t/km2/yr) and KGB (3087.23 t/km2/yr) have been found almost identical. Likewise, the erosion rates in PGB and KGB have been witnessed about 1.18 and 1.14mm/yr, respectively. Sediment yield and erosion rates in PGB and KGB have been found in correspondence with other basins of Central Himalaya. These findings will be beneficial for engineers and water resource managers in the management of water resources and hydropower projects in high-altitude areas and in the planning and designing of water structures (dams, reservoirs etc.) in downstream areas.

Sediment yield estimation and evaluating the best management practices in Nashe watershed, Blue Nile Basin, Ethiopia

Sediment yield estimation along with identification of soil erosion mechanisms is essential for developing sophisticated management approaches, assessing, and balancing different management scenarios and prioritizing better soil and water conservation planning and management. At the watershed scale, land management practices are commonly utilized to minimize sediment loads. The goal of this research was to estimate sediment yield and prioritize the spatial dispersion of sediment-producing hotspot areas in the Nashe catchment using the Soil and Water Assessment Tool (SWAT). Moreover, to reduce catchment sediment output, this study also aims to assess the effectiveness of certain management practices. For calibration and validation of the model, monthly stream flow and sediment data were utilized. The model performance indicators show good agreement between measured and simulated stream flow and sediment yields. The study examined four best management practice (BMP) scenarios for the catchment’s designated sub-watersheds: S0 (baseline scenario), S1 (filter strip), S2 (stone/soil bunds), S3 (contouring), and S4 (terracing). According to the SWAT model result, the watershed’s mean yearly sediment output was 25.96 t/ha. yr. under baseline circumstances. The model also revealed areas producing the maximum sediment quantities indicating the model’s effectiveness for implementing and evaluating the sensitivity of sediment yield to various management strategies. At the watershed scale, treating the watershed with various management scenarios S1, S2, S3, and S4 decreased average annual sediment yield by 34.88%, 57.98%, 39.55%, and 54.77%, respectively. The implementations of the soil/stone bund and terracing scenarios resulted in the maximum sediment yield reduction. The findings of this study will help policymakers to make better and well-informed decisions regarding suitable land use activities and best management strategies.

Erosion Risk Assessment for Prioritization of Conservation Measures in the Watershed of Genale Dawa-3 Hydropower Dam, Ethiopia

Sedimentation is a leading global problem that affects the environment and dams by reducing the live storage capacity of reservoirs and the life expectance of dams. Hence, prioritizing watersheds according to the risk of soil loss is crucial for extending the useful life of dams and reservoirs. The objectives of this study were to assess sediment flow in the Genale Dawa-3 reservoir, identify subbasins that are prone to soil erosion, and evaluate the impact of different management practices on minimizing sediment yields by using the Soil and Water Assessment Tool (SWAT) model. The SWAT model was calibrated and validated by observed streamflow and sediment data based on the SUFI-2 algorithm by SWAT-CUP, and its performance was assessed. The model simulated the average annual sediment yield; the input to the reservoir was 16.83 ton/ha/yr for the period of 1990–2015. From a total of 31 subbasins, 12 were categorized from high to very severe (11–60 ton/ha/yr) sediment-yielding subbasins and selected for sediment management. The simulated scenarios showed that the average annual sediment reductions at critical erosion hot spots in subbasins after the application of filter strips, soil/stone bund, terracing, and contour farming were 35.03%, 66.54%, 80.88%, and 53.11%, respectively. Therefore, this study concluded that reducing sediment yield by implementing terracing in critical areas at risk of soil erosion was more effective than other soil conservation measures. Overall, this research can help planners and decision-makers to implement appropriate soil conservation measures in the most erosive subwatersheds in order to extend the useful life of the Genale Dawa-3 hydropower dam and reservoir.

Climatic and hydrogeomorphic controls on sediment characteristics in the southern Sierra Nevada

The magnitude of sediment yield from headwater catchments is controlled by the interactions among hydrology, geomorphology, and soil disturbance. In montane regions like the Sierra Nevada, snow is one of the main factors controlling the timing and magnitude of hydrological fluxes. However, the role of snow on modulating spatial and temporal variation of sediment yield remains unclear. Using 120-site years of sediment yield data from 10 headwater catchments (drainage area 50–475 ha), we examined the sediment yield characteristics across an elevational gradient (1,777–2,381 m elevation) in the southern Sierra Nevada. Across space and time, we calculated an average annual suspended sediment yield of 62 ± 147 Mg/km2. In contrast, the measured mean annual bedload yield from the study catchments was small, 1.1 ± 2.4 Mg/km2. A linear mixed-effects model showed that maximum annual discharge alone can only explain 24 % (marginal R2 = 0.24) of the variance in sediment yield. Similarly, the hypsometric integral, which is often used as a metric for erosion susceptibility, showed no predictive power (marginal R2 = 0.005). As much as 65 % of the variance in sediment yield can be explained by fixed effects when snow related drivers (i.e., center of flow timing and aspect) were included in the model along with maximum annual discharge, suggesting a strong influence of snowmelt. Moreover, the relationship between area normalized suspended sediment yield (Qs) and unit discharge (Q) was significantly different between rain and snow events (p = 0.001). Both average slope (α) and exponent (β) terms of the Qs=αQβ relationship across the ten catchments were higher for rainfall (α=5.8,β=1.84) than those for snowmelt (α=3.1,β=1.77) events. As the erosion severity and power were higher during rainfall than the snowmelt events, a shift in the precipitation form from snow to rain under a warming climate will likely increase sediment yield. These results provide critical insights on background sediment yield in the southern Sierra Nevada and likely changes under future climate.

Automated catchment scale modelling of hydrological phenomena and water quality

An automated approach to hydrologic and water quality modeling on a catchment scale is presented, one that automatically produces suitable models from domain modeling knowledge and measured data. An essential component of the methodology is the domain knowledge library, comprising knowledge on hydrological and nutrient loading processes and containing alternative formulations for some of them. The library is written in a formalism compatible with the equation discovery tool ProBMoT. Given a user specification of a modeling task, ProBMoT searches the space of alternative candidate models encoded in the library. The generated models are optimized against the provided measured data, and the best-fitted model is proposed as the most suitable for modeling the observed system. The methodology was applied to the Quarteira River catchment (Algarve, Portugal). Analysis of the average annual water balance, sediment yields, and nutrient loadings in the Quarteira River support the findings of the previous research work, while the ProBMoT results are comparable or better than the results obtained with the SWAT model.

Assessing the Water-Resources Potential and Soil Erosion Hotspot Areas for Sustainable Land Management in the Gidabo Watershed, Rift Valley Lake Basin of Ethiopia

For development of a comprehensive sediment management plan, it is crucial to categorize watersheds on the basis of soil erosion hotspot areas to extend the useful life of water bodies (e.g., Gidam reservoir). The goal of this study was to assess the surface water potential and identify erosion hotspot areas of the Gidabo watershed in Ethiopia using the Soil and Water Assessment Tool (SWAT) model. The SUFI-2 (Sequential Uncertainty Fitting Version 2) program was used to calibrate the model, and the model’s performance was evaluated. According to the catchment prioritization analysis, some of the sub-basins with similar land use, land cover, and soil type but with higher slope would generate higher sediment yield. Furthermore, the soil conservation scenarios were developed in SWAT, and the model result showed that average annual sediment yield could be reduced by the application of grassed waterway, filter strips, terracing, and contouring by 49%, 37.53%, 62.32%, and 54.6% respectively. It was concluded that sediment yield reduction by applying terracing was more effective than other conservation measures for affected sub-basins. The surface water potential of the watershed varies spatially from sub-basin to sub-basin, and the mean monthly surface water potential of the watershed is 33 million cubic meters. These findings can help decision-makers to develop appropriate strategies to minimize the erosion rate from erosion hotspot areas and to allocate the watershed water potential for different types of water demands. Strip planting, terracing, or contour farming may be necessary on chosen hotspot erosion sites to reduce the effect of slopes on surface runoff flow velocity and sediment transport capacity.

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.

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

Evaluation of Best Watershed Management Practice for Sediment Yield Reduction (The Case Study of Baro Akobo of Upper Gilo Watershed, Ethiopia)

This study aimed to estimate the sediment yield, evaluating its distribution, and compare the selected Best Management Practices (BMPs) and identify relatively effective management practices to alleviate soil erosion and sedimentation yield in the Upper Gillo watershed. Soil and Water Assessment Tool (SWAT) model with the interface of Geographical Information System (GIS) were used to simulate, streamflow and sediment yield. Meteorological, hydrological and spatial data were used while modeling the Upper Gillo watershed. After the simulation has executed, the model was calibrated using flow and sediment data from 1990–2004 and validated for 2005–2014. The coefficient of determination (R2) and Nash Sutcliff efficiency (NSE) values for the daily flow calibration using SUFI2 are 0.76 and 0.8 respectively and for validation, it was 0.82 and 0.81. For monthly sediment yield by using the SUFI2 calibration technique the model evaluation coefficients R2 and NSE for calibration were computed as 0.78 and 0.69 respectively, for validation, it was 0.64 and 0.72 respectively after calibration was performed, the simulated average annual sediment yield was estimated to be 57.98 million ton/yr at the outlet. The sediment yield distribution analysis showed that 18 sub-basins showed a relatively high sediment yield rate (> 20 ton/ha/yr) among the 45sub basins. The Scenarios practical in this paper were Base scenario, terraces, contouring and introduce strip cropping. Three watershed management scenarios were simulated to compare their effectiveness of sediment yield reduction from the existing baseline condition. The result shows that the mean annual sediment yield could be reduced by 37.59% by applying filter strips, 20.41% by applying to terrace, and 41.99% by applying to contour. Therefore, applying to the terrace is relatively effective to reduce the mean annual sediment yield from the Upper Gillo watershed. Keywords: Best Management Practice, Scenario, Sediment, SWAT model, Upper Gillo Watershed.

Evaluation of Ecosystem-Based Adaptation Measures for Sediment Yield in a Tropical Watershed in Thailand

Ecosystem-based adaptation (EbA) can potentially mitigate watershed degradation problems. In this study, various EbA measures were evaluated using a bio-physical model called the Soil and Water Assessment Tool (SWAT), in a small, forested watershed named Hui Ta Poe, in the northeastern region of Thailand. The developed watershed model was first used to investigate the effect of various degraded watersheds due to land-use changes on the sediment yield in the study area. The most degraded watershed produced an annual average sediment yield of 13.5 tons/ha. This degraded watershed was then used to evaluate the effectiveness of various EbA measures such as reforestation, contouring, filter strips, and grassed waterways in reducing the sediment yield. Under all individual and combined EbA scenarios analyzed, there was a significant reduction in sediment yield; however, the maximum reduction of 88% was achieved with a combined scenario of reforestation, grassed waterways, and filter strips. Reforestation alone was found to be the second-best option, which could reduce the sediment yield by 84%. Contouring alone was the least effective, with a reduction in sediment yield of only 23%. This study demonstrates the usefulness of implementing EbA measures for sediment management strategies to address watershed degradation, which is a severe problem across the globe.

Spatial distributions of nitrogen and phosphorus losses in a basin and responses to best management practices — Jialing River Basin case study

Tracing the main sources and spatial distributions of pollutants and quantifying the effects of various factors on soil erosion and pollution loads are important to allow appropriate management systems to be developed for large complex watersheds and allow water pollution to be controlled efficiently and economically. A distributed water, sediment, and pollutant model was used to qualitatively and quantitatively assess temporal and spatial variations in water and sediment characteristics and nitrogen (N) and phosphorus (P) loss distributions in a basin from a macroscopic point of view and to trace the sources of pollutants, using the Jialing River Basin as an example. Changes in N and P losses in the basin caused by various management practices were assessed. The results indicated that the average annual water and sediment yield in the study area were 103–857 mm and 2.4–1274.1 t/ha, respectively. The loss of total N and P were 1.1–21.6 kg/ha and 0.01–11.2 kg/ha. The spatial distribution varied greatly, but the annual variation trend was relatively stable. The contribution of N from industrial point sources reached 1973 tons, which was dominant. And the total N distribution in the watershed was closely related to woodland. Total P pollution was most severe for cultivated land. The P load caused by fertilization reached 805 tons, which was significantly more than the point source discharge. Assessments of the effects of implementing various management practices in the watershed indicated that N losses would be decreased more effectively by filter belt in woodland than by other practices. The total N loss would be reduced by 4.4% for every 0.5 m filter belt added to woodland. The losses would be decreased more effectively by a cultivated land filter belt and controlling fertilizer application than by other practices. The 0.5 m filter belt of cultivated land can reduce total P by 5%, and reducing fertilization by 5% can reduce total P by 7.3%. Understanding the temporal and spatial distributions of pollutant sources in a river basin and tracing pollutant sources will allow appropriate management practices to be implemented in key areas to effectively control pollutants.

Prioritization of Sub-Watersheds to Sediment Yield and Evaluation of Best Management Practices in Highland Ethiopia, Finchaa Catchment

Excessive soil loss and sediment yield in the highlands of Ethiopia are the primary factors that accelerate the decline of land productivity, water resources, operation and function of existing water infrastructure, as well as soil and water management practices. This study was conducted at Finchaa catchment in the Upper Blue Nile basin of Ethiopia to estimate the rate of soil erosion and sediment loss and prioritize the most sensitive sub-watersheds using the Soil and Water Assessment Tool (SWAT) model. The SWAT model was calibrated and validated using the observed streamflow and sediment data. The average annual sediment yield (SY) in Finchaa catchment for the period 1990–2015 was 36.47 ton ha−1 yr−1 with the annual yield varying from negligible to about 107.2 ton ha−1 yr−1. Five sub-basins which account for about 24.83% of the area were predicted to suffer severely from soil erosion risks, with SY in excess of 50 ton ha−1 yr−1. Only 15.05% of the area within the tolerable rate of loss (below 11 ton ha−1yr−1) was considered as the least prioritized areas for maintenance of crop production. Despite the reasonable reduction of sediment yields by the management scenarios, the reduction by contour farming, slope terracing, zero free grazing and reforestation were still above the tolerable soil loss. Vegetative contour strips and soil bund were significant in reducing SY below the tolerable soil loss, which is equivalent to 63.9% and 64.8% reduction, respectively. In general, effective and sustainable soil erosion management requires not only prioritizations of the erosion hotspots but also prioritizations of the most effective management practices. We believe that the results provided new and updated insights that enable a proactive approach to preserve the soil and reduce land degradation risks that could allow resource regeneration.

The intensity of siltation of a small reservoir in Poland and its relationship to environmental changes

Siltation of reservoirs is an indicator of the intensity of erosion processes and sediment yields of river catchments. An estimation of sediment yield is significant for hydroengineering practices, environmental prediction and modelling. It also reflects environmental changes in the form of climate and land use.The present study aimed to compare the amount of sediment deposited in a small reservoir in Poland, with the estimate of sediment yield from its catchment, using the Universal Soil Loss Equation coupled with a sediment delivery ratio (USLE-SDR) and an estimate of annual bed load transport, provided by a regional bed load formula. The estimate of the annual amount of bed load was based on the flow frequency graph and bed load rating curve of Skibinski. The dam of the reservoir was constructed in 1976. The first reservoir survey was carried out between 1979 and 1980, when the reservoir volume was estimated to be 252,000 m3. Subsequent surveys were carried out in 1991, 2003, 2009 and in the Spring of 2020. These surveys enabled the amount of sediment, deposited in the reservoir, to be measured across four different periods: 1980–1991, 1992–2003, 2004–2009 and 2010–2019. For the same periods, the USLE with a constant SDR (calculated using the approach provided by Vanoni) were used to estimate the quantity (mass) of suspended sediment yield from the contributing area of the catchment. The volume of suspended sediment, deposited in the reservoir, was obtained, taking into account the reservoir trap efficiency and assuming a density of suspended sediment deposits.Hydrological investigations of the Plachty gauging station on the Zagozdzonka River, the left tributary of the Vistula River, have been carried out by the Department of River Engineering at Warsaw University of Life Sciences since 1962. The catchment area at the Plachty gauging station, located just upstream of the reservoir, is 82.4 km2, whereas the catchment area above the dam of the Staw Górny reservoir, is 91.4 km2.The estimated annual sediment yields for the catchment, based on reservoir surveys across four periods between 1980 and 2020, suggest a general decrease over time. This study was also undertaken to examine long-term variability in sediment yield, both in suspended sediment and bed load, related to rainfall-runoff erosivity, river discharge and land use changes, which could influence changes in catchment sediment yield. An analysis of local temperature and catchment runoff revealed a long-term increase in the mean annual temperature and a corresponding decrease in annual discharge.The annual values of total sediment input to the reservoir (suspended and bed load), estimated using the USLE-SDR and a bed load formula with sediment trap efficiency, are very close to the measured amounts of deposits in the reservoir. Annual deposits in the reservoir are decreasing with time. This is presumably caused by the decrease in arable land in the catchment. From the mean annual deposits in the reservoir, around 35% is bed load and 65% is suspended load. The average annual specific suspended sediment yield in the catchment, is ca. 9 Mg/km2.