Sediment Yield Reduction Research Articles

Sustainable and Cost-Effective Management of Degraded Sub-Watersheds using Ecological Management Practices (EMPs) for Genale Basin, Ethiopia

Land, water, and air are the most essential resources blessed by nature to humankind, conserved and maintained with steadfast efforts. This study applies the Modified Universal Soil Loss Equation (MUSLE) to identify erosion prone sub-basins and a non-linear optimization algorithm to determine the optimal area combination of Ecological Management Practices (EMPs) control sediment yield within permissible limits at a minimum cost. The model is practiced for critical sub-basins in the Genale watershed to assess the effectiveness of five EMPs individually and as a combination in controlling sediment yields and peak flow. A relative assessment revealed that terracing as an individual (61.8%) and EMPs combinations (78.5%) are better in reducing sediment yield at the sub-basin scale. Considering the environmental and economic viewpoint, the total cost of EMPs (for five critical sub-basins), applied to reduce sediment yield, is 46.101 million USD (United States Dollar) or (1.844 billion Ethiopian birr). EMPs are environment friendly and cost-effective to reduce sediment yield.

Impacts of Best Management Practices on Runoff, Soil Loss, and Sediment Yield in the Megech Watershed, Ethiopia

This study evaluated the best management practices on how to manage soil losses from catchment and reduce sediment load into a dam reservoir. This study aimed to evaluate the relationship of runoff, soil loss, and sediment yield with best management practice (BMP) scenarios in the GeoWEPP environment for the selected three micro-watersheds (hot spot areas) in the Megech watershed, upper Blue Nile Basin. The impacts of four agricultural BMP scenarios, including forest five years old, corn, soybean; wheat, alfalfa (4 yr) no till; corn, soybean, wheat, alfalfa (4 yr) conservation till; and winter wheat mulch till, on soil loss, runoff, and sediment yield were quantified. The results revealed that soil loss ranges between 41.45–66.11 t/ha/year and sediment yield rates ranges between 36.5–54.8 t/ha/year with the baseline situation (conventional tillage condition) were found to be higher than the tolerable soil loss (10 t/ha/year) in the region. Implementing BMPs on the crop land of the micro-watersheds has positive impacts on all variables’ runoff, soil loss, and sediment yield reductions. Among the implemented BMPs, forests with a five-year perennial (agroforestry) option showed the highest rate of reduction for all runoff, soil loss, and sediment yield, but no cost benefit analysis was included in this study to choose among the BMPs. This study also identified that agricultural BMPs play a great role in reducing runoff, soil loss, and sediment yield in the Megech watershed to minimize on- and off-site impacts. In general, it is important to consider how cost benefit analysis will change throughout project’s implementation among the selected BMP scenarios at the watershed level in the future.

Prioritising interventions for the reduction of erosion in classical gullies: a modelling study

Context Gully erosion is a significant socioeconomic and environmental issue that affects agricultural productivity, infrastructure, and water quality of receiving waters. Despite a variety of interventions to prevent gully formation and rehabilitate existing gullies, cost-effective interventions are specific to individual gullies. Aims The aim of this study was to assess the performance of a suite of gully management interventions across three different classical gullies. Methods A one-dimensional process-based model, MERGE (modelling erosion resistance for gully erosion), was used to quantify the sediment yield exiting the gullies, in response to various management interventions. Key results The net decrease in sediment yield was 2.5–57.4% for each of four interventions applied in isolation and 51.2–78.7% in combination. Reductions in sediment yield for each intervention varied markedly among sites, by a factor of 2.6–78.3 in absolute terms. This resulted in a unique ranking of the interventions by their effectiveness for a given site. Overall, interventions applied in combination were most effective, outperforming those applied in isolation by a factor of 1.24–1.37, but the effect of applying interventions in combination was not additive. Conclusions This study demonstrates the ability of the gully erosion model MERGE to be a useful tool to identify and tailor effective intervention strategies for individual gullies, and be a useful guide for decision making for erosion management. Implications Analysis of expected benefits of gully remediation using tools such as MERGE is important for assessing options at gully sites due to their widely varying response.

Response of Erosive Precipitation to Vegetation Restoration and Its Effect on Soil and Water Conservation Over China's Loess Plateau

AbstractLarge‐scale vegetation restoration profoundly affects ecohydrological and hydrometeorological processes with consequent effects on soil and water conservation. However, it is still unclear how revegetation affects the joint relationship between streamflow and sediment yield from the land‐atmosphere interactions perspective. In this study, we combine in situ hydro‐meteorological observations, satellite observed land surface characteristics, and coupled land‐atmosphere model simulations to address this knowledge gap through a case study focusing on the Loess Plateau, where a megaproject of revegetation has been implemented since 2000. We find that historical annual streamflow and sediment yield have decreased over the Loess Plateau and 12 main revegetated basins, mainly due to enhanced canopy transpiration and soil conservation functions of revegetation. However, the magnitude of sediment yield reduction is much higher than that of streamflow for both mainstream and tributaries of the Yellow River. Specifically, the mean decreasing rate of sediment yield is 2.91 times of streamflow in the mainstream Yellow River, while for tributaries, the mean decline rate of sediment yield is 1.71 times of streamflow. Despite increases in total precipitation amount, erosive precipitation exhibits a clear downward trend over the Loess Plateau after the large‐scale revegetation (2000–2015). This is mainly driven by enhanced local moisture recycling caused by revegetation‐induced redistribution of water and energy budgets. Decreases in erosive precipitation frequency coupled with increased precipitation amount enhance streamflow availability and simultaneously mitigate soil erosion. Our findings highlight the importance of factoring in the two‐way feedbacks between revegetation and erosive precipitation when planning soil and water conservation.

Effectiveness of watershed management measures on soil erosion and sediment yield reduction (Case study: Doholkooh Watershed, South Khorasan Province)

Effectiveness of watershed management measures on soil erosion and sediment yield reduction (Case study: Doholkooh Watershed, South Khorasan Province)

Modeling runoff-sediment influx responses to alternative BMP interventions in the Gojeb watershed, Ethiopia, using the SWAT hydrological model.

The Soil & Water Assessment Tool (SWAT) has been calibrated over a 33-year period to evaluate the Gojeb watershed's hydrological processes, sediment yield with downstream loading to the Gibe III dam, and erosion hotspot locations. Best management practices (BMPs) were run through the model to simulate the effects of watershed intervention scenarios on sediment yield and runoff. Simulation results of BMP intervention were compared with the reference and worst-case scenarios. The simulation of sediment production indicates a clear growing trend. Temporally, the maximum amount of sediment transported out of the watershed is experiential from June to September, and the minimum is in February. A plainly defined similar orientation is observed between precipitation, surface runoff, and sediment load in the landscape. Spatially, the maximum sediment transported out of the watershed is from agricultural landscape units with a slope of over 50%, annual precipitation above 1592mm, and surface runoff over 151mm. This signifies that the watershed is under serious threat from erosion due to vegetation loss, steep slope farming, and high surface runoff. Gibe III is a 243-m high roller compacted gravity dam built on the Omo-Gibe River basin in Ethiopia for hydroelectric power and downstream flood control. It is one of Africa's tallest dams, with an annual electric output of 1870MW that began operation in 2016. Thus, Gibe III could see a loss of storage capacity due to higher-than-expected sedimentation resulting from worsening environmental degradation, which implies that the beneficial uses that depend on this dam - electricity production, regulated irrigation water supply, and flood control - will decline with significant economic losses. Despite that, selected sustainable land management interventions and the application of BMPs to critical erosion-prone hotspot areas can support the overall reduction in total sediment yield and surface runoff.

Changes in the characteristics of flood discharge and sediment yield in a typical watershed in the Hengduan Mountain Region, Southwest China, under extreme precipitation events

Precipitation extremes can pose adverse impacts on local and downstream society, economy, and ecosystems. Accordingly, their characteristics have attracted widespread attention in many regions, such as the world famous Hengduan Mountain Region in Southwest China, where the overall characteristics in precipitation extremes have been widely reported yet. However, the spatial heterogeneity and internal variation of precipitation extremes caused by the complicated topography were rarely reported, moreover, few studies have evaluated the effect of dynamics in precipitation extremes and soil and water conservation measures on changes in flood discharge and sediment yield. In this study, a typical watershed in the Hengduan Mountain Region, the Longchuanjiang watershed, was selected to identify the dynamics in precipitation extremes from 1965 to 2018, and the contributions of soil and water conservation measures on the characteristics in flood discharge and sediment load. The results of this study are as follows. 1) Substantial decreasing trends occurred for both flood discharge and sediment yield from the early period (1965–2008) to the later period (2009–2018) in the Longchuanjiang watershed. 2) The increase in precipitation extremes in the dry-hot valley and decrease in the mountains revealed great internal variation of the characteristics in precipitation extremes in the Longchuanjiang watershed.3) Soil and water conservation measures that were implemented in recent decades, such as terraced farmland, forest and grass plantation, ecological restoration, and small reservoirs, resulted in the significant reduction of both flood discharge and sediment yield under similar extreme precipitation events. This study highlights the discrepancy of dynamics in precipitation extremes in the dry valleys with an entire watershed in the Hengduan Mountain Region, emphasizes the risks of soil erosion in the ecologically fragile dry valley, and assesses the contribution of soil and water conservation measures on changes in characteristics of flood discharge and sediment load in the selected watershed. The study results are of great importance not only for gaining a scientific understanding of changes in precipitation extremes, flood discharge, and sediment yield but also for the objective assessment of the ecological benefits of soil and water conservation projects and deployment of suitable measures in the future.

Impact of Land System Changes and Extreme Precipitation on Peak Flood Discharge and Sediment Yield in the Upper Jhelum Basin, Kashmir Himalaya

The Kashmir valley is prone to flooding due to its peculiar geomorphic setup compounded by the rapid anthropogenic land system changes and climate change. The scarcity of observations is one of the major challenges for understanding various land surface processes in the mountainous and mostly ungauged terrain. The study assesses the impact of land use and land cover (LULC) changes between 1980 and 2020 and extreme rainfall on peak discharge and sediment yield in the Upper Jhelum Basin (UJB), Kashmir Himalaya, India using KINEROS2 model. Analysis of LULC change revealed a notable shift from natural LULC to more intensive human-modified LULC, including a decrease in vegetative cover, deforestation, urbanization, and improper farming practices. The findings revealed a strong influence of the LULC changes on peak discharge, and sediment yield relative to the 2014 timeframe, which coincided with the catastrophic September 2014 flood event. The model predicted a peak discharge of 115,101 cubic feet per second (cfs) and a sediment yield of 56.59 tons/ha during the September 2014 flooding, which is very close to the observed peak discharge of 115,218 cfs indicating that the model is reliable for discharge prediction. The model predicted a peak discharge of 98,965 cfs and a sediment yield of 49.11 tons/ha in 1980, which increased to 118,366 cfs and, 58.92 tons/ha, respectively, in 2020, showing an increase in basin’s flood risk over time. In the future, it is anticipated that the ongoing LULC changes will make flood vulnerability worse, which could lead to another major flooding in the event of an extreme rainfall as predicted under climate change and, in turn, compromise achievement of sustainable development goals (SDG). Therefore, regulating LULC in order to modulate various hydrological and land surface processes would ensure stability of runoff and reduction in sediment yield in the UJB, which is critical for achieving many SDGs.

Potential Hydrological Impacts of Planting Switchgrass on Marginal Rangelands in South Central Great Plains

Woody plant encroachment is an ongoing global issue. In the Southern Great Plains of the United States, the rapid encroachment and coalescence of woody plants are transforming herbaceous-dominated rangelands into woodlands with a detrimental impact on water quality and quantity. In this study, we conducted modeling simulations to assess how converting juniper (Juniperus virginiana) woodland and low to moderately productive grassland into switchgrass (Panicum virgatum) biomass production system would affect streamflow and sediment yields in the Lower Cimarron River, Oklahoma. First, the grassland areas in the basin were divided into productivity classes suitable for rangeland activities based on the soil productivity index. Next, the Soil and Water Assessment Tool was used to develop the basin hydrologic model, calibrated and validated for streamflow in five gaging stations with a percent bias of <10%, Nash–Sutcliffe Efficiency index of >0.76, and R2 of >0.77. Then, the model was used to simulate evapotranspiration (ET), streamflow, groundwater recharge, and sediment loads under different land use conversion scenarios. Results showed that converting existing juniper woodlands, ~4% of the basin, to switchgrass had limited impacts on the water budget and sediment yield. A hypothetical scenario of converting low to moderately productive rangeland to switchgrass increased annual ET by 2.6%, with a decrease in streamflow by 10.8% and a reduction in sediment yield by 39.2% compared to the baseline model. Results indicated that switchgrass could be considered a potential land use alternative to address the juniper encroached grassland with minimal loss in streamflow but a substantial reduction in sediment yield in the southcentral region of the Great Plains.

Nonlinear relationships of runoff and sediment yield with natural and anthropogenic factors at event scale

AbstractUnderstanding how natural and anthropogenic factors affects the watershed runoff and sediment yield at event scale can provide useful insights into watershed hydrological processes to guide watershed management. This article investigates the nonlinear relationships between natural and anthropogenic factors and event runoff and sediment yield with a boosted regression tree (BRT) model for 38 watersheds within the Loess Plateau in China during 2006 to 2016. The BRT model captures the relative importance of each natural and anthropogenic factors to the variability in runoff and sediment yield. The results show that these relationships are complex and highly nonlinear. The event runoff was most related to NDVI in the grass land (NDVI_g), with a 21.3% contribution, followed by 3‐day antecedent precipitation index (AP3), 10‐day antecedent precipitation index (AP10), precipitation (P), and 7‐day antecedent precipitation index (AP7). For event sediment yield, the strongest factor is AP3, with contribution of 33.3%, followed by P, NDVI in the forest land (NDVI_f), AP7, and NDVI in the crop land (NDVI_c). The marginal effect curves produced by the BRT are often characterized by thresholds. For instance, NDVI_f has the greatest effect on event sediment yield reduction when NDVI_f = 0.42, suggesting that a very intense green coverage is not necessary to achieve maximal soil erosion control. Vegetation coverage and meteorological factors can explain 54.7% of event runoff variation and 55.6% of event sediment yield variation. Our study identify the nonlinear relationships between runoff and sediment yield with vegetation cover and meteorological factors and provide scientific support for the planning of subsequent reforestation projects in the Loess Plateau.

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.

Effects of vegetation spatial pattern on erosion and sediment particle sorting in the loess convex hillslope

To address the problem of serious soil erosion on the Loess Plateau, under the conditions of limited vegetation measures, the runoff erosion characteristics and erosion sediment sorting characteristics of vegetation at different positions on the upper slope of convex hillslopes are investigated, and the optimal vegetation spatial pattern is proposed according to the benefits of water storage and sediment reduction at different vegetation positions. The fluctuation degree of flow discharge per unit area of different vegetation spatial patterns is small, and the variation process of sediment discharge per unit area of each vegetation spatial pattern fluctuated sharply with the increase of runoff time. After planting vegetation on the slope, the total runoff yield and sediment yield were reduced. The runoff yield reduction benefit was 19.65% when the grass belt was 6 m away from the slope top; and the sediment yield reduction benefit was more than 70% when the grass belt was 2 m away from the slope top. Under the condition of hydraulic erosion on the slope covered with vegetation, the erosion particles are mainly fine particles, with high silt content and relatively small sand content. The farther the vegetation is arranged from the slope top, the more easily silt of size 0.002–0.05 mm is eroded. The higher effectiveness in terms of reductions of both runoff and sediment yields were obtained when the vegetation is planted in the proximity of the end of the length of the slope.

Simulating the Effects of Agricultural Adaptation Practices onto the Soil Water Content in Future Climate Using SWAT Model on Upland Bystra River Catchment

The article presents predicted changes in soil water content in the Bystra river catchment (eastern Poland) for various scenarios of climate change and adaptation practices obtained on the basis of a SWAT model simulation for three regional climate models driven by the global climate model EC-EARTH for the years 2041–2050 and the RCP 4.5 and 8.5 RCP scenarios. Climate scenarios were put against five adaptation scenarios presenting changes in land use and protective measures compared against a zero scenario of BaU (Business as Usual) kept in the future climate. Adaptation scenarios 1–5 are modifications of Scenario 0 (S-0). The 0–5 scenarios’ analysis was based on comparing soil water content and total runoff, sediment yield, actual evapotranspiration. The first adaptation scenario (AS-1) assumes an increase in afforestation on soils from the agricultural suitability complex of soil 6–8 (semi-dry, permanent dry, semi-wet). The second adaptation scenario (AS-2) assumes the creation of a forested buffer for the Bystra River and its tributaries. The third adaptation scenario (AS-3) shows one of the erosion prevention practices, the so-called filter strips. The fourth adaptation scenario (AS-4) assumes the reduction in plowing on arable land. The fifth adaptation scenario (AS-5) involves increasing soil organic carbon to 2%. Simulations revealed that each of the adaptation scenarios 1, 2, 3, 5 does not generally contribute to increasing the water content in soil on BARL (spring crops), CANP (rape), WWHT (winter crops), CRDY (other crops) on arable lands (which together account for over 50% of the catchment area). However, they can contribute to the reduction in sediment yield, total runoff and changes in actual evapotranspiration. The adaptation scenario 4 (AS-4) shows a slight increase in the soil water content on Bystra catchment in the 2041–2050 perspective. Scenario 4 indicated a slight increase in total runoff and a decrease in sediment yield, which in combination with slightly higher water content reflects the protective role of plant residue mulch, lowering the evaporation from the bare soil surface during warm seasons. The no-till adaptation practice had the highest effect in positively affecting water balance at the catchment scale among the adaptation scenarios considered.

Using WaTEM/SEDEM to Model the Effects of Crop Rotation and Changes in Land Use on Sediment Transport in the Vrchlice Watershed

The Czech landscape has undergone various changes over the last 100 years and has been mainly adapted agriculturally for economic purposes. This has resulted, among other things, in reservoirs being clogged with sediment. The Vrchlice Reservoir was built in 1970 to supply drinking water for around 50,000 inhabitants, and increased sedimentation has been detected in the reservoir in recent years. Water erosion and sediment transport were modeled with WaTEM/SEDEM. Sediment volumes were measured in eight ponds across the watershed for calibration purposes. Modeled results from ponds in watersheds covered mostly with arable lands generally corresponded with the measured values. Although in forested watersheds, the measured sediment volumes greatly exceeded modeled sediment yields, indicating high uncertainty in using USLE-based models in non-agricultural watersheds. The modeled scenarios represented pre-Communist, Communist, and post-Communist eras. For these periods WaTEM/SEDEM was used to evaluate three isolated effects: the effects of various crops on arable lands, the effects of farmland fragmentation, and finally the effects of changes in land use. The change in crops proved to be an important factor causing high siltation rate (potential 23% reduction in sediment yield for historical periods), and land fragmentation played the second important role (potential 15% reduction in sediment yield can be reached by land fragmentation). Across all scenarios, the lowest sediment yield and reservoirs siltation rates were obtained from the pre-Communist and Communist crop share under current land use conditions, and current land use with farmland fragmentation implemented, as it was re-constructed for the pre-Communist era. This supports the idea that the introduction of green areas within arable lands are beneficial to the landscape and can help reduce soil erosion and reservoir siltation.

Tillage-induced microtopography alters time-dependent intrinsic correlation of runoff and sediment yield

Tillage practices change microtopography and hydrological process, which significantly affects soil erosion. The objective of this study is understanding storm-driven microtopography development under different tillage practices and its effects on runoff and soil erosion. A series of simulated rainfall experiments with an intensity of 2.0 mm min−1 were implemented on three 4 m by 0.8 m soil boxes on a 15° slope with different tillage-induced microreliefs including smooth slope (SS), artificial digging (AD), and ridge tillage (RT). The Hilbert-Huang transform (HHT) was used to detect the change trends of runoff and sediment yield, and the time-dependent intrinsic correlation (TDIC) was used to depict intrinsic runoff-sediment relations. The results showed the soil roughness were SS < AD < RT during different rill erosive stages. AD and RT slopes reduced runoff by 11.5–64.5% compared with the SS slope during water erosion. AD and RT slopes also reduced sediment yield by 13.3–83.4% during interrill erosion process, but the sediment yield increased by 59.2–132.1% during rill erosion. Runoff and sediment yield had multi-scale temporal variation characteristics. Ensemble empirical mode decomposition (EEMD) was adapted to decompose the runoff and sediment yield data into different intrinsic mode functions (IMFs). For the high-frequency components (IMF1-IMF3), rougher microrelief led to increase in the periods of runoff and sediment yield, while the trend of the low-frequency components (IMF4-IMF5) was opposite to that of the high-frequency components. This phenomenon was mainly related to the spatial structure of microtopography. Tillage-induced microtopography altered the associations of runoff with sediment yield in different time scales. This study provided new insights into revealing the mechanism of tillage erosion in sloping farmland.

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.

Assessment of Best Management Practices on Hydrology and Sediment Yield at Watershed Scale in Mississippi Using SWAT

The selection and execution of appropriate best management practices (BMPs) in critical areas of a watershed can effectively reduce sediment yield. Objectives of this research include developing a watershed-scale Soil and Water Assessment Tool (SWAT) model for the Big Sunflower River Watershed (BSRW), identifying high sediment yield areas using calibrated and validated model, and assessing the effects of various BMPs. The efficiency of three BMPs, grassed waterways (GWW), vegetative filter strips (VFS), and grade stabilization structures (GSS), and their combinations in reducing sediment yield, were investigated. The model performed well for streamflow (P-factor = 0.72–0.87; R-factor = 0.74–1.27; R2 = 0.60–0.86; NSE = 0.60–0.86) and total suspended solids (TSS) (P-factor = 0.56–0.89; R-factor = 0.43–2.83; R2 = 0.62–0.91; NSE = 0.38–0.91) during calibration and validation. The simulation of individual BMPs revealed that GWW showed the highest sediment yield reduction (up to 44%), followed by VFS (up to 38%) and GSS (up to 7%). Two BMPs’ combinations showed that GSS and GWW had the largest sediment yield reduction potential (up to 47%) while VFS and GSS had the lowest potential (up to 42%). Similarly, a combination of all three BMPs reduced the sediment yield up to 50%. The findings of this study will aid in sustainable watershed management and will be valuable for watershed managers and planners.

Undecomposed litter mixed in the soil can increase interrill erosion on hillslopes: A laboratory study

Soil-litter mixing has been found to affect soil erosion. However, previous studies did not distinguish the effects of litter exposed on the soil surface and that buried in the soil resulting from soil-litter mixing processes. This causes an unclear understanding of the effect of soil-litter mixing on soil erosion. In this research, we hypothesized that after mixing, the exposed litter would decrease soil erosion, while the litter buried in the soil would increase soil erosion. To test this hypothesis, soil boxes were filled with three treatments: soil-litter mixing with surface-exposed litter (CS), soil-litter mixing without surface-exposed litter (S), and soil surface cover (C) at four litter rates (0, 0.10, 0.20, and 0.35 kg m−2). Laboratory rainfall experiments were performed under a soil box slope of 10° and at a rainfall intensity of 80 mm h−1. The results of this study showed that the CS and C treatments reduced runoff velocity, and their velocities changed similarly depending on the surface cover of litter. However, in the S treatment, the litter rate increasedid not change runoff velocity significantly, indicating that runoff velocity was mostly controlled by the litter on the soil surface. Under the same surface cover, the C treatment reduced sediment yield by up to 39%; while the S treatment was found to increase sediment yield by up to 43% compared with the bare soil. The sediment yield of the CS treatment showed a decreasing trend as the litter rate increased. When the litter increased to 0.35 kg m−2, the sediment in CS treatment was 19% lower than in the bare soil. These results demonstrate a counteracting effect of surface litter and buried litter. The promoting effect of the buried litter on sediment yield was explained by the undecomposed litter creating an oversaturated condition and introducing a deforming force that decreased soil resistance to erosion. This study suggests that it is necessary to isolate the effect of exposed litter and buried litter on soil erosion, particularly in the early period after soil-litter mixing when litter is undecomposed.

Evaluating gabion performance in sediment yield reduction of basin under current and future conditions (case study: Dehbar basin)

Evaluating gabion performance in sediment yield reduction of basin under current and future conditions (case study: Dehbar basin)

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.