Total Sediment Yield Research Articles

Response time of fast flowing hydrologic pathways controls sediment hysteresis in a low-gradient watershed, as evidenced from tracer results and machine learning models

Hydrologic controls on the timing of sediment transport and sediment hysteresis patterns remain an open area of investigation in hydrology, especially for low-gradient watersheds with substantial instream sediment deposition. Sediment hysteresis, which describes the mismatch between hydrograph peak and sedigraph peak, aids with elucidation of the mechanisms of sediment transport in watersheds. Most frequently, the controls of hysteresis are attributed to the proximity of sediment sources to monitoring locations in a watershed. However, this assumption, while widely applied, is infrequently verified. We investigated the controls of sediment hysteresis in a low gradient system located in the Bluegrass Region of central Kentucky, USA. Turbidity and conductivity sensors installed at the basin outlet provided data to quantify sediment hysteresis and separate hydrologic flow pathways (i.e., by describing the source of water delivered to the watershed’s outlet) using a tracer-based approach. Predictive hydrologic parameters, including hydrologic pathways, event magnitude, and antecedent conditions, were estimated and grouped based on hydrologic similitude. Thereafter, we identified parameters required to predict sediment hysteresis using a tailored ensemble feature selection approach coupled with three machine learning algorithms—Random Forest, K-Nearest Neighbors, and Gradient Boosted Trees. Results from the analysis of 68 storm events occurring over a two-year period showed that clockwise events accounted for 85 % of the total sediment yield despite comprising only 53 % of the events. The hysteresis index (HI) can be predicted (r = 0.8, RMSE = 0.12) using three, out of the thirty-nine hydrologic parameters considered. The most important predictors of HI reflect the volume of event rainfall and the relative proportions of new water (i.e., water derived from precipitation during the storm event) and old water (i.e., water previously stored in the watershed) comprising the hydrograph. Further analyses reveal that new water timing—which changes with the rainfall volume—and sediment timing are closely linked, suggesting that variations in the hysteresis patterns are controlled by changes in the response time of fast flowing water pathways. This implies that hydrologic pathways, as opposed to sediment proximity to the watershed outlet, control sediment hysteresis in this watershed. These results have important implications for better understanding the mechanisms controlling sediment transport at the watershed scale.

Spatio-temporal soil loss modelling using RUSLE and sediment delivery into a reservoir in a semi-arid region of northern Nigeria

Soil loss is aggravated by uncontrolled deforestation, indiscriminate land clearing for agricultural activities, overgrazing, and urban development that leads to severe soil erosion over the land surface. The main objective of this research is to apply the Revised Universal Soil Loss Equation (RUSLE), in conjunction with remote sensing and GIS, to determine the temporal variation of soil loss from the Gubi watershed in the years 2000 and 2017 and to estimate the sediment delivery into the Gubi reservoir in Northern Nigeria. Datasets of rainfall, soil type, topography, cover management, and support practice were utilized to determine the five RUSLE factors. The research identified five levels of erosion ranging from severe to very low-risk areas. The spatial distribution of erosion hotspots in the catchment area was highlighted. Results revealed increasing levels of erosion from 14,244.31 tons/year in 2000 to 16,792.33 tons/year in 2017. Consequently, the catchment's sediment yield was 6903.65 tons/year and 9172.71 tons/year corresponding to sediment delivery ratios of 48.46 % and 54.62 % in 2000 and 2017 respectively. The sediment inflow into Gubi reservoir was 747.38 tons/year and 950.76 tons/year corresponding to 10.83 % and 10.37 % of the total sediment yield in 2000 and 2017 respectively. Soil erosion vulnerability index maps were produced and the erosion is expected to increase with time as agricultural activities and deforestation continue to occur. The sediment deposits have the potential to reduce the designed life of the reservoir. Best management practices, such as tree planting, mulching, and contour ridging are recommended for soil conservation. There is a need to assess the reservoir sediment deposits so that measures can be taken to maintain the reservoir operations properly.

Evaluation of the EUROSEM on soil erosion simulation for loess plateau, northern China

AbstractThe Loess Plateau region features fragmented landforms, sparse vegetation, and short but intense summer rainstorms that can easily cause severe soil erosion. To evaluate its applicability to a typical Loess Plateau in northern China, an indoor laboratory experimental study was conducted for events with different slope lengths (3, 4, and 5 m) and rainfall intensities (50, 60, 70, 80, 90, 100, 110, and 120 mm/h). EUROSEM (European Soil Erosion Model) was used to simulate the soil erosion process and predict both total runoff and sediment yield. The EUROSEM modeling results were compared with the observed experimental values and analysed to determine the performance of EUROSEM. The results and analysis showed that EUROSEM could effectively simulate the runoff processes. It produced better predictions for the total runoff yield than for the sediment yield, with Nash–Sutcliffe efficiencies of 0.9003 and 0.1820, respectively. The qualified rates of the RE (relative error) between simulated and observed values of the total runoff and sediment yield were 87.5% and 37.5%, respectively. Compared to the sediment yield under rainfall intensities of 50–80 mm/h, those under 90–110 mm/h had lower RE and higher NSE, which increased from −3.9 to 0.5. However, the modeling results deviated more from the experimental data at a rainfall intensity of 120 mm/h. According to this study, EUROSEM is a good fit for simulating the runoff and partial sediment yield processes of the Loess Plateau region's slopes. However, the accurate prediction of sediment yield still requires more research to achieve complete effectiveness using EUROSEM for typical and wide scenarios in China.

Sediment source analysis in the korabelny stream catchment, King George Island, maritime Antarctica: Geomorphological survey, fingerprinting and delivery rate assessment

Research into sediment provenance identification in Antarctica is emerging as a relevant field of study, providing a unique insight into understanding geomorphological processes in extreme climatic environments. This study focusses on the mechanisms of sediment redistribution in the catchment of the Korabelny Stream, located at the western end of the Bellingshausen Ice Dome on King George Island (Shetland Islands). The catchment area of the stream covers 2.83 km2, with 1.17 km2 under the glacier. Two main sediment sources have been identified: a) the glacierized part, extending along the glacier edge and represented by a complex of moraine deposits lacking protective vegetation cover, along with part of the catchment under the glacier; b) the periglacial part, occupying territory with permafrost and a thin loose cover unevenly protected by early successional vegetation. We combine a tracer-based fingerprinting technique, sediment delivery estimates based on sediment flow connectivity index and geomorphological mapping to quantify the sources contribution to sediment yield. The proportional contribution of the glacierized part was 60–66 % of the total sediment yield based on two independent methods, suggesting the reliability of the results. It is noteworthy that sediment transport from the glacierized part exceeds that from the periglacial part. However, a significant portion of the sediment is redeposited in temporary reservoirs formed along the glacier edge and Lake Mesyats, located in the central part of the Korabelny Stream catchment. The main factor determining sediment yield in the catchment is the water reserves in snow at the beginning of the ablation season. In years when water reserves in snow significantly exceed long-term average values, such as observed in the austral summer of 2014–2015 when study was conducted, sediment yield was low. This is attributed to the faster melting of ice on the glacier compared to snow, due to differences in albedo.

Analysis of Erosion and Sedimentation Rates on the Service Life of Telaga Lebur Dam

Dam is a civil construction structure in hydrology. The concept of a dam essentially provides a solution by serving as a water reserve, meaning that during the rainy season, water is collected in the dam reservoir, and during the dry season, the stored water can be used as needed. Dams are highly effective in addressing water scarcity issues, both for raw water supply and irrigation purposes. The purpose of building dams is to create a water supply system to supply water for village residents and for irrigation needs. Water availability in dry climate regions is generally limited. Climate change phenomena exacerbate water scarcity issues. As a precaution and mitigation measure against water scarcity, the Indonesian government is actively constructing dams across various provinces. Particularly in West Nusa Tenggara (NTB), a dry climate province facing challenges in water supply for households and irrigation, dam construction is essential. The level of total erosion hazard rate in the Telaga Lebur Dam Catchment Area is 5463.94 Ton/Ha/Year. 67.78% of the area of the Telaga Lebur Dam Catchment Area (11.23 km²) experiences erosion at a rate of 3703.5 Ton/Ha/Year, classified as very light erosion. 11.58% of the area of the Telaga Lebur Dam Catchment Area (25.90 km²) experiences erosion at a rate of 632.7 Ton/Ha/Year, classified as light erosion. 9.20% of the area of the Telaga Lebur Dam Catchment Area (20.58 km²) experiences erosion at a rate of 502.7 Ton/Ha/Year, classified as moderate erosion. 3.66% of the area of the Telaga Lebur Dam Catchment Area (8.19 km²) experiences erosion at a rate of 200 Ton/Ha/Year, classified as heavy erosion. 7.78% of the area of the Telaga Lebur Dam Catchment Area (17.41 km²) experiences erosion at a rate of 425.1 Ton/Ha/Year, classified as very heavy erosion. The total sediment yield in Telaga Lebur Dam is 16.619 m³/year. The reservoir's useful lifespan based on the analysis results is 11.44 years.

Erosion processes and sediment source tracing on heterogeneous slopes in the red soil region of southern China

AbstractUnderstanding erosion, sediment sources and the spatial distribution along heterogeneous slopes is essential for soil and water conservation. In this study, soils derived from nodular limestone, mud‐like limestone and limestone breccia (abbreviated as SMTL, SMDL and SLBC, respectively) were utilized to establish artificial homogeneous and heterogeneous slopes. The homogeneous slopes MTL, MDL and LBC represent SMTL‐, SMDL‐ and SLBC‐filled‐ slopes, respectively. The heterogeneous slopes were abbreviated as MTL/MDL, MDL/LBC and LBC/MTL. Rare earth elements (REEs; lanthanide, cerium and ytterbium) were used to tag soils on the upper and lower slope sections to track sediment transport and deposition. The results showed that for homogeneous slopes, the LBC slope was the most severely eroded, followed by the MDL and MTL slopes. For heterogeneous slopes, the order of erosion was LBC/MTL > MTL/MDL > MDL/LBC. Upslope sections contributed a sizable portion of the total sediment yield, ranging from 51% to 79%. Over time, the difference in the sediment contribution between the upslope and downslope regions decreased and reached equilibrium. Runoff rates on heterogeneous slopes demonstrated an inverse function (R2 > 0.75) in contrast to a logarithmic distribution (R2 > 0.87) on homogeneous slopes. Heterogeneous slopes displayed minimal intersegment variation and the absence of a consistent ordering of the magnitude of hydraulic parameters. Conversely, the hydraulic parameters of homogeneous slopes were consistently ordered across the slope sections. For sediment transport, all slopes exhibited suspension‐dominated flow with percentages greater than 89%. However, the particle size distribution of the sediment of heterogeneous slopes exhibited greater diversity and complexity because of the coexistence of distinct soils. These findings underscore the importance of customized strategies for soil and water conservation in environments characterized by diverse soil parent materials.

Effect of Blue Agave (Agave tequilana Weber) Management on Soil Erosion

The expansion of blue agave ( Agave tequilana Weber) plantations beyond the plant’s original distribution range in the state of Jalisco, Mexico, has caused a drastic change in land use and crop patterns, exerting pressure on natural resources. This study originated based on a request from landowners who leased their land to a tequila company to grow agave in the municipality of Autlán. Therefore, this study records the effect of crop management on the degradation of non-renewable soil and water resources in plots conventionally managed by the company compared to the one managed by a private owner The sampling unit was 2 m × 5 m runoff lots, with a repetition and a control lot (without vegetation cover) with a 6% slope. Sampling was carried out in the rainy season from July to October, 2020. The results showed different behavior between repetitions. Total sediment yield in the farmer’s plot was 9.260 t ha−1 and in its control 6.844 t ha−1 versus the company’s plot of 13.796 t ha−1 and its control 5.233 t ha−1. These values reflect an increase in soil loss by 26% and 62%, respectively, due to management effects. The difference between sites is due in part to the different rainfall intensities and distribution of recorded rainfall separates the two sites. Given these results, there is a lack of knowledge of the impact of crop management on soil degradation by companies and farmers who lease or plant blue agave, in addition to the absence of a sustainable project that considers the conservation of soil and water, based on agronomic and cultural measures before, during, and after the harvest season by the municipality and state authorities and the agave-tequila companies.

Assessment of plot-scale sediment transport on young moraines in the Swiss Alps using a fluorescent sand tracer

Abstract. Glacial retreat uncovers large bodies of unconsolidated sediment that are prone to erosion. However, our knowledge of overland flow (OF) generation and sediment transport on moraines that have recently become ice-free is still limited. To investigate how the surface characteristics of young moraines affect OF and sediment transport, we installed five bounded runoff plots on two moraines of different ages in a proglacial area of the Swiss Alps. On each plot we conducted three sprinkling experiments to determine OF characteristics (i.e., total OF and peak OF flow rate) and measured sediment transport (turbidity, sediment concentrations, and total sediment yield). To determine and visualize where sediment transport takes place, we used a fluorescent sand tracer with an afterglow as well as ultraviolet (UV) and light-emitting diode (LED) lamps and a high-resolution camera. The results highlight the ability of this field setup to detect sand movement, even for individual fluorescent sand particles (300–500 µm grain size), and to distinguish between the two main mechanisms of sediment transport: OF-driven erosion and splash erosion. The higher rock cover on the younger moraine resulted in longer sediment transport distances and a higher sediment yield. In contrast, the higher vegetation cover on the older moraine promoted infiltration and reduced the length of the sediment transport pathways. Thus, this study demonstrates the potential of the use of fluorescent sand with an afterglow to determine sediment transport pathways as well as the fact that these observations can help to improve our understanding of OF and sediment transport processes on complex natural hillslopes.

Effects of sewage sludge application methods on the transport of heavy metals with runoff and their mechanisms

Woodland utilization is a promising disposal method for sewage sludge (SS). However, the potential risk of heavy metals (HMs) transport with runoff must be considered. Among the various factors influencing HMs loss, SS application methods (Holing application, HA; Broadcasting and mixing application, BM; Broadcasting application, BA) are likely to cause significant effects by altering soil erosion and soil aggregates. This study aimed to determine how SS application methods affect HMs loss, soil aggregates erosion, and how they are related. Accordingly, the losses of HMs in surface runoff, interflow, and sediment were quantified during six simulated rainfalls. The results demonstrated that all methods reduced surface runoff, but BA was the most effective. Additionally, BA significantly reduced the total sediment yield and the total proportion of the <0.05 mm fraction aggregates. Moreover, BA had the smallest cumulative losses of Pb and Cd through surface runoff and Cu, Pb, and Cd through sediment. Sediment was the most important pathway for HMs loss, through which over 76.56 % of HMs were lost. In BA, the <0.05 mm fraction aggregates had the lowest HMs load, whereas in other treatments had the highest (54.33 %–80.33 %). The potential ecological risk coefficient of Cd was beyond “moderate” in all the pathways of BM and “high” in the interflow of each SS treatment. Nonetheless, when the multi-elements were evaluated collectively, the potential ecological risk index for each SS treatment was categorized as “low”. Overall, BA not only reduced soil erosion but also posed no risk of HMs pollution. It should be noted that the loss of Cd in the interflow had a great impact, while the <0.05 mm fraction aggregates played a significant role in the HMs load. Thus, the current study not only provides an effective approach for the environmentally safe disposal of SS but also proposes a scientific method for the application of SS in woodlands.

Prioritizing conservation practice locations for effective water quality improvement using the Agricultural Conservation Planning Framework (ACPF) and the Soil and Water Assessment Tool (SWAT)

Adopting the right agricultural conservation practices (CPs) at the right place is critical to maximizing water quality benefits. The Agricultural Conservation Planning Framework (ACPF) tool identifies all potential CPs and their locations within a target watershed based on the landscape characteristics. The ACPF tool suggests hundreds of CP locations in a watershed, making it challenging to prioritize the CP implementation. We develop and demonstrate an efficient approach using a multicriteria ranking technique for prioritizing the CPs suggested by ACPF, considering pollution hotspots and CP cost and effectiveness to support decision-makers. The pollution hotspots are estimated with simulations from an ecohydrological model, the Soil and Water Assessment Tool (SWAT). The CP cost and effectiveness were estimated from CP installation costs and pollutant reduction efficiencies from the literature. The methodology was demonstrated in the Conewago and Mahantango watersheds in Pennsylvania, US, for grassed waterways (GWWs) and water and sediment control basins (WASCOBs) for sediment load reduction. Multiple CP prioritization scenarios were evaluated with individual and combined criteria for reductions in total sediment load, yield (loading per area), and cost. In single criterion-based prioritization, the cost-based and load-based prioritization indicated cost efficiency and fewer CPs, respectively. The yield-based approach correctly prioritized CPs in sediment loss hotspots in the case study watersheds; however, it needed more CPs to meet the target reductions. The multicriteria approach efficiently prioritized CPs in sediment hotspots to meet target reductions. Although this approach was demonstrated in two case study watersheds and for sediment loss reduction, it is applicable for any location or pollutant for which similar input variables can be provided, thereby providing a means for prioritizing the results of ACPF for implementation in the Mid-Atlantic region of the US.

Assessing the hillslope-channel contributions to the catchment sediment balance under climate change

To get a full understanding of the impacts of global change on the catchment-scale sediment balance, models are needed that combine hillslope soil erosion processes with channel morphodynamics. Here we present a modification to the SPHY-MMF model that includes a novel channel morphodynamics module, which determines erosion and deposition in rills and channels. We applied the model to a Mediterranean study area in southeast Spain, in which we show that channel erosion contributes substantially (35%–40%) to the total sediment yield, highlighting the importance of accounting for channel erosion in catchment-scale sediment budget estimations. The climate change scenarios show that the different erosional processes (i.e. sheet, rill, channel) are projected to decrease or increase, depending on the projected change in annual and extreme precipitation. From this we conclude that interactions between different erosional and depositional processes should be considered when studying the impact of global change on the catchment-scale sediment balance.

Evaluation of best management practices to reduce sediment yield in the upper Gilo watershed, Baro akobo basin, Ethiopia using SWAT

The increasing sediment yield in the watershed is caused by natural and human activities, which significantly shifts the hydro-meteorological in the watershed. The Modified Universal Soil Loss Equation (MUSLE) equation in the Soil and Water Assessment Tool (SWAT) was used to estimate sediment yields for each hydrological response unit (HRU) based on peak runoff, daily runoff volume, area of hydrological response unit, and other estimated and default hydrological model parameters. The amount of sediment yield from each HRU is then summed to give the total soil erosion for the watershed.The spatio-temporal variations of sediment yield in the Upper Gilo watershed was simulated to identify the hotspot area and select the effective management practices (BMPs) for reducing significant problems. Model calibration and validation were carried out using sediment yield data from 1990 to 2004 and 2005 to 2014. The results indicated that the watershed total sediment yield is 1021.8 tonnes/yr. Furthermore, 17 sub-basins (37.8% of total watershed area) are severely threatened by high soil erosion. According to the simulation results, the filter strips, terraces, and contours reduced the watershed sediment yield by up to 53.2%, 45.4%, and 48%. Overall, the selected BMPs are highly effective in reducing sediment yield in watershed-prone areas.

Runoff and sediment characteristics of a typical watershed after continuous soil erosion control in the red soil region of Southern China

To investigate the runoff and sediment characteristics of the watershed after continuous soil erosion control in the red soil region of southern China, hydrological data were collected from 2013 to 2020 in the Zhuxi watershed, which is located in the southeast of the red soil region. The results showed that the monthly suspended sediment concentration and annual sediment yield have significantly decreased since 2017. At the event scale, 180 floods were classified into four flood patterns (A, B, C and D) by the K-medoids clustering method based on the flood duration, runoff depth and peak discharge. Each flood pattern resulted in differing levels of the event sediment yield (D > C > B > A), and Pattern C contributed the most to runoff and sediment yield. The study period was divided into two stages according to the annual sediment yield. Compared with 2013–2016, the total runoff and sediment yield of the 3 major flood patterns (A, B and C) in 2017–2020 decreased by 17.88%∼25.12% and 78.92%∼90.34%, respectively. These flood patterns decreased not only in frequency but also in suspended sediment concentration, which was caused by the changes in the runoff-sediment relationships of flood events. Six types of suspended sediment concentration and discharge (SSC-Q) relations appeared in the flood events, indicating that the sediment sources and sediment transport processes were complex and dynamic. In 2017–2020, the single-valued relation became the dominant type of SSC-Q relations for all flood patterns, which suggests that the sediment supply was inhibited. The results provide a more comprehensive understanding of the runoff and sediment processes of a watershed after continuous soil erosion control, which is beneficial for revealing the development of soil erosion in the red soil region of southern China.

Rill formation and evolution caused by upslope inflow and sediment deposition on freshly tilled loose surfaces

Rill erosion easily occurs on tilled surfaces because the soil shear resistance is less than the runoff shear stress. However, rill erosion formation and evolution on tilled surfaces under upslope inflow conditions remain unclear. The objective of this study was to investigate the rill formation process and rill erosion amount on tilled surfaces via flow scouring under different inflow rates (4, 6, and 8 L min−1) at a 15° slope. Close-range photogrammetric technology was applied to measure the rill morphology during the experiments. The results suggested that the rill formation process due to inflow could be divided into two distinct stages, namely, before and after runoff reached the downslope end, i.e., stages I and II, respectively. At stage I, runoff washed soil particles along the downslope direction. In this process, due to limited transport capacity of runoff, washed soil particles were deposited at the runoff head and formed a soil mound, which blocked the flow path, after which the runoff direction changed within the 6.7°− 50.6° range with an average moving distance of 0.62 m. As a result, a curved rill and a series of soil mounds were left on the surface. The inflow rate affected rill morphology by influencing the runoff direction change angle and runoff moving distance between the mounds on the surface. Herein, the rill formation process is referred to as downslope-trending erosion by inflow (DTEI). At stage II, runoff reached the downslope end, and a rill channel was formed throughout the slope. Thereafter, DTEI was largely reduced, and headward erosion was strengthened. As a result, the rill morphology quickly changed, such as the rill depth and rill width, which gradually increased with ongoing headward erosion. During DTEI, the rill paths were curved due to sediment deposition, and the sediment deposition conditions varied under the different inflow rates. Therefore, the rill curvature (RC) differed (1.039 ± 0.014). The RC decreased with headward erosion progression at stage II. The total sediment yield (TSY) increased with increasing inflow rate. Under inflow rates ranging from 4 to 6 L min−1 and 6–8 L min−1, the TSY increased 2.1–2.4 times. Consequently, DTEI on tilled surfaces significantly affects the initial rill morphology and evolution at the later stage. Hence, on slopes, its role should be considered in rill erosion assessment.

Understanding the Shift of Drivers of Soil Erosion and Sedimentation Based on Regional Process‐Based Modeling in the Mississippi River Basin During the Past Century

AbstractSoil erosion and sedimentation problems remain a major water quality concern for making watershed management policies in the Mississippi River Basin (MRB). It is unclear whether the observed decreasing trend of stream suspended sediment loading to the mouth of the MRB over the last eight decades truly reflects a decline in upland soil erosion in this large basin. Here, we improved a distributed regional land surface model, the Dynamic Land Ecosystem Model, to evaluate how climate and land use changes have impacted soil erosion and sediment yield over the entire MRB during the past century. Model results indicate that total sediment yield significantly increased during 1980–2018, despite no significant increase in annual precipitation and runoff. The increased soil erosion and sediment yield are mainly driven by intensified extreme precipitation (EP). Spatially, we found notable intensified EP events in the cropland‐dominated Midwest region, resulting in a substantial increase in soil erosion and sediment yield. Land use change played a critical role in determining sediment yield from the 1910s to the 1930s, thereafter, climate variability increasingly became the dominant driver of soil erosion, which peaked in the 2010s. This study highlights the increasing influences of extreme climate in affecting soil erosion and sedimentation, thus, water quality. Therefore, existing forest and cropland Best Management Practices should be revisited to confront the impacts of climate change on water quality in the MRB.

Investigating the stability of contour ridge system using rare earth element tracers under natural rainfall in the rocky mountain areas of Northern China

Erratic and intensively erosive natural rainfall is becoming more frequent with the intensification of global climate warming, increasing uncertainty and unpredictable risks of the stability of contour ridge system. However, little attention has been paid to the in situ quantitative evaluation of contour ridge stability under natural rainfall. When water ponds in furrows, contour ridges tend to breach, inducing contour failure followed by ephemeral gully erosion, which greatly affects the stability of contour ridge system. To track sediment sources during ridge slope erosion, contour failure, and ephemeral gully erosion stages, ten rare earth element (REE) tracers were applied in three soil layers (total 0.3 m in depth) at four slope positions in-situ runoff plots under five rainfall levels. Runoff plots were conducted with contour ridgess for sweet potatoes (SP) and peanuts (PT). The stability of contour ridges was gradually weakened when erosion form shifted from ridge slope erosion to contour failure and then to ephemeral gully erosion. Ridge slope erosion controlled contour ridge stability, with contribution of 76.28–80.49 % to the total sediment yield. Sediment yield occupied 40.99 % of the total after contour failure appearing and 55.80 % after ephemeral gully formation. The lower-middle slope was the most fragile area for contour ridge system. Rainstorm (with precipitation 50–100 mm in 24 h) played a destructive role in weakening contour ridge stability, which generated the largest runoff (36.81–39.25 % to the total) and sediment yield (46.75–57.84 % to the total). Rainstorm made the greatest contribution to the occurrence of ridge slope erosion (51.64–59.99 %), contour failure (38.07–40.91 %), and ephemeral gully erosion (24.32–30.53 %). When using REE oxides to determine contour ridge stability, the tagging depth above 0.2 m and the uniform binding of oxides with < 0.05 mm particles should be considered. Thus, some modifications to lower the likelihood of ridge failures under rainstorm conditions may be effective to enhance the stability of contour ridge system.

A fully coupled superficial runoff and soil erosion basin scale model with efficient time stepping

We present a numerical model of soil erosion at the basin scale that allows one to describe surface run-off without a priori identifying drainage zones, river beds and other water bodies. The model is based on robust semi-implicit numerical techniques and guarantees exact mass conservation and positivity of the surface and subsurface water layers. Furthermore, the method is equipped with a geostatistical preprocessor that can perform downscaling of data retrieved from digital databases at coarser resolutions. Numerical experiments on both idealized and realistic configurations demonstrate the effectiveness of the proposed method in reproducing transient high resolution features at a reduced computational cost and to reproduce correctly the main hydrographic features of the considered catchment. Furthermore, probabilistic forecasts can be carried out based on soil data maps automatically generated by the geostatistical preprocessor that are distributed among the available MPI ranks to carry out simulations independently thus reducing the total cost of the simulation. The numerical experiments show the ability of the model to provide robust estimates of water levels, discharge and of the order of magnitude of the total sediment yield.

Response relationship between vegetation structure and runoff-sediment yield in the hilly and gully area of the Loess Plateau, China

The structure of the vegetation has a significant impact on how much runoff and sediment is produced. Choosing the right parameters to evaluate the correlations between vegetation and runoff-sediment yield, however, is fraught with uncertainty. We chose 18 vegetation plots with a range of vegetation types and structural characteristics for this study to investigate the applicability of various vegetation structure parameters in identify in the response relationship between vegetation and runoff-sediment yield through field artificial rainfall experiments. The vegetation coverage, stratified vegetation cover index (Cs), species diversity and functional diversity were among the criteria of vegetation structure. The findings revealed that: (1) There was a significant difference in the runoff start time and sediment yield differed significantly between vegetation types, with shrub communities having a longer start time and the lowest sediment yield; (2) The vegetation coverage of the community had a significant impact on the runoff start time and, when combined with Cs, explained 48% of the runoff start time. (3) Simpson index (D) and functional richness (FRic) significantly influenced the total runoff yield and along with Cs explained 46% of the total runoff yield. Cs, coverage and FRic also positively influenced the runoff end time, with a total explanation of 29%. Functional divergence (FDiv) had a significant negative effect on the total sediment yield. Together with coverage and Cs, FDiv explained 66% of the total sediment yield. These results demonstrated how biodiversity consideration helped to clarify connections between vegetation structure and runoff-sediment yield.

Determination of GERR lifespan using RUSLE method and GIS integration

Soil erosion is a grave and ongoing matter that poses an intimidation to the ecosystem all around the world. On basins with enormous surface areas, sedimentation has a significant impact. The Blue Nile basin is considered one of these basins that would be exposed to erosion and sedimentation after construction of the Grand Ethiopian Renaissance Dam (GERD), which will retain a large amount of sediments. The goal of this study is to calculate the lifespan of the Grand Ethiopian Renaissance Reservoir (GERR). In this research, the Revised Universal Soil Loss Equation (RUSLE) method, with the help of remote sensing and Geographic Information System (GIS), was utilized in order to determine soil erosion and sediment yield from the Blue Nile basin. Accordingly, lifespan of GERR could be estimated. The findings revealed that the total annual soil loss computed for Blue Nile basin is about 4.06*108 t. y−1, the total annual sediment yield equals about 1.21*108 t. y−1 and life span of GERR is estimated about 611 years. The approach presented in this study can be benefited from and applied in other basins that have the same conditions. Decision makers are able to use this approach to get reasonable results and control the problem of soil erosion and sedimentation.

The Response of Sensitive LULC Changes to Runoff and Sediment Yield in a Semihumid Urban Watershed of the Upper Awash Subbasin Using the SWAT+ Model, Oromia, Ethiopia

Land use and land cover (LULC) changes in many parts of river basins have caused water shortages, flood risks, land degradation, soil loss, biodiversity loss, and ecosystem deterioration. LULC change and topography are the main factors that cause land degradation and soil erosion in the Ethiopian highlands. The aim was to evaluate the rate of the LULC change and its effects on runoff and sediment yield in the semihumid subtropical Awash watershed using the SWAT + model. The land use maps of 2000, 2010, and 2020, along with constant climate data from 1992 to 2020, were used to investigate the effects of LULC dynamics on runoff and sediment yields. Agriculture and urbanization both increased at 7.1% and 7.95%, respectively. In contrast, the forest area decreased by 8.8% and shrubland by 3.25% from 2000 to 2020. Bare soil and urban areas covered the majority of the landscape units that were labeled as potential runoff generators. The majority of the soil erosion-prone areas that were classified as severe in the second and third scenarios covered a sizable area of urban, agricultural, and shrubland. These soil erosion hotspots covered an area of 3,777.3 ha (3.18%) and 13,413.1 ha (11.3%), with a total annual sediment yield of 361.93 m/ton and 1239.24 m/ton, respectively. In general, the change in LULC results in the annual sediment yield, with mean annual amounts of 241.8 tons/ha, 408.7 tons/ha, and 732.4 tons/ha for each scenario in the sequence. The model performance was tested using R2 = 0.88, NSE = 0.9, and PBIAS = −2.36, which indicate good agreement between simulated and observed flow, and R2 = 0.82, NSE = 0.86, and PBIAS = 4.38 for the simulated against recorded sediment yield. The increases in sediment yields have serious implications for reservoir siltation downstream of the watershed and warn land use managers to take action.