Evaluating Agricultural Nonpoint‐Source Pollution Using Integrated Geographic Information Systems and Hydrologic/Water Quality Model

Understanding the link between extreme precipitation and changes in runoff and sediment yield is of great significance for regional flood disaster response and soil and water conservation decision-making. This study investigated the spatial and temporal distribution of extreme precipitation (characterized by 10 extreme precipitation indices recommended by the Expert Team on Climate Change Detection and Indices) in the Toudaoguai–Longmen section of the middle Yellow River from 1960 to 2021 and quantified the effects of extreme precipitation on runoff and sediment yield based on the method of partial least squares regression (PLSR). The extreme precipitation index showed an obvious upward trend in the last 20 years, with the increases in the central and northern regions (upstream) being stronger than the increase in the southern region (downstream). However, the runoff and sediment yield decreased significantly due to the implementation of large-scale soil and water conservation measures on the Loess Plateau, with average rates of 94.7 million m3/a and 13.3 million t/a during 1960–2021, respectively. The change points of runoff and sediment yield change occurred in 1979. Compared with those in the period from 1960 to 1979, the reductions in runoff and sediment yield in the years 1980–2021 were 52.7% and 70.6%, respectively. Moreover, extreme precipitation contributed 35.3% and 6.2% to the reduction in runoff in the 1980–1999 and 2000–2021 periods, respectively, and contributed 84.3% and 40.0% to the reduction in sediment yield, respectively. It indicated that other factors (such as large-scale soil and water conservation construction) played main roles in the decrease in runoff and sediment yield in the study area in recent 20 years.

Grass hedges planted at regular intervals on the landscape offer many opportunities to reduce runoff and sediment from leaving fields. Objectives of this study were (1) to evaluate the ability of the WEPP watershed model to simulate grass hedge system effects of sediment trapping (TE), bench terracing (BT), and variable effective soil hydraulic conductivity (HC) on simulated hillslope runoff and sediment yield, and (2) to model the effects of measured effective hydraulic conductivity (Keff) values from a grass hedge management system by comparing predicted runoff and sediment yield values to those measured in a small watershed over an 11-year period. The study was conducted on a 6.6 ha watershed located in the deep loess hills region of southwestern Iowa. Narrow grass hedges of predominantly switchgrass (Panicum virgatum) were planted at 15.4 m intervals in 1991. The WEPP model simulated greater reductions in runoff (9%) and sediment yield (58%) from BT compared to TE and HC effects. Combination of all three effects gave the highest reductions in runoff (22%) and sediment yield (79%) compared to individual effects or any combination of two effects. The watershed model did not adequately simulate slope length reduction effects from the grass hedges. Runoff (r2 = 0.78) and sediment yield (r2 = 0.75) were comparable to observed data when measured Keff values for grass hedge, row crop, and channel areas were used as input data. Measured Keff data from grass hedge, row crop, and channel areas should be used for improved runoff and sediment yield predictions.

The cutslope and fillslope on a newly constructed forest road on the Talladega National Forest near Heflin,Alabama were treated with three erosion control techniques: wood excelsior erosion mat, native grass species, and exoticgrass species. Bare soil plots were used as the experimental controls. Total sediment yield was measured during theperiod 21 September 1995 to 18 March 1996. A randomized complete block design was used to evaluate treatmentmethods on the basis of sediment yield and runoff volume. No significant difference in sediment yield was found from thefillslope among the treatments. However, on the cutslope significant differences were detected among all treatments. Theerosion mat treatment was most effective in mitigating erosion losses with a 98% reduction in cutslope sediment yield and88% reduction in fillslope sediment yield.

Determining the impact of vegetation restoration on runoff and sediment yield is crucial for formulating science-based slope management practices. The study analyzed runoff and sediment yield behavior in relation to varying vegetation cover and components, based on field-simulated rainfall experiments. The results showed that both runoff and sediment yield rates tended to decrease as vegetation cover increased. Vegetation contributed more significantly to the reduction in sediment yield than to the reduction in runoff. For a rainfall intensity of 1.5 mm·min−1, the sediment yield reduced to 37%, 73%, 78%, and 94% under the vegetation coverage of 20%, 40%, 60%, and 90%, respectively. The corresponding sediment yield reduction effects at the rainfall intensity of 2.0 mm·min−1 were 27%, 67%, 78% and 89%, respectively. At a rainfall intensity of 1.5 mm·min−1, the sediment yield reduction contributions of the litter layer, stem-leaf layer, and roots were 36%, 3%, and 51%, respectively. The corresponding sediment yield reduction contributions at the 2.0 mm·min−1 rainfall intensity were 30%, 7%, and 51%, respectively.

Integrated impact assessment of soil and water conservation structures on runoff and sediment yield through measurements and modeling in the Northern Ethiopian highlands

Land use change is a significant factor in accelerating erosion rates, which is expected to increase sedimentation in the reservoir. The reduction in the water storage capacity of the dam is primarily due to sediment accumulation resulting from soil erosion. One of the approaches involves analyzing the erosion hazard level by integrating the Geographical Information System (GIS) and the Soil and Water Assessment Tool (SWAT) to accurately predict the erosion rate. The objective of this research was to assess the erosion hazard level and develop land management strategies to mitigate erosion rates in Sempor Reservoir Watershed of Central Java, Indonesia. The SWAT model employed the Modified Universal Soil Loss Equation (MUSLE) method, utilizing input data on topography, climatology, and land use provided by an authorized agency. Model calibration was conducted using the Calibration Uncertainty Program, which involved 55 iterations with 2,000 simulations per iteration, incorporating 18 sensitive parameters. Furthermore, the comparison of flow discharge between observed and simulated data is validated using statistical parameters. The results indicated that land use coverage and slope significantly influence the erosion rate. The land management strategy scenario demonstrates a reduction in potential erosion rates and sediment yield. Model calibration and validation yielded R² values of 0.87, NSE of 0.86, and PBIAS of 3.6%, indicating an excellent model fit. This suggests that the SWAT model is quite accurate in simulating the catchment area. However, the SWAT model's performance can be further enhanced by improving the adaptability of other calibration parameters.

Sediment contribution of specific areas of a watershed is an important consideration, but one that is often overlooked, when developing watershed management plans. Understanding sediment delivery to the watershed outlet is one method for identifying high contribution areas. In this study, a new methodology for calculating individual subbasin sediment delivery ratio (SDR) was developed within the Soil and Water Assessment Tool (SWAT) for two Michigan watersheds. Subbasins with the greatest SDR had two defining characteristics: high erosion rates and close proximity to the watershed outlet. The impact of best management practice (BMP) implementation (no-tillage and Conservation Reserve Program) on sediment yield reduction at the watershed outlet was compared for two targeting methods (SDR and erosion rate). Identifying SDR of individual subbasins for implementation of BMPs is more effective method for addressing water quality concerns at the watershed outlet than the widely used targeting high risk erosion areas. Watershed SDR was found to be highly variable on a monthly basis, due to changes in sediment yield, which is in turn affected by factors such as precipitation and surface runoff. Finally, watershed SDR calculated using the physically-based SWAT model was compared to four empirically-based areal relationships with SDR. While some area methods reproduced the SWAT-SDR, the variations between areal methods indicate that more detailed physical characteristics should be considered in watershed SDR calculation.

Compared with arable land, there is a paucity of field-based measurements of erosion rates and controls for lowland temperate grassland supporting ruminant agriculture. Despite this evidence gap, reducing diffuse fine sediment pollution from intensively farmed grassland has been recognised as essential for improving compliance with water quality targets. Improved information on erosion rates and controls within intensively managed lowland grazing livestock systems are prerequisites for informing best management practices for soil and water resource conservation.Accordingly, this study assembled such information using the North Wyke farm platform in south west England where flow, suspended sediment concentration, rainfall and soil moisture are monitored quasi-continuously in 15 hydrologically-isolated (1.54–11.12 ha) catchments. This region of the UK is representative of temperate lowland ruminant grazing landscapes with semi permeable soil drainage.Catchment area was the major control on both water and sediment flux. When normalised to catchment area, sediment yields were controlled by the erodibility of the catchment's soils. Ploughing for re-seeding of grass swards was the major factor that affected this. Whilst total rainfall had a small effect on sediment yields, slope and the damage of soils by livestock had no significant effects. This finding may be due to the overriding effects of ploughing and re-seeding of some fields during the study period.Detachment by impacting raindrops mobilised sediment particles across the entire field with diffuse saturation-excess overland flow responsible for their transport. The majority of erosion occurred during the rising limbs of storm events when there is an abundance of easily detached soil particles. Given that erosion and sediment transport are driven mechanistically by processes affecting the entire field areas, a reduction in sediment yield through the implementation of highly spatially-targeted in-field management such as that for feeder ring use, troughs, poached tracks or gateways would likely be very challenging. Instead, stocking density and grazing regime management, as well as carefully planned ploughing and re-seeding will be more beneficial for erosion control.

The Warana river watershed in Western Maharashtra, India has been recognized for exporting some of the highest nitrate-nitrogen loadings in western Maharashtra and is also a major source of sediment and other nutrient loadings. An integrated modeling framework has been constructed with Soil and Water Assessment Tool (SWAT) model and the interactive SWAT CUP. The simulation framework includes a detailed land use and management data such as different crop rotations and an array of nutrient and tillage management schemes, derived from the various source including the state department of Agriculture. This paper presents the calibration and validation of SWAT for the streamflow, sediment losses, and nutrient loadings in the watershed. Streamflow, sediment yield, and nitrate loadings were calibrated for the 1979-1984 period and validated for the 1984-2014 period. Secondary field data on organic nitrogen, organic phosphorus, and mineral phosphorus is used in model to validate for the 2007-2014 period. Model predictions generally performed very well on both an annual and monthly basis during the calibration and validation periods, as indicated by coefficient of determination (R2) and Nash-Sutcliffe simulation efficiency (E) values that exceeded 0.7 in most cases. The first scenario set with application of fertilizer and no sanitation practices and set of land use change scenarios based on taking cropland out of production indicated a significant benefit in reducing sediment yield at the watershed outlet. A second scenario set found that relatively small reductions in nutrient applications resulted in significant reductions in nitrate loadings at the watershed outlet, without affecting crop yields significantly.

Assessing sediment connectivity and soil erosion by water in a representative catchment on the Loess Plateau, China

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

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

Huluka River diversion weir, which diverts water supply for Ambo town, has been under severe sedimentation. In this study, the ArcSWAT model was applied to determine the sediment yield and sediment load of the Ungauged Huluka River watershed through the parameters transfer method. This particular study calibrated and validated the ArcSWAT model on the Guder River gauging station of watershed area 659 km2. The calibrated and validated best values were extended to all the sub-basin to estimate the sediment yield and sediment load of the ungauged Huluka River watershed. The ArcSWAT model was found certain with statistical performance procedures like regression coefficient, Nash–Sutcliffe and percentage of bias. The model was calibrated and validated with accepted statistical performance values on the monthly time scale. The statistical performance like regression coefficient, Nash and percentage of biased were dramatically increased upon the validation period to very good range according to Arnold et al. The estimated average sediment yield of the whole Guder sub-basin was found to be 4.3 (ton/ha). The annual average sediment load contributed from the Huluka River watershed was found to be 37.5 Kiloton/year. The estimated average annual sediment quantities at Guder gauging station and the whole Guder sub-basin were 344.8 Kiloton/year and 1.1 Megaton/year, with data ranging from 1998 to 2014 (17 years). Three different best management practices (BMPs) such as contouring, strip cropping and terracing were evaluated to see their effectiveness on the whole sub-basin. The sediment yield reduction with these BMPs was ranged from 58 to 62% at Guder hydro-gauging station with simulation period of 1998–2014. The sediment yield was strongly decreased to 76% with these BMPs at the Upper Huluka watershed.

Soil and water conservation practices (SWCPs) are fundamental strategies for interrupting sediment connectivity and mitigating soil erosion at the watershed scale. However, traditional design approaches often overlook the spatial heterogeneity of sub-basins and the complex trade-offs between environmental benefits and economic costs. This study proposes a novel multi-objective optimization framework to identify optimal SWCP configurations that balance ecosystem service value (ESV), life-cycle investment costs (IC), and sediment yield reduction. Using the Soil and Water Assessment Tool (SWAT) coupled with a non-dominated sorting genetic algorithm (NSGA-III), we evaluated fifteen SWCP scenarios (combining terracing, contour farming, and check dams) . The results demonstrate that combined SWCPs significantly outperform individual measures in disrupting sediment transport, with the combination of terracing, contour farming, and boulder check dams achieving the highest reductions in sediment yield (SY). While higher investment costs generally correlate with greater sediment reduction, our optimization reveals that low-cost practices like contour farming provide efficient connectivity management despite lower ESV. The optimized solution identified in this study reduced SY by 4.496 × 105 t and streamflow by 36.84 × 105 m³ with a minimal IC of 4.61 × 106 CNY, effectively maximizing the cost-benefit ratio. These findings provide a scientific basis for sustainable watershed management, offering policymakers a tool to navigate the challenges of balancing erosion control, ecological restoration, and economic constraints.

The effectiveness of alluvial gully remediation in Great Barrier Reef catchments