WEPP Model Research Articles

Evaluation of WEPP and Its Comparison with USLE and MUSLE in Yozgat-Kadılı Village

The water erosion is a significant environmental issue in arid and semi-arid regions. It leads to soil degradation, reduced agricultural productivity, and desertification. This article used The WEPP, the USLE, and the MUSLE models to estimate the average soil loss in the Yozgat-Kadılı village. Also, The MUSLE model utilized the WEPP model-estimated runoff for soil loss estimation. The USLE model, which estimates soil erosion using six factors (R, K, L, S, P, and C), can be improved by incorporating the Modified Fournier Index (MFI). Results indicated that the MUSLE model (3.66 t/ha) performed well in estimating soil losses close to the observed value (3.15) in the wheat fields between 1986-1996. the MUSLE (5.31 t/ha) and WEPP (5.88 t/ha) models underestimated soil losses to the observed value (8.75 t/ha) in the fallow field for 1986-1996. The WEPP model estimated the highest average soil loss at 5.18 t/ha in a wheat field, while the USLE model yielded the lowest estimate at 1.28 t/ha between 1969 and 2020. The MUSLE model estimated the highest (4.94 t/ha) and The USLE model estimated the lowest (2.53 t/ha) soil loss in the fallow field between 1969-2020. Results also revealed that the WEPP model is needed to calibrate for estimating soil loss in arid and semi-arid regions.

Comparison of SWAT and WEPP for Modeling Annual Runoff and Sediment Yield in Agewu - Mariyam Watershed, Northern Ethiopia

The Soil and Water Assessment Tool (SWAT) and the Geographic Water Erosion Prediction Project (Geo-WEPP) were applied to compare modeling of annual runoff and sediment yield in the Agewmariam watershed, eastern Amhara Region, Ethiopia. Spatial and temporal data distributions were required as inputs to run both models. Soil texture and other soil properties were measured in the field and in the laboratory, and soil maps were generated from global digital soil maps. Land use maps were created by manually digitizing Google Earth images. Watersheds were defined using watershed DEMs and gradient maps were created for each runoff event. Runoff samples were collected and analyzed for sediment concentrations in the laboratory; average annual runoff and sediment volumes were estimated using the WEPP and SWAT models. The results were satisfactory compared to the observed values, with R2 values of 0.86 and 0.91 for the SWAT and WEPP models, respectively, and NSE values of 0.54 and 0.71 for the monthly runoff. The estimated annual mean runoff and sediment yield at the watershed outlets were 65.54 mm, 146.14 mm, 43t/ha/yr and 41.7t/ha/yr for the WEPP and SWAT models, respectively. Several sub watersheds were determined to be susceptible to soil erosion and were prioritized, so more attention was given to this area to reduce runoff and soil erosion. Therefore, the SWAT and WEPP models were suitable for estimating annual runoff and sediment volumes. Sediment yields simulated from both models were high and alarming and far exceeded the allowable rate of soil loss.

Assessing the controlling factors on watershed soil erosion during intense rainstorm events using radar rainfall and process-based modeling

The evaluation of erosion risk in dry areas is challenging because erosion is often an outcome of individual rainstorms and is highly dependent on rainfall spatiotemporal patterns and on local land-use and topography. This study integrates a hybrid erosion model with rainfall data from high-resolution weather radar to simulate soil erosion during 22 high-intensity flash-flood generating rainstorms in a Mediterranean watershed (69 km2). We examine erosion over individual hillslopes and their spatial average over the watershed, representing intra-watershed and watershed-scale erosion, respectively. Our objectives are to: (a) determine how intra-watershed erosion corresponds to various physiographic factors (rainfall, land-use, topography); (b) determine which of these factors contributes to intra-watershed erosion the most; (c) quantify the effect of temporal variations in rainfall intensities on storm-scale erosion in relation to land-use type. We use for the first time a hybrid erosion model (K2-RHEM-DWEPP) based on the watershed-scale KINEROS2 model, that integrates the hillslope-scale Dynamic WEPP (DWEPP) and RHEM models, which were individually developed to represent erosion processes in croplands and rangelands, respectively. Watershed-scale storm erosion is best correlated with spatially-averaged 10-minutes maximum intensities (R2 = 0.58), and the correlation decreases for longer durations (R2 ≤ 0.54). When the spatially-averaged 10-minutes maximum intensity is multiplied by the area that contributes sediment, a better correlation with watershed-scale erosion is observed (R2 = 0.75). Hillslope erosion rates are higher when both rainfall intensities and topographic slopes are high, while land-use has a second-order effect. Higher storms maximal intensities result in higher hillslope erosion rates, especially over croplands.Our conclusions are useful to target locations for conservation practices and to better understand the effects of climate change on soil erosion.

Performance evaluation of a water erosion tracer using plot-scale experiments and process-based modeling

Socioeconomic and environmental losses caused by water erosion have highlighted the importance of quantifying and understanding the dynamics of soil redistribution in the landscape to develop effective soil management practices. Several methods are applied to estimate erosion/deposition rates and identify sources of sediments, among them, the one that uses rare earth elements (REE) as a tracer stands out. However, an alternative not yet explored that can benefit the accuracy of the estimates provided by the method is using a tracer containing a chemical signature composed of more than one REE. The present study aimed to evaluate the performance of a new water erosion tracer based on montmorillonite labeled with rare earth elements (La40-MMT). The innovative aspects of this La40-MMT tracer include its highly stable multi-chemical signature (Nd3+, La3+, and Pr3+), which enhances tracer detection in the environment, and its low production cost due to the use of an industrial residue in the synthesis process. The tracer was evaluated for a typical soil of the Cerrado biome, using a natural rainfall field-scale plot - NRFP (5 m × 20 m) and a physical predictive erosion model (WEPP). The results showed that the La40-MMT tracer could be used to estimate erosion/deposition rates, with agreement between the values observed with the tracer and the WEPP model. Thus, this study confirmed the great potential of La40-MMT as a tool to identify patterns of soil redistribution at the field scale and aid in the validation of erosion models.

Response of Soil Detachment Rate to Sediment Load and Model Examination: A Key Process Simulation of Rill Erosion on Steep Loessial Hillslopes.

The rate of soil detachment by water flow indicates soil erosion intensity directly. The exact relation between soil detachment rate and actual sediment load in water flow, however, is still unclear, and the existing relationships have not been adequately tested. The aims of the present study were to investigate the response of soil detachment rate to sediment load using rill flume data with loessial soil and to quantitatively examine the soil detachment equations in the WEPP and EUROSEM soil erosion models. Six slopes were combined with seven flow discharges to measure detachment rates under seven sediment loads using a rill flume with a soil-feeding hopper. Significant differences were found among the soil detachment rate by different sediment loads in low sediment load levels, but an insensitive response of soil detachment rate to sediment load was found under high levels of sediment load. The soil detachment rate was proved to be negatively linearly correlated with sediment load. The rill detachment equation in the WEPP model predicted the soil detachment rate by rill flow very well under our experiment condition. The soil detachment equation in the EUROSEM model underestimated the detachment rates under controlled conditions, but removing the setting velocity from the equation greatly improved prediction. Further experiments that could reflect the dynamic convective detachment and deposition process need to be conducted to compare with the present examination results and to further understand rill erosion processes.

Comparison of Critical Shear Stress of Rill Erosion Estimated from Two Methods

Various disputes exist regarding the critical shear stress (τc) of rill erosion determined by linear regression. Alternatively, some researchers have attempted to measure critical shear stress (τo) of rill erosion by observing the start of soil particle detachment and showed promising results. However, few studies have been conducted to evaluate the reliability of the method determining τo. Thus, this study was conducted to identify the reliability of the method determining τo by comparing the values of τc and τo and their relationships with rill erodibility (Kr) and influencing factors, using 360 disturbed soil samples (standing for the freshly tilled condition) from six sampling sites along a 330 km transect in the Loess Plateau. Results indicated that the mean τc was 1.90 times greater than that of τo. No significant relationship was found between τc and Kr. An inverse changing trend between Kr and τo was observed from Yijun to Zizhou, while both Kr and τo exhibited increasing trends from Zizhou to Yulin. The τo of six sampling sites all demonstrated increasing trends with slope gradient (S), which contradicted the statement of the WEPP model that τc was independent of S. The relationships between τc and the measured soil properties were poor, whereas the τo increased exponentially with soil organic matter. Generally, τo did not present significantly better results than τc; the reliability of τo also showed some uncertainties, such as the subjective judgment of the beginning detachment of soil particles. This result has great importance for deepening our understanding of the rill erosion mechanism.

Calibrating the WEPP model to predict soil loss for some calcareous soils

Calibrating the WEPP model to predict soil loss for some calcareous soils

Estimation of soil detachment capacity on steep slopes in permanent gullies under wetting-drying cycles

Permanent gullies, mainly distributed on granite weathering mantles in tropical and subtropical areas, are the major threat to the sustainable development for economy and ecosystem of southern China. Collapsing wall, with its stability influenced by the frequent wetting-drying cycles under the hot and rainy climatic conditions, is the most active part of permanent gully. The free surface along the collapsing wall provides a favorable condition for soil detachment by runoff scouring, however, little attention has been given to the detachment capacity of granite soils under the influence of wetting-drying cycles in permanent gullies. To quantify the impacts of wetting-drying cycles on soil erosion resistance in permanent gullies, the detachment capacity of granite soils (surface soil layer A; lateritic layer B; sandy layer C1; and detritus layer C2) that were collected from the collapsing wall was investigated under 0, 2, 5, and 10 cycles of wetting-drying. The impacts of wetting-drying cycles could be well quantified by soil pore size distribution that was calculated by soil-water characteristic curve (p < 0.01). The content of macro-porosity (>30 μm) increased constantly with increasing W-D cycles, while micro-porosity (<0.2 μm) decreased, especially for soils in the surface and lateritic layers (A and B). Soil erosion resistance of granite soils under the W-D cycles was determined by the integrated effects of soil porosity, and the tested soil detachment capacity soil detachment capacity in a range of 0.008–12.488 kg.m-2 s−1, increased with the increase of W-D cycles. In addition, the rill erodibility (Kr) was significantly influenced by soil bulk density, macro-porosity, and micro-porosity (R2 = 0.930, Nash-Sutcliffe efficiency = 0.910), demonstrating a power function relationship. Moreover, the critical shear stress (τc) had a significant and positive correlation with soil cohesion (R2 = 0.576, p < 0.010). Furthermore, soil detachment capacity could be well predicted by these measurable parameters including bulk density, macro-porosity, micro-porosity, soil cohesion, and shear stress of flowing water (R2 = 0.950, NSE = 0.980), under the theoretical foundation of WEPP model. The obtained results would facilitate the understanding of the formation mechanisms of the permanent gullies, as well as the development of soil conservation measures in southern China.

Comparison and Applicability of Selected Soil Erosion Estimation Models

Soil erosion is a globally challenging issue that hinders agricultural productivity by enhancing land degradation and loss to the top fertile soil. Although it is a global issue, its effect is adverse on farmers dwell in developing countries. Hence, providing information on soil loss is crucial to plan and implement appropriate soil and water conservation measures. Accordingly, erosion estimation models were developed and grouped as empirical, conceptual, and physical-based broad umbrella. This review paper primarily is intended to compare the opportunities and limitations of widely implemented soil erosion estimation models and review their applicability by selecting widely used models such as: USLE, RUSLE, SLEMSA, and WEPP. The result of this review revealed that the so reviewed erosion models have been designed to predict soil loss from sheet and rill erosion. Evidence from studies indicated that R/USLE models can be universally used by calibrating to the local environmental conditions. They are simple, requires less data and computational time, however; they are not event responsive and measure soil loss from gully and stream-bank erosion. But, RUSLE model has different parameter calculation procedure than the USLE. This study also depicts the SLEMSA model treats soil erosion factors as a separate entities and is highly influenced by LS factors. The WEPP model has capability to estimate soil loss in a short time scale and out-of-place erosion rates, but; it only works for individual hillslope. Thus, based on the result of this review the following recommendations are forwarded for further study to fill the gaps; upgrading of R/USLE parameters, modification of topographic sub-model of SLEMSA, and revision of essential parameters in WEPP model to estimate erosion from large catchments.

GIS-BASED WATER EROSION MODELLING: THE CASE OF HIGH SLOPE WATER CATCHMENT AREA, ROMANIA

This paper shows the results of a series of hydrographic simulations by mathematical modelling of the erosion phenomenon. The main goal is to show the importance of using the GIS technique to analyse the erosion process. Our research uses several well-known mathematical models and GIS software. Mathematical modelling was performed with the USLE model running under Geo-Graph software and the WEPP model running under ArcGIS 9.2 software. The multitude of factors involved in modelling and especially their spatialization is the main argument for choosing these two models. Finally, in order to be able to compare the results, in both cases the erosion simulation was conducted in the same hydrographic area, under the same geographical, climatic, pedological and relief conditions. The research focuses on a location with steep slopes affected by significant soil degradation processes. This paper used five input parameters in the simulation process using the USLE model: daily weather forecasting, vegetation or food growing management, land and soil topography. The model is based on daily regulates the hydrological state of the tested soils. Since climate change has had a major impact on soil erosion, the WEEP model has proven to be an efficient tool in erosion modelling, as it allows the entry of a large set of climate data. The WEEP model has also been used worldwide due to its ability to accept a multitude of data sets of soil characteristics. In the present case, in our research, the USLE model was used first, being launched before WEEP, as it has been used worldwide, but the results obtained with the WEEP model were good in almost all our simulations. The main results of this phase of our research show that the erosion is significant and exceeds acceptable limits. Therefore, in conclusion, major support practice actions and an appropriate agricultural practice are recommended to mitigate the effects of erosion process.

Evaluation of WEPP versus EGEM and empirical model efficiencies in predicting ephemeral gully erosion around Mubi area, Northeast Nigeria

Evaluation of prediction models is crucial to achieving valid information on erosion processes and their management choices. WEPP model efficiency in predicting ephemeral gully (EG) erosion was recently tested and compared with both EGEM and empirical models. The models abilities to predict EG erosion were validated using measured estimates at the 6 eroding locations around Mubi area in Northeast Nigeria between April 2008 and October 2009. Each location consisted of 3 watersheds where data on soils, climate, slope, management practices, EG shapes and dimensions were collected. Data on relevant soil properties were collected in the field and then analyzed in laboratory. The mass of soil loss (MSL) predicted by empirical, EGEM and WEPP models were compared with the measured using paired T-test, regression graphs (r2-values), error analysis, and analysis of variance (ANOVA) in a completely randomized design. The EG erosion losses varied significantly (P ≤ 0.05) between sites and years. No significant (P ≤ 0.05) differences were observed between measured and the empirically predicted aggregate MSL. The measured aggregate MSL strongly correlated with those predicted by empirical (r2 = 0.67), than with EGEM (r2 = 0.57), and WEPP (r2 = 0.53) models. Slight over and under-prediction instances against the measured erosion were noted with all the models. The WEPP model was found to slightly over-predict MSL when compared to either the empirical or EGEM model. The prediction quality of the models was generally impressive. Future works should focus more on local inputs such as climate, plants, management, and tillage data for use with WEPP.

Predicting soil erosion hazard in Lattakia Governorate (W Syria)

The main objective of this study is to predict soil erosion in the Lattakia Governorate (W Syria) using the Water Erosion Prediction Project model (WEPP) and to compare the result with that of the RUSLE. Field survey and data collection were carried out, and 44 soil samples were analyzed. In addition, all the necessary input files were prepared for use in the WEPP model and RUSLE. Results show that more than of 80% of the locations studied experience slight to moderate erosion (less than 5 t/ha/y), whereas the rest of the locations experience severe soil erosion hazard. Moreover, the volume of runoff estimated by the WEPP model is in the range of 51–321 mm, and the R2 between the simulated soil erosion and the predicted runoff reached 0.68. Interestingly, the R2 between the WEPP model and RUSLE is 0.56, which indicates a good correlation between the two models.

Evaluation of WEPP and EPM for improved predictions of soil erosion in mountainous watersheds: A case study of Kangir River basin, Iran

In the current study, WEPP and EPM models were used to estimate the amount of soil erosion and sediment in the basin of Kangir. The required data for implementation of the WEPP model were prepared in six categories including soil, climate, management, slope, drainage and reservoir based on which we took the information needed to build soil and management files. Some information such as texture, cation exchange capacity, organic matter, sand content, effective hydraulic flow and critical shear stress was used. After production of all the layers, the WEPP model was implemented using the GEOWEPP software. In this software, erosion and sediment amounts were estimated by three methods: domain, watershed and flow path methods. In the Kangir River watershed, the sediment content was 7.64 t/ha/year, 6.13 t/ha/year and 11.87 t/ha/year. Thus, the two methods of domain 7.64 t/ha/year and flow path 11.83 t/ha/year were closer to the observed sediment 10.5. Based on the EPM model, the sedimentation coefficient of the Kangir basin was 0.81. The results of the research indicate the high erodibility rate of the watershed basin. The erosion-sensitive units were located in the western and southwestern regions of the basin. In the EPM model, the erosion rate (Z) was 0.6 indicating moderate to high erodibility rate in the watershed. Furthermore, the highest erosion rate was in the western and southwestern parts of the watershed. Finally, the results of estimating soil erosion and sediment production in the watershed of Kangir illustrated that the WEPP model has a more accurate estimation of soil erosion and sediment production, and in this model, the flow path method used to estimate the amount of soil erosion and sediment production was close to the observed sediment at the hydrometric station.

WEPP model prediction evaluation of soil water content in northeast Uruguay

WEPP is a process-based model that estimates runoff and water erosion at slope level, maintaining a soil water balance at daily pace. The objective of this work is to adjust and validate the water balance component of the WEPP model in two watershed management situations (afforestation and natural grassland field) to obtain an adjusted tool that determines runoff and erosion. Soil water content data measured with neutron probe 4 times in the year down to 1.3 m depth during 10 years were used, and were compared with WEPP estimates. The results indicate that the WEPP estimations were not good (Efficiency coefficient (E) = 0.03, -1.29, -0.01, -1.74, 0.17 and -0.08 for the profiles) in high slope (C), average slope (D) and low slope (F), in the Grassland and afforested watershed, respectively, with an E considered insufficient and with periods of over and underestimation water content for both management situations. A better fit was obtained by eliminating the data outside of the calibration line in the profile C, with no improvement for the D and F profiles in both management situations. The results indicate that parameters such as evapotranspiration and WEPP equations must be adjusted to achieve better performance.

Soil detachment by overland flow on hillslopes with permanent gullies in the Granite area of southeast China

Permanent gullies are often initiated from rill erosion, followed by the formation of abrupt, deep and wide gullies when topsoil and subsoil are carried away by fast-flowing surface water. Few studies have been performed to evaluate soil detachment processes on hillslopes with permanent gullies, which may significantly affect the further development of gully erosion. Soil detachment was investigated by using natural undisturbed soil samples collected in different spatial locations (upper catchment, middle slope, lower slope, and scour channel) of hillslopes with permanent gullies. The relationships of soil detachment capacity with soil property, root system, and hydraulic parameters were quantified. Selected samples were tested in a hydraulic flume (3.8 m length × 0.2 m width) under five different shear stresses (3.67, 7.81, 10.50, 13.97 and 17.28 Pa). Soil detachment capacity was found to be significantly greater in the scour channel than in the other three hillslope positions. For the initial and stable gullies, the soil detachment capacity was notably reduced in the middle slope relative to the upper catchment and lower slope, while a different trend was observed in the active gully. The variability of soil detachment capacity at different spatial locations showed a negative correlation to bulk density, soil cohesion, clay, organic matter, and root density (P < 0.05), and a positive correlation to total porosity (P < 0.01). The rill erodibility (Kr) showed a power function decrease with soil bulk density, organic matter, and root density (P < 0.01). Critical shear stress (τc) had a significant and positive correlation with soil cohesion. Based on the WEPP model, detachment capacity of soil on hillslopes with permanent gullies could be achieved by using measurable parameters such of shear stress, bulk density, organic matter, root density, and soil cohesion.

Prediction and mapping of erodibility factors (USLE and WEPP) by magnetic susceptibility in basalt-derived soils in northeastern São Paulo state, Brazil

Spatial assessment of soil erosion is essential for the adaptation of agricultural practices and monitoring of soil losses. In this sense, this study aims to assess the efficiency of magnetic susceptibility (MS) as a predictor of soil erodibility factors (K for USLE model; Ki and Kr for WEPP model) fora detailed mapping of Oxisols with different iron contents in northeastern Sao Paulo State, Brazil. This study was carried out in an area of 380 hectares under sugarcane cultivation in Sao Paulo State. Soil samples were collected in a sampling grid (150) and in a transect (86) and physical and chemical analyses and calculations of the erodibility factors/parameters K, Ki, and Kr were performed. Pedotransfer functions (PTFs) were calibrated using simple linear regression analysis to predict the factors/parameters K and Ki using MS as a predictor variable. The observed values of MS and the predicted values of the factors/parameters K, Ki, and Kr were submitted to geostatistical analysis for constructing maps. Magnetic susceptibility can be used as a predictor of erodibility factors (K for USLE model; Ki and Kr for WEPP model) for Oxisols with total iron content ranging from 1 to 20% Fe2O3, with a precision of up to 60% and an accuracy of up to 85%. The results can guide future studies on water erosion in a tropical environment using magnetic soil data as an environmental covariate in the modeling process for large areas.

Estimation of Soil Losses in a Slope Area of Tokat Province through USLE and WEPP Model

Tokat is one of the developing provinces in terms of urbanism. Therefore, the land use changes city-wide which closely affects soil erosion. Numerical estimation of soil erosion is very important to prevent soil losses. In this study, USLE and WEPP Hillslope model were used to estimate the long-term soil losses in a slope area which used to be a pasture land and then turned into a fruit orchard in Büyükbeybağı area of Tokat province. Erosion sensitivity of the soil in the slope area was detected to be very low. Erosivity value of the area is low, soil is resistant to erosion due to pasture land use type and fruit orchard use type does not require intense soil cultivation practices. For all these reasons, both estimation technologies estimated soil losses of the land to be low.

Evaluation of the rusle and disturbed wepp erosion models for predicting soil loss in the first year after wildfire in NW Spain

Severe fire greatly increases soil erosion rates and overland-flow in forest land. Soil erosion prediction models are essential for estimating fire impacts and planning post-fire emergency responses. We evaluated the performance of a) the Revised Universal Soil Loss Equation (RUSLE), modified by inclusion of an alternative equation for the soil erodibility factor, and b) the Disturbed WEPP model, by comparing the soil loss predicted by the models and the soil loss measured in the first year after wildfire in 44 experimental field plots in NW Spain. The Disturbed WEPP has not previously been validated with field data for use in NW Spain; validation studies are also very scarce in other areas. We found that both models underestimated the erosion rates. The accuracy of the RUSLE model was low, even after inclusion of a modified soil erodibility factor accounting for high contents of soil organic matter. We conclude that neither model is suitable for predicting soil erosion in the first year after fire in NW Spain and suggest that soil burn severity should be given greater weighting in post-fire soil erosion modelling.

基于水蚀预报模型的黄土高原水平阶减流阻蚀效应模拟

基于水蚀预报模型的黄土高原水平阶减流阻蚀效应模拟

Flow Resistance Interactions on Hillslopes With Heterogeneous Attributes: Effects on Runoff Hydrograph Characteristics

AbstractAn improved modeling framework for capturing the effects of space and time‐variant resistance to overland flow is developed for intensively managed landscapes. The framework builds on the WEPP model but it removes the limitations of the “equivalent” plane and time‐invariant roughness assumption. The enhanced model therefore accounts for spatiotemporal changes in flow resistance along a hillslope due to changes in roughness, in profile curvature, and downslope variability. The model is used to quantify the degree of influence—from individual soil grains to aggregates, “isolated roughness elements,” and vegetation—on overland flow characteristics under different storm magnitudes, downslope gradients, and profile curvatures. It was found that the net effects of land use change from vegetation to a bare surface resulted in hydrograph peaks that were up to 133% larger. Changes in hillslope profile curvature instead resulted in peak runoff rate changes that were only up to 16%. The stream power concept is utilized to develop a taxonomy that relates the influence of grains, isolated roughness elements, and vegetation, on overland flow under different storm magnitudes and hillslope gradients. Critical storm magnitudes and hillslope gradients were found beyond which the effects of these landscape attributes on the peak stream power were negligible. The results also highlight weaknesses of the space/time‐invariant flow resistance assumption and demonstrate that assumptions on landscape terrain characteristics exert a strong control both on the shape and magnitude of hydrographs, with deviations reaching 65% in the peak runoff when space/time‐variant resistance effects are ignored in some cases.