WEPP Model Research Articles

A Simulation Study to Estimate Effects of Wildfire and Forest Management on Hydrology and Sediment in a Forested Watershed, Northwestern U.S.

Abstract. Suitable fuel reduction treatments are needed in the Colville National Forest, Washington, to reduce the risk of severe wildfire. This study aimed to identify high-risk erosion hillslopes following wildfire to aid in forest fuel reduction planning and to evaluate the effects of fuel treatments on the watershed hydrological response. The specific objectives were (1) to assess the soil burn severity associated with wildfires and use that information to identify critical hillslopes for forest fuel treatments, and (2) to evaluate the potential changes in water yield and peak flows from pre-treatment (undisturbed forest) to post-treatment (thinning and prescribed burn) conditions, in the East Deer Creek Watershed (EDCW), a subwatershed of the Colville National Forest. Assessments were made using a modeling approach for hypothetical wildfire and fuel treatment scenarios. FlamMap, a fire behavior model, was used to predict the spatial distribution of wildfire intensity for a hypothetical event under current vegetation conditions. WEPP simulations were subsequently completed to obtain sediment and water yields based on fire intensity and topography. WEPP erosion estimations following a simulated wildfire showed hillslope sediment yield varying from 0 to 49.4 Mg ha-1 year-1 from the 777 hillslopes, which were ranked in descending order of sediment yield to identify critical hillslopes for fuel treatments. The WEPP model calibrated for a nearby gauged watershed was then applied to the EDCW for pre-treatment and post-treatment conditions. At the watershed scale, the increase in water yield from pre-treatment to post-treatment conditions ranged from 0.7% to 5.6% on hillslopes delivering 10% to 50% of the predicted post-fire sediment. Simulated water balance components at the treated hillslopes showed substantial changes. Surface runoff, subsurface lateral flow, and deep percolation increased 150% (5 mm), 50% (9 mm), and 40% (41 mm), respectively, whereas evapotranspiration (ET) decreased 23% (124 mm). The relative differences between pre- and post-harvest peak flows showed no clear trends as treatment area increased. The results suggest that thinning and prescribed burns to treated hillslopes in the EDCW may lead to an increase in water yield and significant alterations in hydrological processes. Keywords: Fuel treatments, Modeling, Peak flows, Sediment, Water yield, Wildfire.

Application of GUSED‐VBS 2 Model for Flow and Sediment Transport in Vegetated Strips to Improve Water Quality

AbstractVegetated buffer strips change flow hydrology and sediment transport by increasing resistance to the flow and intensifying infiltration. GUSED‐VBS 2 is a process‐based mathematical model developed to simulate flow characteristics and the fate and transport of sediment in the backwater region upstream of vegetated strips and within them. The model also predicts the concentration and delivery of different particle sizes leaving the vegetated strips and reaching open water bodies. GUSED‐VBS 2 assumes that entrainment and deposition processes occur simultaneously and uses the Green–Ampt approach to simulate infiltration and gradually varied flow and kinematic wave approximation to simulate the water profile in the backwater region and within the vegetated strip respectively. The modified GUEST model approach was used to model the fate and transport of sediment in vegetated strips. Field data were used to evaluate the model predictions of the efficiency of vegetated strips in reducing runoff, sediment concentration and sediment delivery, and the results showed that GUSED‐VBS 2 performed much better in controlled conditions compared to field conditions. The performance of the GUSED‐VBS 2 and WEPP models in simulating particle size distribution in the outflow was compared with different model evaluation criteria and GUSED‐VBS 2 showed better performance compared to WEPP. Copyright © 2017 John Wiley & Sons, Ltd.

Quantifying the Binding and Bonding Effects of Plant Roots on Soil Detachment by Overland Flow in 10 Typical Grasslands on the Loess Plateau

Core Ideas Plant root reduced soil detachment by 54%, of which 41% was by root binding effect. Fibrous root was 1.6 times greater than tap root in reducing the soil detachment. Correction coefficients of 10 typical herbs were presented for the WEPP model. Plant roots penetrating the soil may enhance soil resistance and protect the topsoil against scouring by overland flow, but their mechanisms are not fully understood. This study was performed to quantify the binding and bonding effects of plant root systems on the process of soil detachment by overland flow. Ten typical dominant species of herbage representing two different root architectures on the Loess Plateau were selected, and 900 soil samples were collected from these grasslands for detachment capacity measurements under different flow shear stresses. The results showed that the existence of plant root systems greatly reduced the soil detachment capacity by 53.6%, of which 41.4 and 12.2% were attributed to the root binding and bonding effects, respectively. The contribution rate of the binding and bonding effects depended on plant root architecture (i.e., the tap and fibrous roots). For tap root, the average contribution of the plant root for protecting soil from detachment was 41.6%, of which 33.2 and 8.4% were induced by the root binding and bonding effects. For fibrous root, the mean contribution of plant root was 65.7%, of which 49.7 and 16.0% were attributed to the root binding and bonding effects, respectively. Series correction coefficients that took into consideration the root binding and bonding effects of 10 typical dominant plants for their rill erodibility in the Water Erosion Prediction Project model on the Loess Plateau; the result was satisfactory with Nash–Sutcliffe efficiency coefficients that ranged from 0.48 to 0.58.

Projection of phenology response to climate change in rainfed vineyards in north-east Spain

The aim of this research was to predict the changes in vine phenology of some white grape varieties when rainfed vineyards are subjected to climate change. The research was conducted in the north east of Spain, in an area with a Mediterranean climate. Temperature and precipitation changes under two Representative Concentration Pathway (RCP) scenarios – RCP4.5 and RCP8.5 – were simulated based on an ensemble of models. Water losses by runoff were predicted using the WEPP model and changes in evapotranspiration were estimated according to the predicted changes in temperature, wind speed and solar radiation for the same scenarios. Dates of budbreak, bloom, veraison and harvest of three varieties were evaluated: Chardonnay, during the period 1998–2012; and Parellada and Macabeo during the period 1998–2009. Projections for 2030, 2050 and 2070 were made based on the observed phenological dates and the heat accumulation needed to reach each stage and water available recorded in different periods along the growing cycle. An advance of all phenological dates was predicted, higher for veraison and harvest than for the earlier stages and higher for Parellada than for Macabeo and Chardonnay. These stages may advance up to 10 and 16days, respectively, for 2050 and up to 12 and 20days for 2070 under the RCP4.5 scenario. Under RCP8.5 scenario, the advance by 2070 could be up to 23 and 28days. These changes resulted in a shortening of the periods between phenological dates (>10days), higher for Parellada than for Chardonnay and Macabeo. The results also showed an additional advance of bloom for Chardonnay and Macabeo associated with decreasing water available, and an advance of veraison and harvest for all three varieties, associated with decreasing water available, particularly between budbreak and bloom and between bloom and veraison, depending on the variety.

Evaluating the impact of management scenarios and land use changes on annual surface runoff and sediment yield using the GeoWEPP: a case study from the Lighvanchai watershed, Iran

This study was undertaken to evaluate land use change impact and management scenarios on annual average surface runoff (SR) and sediment yield (SY) using the GeoWEPP tool in the Lighvanchai watershed (located in northwestern Iran). Following a sensitivity analysis, the WEPP model was calibrated (2005–2007) and validated (2008–2010) against monthly observed SY and SR. The coefficient of determination (R 2), Nash–Sutcliffe efficiency (NSE), mean bias error (MBE), and root-mean-square error (RMSE) were applied to quantitatively evaluate the WEPP model. The results indicate a satisfactory model performance with R 2 > 0.80 and NSE > 0.60. Therefore, the model for current land use (scenario 1) was run for a 30-year time period (1982–2011). The annual average of SR and sediment load were predicted as 93,584 m3/year and 4340 ton/year, respectively. To reduce the annual average surface runoff and sediment yield at the watershed scale, the second scenario (alfalfa cultivation with suitable tillage) and the third scenario (grassland development) as two management scenarios of land use changes were defined by identifying the critical hillslopes. The rate of SR and sediment load in the second scenario were 42,096 m3/year and 429 ton/year, respectively. For the third scenario, the model predictions were 30,239 m3/year and 226 ton/year, respectively. Compared to the first scenario, the reduction rates in annual average of sediment load were about 90 and 94%, respectively. Moreover, for the second and third management scenarios, the reduction rates in annual average of SR were about 55 and 67%, respectively.

Development of a Coupled Water Quality Model

Abstract. . Nonpoint-source (NPS) pollutants, especially from agriculture, continue to be a primary source of waterquality degradation problems. Effective land management decisions at the field scale must be made to minimize nutrient losses that could pollute streams. Existing NPS models often cannot directly estimate the impacts of different land management practices or determine the effectiveness of combined best management practices (BMPs) in a distributed way at the farm scale. In many cases, they rely on application of the Universal Soil Loss Equation (USLE) or its improved versions, which represent fields in a lumped fashion and use empirical rather than process-based modeling methodologies. In this study, a coupled Water Erosion Prediction Project and Water Quality (WEPP-WQ) model was completed, updated, improved, and evaluated for simulation of hydrology, soil erosion, and water quality. The WEPP model is a well-established process-based model that simulates runoff and erosion processes from a hillslope. The water quality components are based on those of the Soil and Water Assessment Tool (SWAT). A single overland flow element (OFE) on a hillslope is used to represent a single soil and land use management. The WEPP-WQ model was tested by comparing simulated values from the coupled model with observed nutrient and sediment concentrations in surface runoff following storm events at experimental sites near Waterloo in northeastern Indiana and at the Throckmorton Purdue Agricultural Center in west central Indiana. Time series evaluation of the WEPP-WQ model was performed with observed nutrient and sediment losses from an experimental plot near Tifton, Georgia. The model performed quite well in simulating nutrient losses for single storm events, with R2 greater than 0.8, Nash-Sutcliffe efficiency (NSE) greater than 0.65, and percent bias (PBIAS) less than 31% for runoff, sediment, nitrate nitrogen, total nitrogen, soluble phosphorus, and total phosphorus losses. In predicting time series nutrient loss, the WEPP-WQ model simulated daily nitrate nitrogen losses adequately, with the ratio of the root mean square error to the standard deviation of measured data (RSR) less than 0.7, NSE greater than 0.55, and PBIAS within the range of ±40%. Comparisons between simulated soluble phosphorus, total phosphorus, and literature results were performed due to the absence of an available observational dataset. The WEPP-WQ model with a single OFE in this study provides a basic but important step for the development of WEPP-WQ models with multiple OFEs that can evaluate the effectiveness of BMPs Keywords: Modeling, Nitrogen, Phosphorus, Soil erosion, Water quality, WEPP.

The WEPP Model Application in a Small Watershed in the Loess Plateau.

In the Loess Plateau, soil erosion has not only caused serious ecological and environmental problems but has also impacted downstream areas. Therefore, a model is needed to guide the comprehensive control of soil erosion. In this study, we introduced the WEPP model to simulate soil erosion both at the slope and watershed scales. Our analyses showed that: the simulated values at the slope scale were very close to the measured. However, both the runoff and soil erosion simulated values at the watershed scale were higher than the measured. At the slope scale, under different coverage, the simulated erosion was slightly higher than the measured. When the coverage is 40%, the simulated results of both runoff and erosion are the best. At the watershed scale, the actual annual runoff of the Liudaogou watershed is 83m3; sediment content is 0.097 t/m3, annual erosion sediment 8.057t and erosion intensity 0.288 t ha-1 yr-1. Both the simulated values of soil erosion and runoff are higher than the measured, especially the runoff. But the simulated erosion trend is relatively accurate after the farmland is returned to grassland. We concluded that the WEPP model can be used to establish a reasonable vegetation restoration model and guide the vegetation restoration of the Loess Plateau.

The effects of climate change and extreme wildfire events on runoff erosion over a mountain watershed

Summary Increases in wildfire occurrence and severity under an altered climate can substantially impact terrestrial ecosystems through enhancing runoff erosion. Improved prediction tools that provide high resolution spatial information are necessary for location-specific soil conservation and watershed management. However, quantifying the magnitude of soil erosion and its interactions with climate, hydrological processes, and fire occurrences across a large region (>10,000 km2) is challenging because of the large computational requirements needed to capture the fine-scale complexities of the land surface that govern erosion. We apply the physically-based coupled Variable Capacity Infiltration–Water Erosion Prediction Project (VIC–WEPP) model to study how wildfire occurrences can enhance soil erosion in a future climate over a representative watershed in the northern Rocky Mountains – the Salmon River Basin (SRB) in central Idaho. While the VIC model simulates hydrologic processes at larger scales, the WEPP model simulates erosion at the hillslope scale by sampling representative hillslopes. VIC–WEPP model results indicate that SRB streamflow will have an earlier shift in peak flow by one to two months under future climate scenarios in response to a declining snowpack under warming temperatures. The magnitude of peak flow increases with each higher severity fire scenario; and under the highest fire severity, the peak flow is shifted even earlier, exacerbating the effects of climate change. Similarly, sediment yield also increases with higher fire severities for both historical and future climates. Sediment yield is more sensitive to fire occurrence than to climate change by one to two orders of magnitude, which is not unexpected given that our fire scenarios were applied basin wide as worst case scenarios. In reality, fires only occur over portions of the basin in any given year and subsequent years’ vegetation regrowth reduces erosion. However, the effects of climate change on sediment yield result in greater spatial heterogeneities, primarily because of the spatial differences in precipitation projections, while fire conditions were uniformly applied. The combined effects of climate change and a possible continuation of increasing fire frequency and severity will compound excess sediment issues that already exist in this region of the intermountain West.

Soil losses in rainfed Mediterranean vineyards under climate change scenarios. The effects of drainage terraces.

Most vines in the Mediterranean are cultivated on bare soils, due to the scarcity of water. In addition, most traditional soil conservation measures have been eliminated to facilitate the movement of machinery in the fields. In such conditions, high erosion rates are recorded. Given the predicted changes in precipitation and an increasing number of extreme events, an increase in erosion processes is expected. In this study, erosion processes under different climate change scenarios were evaluated as well as the effects of implementing drainage terraces in vineyards. Soil losses were simulated using the WEPP model. The results confirmed the relevance of extreme events on annual soil losses. The WEPP model gave satisfactory results in predicting runoff and soil losses, although the soil losses recorded after some extreme events were under-predicted. The model responded to changes in precipitation and because of that a decrease in precipitation gave rise to a decrease in soil losses. For the scenario in 2050, runoff volumes decreased between 19.1 and 50.1%, while erosion rates decreased between 34 and 56%. However, the expected increase in rainfall intensity may contribute to higher erosion rates than at present. The construction of drainage terraces, perpendicular to the maximum slope, 3 m wide and 30 m between terraces, may lead to an average decrease in soil losses of about 45%.

Spatial discretization of large watersheds and its influence on the estimation of hillslope sediment yield

The combined use of water erosion models and geographic information systems has facilitated soil loss estimation at the watershed scale. Tools such as the Geo-spatial interface for the Water Erosion Prediction Project (GeoWEPP) model provide a convenient spatially distributed soil loss estimate but require discretization to identify hillslopes and channels. In GeoWEPP, the TOpographic PArameteriZation (TOPAZ) model is used as an automated procedure to extract a watershed boundary, hillslopes and channels from a digital elevation model (DEM). Previous studies in small watersheds have shown that the size of the hillslopes and the channel distribution affect the model estimates, but in large watersheds, the effects on the soil loss estimates have yet to be tested. Therefore, the objective of this study was to evaluate the effect of discretization on the hillslope sediment yield estimates using GeoWEPP in two large watersheds (>10 km2). The watersheds were selected and discretized varying the TOPAZ parameters [critical source area (CSA) and minimum source channel length (MSCL)] in a 30-m resolution digital elevation model. The drainage networks built with TOPAZ were compared with each other using the drainage density index. The results showed that the discretization affected hillslope sediment yield estimates and their spatial distribution more than the total runoff. The drainage density index and the hillslope sediment yield were proportional but inversely related; thus, soil loss estimates were highly affected by the spatial discretization. As a result of this analysis, a method to choose the CSA and MSCL values that generates the greatest fraction of hillslopes having profile lengths less than 200 m was developed. This slope length condition is particularly crucial when using the WEPP and GeoWEPP models, in order for them to produce realistic estimates of sheet and rill erosion. Finally, and as a result of this analysis, a more reliable method was developed for selecting the TOPAZ channel network parameters (CSA and MSCL). Copyright © 2015 John Wiley & Sons, Ltd.

Impact of precipitation and runoff on ephemeral gully development in cultivated croplands

Abstract. The goal of this study was to estimate the impacts of precipitation and runoff on ephemeral gully development. A field experiment was conducted during the summer of 2013 on an agricultural field near the city of McPherson in central Kansas, USA. Precipitation data were collected, and the gully headcut was measured every three to four weeks. The rainfall excess was calculated with the WEPP model, whereas headcut soil losses were estimated based on measurements. Headcut measurements showed that there was no gully development during rainfall events of short duration of high or low intensity. However, headcut propagation was clearly detected under saturated soil conditions for a three-day storm. This field study provides data to model the mechanics of ephemeral gully development. Further measurements of precipi-tation and gully morphology are needed for statistical analysis of gully erosion and the associated soil losses.

Quantifying detachment rate of eroding rill or ephemeral gully for WEPP with flume experiments

Summary Ephemeral gullies or rills are major sediment sources and the primary channel to convey runoff and sediments from hillslopes. Quantifying the detachment rate is important for understanding the erosion process of ephemeral gullies. This study suggests a method to estimate the detachment rate for use in WEPP model, using sediment distribution data along an eroding rill or ephemeral gully under controlled flume experiments, conducted at four slope gradients (8.74%, 17.62%, 26.78%, and 36.38%) and four flow rates (32, 64, 128 and 256 L min−1). The experimental soil materials were packed into the flume of 0.5 m wide, 0.6 m deep and 12 m long, to a thickness of 0.5 m at a bulk density of 1300 kg m−3. Regulated water flow was introduced to soil surface at the upper end of flumes. The detachment rate was calculated from the spatial distribution data of sediment concentrations measured with sediment-laden water samples simultaneously taken along the gullies at one meter intervals. Results showed that the detachment rate was well fitted with downslope distance along the rill or ephemeral gully by an exponential equation. The regression parameters indicated that detachment rate decreases linearly with sediment load in the gully flow. The feedback relationship between sediment load and detachment rate in rill or ephemeral gullies could be adequately represented by the first-order coupling equation for loess soil under steep slopes and high flow rates. The detachment rates along the rills or ephemeral gullies were found to increase with slope gradient and flow rate and the detachment rate was positively related to unit stream power and the deficit between max sediment load and the local sediment load.

Evaluation of GUEST and WEPP with a new approach for the determination of sediment transport capacity

Summary Sediment transport capacity (Tc) is a key parameter for all process-based erosion models. The objective of this study was to develop a new approach for accurate determination of Tc under infiltration conditions based on rill morphology and the sediment feedback relationship. This would allow the way in which sediment transport capacity is computed in WEPP and GUEST models. Six-m long rills in three soils were subjected to constant inflow rates (50, 75 and 122 ml s−1) and three flume slope gradients (2%, 4% and 6%). Cross-sections of rills were measured precisely at 0.5 m intervals using a profile-meter prior to and after each experiment. The cumulative net rates of erosion at the end of each section were converted to sediment load along the rill length. The sediment feedback relationship was applied to fit the sediment load values and Tc was determined asymptotically under equilibrium conditions. The results showed that under infiltration conditions, both models tended to under-estimate Tc, however, Tc predicted using the GUEST model had better agreement with the measured Tc values than that predicted with WEPP. Using the proposed value of F = 0.15, the performance of GUEST in predicting Tc could be further improved. Sidewall slumping was found to be a plausible explanation for underestimation of Tc by WEPP, which is not explicitly modeled. In contrast, GUEST takes into account any observed changes in rill morphology. The results also indicated that Tc increased as a function of flow discharge and slope gradient, but was more sensitive to slope gradient than to flow discharge. Moreover, stream power was found to be a better predictor of Tc than shear stress. Yet, regression equations using unit discharge and slope gradient as independent variables, did not achieve any better estimation of Tc than did the GUEST (when F = 0.15). Accurate determination of parameter(s) used in a process-based model such as GUEST will lead to improved Tc estimations. Furthermore, Tc is a process-based parameter which should not ideally be estimated with regression equations.

Evaluation of the WEPP model and digital elevation grid size, for simulation of streamflow and sediment yield in a heterogeneous catchment

ABSTRACTThe paper presents the result of an application of the GeoWEPP model in a heterogeneous semi‐agricultural catchment located in the northern Italian Apennines mountain range. The objectives were: (a) to evaluate the GeoWEPP model in a heterogeneous catchment in a Mediterranean climate and (b) to examine the effect of digital elevation model grid size on hydrological and sediment yield simulations. The catchment is characterized by large heterogeneity in geology, soil type, vegetation cover and topography. In addition, 10% of its area is occupied by calanchi (badlands), characterized by steep, bare soil and accentuated erosion. Experimental streamflow data were compared with those simulated by GeoWEPP for a period of eight years and the results were evaluated by means of statistical indices, with the analysis of the flow duration curve. Simulated sediment yields were compared with experimental data for one year. The streamflow cumulative annual results were satisfactory with NSE oscillating between 0.40 and 0.83 and RMSE between 1.1 and 2.9 mm. Also, the performance of the model with daily streamflow data was positive (NSE = 0.68 and RMSE = 1.9 mm). The flow duration curve indicated that GeoWEPP could represent the experimental streamflow for fluxes over 1 mm d−1. The model performance for simulation of sediment yield was satisfactory with both digital elevation models of different grid sizes (NSE = 0.84 and 0.87). Indeed, the sensitivity analysis tests of the model showed that there was no statistically significant improvement in the accuracy of the digital elevation model between 10 and 2 m resolution. These results were confirmed for both streamflow as well as sediment yield. Additional sensitivity analysis of other model parameters performed on the entire catchment and badlands hillslopes showed that bedrock hydraulic conductivity primarily affected the model in both settings. Copyright © 2014 John Wiley & Sons, Ltd.

Potential Erosion from Bladed Firelines in the Appalachian Region Estimated with USLE-Forest and WEPP Models

Potential Erosion from Bladed Firelines in the Appalachian Region Estimated with USLE-Forest and WEPP Models

WEPP calibration for improved predictions of interrill erosion in semi-arid to arid environments

Modeling soil erosion contributes to the understanding of the erosion processes and needs to predict accurately the erosion rates under different environmental conditions. Few studies have investigated the WEPP's applicability for arid and semi-arid conditions that differ from those where the model was developed. This research was carried out to evaluate and improve the WEPP model for arid and semiarid regions for interrill erosion using a rainfall simulator at plot scale. The results showed that measured interrill erosion rates ranged from 9.3×10−6 to 89.6×10−6kgm−2s−1. In comparison, the WEPP-interrill erosion prediction values were on average 14.5 times lower than the measured ones, which can be ascribed to a systematic error. To calibrate the model, two regression equations were presented to estimate baseline interrill erodibility (Kib) and adjusted interrill erodibility (Kiadj). Accordingly, the baseline interrill erodibility was influenced by surface rock cover much more than any other soil property. Also, Kiadj was functioned as sediment concentration and sand percent. Model validation showed that after calibrating Kib and Kiadj, the coefficient of efficiency enhanced to 0.31 and 0.90, respectively. However, the model tended to overestimate the lower erosion rates and to underestimate the higher erosion rates. To modify interrill erodibility and to achieve a process-based parameter, a simple equation was developed based on stream power. The coefficient of efficiency of 0.61 was obtained for the proposed approach. In general, the model predictions enhanced after calibration, but the model tendency to underestimate high erosion rates was observed. One of the reasons for low accuracy of the WEPP was its dependence on soil empirical parameters used in predicting the sub-model components. The model prediction was found to be improved through process-based calibration of soil parameters.

Rill and interrill erodibility and sediment characteristics of clayey Australian Vertosols and a Ferrosol

For soils and conditions outside the USA, input parameters for physically based soil erosion models, such as the WEPP model, are usually not available, particularly for tropical soils. In a laboratory study, small erosion pans and a programmable rain simulator were used to determine interrill erodibility, whereas in the field, rills were physically allocated in the field as plots of 0.1 by 10 m within a ridge–furrow arrangement and five water-inflow rates were applied sequentially to determine rill erodibility and critical hydraulic shear. During the rain or inflows, runoff samples were taken and flow was characterised. The soils tested were Grey Vertosol, Black Vertosol, and Red Ferrosol. The fall velocity parameter, V50, for rill soil and eroded sediment followed the order Red Ferrosol > Grey Vertosol > Black Vertosol, which Black Vertosol was the same order as observed for V50 and mean weight diameter (MWD) of aggregates in the interrill erosion experiment and D50 of interrill eroded sediment, demonstrating differences between soils in dispersion and aggregate stability. The estimated values obtained by the WEPP model were not comparable to laboratory interrill erodibility values or to field rill erodibility values. Thus, erodibility parameters for physically based erosion models such a WEPP should be determined in the field for tropical soils, and new equations need to be developed to estimate such values based on soil properties for tropical soils.

Application of WEPP Model to Estimate Soil Erosion and Sediment Runoff

Application of WEPP Model to Estimate Soil Erosion and Sediment Runoff

Effects of different terrace protection measures in a sloping land consolidation project targeting soil erosion at the slope scale

Land consolidation of sloped areas using terrace construction is undertaken to improve water conservation, control soil erosion and enhance soil fertility. The subsequent soil and water conservation effects of this practice have received much attention. Quantitatively analyzing the effects of protective measures on soil erosion will have significant practical applications. In this study, changes in soil and water conservation were compared under 64 scenarios of varying terrace protection measures (coverage series) and six configurations (high, medium and low grass coverage combinations). These scenarios were simulated using the process-based soil erosion WEPP model and considered the physical constraints and conditions of typical land consolidation projects. Results showed large differences in soil loss and sediment yield in scenarios of different grassland coverage. Sediment yield was found to have a strong correlation with rainfall intensity. Compared to unstructured slopes, the sediment trapping rate of terraced slopes increased with grassland coverage but negligible variation was found with change in rainfall intensity. The results of different spatial configuration scenarios of high, medium and low grass coverage indicated that protective measures worked best when located at the lowest position along slopes.

다양한 강우강도 및 패턴에 따른 WEPP 모형의 유출‧첨두유출‧토양유실량 평가

Recently, changes in rainfall intensity and patterns have been causing increasing soil loss worldwide. As a result, the water ecosystem becomes worse and crops yield are reduced with soil loss and nutrient loss with it. Many studies have been proposed to estimate runoff and soil loss to predict or decrease non-point source pollution. Although the USLE has been used for many years in estimating soil losses, the USLE cannot reflect effects on soil loss of changes in rainfall intensity and patterns. The WEPP, physically based model, is capable of predicting soil loss and runoff using various rainfall intensity. In this study, the WEPP model was simulated for sediment yield, runoff and peak runoff using data of 5, 10, 30, 60 minute term rainfall, Huff`s method and design rainfall. In case of rainfall interval of 5 minutes and 60 minutes, the sediment and runoff values decreased by 24% and 19%, respectively. The peak rate runoff values decreased by 16% when rainfall interval changed from 5 minutes to 60 minutes, indicating the peak rate runoff values are affected by rainfall intensity to some degrees. As a result of simulating using Huff`s method, all values (sediment yield, runoff, peak runoff) were found to be the greatest at third quartile. According to the analysis under various design rainfall conditions (2, 3, 5, 10, 20, 30, 50, 100, 200, 300 years frequency), sediment yield, runoff, and peak runoff of 906.2%, 249.4% and 183.9% were estimated using 2 year to 300 year frequency rainfall data.