Soil Erosion Assessment Research Articles

Development of an intelligent system based on ANFIS model for predicting soil erosion

This study explores capability of adaptive neuro-fuzzy interface system (ANFIS) model for soil erosion assessment of which various parameters are involved and the parameters interaction is highly nonlinear. Soft computing technique has been applied widely in various fields, but its application in soil science is limited. A number of models have been established in predicting soil erosion such as a revised universal soil loss equation (RUSLE) model whereby parameters of the RUSLE model are employed in testing the ANFIS model in this study. Besides, a new parameter of biomass microbe (Mf) is introduced and its effectiveness in controlling erosion is demonstrated. A hilly area near the Guthrie Corridor Expressway, Malaysia, is chosen as a study area whereby five experimental plots size of 8 × 8 m and 5 × 5 m are developed. These five plots are characterized by either natural or planted vegetation or either with or without microbe bio-fertilizer. Input parameters of RUSLE, i.e. rainfall erosivity, soil erodibility, slope length and steepness, vegetation and support practice, are measured, and observed erosion is monitored for 1 year. The microbe factor presented as Mf is examined by pairing the plot with and without microbe while keeping other similar characteristic for those plots. Result shows a satisfactory achievement between observed and predicted model by ANFIS with R2, RMSE and MAE being 0.8275, 1.4276 and − 0.0165, respectively. In terms of a relationship between the Mf factor and soil erosion, it is noticed that the soil erosion is inversely proportional to the Mf when the entire erosion conservation practices are unchanged for a given period. Therefore, the application of microbes could be an alternative or additional erosion conservation technique in soil conservation works.

Evaluation of water erosion at a mountain catchment in Poland using the G2 model

The Western Carpathians region in southern Poland is characterized by high erosion risk due to steep slopes, flysch formation and intense precipitation with frequent storm events. The G2 model, based on the principles of the Universal Soil Loss Equation (USLE), was used to investigate soil erosion assessment, except that the yearly rainfall erosivity factor was substituted for by the monthly one. The plant cover factor was determined based on the CORINE land cover 2012 database and field observations of vegetation stages. Slope intercept was estimated by applying a Sobel filter. Terrain properties were calculated from a 5 m DEM of the area. Modeling investigations were carried out in the agricultural basin of the mountain catchment (1.47 km2) in the years 2011–2014. Rainfall data were collected from weather stations, and soil properties were measured in 43 locations. The G2 model estimated total annual soil loss as between 3.37 Mg ha−1 (2012) and 31.05 Mg ha−1 (2014). The erosive events that contributed most to yearly erosion occurred in May (2014: 80.40% of yearly total) and June (2013: 57.08%). Redundancy analysis based on land-use types provided factors affecting soil erosion by water. In conclusion, the G2 model was useful in erosion estimation in a steep-sloped agricultural basin with a variable hydrological regime.

A multilayer perceptron model for the correlation between satellite data and soil vulnerability in the Ferlo, Senegal

ABSTRACTSoil erosion processes which contribute to desertification and land degradation, constitute major environmental and social issues for the coming decades. This is particularly true in arid areas where rural populations mostly depend on soil ability to support crop production. Assessment of soil erosion across large and quite diverse areas is very difficult but crucial for planning and management of the natural resources. The purpose of this paper is to investigate a prediction model for soil vulnerability to erosion based on the use of the information contained in satellite images. Based on neural networks models, the used approach in this paper aims at checking a correlation between the digital content of satellite images and soil vulnerability factors: erosivity (R), the soil erodibility (K), and the slope length and steepness (LS); vulnerability (V) as described in the RUSLE model. Significant results have been obtained for R and K factors. This promising pilot study was conducted in South Ferlo, Senegal, a region with Sahelian environmental characteristics.

Assessment of soil erosion using RUSLE, GIS and remote sensing in NW Ethiopia

This study integrates the Revised Universal Soil Loss Equation (RUSLE) with GIS and remote sensing techniques to assess soil erosion severity in the Dembecha District, Northwestern Ethiopia. Digital elevation model (DEM), land use/land cover (LU/LC) maps, and rainfall and soil data were used as an input to identify the most erosion prone areas. Accordingly, the district was classified into five soil loss severity classes: very slight (24%), slight (49%), moderate (11%), severe (3%) and very sever (13%) risk classes. Most of the district was characterized by very slight to slight soil erosion rates which is associated with the gentle slope covered by Alisols and Cambisols. The mean annual soil loss in the district is estimated to be 49 t ha−1 yr−1, i.e. total soil loss of 526,996 t yr−1. Hence, soil and water conservation (SWC) measures should prioritize based on soil erosion severity levels.

A review of radiometric analysis on soil erosion and deposition studies in Africa

Soil erosion is one of the main soil degradation phenomena that threaten sustainable use of soil productivity thus affecting food security. In addition, it leads to reservoir storage capacity loss because of sedimentation. This not only affects water quantity but also water quality. Worldwide, annual loss in reservoir storage capacity due to sedimentation is 0.5 to 1%. Similarly, about 27% of land in Africa is largely degraded by erosion. As a result, there is need to minimize soil erosion and deposition through site specific estimation of soil erosion and deposition rates in the reservoirs. To achieve this, Fallout RadioNuclides (FRNs) are some of the methods in use. The most common radionuclides include; <sup>137</sup>Cs, <sup>210</sup>Pb and <sup>7</sup>Be. Only few countries in Africa have exploited these FRNs. In these countries, <sup>137</sup>Cs has been largely exploited but in some regions, it has been reported to be below minimum detection limit. Using <sup>137</sup>Cs and <sup>210</sup>Pb, maximum reference inventory in Africa is found to be 1450 and 2602 Bq/m<sup>2</sup>, respectively. However, there is minimal application of <sup>7</sup>Be within the continent. Also, very little has been done in Africa to assess chronology and sedimentation rates of reservoirs using FRNs measured from sediment cores. In conclusion, a gap still exists on FRNs application in Africa in assessing soil erosion, deposition and reservoir sedimentation.

Assessment of soil erosion and sediment yield using erosion potential method: Case study - Vrbas river basin (B&H)

Soil erosion is one of the most significant forms of land degradation in the Bosnia and Herzegovina. The mapping of soil erosion in B&H, as in the study area, was realized 30 years ago (1979-1985). The past decades has been marked by the changes which retained visible tracks and caused numerous changes in the intensity of erosion processes. In this paper, the mapping of the recent state of erosion intensity was performed, and then an analysis of changes was made in relation to the state of 30 years ago. The erosion potential method (EPM) was used for mapping the soil erosion and calculation of gross annual erosion and sediment yield. Erosion Map of the Vrbas river basin was made in the scale of 1:25,000. This Erosion Map counts a total of 69 topographic sections and 4,524 erosion polygons (plots). According to the Erosion Map of the Vrbas river basin, 5,666.88 km2 of the study area is affected by erosion, while 621.71 km2 are accumulating sediments. Annual gross erosion in the Vrbas river basin is 1,223,989.60 m3/year, while sediment yield is 366,088.10 m3/year. These research results are important because this is the first soil erosion map for the Vrbas river basin with EPM methodology for the whole river basin on territory of Bosnia and Herzegovina. The results can be applied in the field of spatial and urban planning, water and soil management on the local and regional level.

Updated Measurements in Vineyards Improves Accuracy of Soil Erosion Rates

Core Ideas Stock unearthing method assumes that soil surface is planar between vines.Improved stock unearthing method enhances the survey due to extra measurements.Indispensable to consider the timing of the measures in relation to tillage events.Stock unearthing method underestimates soil erosion rates by –14.2% in 1‐d plowed vineyards.Stock unearthing method underestimates erosion rates by –37.8% in 86‐d plowed vineyards. Vineyards have proven to be one of the most degraded agricultural ecosystems due to very high erosion rates, which are typically measured at fine temporal and spatial scales. Long‐term soil erosion measures are rare, but this information may be indispensable for a proper understanding of the vineyard soil system, landscape evolution, and crop production. The stock unearthing method (SUM) is a common topographical measurement technique developed to assess long‐term erosion rates. The reliance of the SUM has been questioned and should be replaced by an improved measurement technique. In this paper, we demonstrate the added value (improved accurate, low cost, and faster than photogrammetrically methods) of the improved stock unearthing method (ISUM). It was shown that large errors may have been made in previous assessments of soil erosion on vineyards, as the old method did not make measurements in the inter‐row area or consider the timing of the erosion assessment in relation to tillage events. We found that this caused the SUM to severely underestimate soil erosion rates by –14.2 and –37.8% in 1‐ and 86‐d tillage vineyards in one location, respectively. Furthermore, the increased measurement resolution attained from the ISUM allowed for the detailed assessment of micro‐topographical change. Soil loss maps were able to detect the locational changes in soil depletion and accumulation, as well as continuous soil movement features in the inter‐row areas. Ultimately, this leads to a more accurate estimate of the actual soil erosion rates in vineyards.

Development of GIS Interface Tool for GAMES Model and Its Application to an Agricultural Watershed in Southern Ontario

Soil erosion is an important economic and environmental concern throughout the world. In order to assess soil erosion risk and conserve soil and water resources, soil erosion modeling at the watershed scale is imperative. The Guelph model for evaluating effects of Agricultural Management System on Erosion and Sedimentation (GAMES) is tailor-made for such applications; it, however, requires a significant amount of spatial information which needs to be pre-processed using a Geographic Information System (GIS). The GAMES model currently lacks any such automated tools. As such, the GAMES was loosely coupled to a GIS interface to manage the large spatial input data and to produce efficient cartographic representations of model output results. The developed interface tool was tested to simulate the Kettle Creek paired watershed in Southern Ontario, Canada. Result demonstrated that the GIS-assisted procedure increased the ability of the GAMES model in simulating such a spatially varied watershed and made the process more efficient and user-friendly. Furthermore, the quality of reporting and displaying resultant spatial output was also significantly improved. The developed GAMES interface could be applied to any watershed, and the enhancement could be used to assess soil erosion risk and conserve soil and water resources in an effective way.

Assessment of soil erosion on hillslopes (a case study carried out in the Ashan drainage basin, Iran)

The objective of this study is to determine the rate of soil erosion on slopes of differing steepness and its effects on agricultural land and pastures in the drainage basin around Ashan. Exogenous factors like water and wind and endogenous elements such as erodibility of the soil have key roles in erosion and the results of this study will help in the management of soil and soil conservation programs. Soil erosion in the drainage basin around Ashan has accelerated and because of this it is important to determine the erodibility of the soil. In this study, the soil on four different hill slopes was sampled and after drying, soil size distribution and soil texture and the organic content of forty samples, and the k-factor (erodibility) using the USLE equation, were determined. According to the results of the ANOVA test there are strong relationships between the variables, which is illustrated by box plots. The results indicate that erodibility is significantly (p < 0.05) associated with the type of land use and landforms. The highest levels of erosion were recorded on the back-slope and the least at the summit and on the toe-slope. Discriminant function analysis was used to determine the discriminatory power of the erodibility factor associated with the different uses of land and landform components. According to the DFA results, the K factors indicate the use of the land and landforms were the most significant factors, with significances of 0.000 and 0.002, respectively.

Modelling spatial and temporal variations of annual suspended sediment yields from small agricultural catchments

Estimates of sediment yield are important for ecological and geomorphological assessment of fluvial systems and for assessment of soil erosion within a catchment. Many regulatory frameworks, such as the Convention for the Protection of the Marine Environment of the North-East Atlantic, derived from the Oslo and Paris Commissions (OSPAR) require reporting of annual sediment fluxes. While they may be measured in large rivers, sediment flux is rarely measured in smaller rivers. Measurements of sediment transport at a national scale can be also challenging and therefore, sediment yield models are often utilised by water resource managers for the predictions of sediment yields in the ungauged catchments. Regression based models, calibrated to field measurements, can offer an advantage over complex and computational models due to their simplicity, easy access to input data and due to the additional insights into factors controlling sediment export in the study sites. While traditionally calibrated to long-term average values of sediment yields such predictions cannot represent temporal variations. This study addresses this issue in a novel way by taking account of the variation from year to year in hydrological variables in the developed models (using annual mean runoff, annual mean flow, flows exceeded in five percentage of the time (Q5) and seasonal rainfall estimated separately for each year of observations). Other parameters included in the models represent spatial differences influenced by factors such as soil properties (% poorly drained soils and % peaty soils), land-use (% pasture or % arable lands), channel slope (S1085) and drainage network properties (drainage density). Catchment descriptors together with year-specific hydrological variables can explain both spatial differences and inter-annual variability of suspended sediment yields. The methodology is demonstrated by deriving equations from Irish data-sets (compiled in this study) with the best model efficiency of 0.84 and best model fit of adjusted R2 of 0.82. Presented approach shows the potential for regression based models to model contemporary suspended sediment yields in small river systems.

Utilizing New and Innovative Tools to Mitigate Surficial Erosion in Mediterranean Environments

Aim of study: Soil erosion is a serious environmental problem since it can have major impacts on the human society. Climate change is only expected to exacerbate soil erosion. The aim of this study was to use new technologies to measure more accurately and address holistically soil erosion mitigation in Greece. Area of study: The study area was on Thasos Island, Greece that has flat and steep slope areas, different types of land-uses and frequent wildfires that allowed to assess soil erosion under different conditions. Material and Methods: Soil erosion was estimated at two different scales (micro and macroscale). For the miscrocale, different sensors along with the use of ultrasonic technology were employed to measure erosion and other influencing factors. For the macroscale, firstly a soil loss equation in GIS was utilized. In addition, an Integrated Information System was developed for stakeholders. Main results: A new tool that measures accurately and continuously soil erosion was developed. The Automated Soil Erosion Monitoring System (ASEMS) can monitor and store important environmental variables at a specific location (microscale). The variables it measured were: i) soil erosion/deposition (ground level changes), ii) soil moisture, iii) soil temperature, iv) rainfall and v) air temperature. Finally, an Integrated Information System (I 2 S) that allowed to mitigate soil erosion for large areas (macroscale) was developed. Highlights: New tools (ASEMS and I 2 S) and a calibrated equation in GIS were developed that could be utilized by government agencies in Greece to accomplish sustainable, effective and cost-efficient mitigation of soil erosion. These tools are also applicable in other regions of the Mediterranean.

Participatory assessment of soil erosion severity and performance of mitigation measures using stakeholder workshops in Koga catchment, Ethiopia

Farmers possess a wealth of knowledge regarding soil erosion and soil and water conservation (SWC), and there is a great demand to access it. However, there has been little effort to systematically document farmers' experiences and perceptions of SWC measures. Sustainable Land Management (SLM) has largely evolved through local traditional practices rather than adoption based on scientific evidence. This research aimed to assess soil erosion and performance of different SWC measures from the farmers' perspective by documenting their perceptions and experiences in Koga catchment, Ethiopia. To this aim, workshops were organised in three sub-catchments differing in slopes and SWC measures. Workshops included group discussions and field monitoring of erosion indicators and systematically describing the status of soil erosion, soil fertility and yield to assess the performance of SWC measures. Results show that farmers are aware of the harmful effects of ongoing soil erosion and of the impacts of mitigation measures on their farms. Sheet erosion was found to be the most widespread form of erosion while rill damage was critical on plots cultivated to cereals on steep slopes. The average rill erosion rates were 24.2 and 47.3 t/ha/y in treated and untreated farmlands, respectively. SWC reduced rill erosion on average by more than 48%. However, the impacts of SWC measures varied significantly between sub-watersheds, and farmers believed that SWC measures did not prevent erosion completely. Comparatively, graded stone-faced soil bunds revealed maximum desired impacts and were most appreciated by farmers, whereas level bunds caused water logging. Most traditional ditches were highly graded and begun incising and affected production of cereals. Despite the semi-quantitative nature of the methodology, using farmers' perceptions and experiences to document land degradation and the impacts of SWC measures is crucial as they are the daily users of the land and therefore directly affecting the success or failure of SWC measures.

Prediction of spatial soil loss impacted by long-term land-use/land-cover change in a tropical watershed

The devastating effect of soil erosion is one of the major sources of land degradation that affects human lives in many ways which occur mainly due to deforestation, poor agricultural practices, overgrazing, wildfire and urbanization. Soil erosion often leads to soil truncation, loss of fertility, slope instability, etc. which causes irreversible effects on the poorly renewable soil resource. In view of this, a study was conducted in Kelantan River basin to predict soil loss as influenced by long-term land use/land-cover (LULC) changes in the area. The study was conducted with the aim of predicting and assessing soil erosion as it is influenced by long-term LULC changes. The 13,100 km2 watershed was delineated into four sub-catchments Galas, Pergau, Lebir and Nenggiri for precise result estimation and ease of execution. GIS-based Universal Soil Loss Equation (USLE) model was used to predict soil loss in this study. The model inputs used for the temporal and spatial calculation of soil erosion include rainfall erosivity factor, topographic factor, land cover and management factor as well as erodibility factor. The results showed that 67.54% of soil loss is located under low erosion potential (reversible soil loss) or 0–1 t ha−1 yr−1 soil loss in Galas, 59.17% in Pergau, 53.32% in Lebir and 56.76% in Nenggiri all under the 2013 LULC condition. Results from the correlation of soil erosion rates with LULC changes indicated that cleared land in all the four catchments and under all LULC conditions (1984–2013) appears to be the dominant with the highest erosion losses. Similarly, grassland and forest were also observed to regulate erosion rates in the area. This is because the vegetation cover provided by these LULC types protects the soil from direct impact of rain drops which invariably reduce soil loss to the barest minimum. Overall, it was concluded that the results have shown the significance of LULC in the control of erosion. Maps generated from the study may be useful to planners and land use managers to take appropriate decisions for soil conservation.

Soil erosion assessment in the core area of the Loss Plateau

In order to explore the spatiotemporal evolution of erosion and sediment yield before and after Grain for Green Project in the Loss Plateau. The soil loss of Yulin is estimated by Chinese Water Erosion on Hill Slope Prediction Model. The result shows that the spatiotemporal variations of soil erosion are largely related to rainfall erosion distribution, slope, and land use type. The overall soil erosion categories in the south region are higher than that of the northwest. Mid slopes and valleys are the major topographical contributors to soil erosion. With the growth of slope gradient, soil erosion significantly increased. The soil loss has a decreasing tendency after Grain for Green Project. The results indicate that the vegetation restoration as part of the Grain for Green Project on the Loess Plateau is effective.

The age of vines as a controlling factor of soil erosion processes in Mediterranean vineyards

Vineyards incur the highest soil and water losses among all Mediterranean agricultural fields. The state-of-the-art shows that soil erosion in vineyards has been primarily surveyed with topographical methods, soil erosion plots and rainfall simulations, but these techniques do not typically assess temporal changes in soil erosion. When vines are planted they are about 30cm high×1cm diameter without leaves, the root system varies from 2 to over 40cm depth, and sometimes the lack of care used during transplanting can result in a field with highly erodible bare soils. This means that the time since vine plantation plays a key role in soil erosion rates, but very little attention has been paid to this by the scientific community. Thus, the main goal of this research was to estimate soil losses and assess soil erosion processes in two paired vineyard plantations of different ages. To achieve this goal, the improved stock unearthing method (ISUM) was applied to vineyards on colluvial parent materials with similar soil properties, topographical characteristics and land managements in the Les Alcusses Valley, southwestern Valencia province, Spain. Our findings suggested that the old vineyards showed lower erosion rates (−1.61Mgha−1yr−1) than those that were recently planted (−8.16Mgha−1yr−1). This is because of the damage that the plantation of the vines causes to soil. Tillage after planting (4 times per year) resulted in changes in the inter-row and row morphology, promoting the development of a ridge underneath the vines that disconnected the inter-rows and reduced soil losses with time. After the second year and until the 25th year after plantation, soil erosion was approximately 1Mgha−1y−1, which means that most of the erosion took place during the first two years after the plantation. Soil conservation strategies should be applied immediately after the plantation works to allow sustainable grape production. That is when soil erosion most needs to be controlled.

First use of a compound-specific stable isotope (CSSI) technique to trace sediment transport in upland forest catchments of Chile

Land degradation is a problem affecting the sustainability of commercial forest plantations. The identification of critical areas prone to erosion can assist this activity to better target soil conservation efforts. Here we present the first use of the carbon-13 signatures of fatty acids (C14 to C24) in soil samples for spatial and temporal tracing of sediment transport in river bodies of upland commercial forest catchments in Chile. This compound-specific stable isotope (CSSI) technique was tested as a fingerprinting approach to determine the degree of soil erosion in pre-harvested forest catchments with surface areas ranging from 12 to 40ha. For soil apportionment a mixing model based on a Bayesian inference framework was used (CSSIAR v.2.0). Approximately four potential sediment sources were used for the calculations of all of the selected catchments. Unpaved forestry roads were shown to be the main source of sediment deposited at the outlet of the catchments (30–75%). Furthermore, sampling along the stream channel demonstrated that sediments were mainly comprised of sediment coming from the unpaved roads in the upper part of the catchments (74–98%). From this it was possible to identify the location and type of primary land use contributing to the sediment delivered at the outlet of the catchments. The derived information will allow management to focus efforts to control or mitigate soil erosion by improving the runoff features of the forest roads. The use of this CSSI technique has a high potential to help forestry managers and decision makers to evaluate and mitigate sources of soil erosion in upland forest catchments. It is important to highlight that this technique can also be a good complement to other soil erosion assessment and geological fingerprinting techniques, especially when attempting to quantify (sediment loads) and differentiate which type of land use most contributes to sediment accumulation.

Environmental Impact Assessment (EIA) and Assessment of Soil Loss in Sandur Taluk due to Mining Activity in and Around Bellary District, South India

The catchment boundary of Sandur Taluk covers an area about 1254.02 sq km. It is well known for repository of Iron and manganese ore mineralization, more than hundred mining companies were operated within the Sandur Taluk and majority of hillocks have undergone by mining activity. The Sandur Taluk is affected by excavation of Iron ore. An attempt is made to Environmental Impact Assessment (EIA) by attributing various parameters like Land Use Land cover, Soil, Geomorphology, and catchment boundary etc., The erosion is a natural geomorphic process occurring continually over the earth’s surface and it largely depends on topography, vegetation, soil and climatic variables and, therefore, exhibits pronounced spatial variability due to catchments heterogeneity and climatic variation. This problem can be circumvented by discrediting the catchments into approximately homogeneous sub-areas using Geographic Information System (GIS). Soil erosion assessment modeling was carried out based on the Revised Universal Soil Loss Equation (RUSLE). A set of factors are involved in RUSLE equation are A = Average annual soil loss (mt/ha/year), R = Rainfall erosivity factor (mt/ha/year), k = Soil erodibility factor, LS = Slope length factor, C = Crop cover management factor, P = Supporting conservation practice factor. These factors extracted from different surface features by analysis and brought in to raster format. The output depicts the amount of sediment rate from a particular grid in spatial domain and the pixel value of the outlet grid indicates the sediment yield at the outlet of the watershed.

ASSESSMENT OF SOIL EROSION BY SIMULATING RAINFALL ON AN EQUATORIAL ORGANIC SOIL

Soil erosion occurs on construction sites partly due to site clearing that exposes the land to the erosive power of rainfall. A proposed construction project requires the submission of an Environmental Impact Assessment EIA) to assess the impact of the project on the environment. Assessment of soil erosion is included in the EIA, but the equation to estimate soil erosion known as the Universal Soil Loss Equation (USLE) is only applicable to a soil containing up to four percent organic matter. This limitation of USLE requires an alternative that can predict soil erosion on an organic soil. This study attempts to assess erosion that occurs on an organic soil by simulated rainfall. Field soil samples were reconstructed into three shapes and exposed to simulated rainfall. Results indicate that the amount of organic soil loss decreases with increasing duration of rainfall. Particle size distribution shows that particles with sizes finer than coarse sand (1.7 mm) remained on the slopes. Equations were developed from the graphs of soil loss versus duration of simulated rainfall to estimate soil loss occurring on slopes covered by an organic soil. The outcome of this study can be a precursor to developing an equation to estimate soil erodibility of a slope overlain by an organic soil.

Dynamics of soil fragment size distribution under successive rainfalls and its implication to size-selective sediment transport and deposition

Changes in soil fragment size distribution (FSD) under the impacts of successive rainfall events can have strong effects on sediment export during erosion events. However, field observations on the temporal dynamics of FSD under changing rainfall conditions are rare. In this study, we applied five successive artificial rainfall events with two different rainfall intensities (25.8 and 49.1mmh−1) on two replicated agricultural soil plots over a period of five weeks. Surface soil samples were taken immediately before and after each rainfall event and also in between the rainfall events in order to monitor surface aggregate stability and soil FSD. The FSDs resulting from rainfall-induced aggregate breakdown were used as inputs into a size-selective sediment transport model in order to assess how the variations in FSD would affect the concentration and size of exported sediments. Aggregate stability at first decreased due to generally wet conditions, but then increased with soil drying, until reaching a plateau towards the end of the experimental period. It did not fully recover to initial levels though, probably due to loss of stabilizing agents over time. Independent of soil moisture, notable re-aggregation occurred after each event but again did not reach the full restoration of the initial state even after up to 10days of regeneration. In contrast to aggregate stability and irrespective of pre-event re-aggregation, the percentage of coarse fragments in post-event FSDs continued to decrease from event to event, suggesting that in addition to the previously re-formed aggregates also new coarse aggregates were broken down. The model simulations showed that the temporal variations in post-event FSD would have had as much influence on the amount and size distribution of sediments exported with surface runoff as a 3-fold variation in unit discharge, suggesting the importance of quantifying rainfall-induced FSD in soil erosion assessment.

Critical assessment of jet erosion test methodologies for cohesive soil and sediment

The submerged Jet Erosion Test (JET) is a commonly used technique to assess the erodibility of cohesive soil. Employing a linear excess shear stress equation and impinging jet theory, simple numerical methods have been developed to analyze data collected using a JET to determine the critical shear stress and erodibility coefficient of soil. These include the Blaisdell, Iterative, and Scour Depth Methods, and all have been organized into easy to use spreadsheet routines. The analytical framework of the JET and its associated methods, however, are based on many assumptions that may not be satisfied in field and laboratory settings. The main objective of this study is to critically assess this analytical framework and these methodologies. Part of this assessment is to include the effect of flow confinement on the JET. The possible relationship between the derived erodibility coefficient and critical shear stress, a practical tool in soil erosion assessment, is examined, and a review of the deficiencies in the JET methodology also is presented. Using a large database of JET results from the United States and data from literature, it is shown that each method can generate an acceptable curve fit through the scour depth measurements as a function of time. The analysis shows, however, that the Scour Depth and Iterative Methods may result in physically unrealistic values for the erosion parameters. The effect of flow confinement of the impinging jet increases the derived critical shear stress and decreases the erodibility coefficient by a factor of 2.4 relative to unconfined flow assumption. For a given critical shear stress, the length of time over which scour depth data are collected also affects the calculation of erosion parameters. In general, there is a lack of consensus relating the derived soil erodibility coefficient to the derived critical shear stress. Although empirical relationships are statistically significant, the calculated erodibility coefficient for a given critical shear stress has an uncertainty of several orders of magnitude. This study shows that JET results should be used with caution and the magnitude of the uncertainty in the derived erodibility parameters should be carefully considered.