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Streambank stabilization techniques, designed to maximize localized streambank shear strength and/or minimize the forces acting on a streambank, have been in existence for centuries and are still a popular river management technique used by practitioners worldwide. The purpose of this literature review is to identify common streambank stabilization techniques, compile and summarize the recent peer-reviewed journal articles on these techniques, and determine research needs. Eleven general streambank stabilization practices, consisting of both instream structures and streambank management techniques, are identified in this literature review. Over 140 peer-reviewed journal articles on these techniques have been published over the last 20 years. To improve design and implementation of streambank stabilization techniques, two major research needs were identified: (1) further assess and quantify the spatiotemporal effects that streambank stabilization practices have on bank erosion, hydraulics, sediment transport, and habitat and (2) continue to improve numerical models for streambank stabilization design in order to holistically evaluate and address these effects. In addition, a list of specific research needs for each stabilization technique is provided. To help address these research needs, it is recommended that future streambank stabilization publications should (1) use consistent technique nomenclature, (2) provide characteristic details about the techniques and channels studied, (3) justify the experimental setup, and (4) explain how the research will improve streambank stabilization design. [ABSTRACT FROM AUTHOR]

While manmade slopes are traditionally constructed with planar cross-sections, natural stable slopes are usually curvilinear with significant concavity of the profile. This concavity occurs as a result of evolutionary processes in which rain-driven erosion and sediment transport are balanced through slope shape adjustments. At the point of equilibrium, a relatively steady concavity with a uniform erosion rate is observed over time. Nevertheless, a true equilibrium state is possible only if mechanical stability is satisfied. In this study, concave profiles in rainfall erosion equilibrium were found based on the principles of the well-known RUSLE2 model. Results showed the existence of a family of steady shapes satisfying the condition of uniform normalized erosion rate. Those steady concave shapes that also satisfied long-term mechanical stability were then investigated. The overall results suggest that concave slopes can be constructed to achieve both minimal steady-state erosion equilibrium and mechanical stability, leading to more natural and sustainable landforms with minimal sediment delivery during initial slope adjustments. [ABSTRACT FROM AUTHOR]

Plastic-covered ridge-furrow cultivation (plastic mulch) can substantially influence runoff and soil erosion on agricultural land. However, the impact of this management practice in combination with complex farmland topography has not been thoroughly investigated. The goal of this study was to identify how topography influences runoff patterns and erosion rates of plastic mulch cultivation. We measured runoff and sediment transport on two mountainous fields in South Korea, one with a concave topography and one with a convex topography, during monsoonal rain events. We used the EROSION 3D model to compare flow and sediment transport between plastic mulch, uncovered ridges, and a smooth soil surface. We found the highest runoff and erosion rates from both of the fields with plastic mulch due to the impermeable surface. For the uncovered ridges, we identified 140% higher erosion compared to the smooth surface on the concave field, but 20% lower erosion on the convex field. The simulated sediment transport patterns showed that the ridge-furrow system concentrated overland flow on the concave field, resulting in high erosion rates. On the convex field, the ridge-furrow system prevented flow accumulation and erosion. Our results demonstrate that the effect of ridge-furrow systems on erosion is controlled primarily by the topography. These results have practical consequences for watershed conservation planning and the application of large-scale erosion models. Nevertheless, further research is needed to fully understand the impact of this management system on runoff and erosion on mountainous farmland. [ABSTRACT FROM AUTHOR]

This article introduces a special collection of 16 research articles on new developments and applications of the Soil and Water Assessment Tool (SWAT) to address various environmental issues at a range of geographic and temporal scales. Highlights include addition of a subdaily erosion and sediment transport algorithm, a biozone module, and a new algorithm for shallow water table depth. Model applications include climate change impact assessments, model adaptation to regional environmental conditions, watershed-scale soil erosion assessments, and linkages to other models. A summary of reported model performance indicates that 85% of daily flow calibration statistics reported in this collection were satisfactory or better, with very good performance in four of the 20 calibration results and in three of the 19 validation results. Details of reported model parameters for calibration of flow and water quality constituents are provided for other SWAT modelers. This collection builds upon a previous ASABE 2010 SWAT Special Collection, demonstrating continued developments to enhance SWAT's capabilities and highlighting SWAT's continued expansion in international applications, especially in Asia. [ABSTRACT FROM AUTHOR]

Transport capacity of overland flow is related to sediment particle size. The WEPP (Water Erosion Prediction Project) model considers soil particle size in the sediment transport capacity equation; however, the equation does not work well for steep slopes. This study introduces sediment particle size into the determination of transport capacity on steep slopes by quantifying the relationship between sediment particle size and transport coefficient using the modified sediment transport capacity equation for steep slopes from the WEPP model. The relationship is based on the measured sediment transport coefficient associated with different sediment particle sizes in a hydraulic flume. The experiment used five sediment particle sizes (0.10, 0.22, 0.41, 0.69, and 1.16 mm), on five slopes (8.7%, 17,4%, 35.9%, 34.2%, and 42.3%), and with five flow rates (0.66, 1.32, 2.63, 3.95, and 5.26 X 10-3 m² s-1). The results showed that the sediment transport coefficient decreased significantly with increasing sediment size. The relationship was well described by a power function with transport coefficient as dependent variable and sediment particle size as independent variable. The sediment transport capacity equation could be modified using two independent terms: the sediment particle size power function, representing sediment properties, and flow shear stress, representing flow hydraulics. However, both the WEPP transport capacity equation and the modified equation did not predict the measured transport capacity well for steep slopes. Further studies are needed to improve the performance of the modified equation using fine sediment particles beyond the range of this study. [ABSTRACT FROM AUTHOR]

Various methods are used to estimate sediment transport through riparian buffers and grass filters, with the sediment delivery ratio having been the most widely applied. The U.S. Forest Service developed a sediment delivery ratio using the stiff diagram and a logistic curve to integrate some of the factors influencing sediment delivery heuristically. This study independently tested the Forest Service sediment delivery ratio contrasted with artificial neural networks to represent the multiple nonlinearities between important factors and sediment delivery. The Forest Service sediment delivery ratio was not adequate when compared to published sediment yields from 30 small experimental buffers from three countries, including four forested buffers. However, artificial neural networks gave estimates of the delivery ratio that were highly correlated to the observations. The 30 buffer observations produced such good estimates of the sediment delivery ratio with both seven and five buffer parameters that this study suggests that as few as 30 sediment yield observations can be the basis for applying neural networks to interpolate the complex, multiple nonlinearities of hydrology and sediment transport on riparian buffers. [ABSTRACT FROM AUTHOR]

Ephemeral gully erosion can cause severe soil degradation and contribute significantly to total soil losses in agricultural areas. Physically based prediction technology is necessary to assess the magnitude of these phenomena so that appropriate conservation measures can be implemented, but such technology currently does not exist. To address this issue, a conceptual and numerical framework is presented in which ephemeral gully development, growth, and associated soil losses are simulated within the Annualized Agricultural Non-Point Source (AnnAGNPS) model. This approach incorporates analytic formulations for plunge pool erosion and headcut retreat within single or multiple storm events in unsteady, spatially varied flow at the sub-cell scale, and addresses five soil particle-size classes to predict gully evolution, transport-capacity and transport-limited flows, gully widening, and gully reactivation. Single-event and continuous simulations demonstrate the model's utility for predicting both the initial development of an ephemeral gully and its evolution over multiple runoff events. The model is shown to recreate reasonably well the dimensions of observed ephemeral gullies in Mississippi. The inclusion of ephemeral gully erosion within AnnAGNPS will greatly enhance the model's predictive capabilities and further assist practitioners in the management of agricultural watersheds. [ABSTRACT FROM AUTHOR]

This article describes a prototype modeling system for assessing forest management-related erosion at its source and predicting sediment transport from hillslopes to stream channels and through channel networks to a watershed outlet. We demonstrate that it is possible to develop a land management tool capable of accurately assessing the primary impacts of spatiotemporally varied forest management practices on sediment yield and delivery at hillslope to watershed scales in a single simulation. The modeling system consists of four components: (1) the TOpographic ParameteriZation (TOPAZ) model for discretizing hillslope and channel elements, (2) the Water Erosion Prediction Project (WEPP) model for evaluating hillslope-scale surface erosion processes, (3) the National Center for Computational Hydrodynamics and Engineering's one-dimensional (CCHEID) hydrodynamic-sediment transport model, and (4) an interface program to manage relational databases and data transfer between modules. The coupled models were calibrated and validated with observed flow and sediment load data from the North Fork Caspar Creek Experimental Watershed in coastal northern California. The coupled models' predictions of peak flow rate and total flow volume were not significantly different from observed values. Predicted sediment concentrations were significantly different from observed values, but within typical ranges for sediment transport equations. We recommend that the WEPP model be improved to allow access to sub-daily time scale results so that it can be better integrated with other watershed models. [ABSTRACT FROM AUTHOR]