Evaluating a process‐based model for use in streambank stabilization: insights on the Bank Stability and Toe Erosion Model (BSTEM)

Abstract

Streambank retreat is a complex cyclical process involving subaerial processes, fluvial erosion, seepage erosion, and geotechnical failures and is driven by several soil properties that themselves are temporally and spatially variable. Therefore, it can be extremely challenging to predict and model the erosion and consequent retreat of streambanks. However, modeling streambank retreat has many important applications, including the design and assessment of mitigation strategies for stream revitalization and stabilization. In order to highlight the current complexities of modeling streambank retreat and to suggest future research areas, this paper reviewed one of the most comprehensive streambank retreat models available, the Bank Stability and Toe Erosion Model (BSTEM), which has recently been integrated with several popular hydrodynamic and sediment transport models including the Hydrologic Engineering Centerˈs River Analysis System (HEC-RAS). The objectives of this paper were to: (i) comprehensively review studies that have utilized BSTEM and report their findings, (ii) address the limitations of the model so that it can be applied appropriately in its current form, and (iii) suggest directions of research that will help make the model a more useful tool in future applications. The paper includes an extensive overview of peer reviewed studies to guide future users of BSTEM. The review demonstrated that the model needs further testing and evaluation outside of the central United States. Also, further development is needed in terms of accounting for spatial and temporal variability in geotechnical and fluvial erodibility parameters, incorporating subaerial processes, and accounting for the influence of riparian vegetation on streambank pore-water pressure dynamics, applied shear stress, and erodibility parameters.

Watershed Variability in Streambank Erodibility and Implications for Erosion Prediction

“…This was expected as soil erodibility parameters suggested highly erodible soil properties and also because the presence of heavy vegetation on the bank face, which can significantly decrease the applied τ reaching the detachable soil particles or aggregates [9,[51][52][53][54][55]. This highlights the need to account for the impact of vegetation or meanders on applied τ during model setup and calibration.…”

“…Applied τ can be impacted by the presence of meanders (increased τ) or bank face vegetation roots and/or above-ground biomass (decreased τ) [28,[51][52][53][54][55], which is not taken into account in the one-dimensional calculation of τ [9] in CONCEPTS. Because the model does not allow for the direct adjustment of τ, an ν-factor can be used to indirectly adjust τ by adjusting erodibility parameters as discussed in Langendoen et al [42] and Daly et al [37]:…”

“…The two erodibility parameters, τ c and k d , are soil dependent. Models such as the Bank Stability and Toe Erosion Model (BSTEM), Conservational Channel Evolution and Pollutant Transport System (CONCEPTS), and HEC-RAS with BSTEM use the linear excess shear-stress equation to predict fluvial erosion and require τ c and k d as input [7][8][9]. The Soil and Water Assessment Tool (SWAT) either allows the user to input τ c and k d , or calculates the parameters based on soil characteristics and empirical relationships [10].…”

“…Only a few studies have investigated how parameters vary on the watershed scale [13] and single values of τ c and k d are still widely used for an entire watershed. While in situ testing with the JET is recommended to determine erodibility parameters [9], running multiple tests at multiple sites within a watershed or stream system becomes time consuming, as it takes at least an hour to run a single JET. The amount of tests needed to adequately characterize the erodibility parameters for each site of interest on an entire stream reach or watershed may be very high and access to certain locations may be limited.…”

Bank Retreat and Streambank Morphology of a Meandering River during Summer and Single Flood Events in Northern Norway

“…At the lower end of the scale, investigations of fluvial morphological processes on small-scale models in the laboratory have been conducted [5][6][7][8][9]. Finally, more sophisticated numerical models have appeared [10][11][12] in recent years.…”