Impact of Bank Stabilization Structures on Upstream and Downstream Bank Mobilization at Cedar River, Nebraska

Abstract

HighlightsStabilization structures are only effective at stabilized segments.Erosion increased in two of the six segments in the post-stabilization period.Deposition decreased in all six segments in the post-stabilization period.Jetties are effective at reducing erosion but are also prone to fail.Abstract. The effectiveness of streambank stabilization structures is insufficiently quantified. Although such structures clearly reduce or eliminate streambank erosion at the local scale, little is known about associated effects on unstabilized reaches immediately upstream and downstream. This study measured streambank erosion and deposition in stretches of the Cedar River, 1.5 meander wavelengths upstream and downstream from 24 stabilization structures that included jetties, rock vanes, root wads, and gravel protection. We also measured erosion and deposition on the streambanks directly opposite the stabilized locations. We compared measurements from the pre-stabilization period (1993-2005) with those from the post-stabilization period (2005-2018) using historical imagery in ArcGIS. Upon completion of this analysis, we were able to reject an initial hypothesis that local and adjacent streambank segment erosion rates would be significantly less after stabilization, and that deposition rates would be greater in stabilized locations and adjacent stream segments. Instead, the differences in erosion from pre- to post-stabilization showed little or no statistical significance. Rather, our data indicated that streambank erosion decreased in only four of the six stream segments and was predominantly confined to the stabilized segment. Overall deposition decreased in all six stream segments after bank stabilization. In reaches where wooden jetties were installed, partial or total failure was common, and further increases in erosion and decreases in deposition were more pronounced. We conclude that streambank stabilization on the Cedar River is effective only at the location of installation; there is no measurable effect on adjacent unstabilized reaches. Our results demonstrate the need for improved streambank monitoring practices and better understanding of how streambank stabilization impacts an entire river system. Such advances will enhance stream restoration design and implementation, as well as support future river management efforts. Keywords: Adjacent stream reach, Deposition, Jetty, Erosion, Streambank stabilization.

Can deciduous tree revetments reduce streambank erosion rates on a sand‐bed stream?

“…These results are similar to those obtained by Russell et al (2021) on the Cedar River in Nebraska in the United States, where tree revetments (or jetties), similar to those installed on the Lower Smoky Hill River, were monitored over a 12‐year period. The researchers found that if tree revetments remained fully or partially functional, bank erosion decreased following installation, supporting the finding that deciduous tree revetments installed on the Lower Smoky Hill River may have decreased bank erosion in the short term.…”

“…The researchers found that if tree revetments remained fully or partially functional, bank erosion decreased following installation, supporting the finding that deciduous tree revetments installed on the Lower Smoky Hill River may have decreased bank erosion in the short term. However, in the case of revetment failure, Russell et al (2021) also found that bank erosion was exacerbated, above pre‐installation rates. To further evaluate the results obtained on the Lower Smoky Hill River, flow events experienced, bank stratigraphy differences, meander planform characteristics and structure force balance assessments are discussed and incorporated into this analysis in the following discussion sections.…”

“…Improper anchoring of large wood structures has been reported as the primary failure mechanism in several case studies of large wood structures (e.g., Miller & Kochel, 2013; Russell et al, 2021; Shelley et al, 2022; Shields et al, 2006). Therefore, a large wood (LW) design spreadsheet developed by Rafferty (2017) was used on the designed deciduous tree revetments (Figure 1) to assist in conducting vertical (i.e.…”

“…To the authors' and designers' knowledge, the described deciduous tree revetment is a novel approach of using wood in streambank stabilization projects; however, similarities with other types of streambank stabilization techniques do exist. Tree revetments or jetties, described by Russell et al (2021), are most like deciduous tree revetments; however, no form of anchoring (e.g. footer log and duckbill anchor) were used.…”

Illustrating land cover change associated with erosion management of the Little Blue River, Kansas, USA

“…Increased terrestrial land area, particularly through more permanent tree cover instead of short-lived crop cover, relative to river water and sediments area served as the indicator of streambank stability. In the case of the Little Blue River, the river was dynamic (Figure 2) and we did not attempt to measure river points or segments (e.g., 1.5 meander wavelengths upstream and downstream of stabilized locations with exclusion of segments of channel migration and oxbow formation; Russell et al, 2021). Consequently, we developed an approach to directly measure land cover change in fixed land parcels, from the perspective of erosion management in streambanks and land adjacent to streambanks, rather than an isolated focus on streambanks alone.…”