Evolution of three streambanks before and after stabilization and record flooding

Abstract

Stabilization projects are increasingly used to mitigate the effects of anthropogenic streambank erosion, yet the effectiveness of stabilization has been insufficiently measured. Sound monitoring practices inform adjustments in implementation and maintenance, which improve engineered effectiveness. Thus, the objectives of this study were to: 1) measure streambank migration from in three reaches stabilized with wooden jetties following a major flooding event, and 2) quantify deposition around the jetties between pre-flood and post-flood. Streambank deposition was measured in 2019 with a River Surveyor and Global Positioning System (GPS). Bank erosion rates in Reaches 1, 2 and 3 were 0.41, 0.96 and 0.07 m2 m−1 yr−1, respectively, from pre-installation of wooden jetties. After streambanks in these reaches were stabilized, Reach 1 experienced 0.11 m2 m−1 yr−1 of erosion while Reaches 2 and 3 had 0.13 and 0.01 m2 m−1 yr−1 of deposition. Deposition increased in 2019 (1.61 and 0.81 m2 m−1) following a high magnitude flood. We utilized a new method for quantifying accumulated sediment in stream beds and banks. Our application of this new method demonstrates that jetties in the Cedar River have decreased streambank migration and increased sediment deposition at the point of implementation. The quantification of stream-sediment dynamics near jetties provides crucial information for stream-restoration design and decision-making, specifically for bioengineering design implementation.