Quantifying Effectiveness of Streambank Stabilization Practices on Cedar River, Nebraska

Abstract.

Excessive sediment is a major pollutant to surface waters worldwide. In some watersheds, streambanks are a significant source of this sediment, leading to the expenditure of billions of dollars in stabilization projects. Although costly streambank stabilization projects have been implemented worldwide, long-term monitoring to quantify their success is lacking. The objectives of this project were to quantify streambank retreat before and after the stabilization of 18 streambanks on the Cedar River in north central Nebraska, USA; assess the impact of a large flood event; and determine the most cost-efficient practice. The stabilized streambanks included jetties (10), rock-toe protection (1), slope reduction/gravel bank (1), a retaining wall (1), rock vanes (2) and tree revetments (3). Seventeen of the sites were installed from 2000 to 2004 and one in 1950. Streambank retreat and accumulation were quantified using aerial images from 1993 to 2016. Though streambank retreat has been significant throughout the study period, a breached dam in 2010 caused major flooding and streambank erosion on the Cedar River. This large-scale flood enabled us to quantify the effect of one extreme event and evaluate the effectiveness of the stabilized streambanks. With a 70% success rate, we found that jetties were the most cost-efficient practice and yielded the most deposition. If minimal risk is unacceptable, a more costly yet immobile practice such as a gravel bank or retaining wall is recommended.