Quantifying Effectiveness of Streambank Stabilization Practices on Cedar River, Nebraska

Naisargi Dave,Aaron Mittelstet

doi:10.3390/w9120930

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. There is a critical need to document the long-term success of streambank restoration projects. The objectives of this research were to (1) quantify streambank retreat before and after the stabilization of 18 streambanks on the Cedar River in North Central Nebraska, USA; (2) assess the impact of a large flood event; and (3) determine the most cost-efficient stabilization 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). 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, 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.

Highlights

Sediment is a primary pollutant to surface water and a leading cause of water quality impairment [1]
Similar to what we discovered, Brown [30] found that 27% of the banks protected with rootwad revetment partially or fully failed to protect the streambank and that outflanking occurred at 25% of the rock vanes assessed
Streambank erosion has increased due to land use change and urbanization

Summary

Introduction

Sediment is a primary pollutant to surface water and a leading cause of water quality impairment [1]. Though erosion is a natural and even necessary process [2], the rate of erosion has been accelerated due to human activities such as farming and urbanization. Streambank erosion is the main source of sediment to rivers and streams [3]. The excess sediment affects the water chemistry, aquatic organisms, and the water clarity in our streams and reservoirs. Excess sediment is aesthetically displeasing, increases the cost of treating drinking water, decreases water clarity, and has an overall negative impact on the aquatic ecosystem [4,5,6,7,8]. The increased turbidity affects the water aesthetics and reduces photosynthesis and organisms’ visibility

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Conclusion