Bank Erosion Processes in Regulated Navigable Rivers

G Duró,W S J Uijttewaal,D Roelvink,A Crosato,M G Kleinhans

doi:10.1029/2019jf005441

Abstract

AbstractVessel‐induced waves affect the morphology and ecology of banks and shorelines around the world. In rivers used as waterways, ship passages contribute to the erosion of unprotected banks, but their short‐ and long‐term impacts remain unclear. This work investigates the effects of navigation on bank erosion along a reach of the regulated Meuse River with recently renaturalized banks. We apply UAV‐SfM photogrammetry, RTK‐GPS, acoustic Doppler velocimetry, aerial and terrestrial photography, soil tests, and multibeam echosounding to analyze the progression of bank retreat after riprap removal. After having analyzed the effects of ship‐generated waves and currents, floods, and vegetation dynamics, a process‐based model is proposed to estimate the long‐term bank retreat. The results show that a terrace evolves in length and depth across the bank according to local lithology, which we clustered in three types. Floods contribute to upper‐bank erosion‐inducing mass failures, while near‐bank flow appears increasingly ineffective to remove the failed material due to terrace elongation. Vegetation growth at the upper‐bank toe reduces bank failure and delays erosion, but its permanence is limited by terrace stability and efficiency to dissipate waves. The results also indicate that long‐term bank retreat is controlled by deep primary waves acting like bores over the terrace. Understanding the underlying drivers of bank evolution can support process‐based management to optimize the benefits of structural and functional diversity in navigable rivers.

Highlights

Human interference on natural dynamics has globally increased to alarming levels, especially on large water courses (Best, 2018)
The analysis of data indicates that the terrace is shaped by the regular action of ship waves hitting the bank at regulated water levels during low flows, whereas flow currents are incapable of entraining sediment once a well‐developed terrace is formed
We discussed the relative contributions of ship waves and floods to bank erosion, observations on vegetation dynamics

Summary

Introduction

Human interference on natural dynamics has globally increased to alarming levels, especially on large water courses (Best, 2018). Ship waves can be an important driver of river bank erosion (Houser, 2010; Liedermann et al, 2014; Nanson et al, 1994; Parnell et al, 2007; Styles & Hartman, 2019; Zaggia et al, 2017), with economic (e.g., Rapaglia et al, 2015) and ecological implications (e.g., Gabel et al, 2012). Bank erosion is controlled by means of hard measures, such as riprap, but recent approaches searching to balance technical and ecological requirements (Boeters et al, 1997; Heibaum & Fleischer, 2015) allow for some natural processes. The knowledge gap is mainly due to the many and complex interacting factors that are involved in the erosion process, especially when ship waves are present. Banks commonly erode because flow currents steepen and undermine them until collapse, after which the toe is temporarily protected by slump blocks

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