Modeling Streambank and Artificial Gravel Deposit Erosion for Sediment Replenishment

Lukas Vonwiller,Robert Boes,David Vetsch

doi:10.3390/w10040508

Abstract

Sediment replenishment by artificial gravel deposits is a measure to increase sediment supply in gravel-bed rivers. Thereby, streambank erosion is the dominant process for gravel entrainment. In this contribution, we quantitatively validate a numerical morphodynamic 2D model and the relevant model approaches to reproduce non-cohesive streambank erosion. Therefore, a calibration and a sensitivity analysis of the relevant model approaches and parameters are carried out based on a reference laboratory experiment on streambank erosion in a straight channel from the literature. The relevant model approaches identified to successfully reproduce lateral streambank erosion are the gravitational bank collapse, the lateral bed slope effect on the bed load transport direction and the local bed slope effect on the critical Shields stress. Based on these findings, the numerical model was compared against data from laboratory experiments on gravel deposit erosion. Thereby, the focus was on the influence of the hydraulic discharge, the grain size distribution of the sediment and the geometrical quantities of the gravel deposits, such as the width, height and length of the deposit. It is shown that the dynamics of the erosion process were well reproduced by the numerical model using non-uniform sediment. Furthermore, the erosion rates were in good agreement with the laboratory experiments, except for the initial phase of the experiments, where the erosion rates were highest and settling of the gravel deposit was observed in the laboratory experiments. Overall, the numerical model proved to be a suitable tool to predict the erosion process of artificial gravel deposits, and hence, can be recommended for the design of sediment replenishment measures.

Highlights

Many trained gravel-bed rivers suffer from a distinct sediment deficit
This article is structured as follows: First, we describe the numerical 2D model focusing on the relevant model approaches for sediment transport, the two laboratory experiments and the setup used for numerical modeling
We present a numerical 2D model for the morphodynamic erosion process of both streambanks in straight channels and artificial gravel deposits consisting of non-cohesive sediment

Summary

Introduction

Many trained gravel-bed rivers suffer from a distinct sediment deficit. In most cases, the sediment continuity is interrupted by dams, run-of-river (ROR) hydropower plants (HHPs) or sediment traps. Thereby, the main objectives are to reestablish bed load transport, to enhance aquatic habitat for macroinvertebrates, plants and fish and to protect infrastructure by preventing further degradation [1,2,3,4,5]. This technique has been applied worldwide, for example for the rivers Reuss [6], Limmat, and Aare in Switzerland [7], for the rivers Moosach, Lech, and Isar in Germany [8], for the Trinity River in the U.S State of California [9] and for the Nunome River and several other rivers in the Kizu River basin in Japan [10]. Additional sediment is obtained from sediment traps [7], stone quarries and gravel pits [7] or is excavated upstream of an ROR-HHP [6]

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