Modeling Streambank and Artificial Gravel Deposit Erosion for Sediment Replenishment

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.

Morphological development of river widenings with variable sediment supply

“…River widenings are characterized by a locally increased channel width and resulting local morphological adjustments [40]. Dynamic river widenings are more likely to display a barpool morphology than fully developed braiding, due to their limited spatial extent and the degradational state commonly associated with channelized gravel-bed rivers [29]. This assumption is supported by reports on several dynamic river widenings in Austria and Switzerland [35,41].…”

“…Venditti et al [28], however, described the degradation of alternate bars either by migrating out of the channel or by vertical erosion, resulting in a plane bed. The contrasting behavior was explained with different values of relative submergence of the bar tops and it was concluded that bar emergence will more likely occur, especially if the decrease of sediment supply is accompanied by a reduction of peak flows [29]. This is a realistic scenario for river reaches below storage power plants.…”

Streambank Erosion: Advances in Monitoring, Modeling and Management

“…The research articles included in this special issue specifically targeted three areas that are key to better understanding streambank erosion and failure, namely, monitoring [8][9][10][11], modeling [12][13][14][15][16][17], and management [18][19][20][21]. As an ensemble, the articles highlight the value of monitoring campaigns to characterize the effect of external drivers (e.g., hydrologic events), the capabilities and limitations of numerical models for predicting the response of the system (e.g., stream restoration design), and the effectiveness of management practices to prevent and mitigate the impacts of streambank erosion and failure.…”

“…Their results show that the model's predictions are highly dependent on the bank physical properties at the sub-reach scale, particularly for the case of soil cohesion and friction angle. Finally, Vonwiller et al [17] validated a 2D hydro-morphodynamic model and performed sensitivity analyses to examine the suitability of various approaches (e.g., gravitational bank collapse) to simulate non-cohesive bank erosion in straight channels and the erosion of artificial gravel deposits.…”

“…The research articles included in this special issue addressed some of these challenges, as well as shed light on some topics that deserve further exploration. The latter topics include: (1) examining the effect of stratigraphic position on the quantification of sediment and total phosphorus loading to streams [19]; (2) accounting for the effects of vegetation, meandering, and weakening and weathering processes in the development, calibration, and application of numerical models [12,14,17]; (3) developing a better understanding of the physical mechanisms that govern gully progression and development, especially those in riparian areas [10]; (4) establishing a standardized procedure for running and post-processing the results of erodibility tests [15]; and (5) developing a better understanding of influential factors such as water chemistry on streambank erosion [21].…”