Prediction of Bank Erosion in a Reach of the Sacramento River and its Mitigation with Groynes

Abstract

The paper reports on the prediction of flow in a reach of the Sacramento River with focus on a part of the river's bank where serious erosion has occurred. The simulations were obtained using a three-dimensional Navier-Stokes solver which utilized body-fitted coordinates to represent the complex river bathymetry. Comparative predictions were obtained using a two-dimensional, depth-averaged formulation. Local (nested) mesh refinement was employed to provide the necessary resolution of the bank geometry in the region of interest. The study focuses on the assessment of the effectiveness of a particular arrangement of groynes which was found in physical model studies to significantly reduce the rate of erosion in the region under consideration. To validate the computational models, predictions were first obtained for the case of turbulent flow in a straight rectangular channel with one groyne. Measurements of velocity and boundary shear stress were used for model validation. For the reach of the Sacramento River under consideration, velocity measurements obtained in the large-scale physical model were also used to check the computational model prior to its use for prediction of the river flow with groynes. Here, too, both depth-averaged and three-dimensional computations were performed with the objective being to determine the influence of the groynes on the flow velocity. The bank erosion rate was estimated by coupling the 'excess shear stress' method to the computed mean velocity field. The results show that for the groynes configuration that was found optimal in the physical-model studies, and that was actually implemented in the Sacramento River, the groynes are effective in reducing the bank erosion of the affected zone but at the cost of transferring a far less severe problem further downstream.

An immersed boundary method for unstructured meshes in depth averaged shallow water models

“…The geometry and flow conditions of the case A1 from Rajaratnam et al [35] are used to compare the numerical results with the experimental velocity data ( Figure 4). This case has been reproduced by other authors as Ercan et al [11], Tingsanchali et al [12], Chung et al [18] or Wu et al [47].…”

“…Depth averaged shallow water models have a broad range of applications in hydraulic engineering as flood inundation in urban areas [1][2][3][4][5], dam break modelling [6][7][8][9], flow around hydraulic structures [10][11][12] and flow in rivers and estuaries [13][14][15][16]. These kind of studies often imply the necessity of modelling complex geometries, which results in time-consuming mesh generation operations to adapt the model boundaries to the solid obstacles.…”

Hydrodynamic characteristics and related mass-transfer properties in open-channel flows with rectangular embayment zone

“…However, three-dimensional current dynamics around the groynes have not be investigated yet, and it thus makes more difficult to accomplish the goals of these studies. Ercan and Younis (2009) have examined efficiency of the groyne in reducing a bank erosion by using two and three dimensional numerical schemes. In actual rivers, it is of importance to select efficient alternative designs of spur dykes and groynes in river managements.…”

Impact of reach geometry on stream channel sensitivity to extreme floods

“…Linearized bed theory provides some quantitative insight into the role of stream curvature on channel bank shear stress and channel evolution, but this approach is only valid for gently curving bends where the radius of curvature is much greater than the channel width (Ikeda et al, 1981). More complicated channel geometries can be analyzed using numerical hydrodynamic and sediment transport models, but neither of these approaches are well suited for rapid regional-scale assessments of flood risks (Blanckaert and de Vriend, 2003;Ferguson et al, 2003;Seminara, 2006;Camporeale et al, 2007;Rüther and Olsen, 2007;Ercan and Younis, 2009). In order to facilitate a regional-scale, pre-flood assessment of the impact of channel geometry on susceptibility to bank erosion, we introduce a new parameter, here called the bend stress parameter, which is proportional to the centripetal force F c exerted along a concave bank.…”

“…Linearized bed theory provides some quantitative insight into the role of stream curvature on channel bank shear stress and channel evolution, but this approach is only valid for gently curving bends where the radius of curvature is much greater than the channel width (Ikeda et al ., ). More complicated channel geometries can be analyzed using numerical hydrodynamic and sediment transport models, but neither of these approaches are well suited for rapid regional‐scale assessments of flood risks (Blanckaert and de Vriend, ; Ferguson et al ., ; Seminara, ; Camporeale et al ., ; Rüther and Olsen, ; Ercan and Younis, ).…”