Turbulent Flow Around Submerged Bendway Weirs and Its Influence on Channel Navigation

Abstract

Flow in curved channel bends is typically characterized by helical secondary currents (HSC) which play an important role in redistributing the momentum of river flow in a crosssection, resulting in lateral sediment transport, bank erosion and channel migration. Secondary current introduces difficulties for channel navigation because it tends to force barges toward the outer bank. Submerged weirs (SWs) are engineering structures designed to improve navigability of bendways. They have been constructed along many bends of the Mississippi River for improving barge navigation through these bends (Davinroy & Redington, 1996). Because of the complexity of channel morphology and flow conditions, not all the installed SWs were effective as expected (Waterway Simulation Technology, Inc., 1999). It is necessary, therefore, to study the turbulent flow field around submerged weirs and the mechanisms affect navigation. The HSCs can be computed analytically if the channel form and cross-section can be approximated as circular and rectangular (Rozovskii, 1961). Curved channel flows can be simulated by depth averaged models. Although the main flow distribution can be predicted quite satisfactorily using two-dimensional (2D) models (Jia et al., 2002a; Jin & Steffler, 1993), the secondary flow resulting from hydraulic structures is difficult to simulate with these models. The approach of embedding an analytical solution (Hsieh and Yang, 2003) or threedimensional (3D) simulation results (Duan et al., 2001) into a 2D model may not be appropriate when submerged weir(s) are present. Compared with two-dimensional models, three-dimensional models are more suitable and have been widely used for open channel flow simulations particularly for flows in curved channels. From early research by Leschziner & Rodi (1979) to the growing popularity of applications by Jia & Wang (1992), Wu et al. (2000), Morvan et al. (2002), Wilson et al. (2003), Olson (2003) etc., threedimensional numerical models have been proven to be capable of predicting general helical currents in curved channels. Wilson et al. (2003) solved a multiple-bend curved-channel flow problem using the k- closure and rigid lid assumption with a finite volume code of non-orthogonal structured grid. Morvan et al. (2002) simulated flow in a meander channel with flood plains. Both the k- closure and Reynolds stresses model were applied with a rigid lid. Olsen (2003) applied a 3D model with the kclosure to simulate the channel meandering process. Natural river flow, sedimentation and bed change were computed by Wu et al. (2000) using a 3D model, with k- closure used for the hydrodynamics