Submitted to: Meeting Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 8/1/2005
Publication Date: 9/1/2005
Citation: Kuhnle, R.A., Jia, Y., Alonso, C.V. 2005. Measured and simulated flow near spur dikes. In: Proceedings U.S.-China Workshop on Advanced Computational Modeling in Hydroscience and Engineering, September 19-21, 2005, Oxford, MS. CD-ROM. Interpretive Summary: Unstable boundaries are often associated with the channels of agricultural watersheds. Erosion of the unstable channel boundaries may threaten valuable agricultural lands and structures. One method that has been used to prevent the erosion of stream banks is to construct structures, such as spur dikes, that divert the fast moving flow away from the sides of the channel. The exact ways in which effective flow diverting structures operate in streams and rivers is poorly understood, however. A study was conducted in the laboratory using a model stream channel and a model flow diverting structure (spur dike) to improve the understanding of how the flowing water interacts with the spur dike to divert the high velocity flow away from the bank and protect it from erosion. An accurate method of predicting the direction and speed of the flowing water near a spur dike would be a valuable aid in improving the design of successful structures. To accomplish this goal the velocity of the water was measured at a closely-spaced grid around the model spur dike and compared to velocities generated with a computer model developed by researchers from the University of Mississippi. For speed and direction of the water the measurements and generated values agreed closely. More research, however, needs to be done to improve understanding of how the moving water interacts with the materials composing the bank. This new information collected will improve the understanding of the protection of stream banks from erosion by flowing water in streams and rivers. This type of information is necessary for effective environmentally-aware management of watersheds.
Technical Abstract: To improve understanding of the flow and scour processes associated with spur dikes more fully, 3-dimensional flow velocities were measured using an acoustic Doppler velocimeter at a closely spaced grid over a fixed flat bed and a fixed scoured bed with a submerged trapezoidal shaped spur dike. Flow velocities were measured at 2592 points for the flat bed and 3484 points for the scoured bed in the vicinity of the spur dike and the scour hole. General distribution of velocities and detailed near field flow structures were revealed by the measurements. Some important differences between the flow fields measured in this study and those measured for non-submerged vertical obstructions were observed in this study. Numerical simulation was performed using the free surface turbulent flow model, CCHE3D. The numerical simulation of the flow velocity field generally showed very good agreement between the computation results and the measurements. Bed shear stress fields derived from measured and simulated data showed some discrepancies. The numerical simulation results indicate the CCHE3D model can be used to reasonably predict near-field flows around hydraulic structures; however, further research is needed for accurate prediction of local scour using measured and simulated flows.