|ALONSO, CARLOS - Retired ARS Employee|
Submitted to: International Journal of Sediment Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/5/2012
Publication Date: 5/10/2013
Citation: Kuhnle, R.A., Alonso, C.V. 2013. Flow near a model spur dike with a fixed scoured bed. International Journal of Sediment Research. 28(3):349-357.
Interpretive Summary: The streams of agricultural watersheds often have unstable channel boundaries. The erosion associated with unstable channels may destroy valuable lands, threaten infrastructure, and negatively impact the habitat for fish and other aquatic organisms. Improved techniques to stabilize channel boundaries effectively and efficiently without destroying aquatic habitats are needed. One common structure used to stabilize channel boundaries is termed the spur dike. These structures are built out from the bank into the channel and serve to deflect flow away from the bank. Yet knowledge of precisely how spur dikes interact with the flow to protect channel banks is unknown. In this study detailed velocities of the flow in the vicinity of a model spur dike in a laboratory model stream channel were measured. These velocities allow the forces of the flow on the stream channel to be calculated and related to the rate of local erosion around a spur dike. This knowledge will lead to a more complete understanding of how spur dikes interact with the flow and allow watershed managers to design more effective channel protection structures.
Technical Abstract: Three-dimensional flow velocities were measured using an acoustic Doppler velocimeter at a closely spaced grid over a fixed scoured bed with a submerged spur dike. Three-dimensional flow velocities were measured at 3484 positions around the trapezoidal shaped submerged model spur dike over a fixed scoured bed. General velocity distributions and detailed near field flow structures were revealed by the measurement. Clear differences were revealed between flow over fixed flat and scoured beds. Strong lateral flows were the dominant cause of the observed local scour. Shear stresses were higher for the scoured bed than in the flat bed case. Decreasing rates of scour as the scour hole developed were attributed to increases in critical shear stress in the scour holes caused by the increase in the length and magnitude of adverse slopes associated with the two main scour holes.