Baffle-post structures for flow control in open channels
Date
2015
Authors
Ubing, Caroline, author
Thornton, Christopher, advisor
Ettema, Robert, advisor
Bledsoe, Brian, committee member
Wohl, Ellen, committee member
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Abstract
This thesis presents theory and laboratory findings regarding the hydraulic performance of baffle-post structures used as a means for controlling flow in open channels. Such structures comprise one to two parallel rows of posts that extend slightly higher than the anticipated depth of flow, and offer a useful means for retarding flow in various channel situations where there is a need to reduce flow energy, possibly to reduce flow capacity to transport bed sediment and manage channel morphology. Observations and data regarding headloss and discharge coefficients and backwater flow profiles associated with varying structure geometry were obtained so as to determine the extent to which a baffle-post structure will retard an approach flow and reduces its capacity to convey bed sediment. The creation of a M₁ gradually varied flow profile in the upstream reach complicates the use of headloss to characterize hydraulic performance of the baffle-post structures. Instead, the parameter, y₁/y₀, offers a practical means for describing such performance; y₁= flow depth at the upstream face of the structure, and y₀= the depth of uniform flow prior to use of a structure. The most influential geometric variable was influencing structure performance was the lateral spacing between posts, s; it is expressed non-dimensionally as s/D, where D = post diameter. Qualitative results regarding sediment transport confirm a reduction in bed-sediment transport rate upstream of the structure. However, the turbulent flow structures at the baffle-post structures promote local scour at the base of such structures. Due to the flow acceleration between posts, baffle-posts structures could potentially obstruct fish and other aquatic life passage along the channel.
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Subject
grade control structures
hydraulic structures
flow control
sediment transport
head loss coefficient