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The effects of scour on the flow field at a bendway weir

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dc.contributor.authorGarfield, Mason, author
dc.contributor.authorEttema, Robert, advisor
dc.contributor.authorThornton, Christopher, committee member
dc.contributor.authorWohl, Ellen, committee member
dc.date.accessioned2019-09-10T14:35:48Z
dc.date.available2019-09-10T14:35:48Z
dc.date.issued2019
dc.description.abstractBendway weirs (BWs) are rock structures commonly used for controlling the thalweg location in alluvial channels, especially bends. Although there are many studies analyzing the effect of BWs on bend flow fields, there is little known about the effects of scour on the modified flow field. Many physical and numerical models of BWs use a fixed bed with the existing river bathymetry, assuming that the effects of scour are negligible. This study analyzed the effects of the scour on the flow field using SRH-2D, a 2-dimensional numerical model solving the full St. Venant equation (also termed the dynamic wave equation). In addition, the study used small scale and large scale hydraulic models and a 3-dimensional numerical model, FLOW-3D, to validate and calibrate the 2-D model. Using FLOW-3D, the 3-dimensional flow field was used to identify areas where SRH-2D was accurate and where it was lacking. The small scale hydraulic model was used to determine the effect of streamwise blockage on scour using plates. Results from the small scale hydraulic model indicate that when the degree of streamwise blockage (L/B where L is the width of the plate and B is the width of the flume) and submergence (Y/H where Y is the flow depth and H is the height of the plate) remained the same, but the acute angle to the flume wall varied (α), the maximum scour depth did not change significantly. Accordingly, the scour morphology from the tests with α = 90° could be applied to tests with α = 30° and 60° using the 2-D model. When comparing the flow field using SRH-2D to FLOW-3D, it was found that the maximum depth-averaged velocity was closer to FLOW-3D's when Y/H = 1.25 than when Y/H = 2.0. This finding likely results from the greater effect of blockage directing the flow around the BW than the deeper case, where the flow has a higher vertical velocity over the top of the BW. The 2-D model cannot take this into account, leading to error. The pre- and post-scour maximum velocity magnitude and locations were compared to determine the effect of scour on the flow field using the 2-D model. A deep flow depth (Y/H = 2.0) and a shallower flow depth (Y/H = 1.25) were run for different BW orientations, (α=30°,60°,and 90°) to determine the applicability of the effect of scour on the flow field. The analysis found that, when Y/H = 2.0, the difference in the maximum velocity magnitude and location between pre-and post-scour were fairly negligible for all orientations, whereas when Y/H =1.25, the effects of the scour on the flow field were more prominent. Overall it was found that the scour morphology is important to take into consideration for a fixed bed numerical or physical model when analyzing flow depths slightly overtopping the BW, but has little effect when the flow is twice the size of the BW.
dc.format.mediumborn digital
dc.format.mediummasters theses
dc.identifierGarfield_colostate_0053N_15548.pdf
dc.identifier.urihttps://hdl.handle.net/10217/197324
dc.languageEnglish
dc.language.isoeng
dc.publisherColorado State University. Libraries
dc.relation.ispartof2000-2019
dc.rightsCopyright and other restrictions may apply. User is responsible for compliance with all applicable laws. For information about copyright law, please see https://libguides.colostate.edu/copyright.
dc.subjectFLOW-3D
dc.subjectSRH-2D
dc.subjectnumerical modeling
dc.subjectbendway weirs
dc.titleThe effects of scour on the flow field at a bendway weir
dc.typeText
dcterms.rights.dplaThis Item is protected by copyright and/or related rights (https://rightsstatements.org/vocab/InC/1.0/). You are free to use this Item in any way that is permitted by the copyright and related rights legislation that applies to your use. For other uses you need to obtain permission from the rights-holder(s).
thesis.degree.disciplineCivil and Environmental Engineering
thesis.degree.grantorColorado State University
thesis.degree.levelMasters
thesis.degree.nameMaster of Science (M.S.)

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