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Colorado State University

1.
Garfield, Mason.
Effects of scour on the flow field at a *bendway* weir, The.

Degree: MS(M.S.), Civil and Environmental Engineering, 2019, Colorado State University

URL: http://hdl.handle.net/10217/197324

Bendway 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.
*Advisors/Committee Members: Ettema, Robert (advisor), Thornton, Christopher (committee member), Wohl, Ellen (committee member).*

Subjects/Keywords: FLOW-3D; SRH-2D; numerical modeling; bendway weirs

Record Details Similar Records

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APA · Chicago · MLA · Vancouver · CSE | Export to Zotero / EndNote / Reference Manager

APA (6^{th} Edition):

Garfield, M. (2019). Effects of scour on the flow field at a bendway weir, The. (Masters Thesis). Colorado State University. Retrieved from http://hdl.handle.net/10217/197324

Chicago Manual of Style (16^{th} Edition):

Garfield, Mason. “Effects of scour on the flow field at a bendway weir, The.” 2019. Masters Thesis, Colorado State University. Accessed April 12, 2021. http://hdl.handle.net/10217/197324.

MLA Handbook (7^{th} Edition):

Garfield, Mason. “Effects of scour on the flow field at a bendway weir, The.” 2019. Web. 12 Apr 2021.

Vancouver:

Garfield M. Effects of scour on the flow field at a bendway weir, The. [Internet] [Masters thesis]. Colorado State University; 2019. [cited 2021 Apr 12]. Available from: http://hdl.handle.net/10217/197324.

Council of Science Editors:

Garfield M. Effects of scour on the flow field at a bendway weir, The. [Masters Thesis]. Colorado State University; 2019. Available from: http://hdl.handle.net/10217/197324

Colorado State University

2.
Hogan, Taylor.
Effects of bend radius on flow around a configuration of *bendway* *weirs*: insight from a numerical model, The.

Degree: MS(M.S.), Civil and Environmental Engineering, 2019, Colorado State University

URL: http://hdl.handle.net/10217/197362

Bendway weirs have been used and refined for decades by hydraulic engineers to control thalweg location within alluvial rivers and to decrease flow velocity along the outer bank of channel bends. Although these structures have been used in a variety of applications, there are still a wide range of acceptable design parameters that vary in accordance with the specific design methodology being used. Since the early 2000s, Colorado State University's Hydraulics Lab has assisted The U.S Bureau of Reclamation (USBR) in refining the design of bendway weirs and similar in-stream rock structures. During this period of time, Colorado State University and The USBR have utilized hydraulic and numerical models to develop systematic design guidelines for bendway weirs and other in-stream rock structures. Hydraulic modeling has also provided a large database of velocity and water surface measurements that have been used to calibrate and validate subsequent numerical models. The partnership between Colorado State University and the USBR has led to design recommendations and equations in which the effect of many variables and their sensitivity in overall bendway weir design has been identified. This study investigates the parameter radius of curvature over channel top width, Rc/Tw, and its effect on the flow field around bendway weirs, as its significance in bendway weir design is not well known. To investigate the effects of Rc/Tw on the bendway weir flow field, the 2D numerical model SRH-2D was used in conjunction with AutoCAD Civil3D software. The SRH-2D model was created using the bathymetry of the hydraulic model and then also calibrated and validated using data collected in the hydraulic model. AutoCAD Civil3D was used to create four different bend radii while holding Tw constant, representing Rc/Tw values between 3.0 and 8.0 which are typical of the Middle Rio Grande that the hydraulic model represented. Two additional trapezoidal channel models were also created to isolate the possible effects from specific channel geometry on the bendway weir flow field comparisons. 2D numerical modeling results revealed that the bend radius of curvature had negligible effect on the bendway weir flow field. Velocity patterns in the trapezoidal and native bathymetry channels changed negligibly in location and magnitude across varying bend radii. Cross-sectional velocity distributions were also evaluated and showed that the inner and middle third lateral sections of the channel showed the same (within fractions of a percent) velocity increase after the installation of bendway weirs. The outer fifth of the channel resulted in 6% velocity decrease only varying approximately 0.1% between bend radii. Overall numerical modeling results showed that the bendway weir flow field was negligibly affected by the bend radius of curvature, Rc.
*Advisors/Committee Members: Thornton, Christopher (advisor), Ettema, Robert (advisor), Williams, John (committee member).*

Subjects/Keywords: change of bend radius; bendway weirs; SRH-2D

Record Details Similar Records

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APA · Chicago · MLA · Vancouver · CSE | Export to Zotero / EndNote / Reference Manager

APA (6^{th} Edition):

Hogan, T. (2019). Effects of bend radius on flow around a configuration of bendway weirs: insight from a numerical model, The. (Masters Thesis). Colorado State University. Retrieved from http://hdl.handle.net/10217/197362

Chicago Manual of Style (16^{th} Edition):

Hogan, Taylor. “Effects of bend radius on flow around a configuration of bendway weirs: insight from a numerical model, The.” 2019. Masters Thesis, Colorado State University. Accessed April 12, 2021. http://hdl.handle.net/10217/197362.

MLA Handbook (7^{th} Edition):

Hogan, Taylor. “Effects of bend radius on flow around a configuration of bendway weirs: insight from a numerical model, The.” 2019. Web. 12 Apr 2021.

Vancouver:

Hogan T. Effects of bend radius on flow around a configuration of bendway weirs: insight from a numerical model, The. [Internet] [Masters thesis]. Colorado State University; 2019. [cited 2021 Apr 12]. Available from: http://hdl.handle.net/10217/197362.

Council of Science Editors:

Hogan T. Effects of bend radius on flow around a configuration of bendway weirs: insight from a numerical model, The. [Masters Thesis]. Colorado State University; 2019. Available from: http://hdl.handle.net/10217/197362

Colorado State University

3.
Siefken, Seth.
Computational fluid dynamics models of Rio Grande bends fitted with rock vanes or *bendway* * weirs*.

Degree: MS(M.S.), Civil and Environmental Engineering, 2019, Colorado State University

URL: http://hdl.handle.net/10217/197259

Rock vanes (also known as stream barbs) and bendway weirs are two types of transverse rock structures used to modify the flow field in river bends. This study examines the effectiveness of the two types of structures at reducing velocity along the outer bank of river bends to protect the bank from erosion. A numerical model using the commercially available FLOW-3D software was used to evaluate the effect of various rock vane and bendway weir configurations on the flow field through two river bends typical of the Middle Rio Grande. The model was calibrated and validated using data from a previous physical model study of rock vanes. 33 different rock vane configurations were tested in the numerical model to evaluate the effect of altering planform angle, crest slope, projected length, and structure spacing. In addition, 14 different bendway weir configurations were tested to provide a comparison of the relative performance of bendway weirs and rock vanes. The numerical modeling results indicate that rock vanes are more effective at reducing the velocity along the outer bank of a bend than bendway weirs. Modelling showed that the completely submerged crest of bendway weirs allows a substantial amount of flow to pass over the crest, limiting their effectiveness in reducing velocity along the bank. In contrast, rock vanes, with a sloped crest intersecting the waterline at the design flow rate, directed more flow around the tip of the structure rather than over the crest and were much more effective at reducing velocity along the bank. Based on the modeling results, it is recommended that bendway weirs not be installed for the purpose of erosion protection along riverbanks. The reduction in velocity along the bank produced by the various rock vane configurations varied considerably with the geometry of the configuration. Based on the results, the following conclusions are made regarding rock vane geometry: (1) Rock vanes should be installed at a planform angle between 45° and 90° to the river bank. (2) There exists an optimal projected length of rock vane, which lies in the neighborhood of 1/5 to 1/3 of the channel top-width. (3) Rock vanes with a 10% crest slope perform well, although decreasing the crest slope will decrease the velocity along the outer bank and vice versa. (4) Decreasing the spacing of rock vanes decreases the velocity along the outer bank, up to a limit. A design equation was developed to predict the velocity reduction along the bank of a river bend produced by a given configuration of rock vanes, based on the geometry of the rock vanes and the river channel. The equation provided good predictions for the range of configurations tested, having a coefficient of determination r2 = 0.83 and predicting the velocity reduction along the outer bank to within 15 percentage points for all of the tested configurations.
*Advisors/Committee Members: Ettema, Robert (advisor), Thornton, Christopher (committee member), McGrath, Daniel (committee member).*

Subjects/Keywords: bendway weirs; erosion protection; stream barbs; computational fluid dynamics; bank stabilization; rock vanes

Record Details Similar Records

❌

APA · Chicago · MLA · Vancouver · CSE | Export to Zotero / EndNote / Reference Manager

APA (6^{th} Edition):

Siefken, S. (2019). Computational fluid dynamics models of Rio Grande bends fitted with rock vanes or bendway weirs. (Masters Thesis). Colorado State University. Retrieved from http://hdl.handle.net/10217/197259

Chicago Manual of Style (16^{th} Edition):

Siefken, Seth. “Computational fluid dynamics models of Rio Grande bends fitted with rock vanes or bendway weirs.” 2019. Masters Thesis, Colorado State University. Accessed April 12, 2021. http://hdl.handle.net/10217/197259.

MLA Handbook (7^{th} Edition):

Siefken, Seth. “Computational fluid dynamics models of Rio Grande bends fitted with rock vanes or bendway weirs.” 2019. Web. 12 Apr 2021.

Vancouver:

Siefken S. Computational fluid dynamics models of Rio Grande bends fitted with rock vanes or bendway weirs. [Internet] [Masters thesis]. Colorado State University; 2019. [cited 2021 Apr 12]. Available from: http://hdl.handle.net/10217/197259.

Council of Science Editors:

Siefken S. Computational fluid dynamics models of Rio Grande bends fitted with rock vanes or bendway weirs. [Masters Thesis]. Colorado State University; 2019. Available from: http://hdl.handle.net/10217/197259