The rock cross vane, an in-stream boulder structure, consists of a U-shaped weir with the apex upstream at bed elevation and upward sloping arms that tie into downstream banks. The structure provides grade control, bank protection and scour pool development via a protected drop and arms that turn flow away from the banks. A physical model was used to measure the velocity distribution changes caused by a range of geometric configurations of the structure. Results showed linear and quadratic effects of drop ratio, cross product effects of drop ratio and arm angle, drop ratio and arm slope, and arm angle and arm slope on the velocity ratio (the average center velocity to the average outer velocity) of a cross section located two bankfull widths downstream of the drop. The Rock Cross Vane Rapid Assessment Tool (RCV-RAT) was developed to rate rock cross vane failures and assess the causes of structure weakness on NC stream restoration projects. Failure ratings were analyzed for significant correlations to project parameters, class effects of project, and correlations between dependent variables (alpha =0.05). Of the 120 rock cross vanes observed, 109 had at least one incidence of failure ranging from slight to extreme. From this data, an FMEA was developed to compare the risks of the various modes of failure for the rock cross vane and to adapt the FMEA for use in North Carolina stream projects. It was concluded that sufficient drop is necessary for scour pool development, while steep, narrow arms leading to a constricted flow area minimally contribute to scour pool development and may risk bank instability at the structure and at downstream banks. Rock cross vanes that can tolerate rapid lateral migration of the stream post-construction should be developed and tested due to the observed problems of structure side cutting. The final chapter reviews literature for the main effects of stream restoration on benthic macroinvertebrate communities and the expected return of benthic macroinvertebrate communities post-restoration to address what impacts the rock cross vane might have on benthic macroinvertebrates and to recommend practices that might reduce these impacts.
| Identifer | oai:union.ndltd.org:NCSU/oai:NCSU:etd-03122007-111706 |
| Date | 20 April 2007 |
| Creators | Puckett, Paige R |
| Contributors | Gregory D. Jennings, James D. Gregory, Garry L. Grabow, Michael D. Boyette |
| Publisher | NCSU |
| Source Sets | North Carolina State University |
| Language | English |
| Detected Language | English |
| Type | text |
| Format | application/pdf |
| Source | http://www.lib.ncsu.edu/theses/available/etd-03122007-111706/ |
| Rights | unrestricted, I hereby certify that, if appropriate, I have obtained and attached hereto a written permission statement from the owner(s) of each third party copyrighted matter to be included in my thesis, dis sertation, or project report, allowing distribution as specified below. I certify that the version I submitted is the same as that approved by my advisory committee. I hereby grant to NC State University or its agents the non-exclusive license to archive and make accessible, under the conditions specified below, my thesis, dissertation, or project report in whole or in part in all forms of media, now or hereafter known. I retain all other ownership rights to the copyright of the thesis, dissertation or project report. I also retain the right to use in future works (such as articles or books) all or part of this thesis, dissertation, or project report. |
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