The physical role of transverse deep zones in improving constructed treatment wetland performance
Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Civil and Environmental Engineering, 2007.
| Main Author: | |
|---|---|
| Other Authors: | |
| Format: | Thesis |
| Language: | eng |
| Published: |
Massachusetts Institute of Technology
2008
|
| Subjects: | |
| Online Access: | http://hdl.handle.net/1721.1/42052 |
| _version_ | 1826214390105374720 |
|---|---|
| author | Lightbody, Anne F. (Anne Fraser), 1977- |
| author2 | Heidi M. Nepf. |
| author_facet | Heidi M. Nepf. Lightbody, Anne F. (Anne Fraser), 1977- |
| author_sort | Lightbody, Anne F. (Anne Fraser), 1977- |
| collection | MIT |
| description | Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Civil and Environmental Engineering, 2007. |
| first_indexed | 2024-09-23T16:04:38Z |
| format | Thesis |
| id | mit-1721.1/42052 |
| institution | Massachusetts Institute of Technology |
| language | eng |
| last_indexed | 2024-09-23T16:04:38Z |
| publishDate | 2008 |
| publisher | Massachusetts Institute of Technology |
| record_format | dspace |
| spelling | mit-1721.1/420522019-04-11T02:59:08Z The physical role of transverse deep zones in improving constructed treatment wetland performance Lightbody, Anne F. (Anne Fraser), 1977- Heidi M. Nepf. Massachusetts Institute of Technology. Dept. of Civil and Environmental Engineering. Massachusetts Institute of Technology. Dept. of Civil and Environmental Engineering. Civil and Environmental Engineering. Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Civil and Environmental Engineering, 2007. This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections. Includes bibliographical references (p. 254-274). Velocity heterogeneity is often present in wetland systems and results in some influent water remaining in the wetland for less than the expected residence time. This phenomenon, known as short-circuiting, alters the distribution of the chemical and biological transformations that occur within the wetland and decreases performance in constructed treatment wetlands. In this thesis, field observations, experiments in a laboratory physical model, and mathematical modeling are used to explore the ability of transverse deep zones to mitigate the negative effect of short-circuiting on constructed wetland performance. Field observations were used to quantify short-circuiting in a 360-acre constructed treatment wetland in Augusta, Georgia. In each of the three marsh sections examined, between three and six narrow flowpaths were found that together carried 20-70% of the flow at a velocity at least ten times faster than the rest of the marsh. One known method for offsetting the deleterious effect of short-circuiting flowpaths is to include several transverse deep zones within each wetland cell. To study the physical mechanisms behind this proposed strategy, laser-induced fluorescence (LIF) was used within a laboratory scale model of a short-circuiting wetland with a transverse deep zone. Water exiting a fast flowpath formed a jet that initially entrained co-flowing fluid and spread laterally but then, due to the drag present within the system, reached a final width that depended on the width of the upstream flowpath. Finally, the understanding of flow patterns gained by the field and laboratory experiments were combined into an analytical streamtube model. (cont.) Modeled results revealed that a transverse deep zone can offset the adverse impact of short-circuiting flowpaths through two separate mechanisms. When lateral mixing is present within the deep zone, it dilutes the water that has traveled through the fast flowpath. In addition, deep zones likely reduce the probability that fast flowpaths will align throughout the entire wetland, which increases the probability that all water will receive some treatment even when no lateral mixing is present within the deep zones. These results indicate that deep zones may improve performance when properly sized and located within a constructed treatment wetland. by Anne F. Lightbody. Ph.D. 2008-09-02T17:55:04Z 2008-09-02T17:55:04Z 2007 2007 Thesis http://hdl.handle.net/1721.1/42052 230940219 eng M.I.T. theses are protected by copyright. They may be viewed from this source for any purpose, but reproduction or distribution in any format is prohibited without written permission. See provided URL for inquiries about permission. http://dspace.mit.edu/handle/1721.1/7582 289 p. application/pdf Massachusetts Institute of Technology |
| spellingShingle | Civil and Environmental Engineering. Lightbody, Anne F. (Anne Fraser), 1977- The physical role of transverse deep zones in improving constructed treatment wetland performance |
| title | The physical role of transverse deep zones in improving constructed treatment wetland performance |
| title_full | The physical role of transverse deep zones in improving constructed treatment wetland performance |
| title_fullStr | The physical role of transverse deep zones in improving constructed treatment wetland performance |
| title_full_unstemmed | The physical role of transverse deep zones in improving constructed treatment wetland performance |
| title_short | The physical role of transverse deep zones in improving constructed treatment wetland performance |
| title_sort | physical role of transverse deep zones in improving constructed treatment wetland performance |
| topic | Civil and Environmental Engineering. |
| url | http://hdl.handle.net/1721.1/42052 |
| work_keys_str_mv | AT lightbodyannefannefraser1977 thephysicalroleoftransversedeepzonesinimprovingconstructedtreatmentwetlandperformance AT lightbodyannefannefraser1977 physicalroleoftransversedeepzonesinimprovingconstructedtreatmentwetlandperformance |