Retention time and dispersion associated with submerged aquatic canopies
The shear layer at the top of a submerged canopy generates coherent vortices that control exchange between the canopy and the overflowing water. Unlike free shear layers, the vortices in a canopy shear layer do not grow continuously downstream but reach and maintain a finite scale determined by a ba...
| Main Authors: | , , , |
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| Format: | Article |
| Language: | en_US |
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American Geophysical Union
2012
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| Online Access: | http://hdl.handle.net/1721.1/68012 |
| _version_ | 1826213038496153600 |
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| author | Nepf, Heidi Ghisalberti, Marco White, B. Murphy, E. |
| author2 | Massachusetts Institute of Technology. Department of Civil and Environmental Engineering |
| author_facet | Massachusetts Institute of Technology. Department of Civil and Environmental Engineering Nepf, Heidi Ghisalberti, Marco White, B. Murphy, E. |
| author_sort | Nepf, Heidi |
| collection | MIT |
| description | The shear layer at the top of a submerged canopy generates coherent vortices that control exchange between the canopy and the overflowing water. Unlike free shear layers, the vortices in a canopy shear layer do not grow continuously downstream but reach and maintain a finite scale determined by a balance between shear production and canopy dissipation. This balance defines the length scale of vortex penetration into the canopy, δ e , and the region of rapid exchange between the canopy and overflow. Deeper within the canopy, transport is constrained by smaller turbulence scales. A two-box canopy model is proposed on the basis of the length scale δ e . Using diffusivity and exchange rates defined in previous studies, the model predicts the timescale required to flush the canopy through vertical exchange over a range of canopy density and height. The predicted canopy retention times, which range from minutes to an hour, are consistent with canopy retention inferred from tracer observations in the field and comparable to retention times for some hyporheic regions. The timescale for vertical exchange, along with the in-canopy velocity, determines the minimum canopy length for which vertical exchange dominates water renewal. Shorter canopies renew interior water through longitudinal advection. Finally, canopy water retention influences longitudinal dispersion through a transient storage process. When vertical exchange controls canopy retention, the transient storage dispersion increases with canopy height. When longitudinal advection controls water renewal, dispersion increases with canopy patch length. |
| first_indexed | 2024-09-23T15:42:22Z |
| format | Article |
| id | mit-1721.1/68012 |
| institution | Massachusetts Institute of Technology |
| language | en_US |
| last_indexed | 2024-09-23T15:42:22Z |
| publishDate | 2012 |
| publisher | American Geophysical Union |
| record_format | dspace |
| spelling | mit-1721.1/680122022-10-02T03:31:45Z Retention time and dispersion associated with submerged aquatic canopies Nepf, Heidi Ghisalberti, Marco White, B. Murphy, E. Massachusetts Institute of Technology. Department of Civil and Environmental Engineering Nepf, Heidi Nepf, Heidi Murphy, E. The shear layer at the top of a submerged canopy generates coherent vortices that control exchange between the canopy and the overflowing water. Unlike free shear layers, the vortices in a canopy shear layer do not grow continuously downstream but reach and maintain a finite scale determined by a balance between shear production and canopy dissipation. This balance defines the length scale of vortex penetration into the canopy, δ e , and the region of rapid exchange between the canopy and overflow. Deeper within the canopy, transport is constrained by smaller turbulence scales. A two-box canopy model is proposed on the basis of the length scale δ e . Using diffusivity and exchange rates defined in previous studies, the model predicts the timescale required to flush the canopy through vertical exchange over a range of canopy density and height. The predicted canopy retention times, which range from minutes to an hour, are consistent with canopy retention inferred from tracer observations in the field and comparable to retention times for some hyporheic regions. The timescale for vertical exchange, along with the in-canopy velocity, determines the minimum canopy length for which vertical exchange dominates water renewal. Shorter canopies renew interior water through longitudinal advection. Finally, canopy water retention influences longitudinal dispersion through a transient storage process. When vertical exchange controls canopy retention, the transient storage dispersion increases with canopy height. When longitudinal advection controls water renewal, dispersion increases with canopy patch length. National Science Foundation (U.S.) (grant EAR0309188) 2012-01-06T16:59:12Z 2012-01-06T16:59:12Z 2007-04 2006-11 Article http://purl.org/eprint/type/JournalArticle 0043-1397 W04422 http://hdl.handle.net/1721.1/68012 Nepf, H. et al. “Retention time and dispersion associated with submerged aquatic canopies.” Water Resources Research 43.4 (2007): p. 1-10.©2007 American Geophysical Union. en_US http://dx.doi.org/10.1029/2006WR005362 Water Resources Research Article is made available in accordance with the publisher's policy and may be subject to US copyright law. Please refer to the publisher's site for terms of use. application/pdf American Geophysical Union Prof. Nepf |
| spellingShingle | Nepf, Heidi Ghisalberti, Marco White, B. Murphy, E. Retention time and dispersion associated with submerged aquatic canopies |
| title | Retention time and dispersion associated with submerged aquatic canopies |
| title_full | Retention time and dispersion associated with submerged aquatic canopies |
| title_fullStr | Retention time and dispersion associated with submerged aquatic canopies |
| title_full_unstemmed | Retention time and dispersion associated with submerged aquatic canopies |
| title_short | Retention time and dispersion associated with submerged aquatic canopies |
| title_sort | retention time and dispersion associated with submerged aquatic canopies |
| url | http://hdl.handle.net/1721.1/68012 |
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