Testing floc settling velocity models in rivers and freshwater wetlands
<p>Flocculation controls mud sedimentation and organic carbon burial rates by increasing mud settling velocity. However, calibration and validation of floc settling velocity models in freshwater are lacking. We used a camera, in situ laser diffraction particle sizing, and suspended sediment co...
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Copernicus Publications
2024-11-01
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| Series: | Earth Surface Dynamics |
| Online Access: | https://esurf.copernicus.org/articles/12/1267/2024/esurf-12-1267-2024.pdf |
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| author | J. A. Nghiem G. K. Li G. K. Li J. P. Harringmeyer G. Salter C. G. Fichot L. Cortese M. P. Lamb |
| author_facet | J. A. Nghiem G. K. Li G. K. Li J. P. Harringmeyer G. Salter C. G. Fichot L. Cortese M. P. Lamb |
| author_sort | J. A. Nghiem |
| collection | DOAJ |
| description | <p>Flocculation controls mud sedimentation and organic carbon burial rates by increasing mud settling velocity. However, calibration and validation of floc settling velocity models in freshwater are lacking. We used a camera, in situ laser diffraction particle sizing, and suspended sediment concentration–depth profiles to measure flocs in Wax Lake Delta, Louisiana. We developed a new workflow that combines our multiple floc data sources to distinguish between flocs and unflocculated sediment and measure floc attributes that were previously difficult to constrain. Sediment finer than <span class="inline-formula">∼10</span> to 55 <span class="inline-formula">µ</span>m was flocculated with median floc diameter of 30 to 90 <span class="inline-formula">µ</span>m, bulk solid fraction of 0.05 to 0.3, fractal dimension of <span class="inline-formula">∼2.1</span>, and floc settling velocity of <span class="inline-formula">∼0.1</span> to 1 mm s<span class="inline-formula"><sup>−1</sup></span>, with little variation along water depth. Results are consistent with a semi-empirical model indicating that sediment concentration and mineralogy, organics, water chemistry, and, above all, turbulence control floc settling velocity. Effective primary particle diameter is <span class="inline-formula">∼2</span> <span class="inline-formula">µ</span>m, about 2 to 6 times smaller than the median primary particle diameter, and is better described using a fractal theory. Flow through the floc increases settling velocity by an average factor of 2 and up to a factor of 7 and can be described by a modified permeability model that accounts for the effect of many primary particle sizes on flow paths. These findings help explain discrepancies between observations and an explicit settling model based on Stokes' law that depends on floc diameter, permeability, and fractal properties.</p> |
| format | Article |
| id | doaj-art-c056cabaac2a42c884acbbd9a9b51b5a |
| institution | OA Journals |
| issn | 2196-6311 2196-632X |
| language | English |
| publishDate | 2024-11-01 |
| publisher | Copernicus Publications |
| record_format | Article |
| series | Earth Surface Dynamics |
| spelling | doaj-art-c056cabaac2a42c884acbbd9a9b51b5a2025-08-20T02:14:22ZengCopernicus PublicationsEarth Surface Dynamics2196-63112196-632X2024-11-01121267129410.5194/esurf-12-1267-2024Testing floc settling velocity models in rivers and freshwater wetlandsJ. A. Nghiem0G. K. Li1G. K. Li2J. P. Harringmeyer3G. Salter4C. G. Fichot5L. Cortese6M. P. Lamb7Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA 91125, USADivision of Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA 91125, USADepartment of Earth Science, University of California, Santa Barbara, Santa Barbara, CA 93106, USADepartment of Earth and Environment, Boston University, Boston, MA 02215, USADivision of Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA 91125, USADepartment of Earth and Environment, Boston University, Boston, MA 02215, USADepartment of Earth and Environment, Boston University, Boston, MA 02215, USADivision of Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA 91125, USA<p>Flocculation controls mud sedimentation and organic carbon burial rates by increasing mud settling velocity. However, calibration and validation of floc settling velocity models in freshwater are lacking. We used a camera, in situ laser diffraction particle sizing, and suspended sediment concentration–depth profiles to measure flocs in Wax Lake Delta, Louisiana. We developed a new workflow that combines our multiple floc data sources to distinguish between flocs and unflocculated sediment and measure floc attributes that were previously difficult to constrain. Sediment finer than <span class="inline-formula">∼10</span> to 55 <span class="inline-formula">µ</span>m was flocculated with median floc diameter of 30 to 90 <span class="inline-formula">µ</span>m, bulk solid fraction of 0.05 to 0.3, fractal dimension of <span class="inline-formula">∼2.1</span>, and floc settling velocity of <span class="inline-formula">∼0.1</span> to 1 mm s<span class="inline-formula"><sup>−1</sup></span>, with little variation along water depth. Results are consistent with a semi-empirical model indicating that sediment concentration and mineralogy, organics, water chemistry, and, above all, turbulence control floc settling velocity. Effective primary particle diameter is <span class="inline-formula">∼2</span> <span class="inline-formula">µ</span>m, about 2 to 6 times smaller than the median primary particle diameter, and is better described using a fractal theory. Flow through the floc increases settling velocity by an average factor of 2 and up to a factor of 7 and can be described by a modified permeability model that accounts for the effect of many primary particle sizes on flow paths. These findings help explain discrepancies between observations and an explicit settling model based on Stokes' law that depends on floc diameter, permeability, and fractal properties.</p>https://esurf.copernicus.org/articles/12/1267/2024/esurf-12-1267-2024.pdf |
| spellingShingle | J. A. Nghiem G. K. Li G. K. Li J. P. Harringmeyer G. Salter C. G. Fichot L. Cortese M. P. Lamb Testing floc settling velocity models in rivers and freshwater wetlands Earth Surface Dynamics |
| title | Testing floc settling velocity models in rivers and freshwater wetlands |
| title_full | Testing floc settling velocity models in rivers and freshwater wetlands |
| title_fullStr | Testing floc settling velocity models in rivers and freshwater wetlands |
| title_full_unstemmed | Testing floc settling velocity models in rivers and freshwater wetlands |
| title_short | Testing floc settling velocity models in rivers and freshwater wetlands |
| title_sort | testing floc settling velocity models in rivers and freshwater wetlands |
| url | https://esurf.copernicus.org/articles/12/1267/2024/esurf-12-1267-2024.pdf |
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