Observations of flocs in an estuary and implications for computation of settling velocity
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Abstract
The settling velocity (ws) in estuarine environments can impact whether a region is eroding or accreting sediment on the bed, yet determining this rate can be an indirect process requiring a number of assumptions. Accurate determination of ws is especially needed for numerical models to reproduce observed sediment concentrations at the appropriate timescale. We collected information on suspended sediment flocculation at a channel site (13 m deep) and a shallows site (4 m deep) within South San Francisco Estuary, alongside timeseries of flow, wave statistics, turbulent shear, and bottle samples analyzed for both ws and particle size. Using the measurements of floc size and settling velocity, we performed a sensitivity analysis on the unknown parameters in the general explicit formula for settling velocity. The collected particle size distribution data show that multiple classes of flocs are present; these are characterized as flocculi, microflocs, and macroflocs. We show that ws of flocculi is closest to ws for the full distribution. The determined parameter values lead to near-bed mass-weighted settling velocities (standard deviation) of 1.18 (0.55) and 0.22 (0.15) mm/s at the channel and shallows sites, respectively. Modeling efforts can use this work to help select an appropriate sediment model and parameter values.
Study Area
| Publication type | Article |
|---|---|
| Publication Subtype | Journal Article |
| Title | Observations of flocs in an estuary and implications for computation of settling velocity |
| Series title | Journal of Geophysical Research: Oceans |
| DOI | 10.1029/2022JC019402 |
| Volume | 129 |
| Issue | 8 |
| Publication Date | August 04, 2024 |
| Year Published | 2024 |
| Language | English |
| Publisher | American Geophysical Union |
| Contributing office(s) | Woods Hole Coastal and Marine Science Center |
| Description | e2022JC019402, 21 p. |
| Country | United States |
| State | California |
| Other Geospatial | South San Francisco Estuary |