Cohesive sediment flocculation in a partially-stratified estuary
Abstract/Contents
- Abstract
- This research is focused on understanding cohesive sediment dynamics and transport in the San Francisco Bay-Delta (SFBD) estuary, which is a partially-stratified estuary. Cohesive sediments play an essential role in coastal systems because they act as carriers for contaminant transport, affect aquatic organisms through turbidity, and cause build-up in navigation channels. One of the fundamental challenges in the study of this multi-faceted chemical, biological, and physical problem is the dynamic process of cohesive sediment flocculation. We studied cohesive sediment flocculation using high-resolution transect and stationary measurements of stratified turbulence and floc properties collected between 2008 and 2015. We make the following main observations. First, we show that the expected floc fall velocity is O(0.01-1) mm/s, which is at least two orders of magnitude higher than the expected fall velocity of its disaggregated constituents. Second, we show that the floc size is not significantly affected by changes in salinity, sediment concentration, or biological activity. Moreover, a comparison between the freshwater and saltwater flocculation dynamics shows that the traditional notion of enhanced floc aggregation at the onset of salinity is not appropriate in this estuary. Third, and most importantly, we conclude that the physical processes are the most dominant control on floc size, rather than the biological or chemical factors. Using the turbulent shear rate (G), we show that the floc size scaled inversely with the strength of G. Over tidal timescales, the smallest floc sizes are typically observed during slack water, and the largest floc sizes are typically observed at peak current velocities. However, while G is the primary control on floc size changes in time, we found that other physical processes, such as differential settling, cannot be ignored. These secondary effects are most evident during the tidal transitions, coinciding with when stratification is at its strongest and the largest top-bottom difference in floc sizes is observed. In previous laboratory and field studies, this interplay between turbulence, stratification, and differential settling on flocculation has often been ignored either by design or was not accounted for.
Description
| Type of resource | text |
|---|---|
| Form | electronic; electronic resource; remote |
| Extent | 1 online resource. |
| Publication date | 2017 |
| Issuance | monographic |
| Language | English |
Creators/Contributors
| Associated with | Huang, Ivy B |
|---|---|
| Associated with | Stanford University, Civil & Environmental Engineering Department. |
| Primary advisor | Monismith, Stephen Gene |
| Thesis advisor | Monismith, Stephen Gene |
| Thesis advisor | Fringer, Oliver B. (Oliver Bartlett) |
| Thesis advisor | Manning, Andrew J |
| Thesis advisor | Ouellette, Nicholas (Nicholas Testroet), 1980- |
| Advisor | Fringer, Oliver B. (Oliver Bartlett) |
| Advisor | Manning, Andrew J |
| Advisor | Ouellette, Nicholas (Nicholas Testroet), 1980- |
Subjects
| Genre | Theses |
|---|
Bibliographic information
| Statement of responsibility | Ivy B. Huang. |
|---|---|
| Note | Submitted to the Department of Civil and Environmental Engineering. |
| Thesis | Thesis (Ph.D.)--Stanford University, 2017. |
| Location | electronic resource |
Access conditions
- Copyright
- © 2017 by Ivy Bifu Huang
- License
- This work is licensed under a Creative Commons Attribution Non Commercial 3.0 Unported license (CC BY-NC).
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