Cohesive sediment flocculation in a partially-stratified estuary

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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.


Type of resource text
Form electronic; electronic resource; remote
Extent 1 online resource.
Publication date 2017
Issuance monographic
Language English


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-


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

© 2017 by Ivy Bifu Huang
This work is licensed under a Creative Commons Attribution Non Commercial 3.0 Unported license (CC BY-NC).

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