Semester of Graduation

Spring 2023

Degree

Master of Science (MS)

Department

Department of Oceanography and Coastal Sciences

Document Type

Thesis

Abstract

Mud settling velocity is controlled by flocculation, which in turn strongly depends on turbulence and on the chemistry and biology of the water-sediment mixture. As a result, mud settling velocity can be poorly constrained in coastal areas and vary in space and time by orders of magnitude. Here we quantified mud settling velocity in Barataria Basin, a deltaic estuary in Louisiana (USA), using three independent methods: eddy covariance (one station for 200 days), floc cameras (4 stations at one time), and Rouse profile inversion (14 stations, replicated 10-30 times each). Eddy covariance indicates that settling velocity increases with turbulence, at least within the range experienced at the site (shear rate G up to 10 Hz). Settling velocity increases with salinity (in the 0 to 6 psu range) for moderate turbulence levels (5<G<10 >Hz), but it is nearly independent of salinity for low levels of turbulence (G<5 >Hz). Consistent with this finding, floc camera measurements – which were taken at low turbulence levels – indicate similar floc sizes for salinities from 0.4 to 20 psu. Settling velocity estimated from a Rouse profile inversion also lacks a dependence on salinity, likely because they were taken at low turbulence levels. This study is novel in that it used three methods to predict the settling velocity of mud within Barataria Basin, and quantified settling velocity values in the range 0.1 to 1 mm/s, with most values between 0.2 and 0.5 mm/s. Overall these measurements confirm that mud is flocculated in both the saline and freshwater zones of Barataria Basin, and that turbulence is the largest factor controlling its settling velocity. Nonetheless, salinity could increase mud settling velocity up to a factor of two. These results could inform the management of sediment imported into estuaries from freshwater sources, such as natural drainage, crevasse splays, and engineered river diversions.

Date

4-4-2023

Committee Chair

Mariotti, Giulio

DOI

10.31390/gradschool_theses.5735

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