American Society of Civil Engineers


In Situ Measurements of Settling Velocity near Baimao Shoal in Changjiang Estuary


by YuYang Shao, (State Key Laboratory of Hydrology, Water Resources and Hydraulic Engineering, Hohai Univ., Nanjing, China.), Yixin Yan, (State Key Laboratory of Hydrology, Water Resources and Hydraulic Engineering, Hohai Univ., Nanjing, China.), and Jerome Pea-Yea Maa, (Virginia Institute of Marine Science, College of William and Mary, Gloucester Point, VA 23062.)

Journal of Hydraulic Engineering, Vol. 137, No. 3, March 2011, pp. 372-380, (doi:  http://dx.doi.org/10.1061/(ASCE)HY.1943-7900.0000312)

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Document type: Case Studies
Abstract: At the South Branch of the Changjiang Estuary near Baimao Shoal, two in situ approaches were used to estimate the settling velocity, ws, of suspended, fine-grained sediments. The first approach was used when the current was less than 1.5 m/s and was based on measurements from an optical backscatter sensor (OBS-3A) and a laser in situ scattering and transmissometer (LISST-100, Type C). A modification, using the measured ratio of volume concentration for each floc size class to the total volume concentration as a weighting factor. To improve a previously published approach, a better algorthim was implemented to estimate ws. Results of the modified approach (0.4 to 4.6 mm/s) are about twice those of the original approach, which assumes that all sizes of flocs have the same floc density. The second approach used the Rouse equation to estimate the depth-averaged ws when the current was strong and nearly steady around maximum ebb. Results from the second approach show a much greater depth-averaged ws (4–8.5 mm/s). This is attributed to the large bed shear stresses (between 3 and 3.6 Pa) bringing large sediments into the water column.


ASCE Subject Headings:
Sediment
Fine-grained soils
Settling velocity
Estuaries
China
Shoaling

Author Keywords:
Cohesive sediments
Fine-grained sediments
Floc size
Floc density
Settling velocity
Changjiang Estuary
Baimao Shoal