The study on the criteria used to distinguish floc sedimentation and gel-like network sedimentation of cohesive fine-grained sediment in a turbulent flow has rarely been carried out. In this preliminary study, we deri...The study on the criteria used to distinguish floc sedimentation and gel-like network sedimentation of cohesive fine-grained sediment in a turbulent flow has rarely been carried out. In this preliminary study, we derive three criteria to distinguish these two different sedimentation phases by considering the comparison of the time that a characteristic floc takes to settle through mean distance between characteristic flocs and the time that it takes to move through the same distance under the influence of a turbulent flow. These criteria incorporate physical and chemical factors that have been verified to have some influences on the sediment flocculation in some published literatures, and a simple analysis result is found to be consistent with our qualitative understandings of flocculation phenomenon of cohesive fine-grained sediment.展开更多
In coastal environments, fine-grain sediments often aggregate into large and porous flocs. ElectroMagnetic Current Meters （EMCM） and Laser In Situ Scattering and Transmissometry （LISST-ST） have been deployed withi...In coastal environments, fine-grain sediments often aggregate into large and porous flocs. ElectroMagnetic Current Meters （EMCM） and Laser In Situ Scattering and Transmissometry （LISST-ST） have been deployed within a Spartina alterniflora marsh of the Luoyuan Bay in Fujian Province, China, to measure the current velocity, the floc size and the settling velocity between 15 and 22 January 2008. During the observations, the near-bed water was collected in order to obtain the suspended sediment concentration （SSC） and constituent grain size. Data show that： （1） the nearbed current velocities vary from 0.1 to 5.6 cm/s in the central Spartina alterniflora marsh and 0.1–12.5 cm/s at the edge; （2） the SSCs vary from 47 to 188 mg/dm 3 . The mean grain size of constituent grains varies from 7.0 to 9.6 μm, and the mean floc sizes （MFS） vary from 30.4 to 69.4 μm. The relationship between the mean floc size and settling velocity can be described as： w s =ad b , in which w s is the floc settling velocity （mm/s）, a and b are coefficients. The floc settling velocity varies from 0.17 to 0.32 mm/s, with a mean value of 0.26 mm/s, and the floc settling velocity during the flood tide is higher than that during the ebb tide. The current velocity and the SSC are the main factors controlling the flocculation processes and the floc settling velocity.展开更多
文摘The study on the criteria used to distinguish floc sedimentation and gel-like network sedimentation of cohesive fine-grained sediment in a turbulent flow has rarely been carried out. In this preliminary study, we derive three criteria to distinguish these two different sedimentation phases by considering the comparison of the time that a characteristic floc takes to settle through mean distance between characteristic flocs and the time that it takes to move through the same distance under the influence of a turbulent flow. These criteria incorporate physical and chemical factors that have been verified to have some influences on the sediment flocculation in some published literatures, and a simple analysis result is found to be consistent with our qualitative understandings of flocculation phenomenon of cohesive fine-grained sediment.
基金The National Natural Science Foundation of China under contract No. 40606012the Scientific Research Foundation of Third Institute of Oceanography, State Oceanic Administration under contract No. 2009015
文摘In coastal environments, fine-grain sediments often aggregate into large and porous flocs. ElectroMagnetic Current Meters （EMCM） and Laser In Situ Scattering and Transmissometry （LISST-ST） have been deployed within a Spartina alterniflora marsh of the Luoyuan Bay in Fujian Province, China, to measure the current velocity, the floc size and the settling velocity between 15 and 22 January 2008. During the observations, the near-bed water was collected in order to obtain the suspended sediment concentration （SSC） and constituent grain size. Data show that： （1） the nearbed current velocities vary from 0.1 to 5.6 cm/s in the central Spartina alterniflora marsh and 0.1–12.5 cm/s at the edge; （2） the SSCs vary from 47 to 188 mg/dm 3 . The mean grain size of constituent grains varies from 7.0 to 9.6 μm, and the mean floc sizes （MFS） vary from 30.4 to 69.4 μm. The relationship between the mean floc size and settling velocity can be described as： w s =ad b , in which w s is the floc settling velocity （mm/s）, a and b are coefficients. The floc settling velocity varies from 0.17 to 0.32 mm/s, with a mean value of 0.26 mm/s, and the floc settling velocity during the flood tide is higher than that during the ebb tide. The current velocity and the SSC are the main factors controlling the flocculation processes and the floc settling velocity.
