Pollutant advective spreading in beach sand exposed to high-energy tides

yesThis paper presents field measurements in which dye solute was injected into coastal sand to investigate contaminant advection in intertidal beach sand. The measurements show the pathways of a contaminated plume in the unsaturated zone during both the flood and ebb tides. A prescribed amount of dye tracer solution was directly injected through the topsoil, with average porosity 0.3521±0.01, at predetermined locations of the River Mersey’s outer estuarial beach during ebb-tide. The injected dye was monitored, sampled and photographed over several tidal cycles. The distinctive features of the plume (full two dimensional cross-sections), sediments and water-table depth were sampled in-situ, close to the injection point (differing from previous contaminant monitoring tests in aquifers). The advective movement is attributed to tidal impact which is different from contaminant transport in aquifers. The experimental results show that plumes have significantly large spatial variability, diverging upwards and converging downwards, with a conical geometric shape which is different from the usual spherical/elliptical shape reported in literature. The mean vertical motion of the plume reaches three times the top-width within ten tidal cycles, exceeding the narrow bottom-width by a factor of order 2. The observed transport features of the plume within the beach sand have significant relevance to saltwater intrusion, surface water and groundwater quality. The field observations are unique and can serve as a valuable benchmark database for relevant numerical studies.China Ministry of Science and Technology 973 program (2014CB745001), Special Program of future development in Shenzhen (201411201645511650) and Shenzhen Key Laboratory for Coastal Ocean Dynamic and Environment（ZDSY20130402163735964)

Pollutant advective spreading in beach sand exposed to high-energy tides

yesThis paper presents field measurements in which dye solute was injected into coastal sand to investigate contaminant advection in intertidal beach sand. The measurements show the pathways of a contaminated plume in the unsaturated zone during both the flood and ebb tides. A prescribed amount of dye tracer solution was directly injected through the topsoil, with average porosity 0.3521±0.01, at predetermined locations of the River Mersey’s outer estuarial beach during ebb-tide. The injected dye was monitored, sampled and photographed over several tidal cycles. The distinctive features of the plume (full two dimensional cross-sections), sediments and water-table depth were sampled in-situ, close to the injection point (differing from previous contaminant monitoring tests in aquifers). The advective movement is attributed to tidal impact which is different from contaminant transport in aquifers. The experimental results show that plumes have significantly large spatial variability, diverging upwards and converging downwards, with a conical geometric shape which is different from the usual spherical/elliptical shape reported in literature. The mean vertical motion of the plume reaches three times the top-width within ten tidal cycles, exceeding the narrow bottom-width by a factor of order 2. The observed transport features of the plume within the beach sand have significant relevance to saltwater intrusion, surface water and groundwater quality. The field observations are unique and can serve as a valuable benchmark database for relevant numerical studies.China Ministry of Science and Technology 973 program (2014CB745001), Special Program of future development in Shenzhen (201411201645511650) and Shenzhen Key Laboratory for Coastal Ocean Dynamic and Environment（ZDSY20130402163735964)

COMPARISONS OF DYE PLUME MIGRATION AT THE NEAR-WALL REGION OF TWO DIFFERENT FLAT BEDS ROUGHENED WITH 7 MM AND 10 MM SYNTHETIC PLEXIGLAS BEADS

The detection of moving particles and the ability of processing the captured images using highspeed cameras can be an effective means of monitoring the sliding, and rolling movement of bedload sediment along river beds. In this study, two different types of synthetic Plexiglas Beads of size 7mm and 10mm with porosity 0.7125 and 0.8522 respectively were used for the evaluation of the velocity profiles in a flume bath. Potassium permanganate (KMnO4) crystal of molecular weight 158.03 and density 1450 kg/m3 was used as a passive dye-tracer. The cavity region of the flat plate was attached to the oscillatory mechanism in the flume bath where plume activities were monitored. When there is oscillatory flow, the crest of roughness elements induce elevation zones to force (advection) the flow upwards and pull it down at the trough phases as the tracer plume scales over the obstacles, establishing low and high pressure zones in the flow. The enhanced particles in the process mix and dissolve or decay faster with increasing oscillatory frequency, resulting into inter-particle collisions which initiate the conditions of advection and shear dispersion. This phenomenon could be a combination or coupling of the processes of gradient fluctuations enhanced through dispersion due to pressure in the macroscopic pore-fluid field caused by the oscillatory motion. The lightening as the dye-particles cascade in the porous medium is associated with mixing-gain due to the enhanced oscillatory motion. It was observed that the depth of the tracer-blob entrapment is inversely proportional to the friction velocity

Solute and particulate transport at the interface of near-shore permeable estuarine beach-sand : an experimental study of the outer reaches of River Mersey estuary, N W England

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COMPARISONS OF DYE PLUME MIGRATION AT THE NEAR-WALL REGION OF TWO DIFFERENT FLAT BEDS ROUGHENED WITH 7 MM AND 10 MM SYNTHETIC PLEXIGLAS BEADS

The detection of moving particles and the ability of processing the captured images using high-speed cameras can be an effective means of monitoring the sliding, and rolling movement of bed-load sediment along river beds. In this study, two different types of synthetic Plexiglas Beads of size 7mm and 10mm with porosity 0.7125 and 0.8522 respectively were used for the evaluation of the velocity profiles in a flume bath. Potassium permanganate (KMnO4) crystal of molecular weight 158.03 and density 1450 kg/m3 was used as a passive dye-tracer. The cavity region of the flat plate was attached to the oscillatory mechanism in the flume bath where plume activities were monitored. When there is oscillatory flow, the crest of roughness elements induce elevation zones to force (advection) the flow upwards and pull it down at the trough phases as the tracer plume scales over the obstacles, establishing low and high pressure zones in the flow. The enhanced particles in the process mix and dissolve or decay faster with increasing oscillatory frequency, resulting into inter-particle collisions which initiate the conditions of advection and shear dispersion. This phenomenon could be a combination or coupling of the processes of gradient fluctuations enhanced through dispersion due to pressure in the macroscopic pore-fluid field caused by the oscillatory motion. The lightening as the dye-particles cascade in the porous medium is associated with mixing-gain due to the enhanced oscillatory motion. It was observed that the depth of the tracer-blob entrapment is inversely proportional to the friction velocity.</jats:p