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Author

D. Eisma

Bio: D. Eisma is an academic researcher. The author has an hindex of 1, co-authored 1 publications receiving 102 citations.

Papers
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01 Jan 1993
TL;DR: In this article, an in situ suspension camera in combination with an image-analysis system was developed at NIOZ to measure the in situ particle size of suspended matter in very clear ocean water.
Abstract: Abstract An in situ suspension camera in combination with an image-analysis system was developed at NIOZ to measure the in situ particle size of suspended matter. It differs from other methods in that in sit particle size is measured from ∼ 4 μm upwards in a relatively simple and direct way. It can be used in any waters down to ∼ 4000 m depth (with some adjustments to 7000 m) and in water with a suspended matter concentration up to 200 mg·dm −3 . In very clear ocean water the system becomes inconvenient because of the large number of photographs that have to be taken to obtain a reliable size distribution. This paper describes the camera and the image-analysis system and gives some results of measurements in the Scheldt river and estuary in April 1989. These measurements show a continuous size distribution by volume between 3.6 μm and 644 μm and a good agreement of the data obtained with the 1:1 and 1:10 cameras.

105 citations


Cited by
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Journal ArticleDOI
TL;DR: A field study of the tidal currents, cohesive sediment dynamics and transport of organic carbon in a highly vegetated mangrove swamp was carried out at Middle Creek, Cairns, Australia as discussed by the authors.
Abstract: A field study of the tidal currents, cohesive sediment dynamics and transport of organic carbon in a highly vegetated mangrove swamp was carried out at Middle Creek, Cairns, Australia. The interaction of tidal currents and the vegetation generated jets, eddies and zones of stagnant waters which were numerically modelled. A high value of the Manning friction coefficient (n=0·1) was derived by the dense vegetation. About 80% of the suspended sediment brought in from coastal waters at spring flood tide was trapped in the mangroves, corresponding to about 10–12 kg of sediment m−1creek length/spring tide, resulting in a rise of the substrate by about 0·1 cm year−1. The selective trapping of clay was caused by flocculation of the finer particles in the mangroves. There was an indication of a slight inwelling of organic carbon. Creek water was readily differentiated from mangrove water by large differences in the molecular weight distribution of the dissolved organic carbon.

482 citations

Journal ArticleDOI
TL;DR: The sediment particles carried in suspension into the mangrove forest during tidal inundation are cohesive, mainly clay and fine silt, and form large flocs as mentioned in this paper, which remain in suspension as a result of the turbulence created by the flow around the vegetation.
Abstract: The tidal currents in mangrove forests are impeded by the friction caused by the high vegetation density The tidal currents are also complex comprising eddies, jets and stagnation zones The sediment particles carried in suspension into the forest during tidal inundation are cohesive, mainly clay and fine silt, and form large flocs These flocs remain in suspension as a result of the turbulence created by the flow around the vegetation The intensity of sedimentation is largest for trees forming a complex matrix of roots such as Rhizophora sp and smallest for single trees such as Ceriops sp The flocs settle in the forest around slack high tide At ebb tides the water currents are too small to re-entrain this sediment Hence the inundation of coastal mangrove forests at tidal frequency works as a pump preferentially transporting fine, cohesive sediment from coastal waters to the mangroves Mangroves are thus not just opportunistic trees colonising mud banks but actively contribute to the creation of mud banks

247 citations

Journal ArticleDOI
TL;DR: In this article, an instrument was developed to observe the settling of individual flocs in turbid water in order to measure size and settling velocity spectra of estuarine cohesive suspended sediments.

232 citations

Journal ArticleDOI
TL;DR: In this paper, the authors examined the interrelationships between floc characteristics over increasing turbidity (80-200 mg l −1 ) and turbulent shear (0-0.6 N m −2 ) environments, by the use of a laboratory flume within which a suspension can be sheared at a controlled rate, and with an unintrusive macro-lens miniature video camera mounted in a viewing port on the flume channel wall.

229 citations

01 Jan 2006
TL;DR: In this article, the authors proposed a new model to predict the settling velocity and effective density of flocs based on the concept of fractal geometry, but with the assumption of variable fractal dimension with the floc size.
Abstract: New models to predict settling velocity and effective density of flocs are proposed. The models are based on the concept of fractal geometry, but with the assumption of variable fractal dimension with the floc size. The best results are obtained when the fractal dimension is estimated by a power law function of the floc diameter. The models are compared with observations from 26 published data sets relating floc size to settling velocity measured under various conditions and at different locations. The floc size covered by the data varies between 1.4 and about 25,500 µm. Five commonly used models are also compared to these data and found to reproduce inadequately the full range of the observations. Sensitivity analysis shows that, with the proposed models, the spread in the data may be reproduced by varying the size of primary particles from about 0.05 to 20 µm. The new models are proposed for integration into numerical models to simulate sediment transport of cohesive sediments, contaminants, and biological microorganisms such as phytoplankton. RESUME Des modeles nouveaux sont proposes pour predire la vitesse de sedimentation et la densite effective des flocs d’argile. Les modeles sont bases sur le concept de geometrie fractale, mais avec l’hypothese de dimension fractale variable avec la taille des flocs. Les meilleurs resultats sont obtenus lorsque la dimension fractale est estimee par une fonction puissance du diametre des flocs. Les modeles proposes sont compares avec les observations provenant de vingt-six series de donnees publiees. Ces dernieres relient la taille des flocs a la vitesse de sedimentation mesuree dans des conditions variees et a des endroits differents. La taille des flocs concernes par les donnees varie entre 1.4 et 25500 µm. Cinq modeles utilises frequemment sont aussi compares a ces donnees et sont apparus inadequats de reproduire les observations. L’analyse de sensitivite montre qu’avec les modeles proposes, les donnees peuvent etre reproduites en variant la taille des particules primaires composant les flocs d’environ 0.05 a 20 µm. Les nouveaux modeles sont proposes pour integration dans les modeles numeriques pour simuler le transport de sediments cohesifs, de contaminants et de microorganismes biologiques comme le phytoplancton.

197 citations