Effect Of Sediment Concentration Research Articles

The effect of suspension on mean velocity profile

The vertical gradient of suspended sediment concentration often exists in estuarine and coastal regions. The existence of such concentration gradient, particular that of cohesive suspended sediment concentration gradient, affects the flow velocity profile. Based on the wave-current full depth combined model, k-ɛ turbulent model is employed in this paper to simulate the effect of sediment concentration on the wave-current flow. A quantitative analysis of change mechanism of mean velocity profile is presented. The results show that the change mechanism of Eulerian mean current velocity under clear water is different from that under sediment-water mixed flow.

The effect of sediment concentration on bedload roughness

Bedload roughness is the roughness produced by sediment transported near the bed. While it is well established that the magnitude of this roughness is proportional to the thickness of the moving sediment layer, the effect of sediment concentration remains largely unknown. This paper presents the results of a flume experiment that was designed to investigate the effect of sediment concentration on bedload roughness. The experiment consisted of creating flow conditions where bedload transport is supply-limited and injecting gravel size particles (D50=7·4 mm) at the upstream end of the flume in order to produce bedload transport. While keeping flow conditions constant, sediment concentration was varied by successively increasing the injection rate of gravel in the flow. For each injection rate, flow velocity profiles were measured in order to evaluate changes of mean flow velocity U, shear velocity u*, roughness length zo and resistance to flow f. The results indicate that low sediment concentration affects mainly the near bed portion of the flow where it causes a reduction of mean flow velocity and an increase of shear velocity and roughness length. For larger sediment concentration, the whole flow velocity profile becomes affected by bedload roughness but the importance of this effect always remain larger near the bed. As sediment concentration is augmented, mean flow velocity is consistently reduced but shear velocity and roughness length increase until a plateau is reached where these two variables become constant. Copyright © 1999 John Wiley & Sons, Ltd.

The effect of sediment concentration on bedload roughness

The effect of sediment concentration on bedload roughness

Sorption of Benzo[a]pyrene and Phenanthrene on Suspended Harbor Sediment as a Function of Suspended Sediment Concentration and Salinity: A Laboratory Study Using the Cosolvent Partition Coefficient

The sorption of benzo[a]pyrene (BaP) and phenanthrene (PHE) on sediment collected in the harbor of Rotterdam was studied in batch experiments using 14 C-labeled compounds. In order to simulate various estuarine conditions, we investigated the effects of various sediment concentrations and salinities on sorption of these compounds. We determined the apparent partitioning as well as the cosolvent partitioning between the liquid and solid phases. The apparent partition coefficient (K p App ) is influenced by the presence of colloids and dissolved organic matter. The influence of these components is minimized by the use of the cosolvent method in which the partition coefficient (K p * ) is determined by extrapolation of the partition coefficients obtained in a variety of solutions with water and methanol. The effect of sediment concentration on sorption was investigated at five different sediment concentrations ranging from 0.064 to 10.8 g/L. In contrast to K p * , K p App was found to be sensitive to the sediment concentration. Log K p * (with K p * in L/kg), determined for different sediment concentrations, was 5.2-6.3 for BaP and 2.8-3.6 for PHE,whereas log K p App was 4.1-5.6 for BaP and 2.9-4.0 for PHE. The salt concentration was varied with dilutions of Milli-Q water and seawater ; the salinity ranged from 0 to 35. The influence of salinity on K p * was small ; the increase in log K p * from freshwater to seawater is approximately 0.2 for BaP and 0.1 for PHE.

Particle-solution behaviour of plutonium in an estuarine environment, Esk Estuary, UK

The particle-solution ( K d ) relationships of Pu(III,IV) in the Esk Estuary are investigated, using new experimental data together with a synthesis of our earlier work. Adsorption of 236Pu(IV) by a suspension of intertidal mud (40 mg L −1) from the Esk Estuary was determined after 1 h, as a function of salinity and pH, in a series of controlled laboratory experiments. Desorption of 239, 240Pu(III,IV) from this environmentally contaminated sediment was determined concurrently. The short term (i.e., within a tidal cycle) non-conservative behaviour of Pu(III,IV) in both the laboratory experiments and the estuary appears to be dominated by a rapid, reversible surface complexation reaction, although only a small fraction (<5%) of the 239,240Pu(III,IV) activity of the environmentally contaminated sediment is able to participate in the reaction. The existence of this exchangeable or labile fraction can explain the apparent dependence of Pu(III,IV) K d on sediment concentration. Thus, a single K d value is able to describe both the observed adsorption and desorption behaviour and the effect of sediment concentration, when desorption is expressed with respect to the labile 239,240Pu(III,IV) fraction. For example, in R. Esk water, the adsorption of 236Pu(III,IV) and the desorption of 236,240Pu(III,IV), over a two order of magnitude concentration range of unwashed Esk Estuary sediment, can be accounted for by a single K d of ∼3 × 10 3 L kg −1. The K d for the labile Pu(III,IV) fraction varies mainly as a function of salinity. pH is not an important factor over the pH range 4–9, although H + ion exchange does occur, probably through a similar surface complexation reaction. The kinetic and equilibrium characteristics of the Pu (III,IV) sorption behaviour conform to the pattern observed by Jannasch et al. (1988) and other workers for a range of trace elements.

Flocculation of fine‐grained sediments due to differential settling

The flocculation of fine‐grained particles depends on collisions due to Brownian motion, fluid shear, and differential settling. Previous experimental work on the flocculation of fine‐grained sediments has emphasized the effects of fluid shear. These effects are significant in high‐turbulence regions. However, as the turbulence and fluid shear decrease, as, for example, in open waters away from shore, differential settling becomes the dominant mechanism for flocculation. In the present article, previous work on the effects of fluid shear is reviewed. However, the emphasis is on recent experimental work on the effects of differential settling on the flocculation of fine‐grained, primarily inorganic particles. The transition in effects between situations where fluid shear is dominant and the other extreme, where differential settling is dominant, was also investigated and is discussed. The sediments used in these studies were natural bottom sediments from the Detroit River inlet to Lake Erie. The tests were initiated with disaggregated sediments and were continued as the particles aggregated and formed flocs. These flocs then grew until a steady state size distribution was reached. In order to reach a steady state the differential settling tests sometimes continued for as long as 30 days; they were done in both freshwater and seawater at sediment concentrations from 1 mg/L to 200 mg/L and with and without treatment to remove organic matter. Floe size distributions as a function of time were determined. From the experiments it is shown that the times to steady state and the steady state median diameters are much larger when differential settling is the dominant mechanism for flocculation than when fluid shear is the dominant mechanism for flocculation. It is also shown that the effects of sediment concentration and salinity are qualitatively similar; i.e., as these quantities increase, both the time to steady state and the steady state floe size decrease. Settling speeds of the flocculated particles were also measured; the settling speeds of flocs are much larger and increase more rapidly with floc diameter when produced by differential settling than when fluid shear is dominant.

Resuspension and clearing of dredge spoils after dredging, Cleveland Bay, Australia

ABSTRACT: During dredging operation, fine sediment is released in the navigation channel of the Port of Townsville, Australia, as a result of mechanical disturbance of the bed and of the overflow from the storage tanks of the dredger. Some of this sediment is advected away from the dredging site toward the beach and reef areas and could result in environmental damage if not managed properly. Field monitoring was conducted for salinity, temperature, suspended sediment, and acoustic profiles at several sites before and after dredging. Laboratory investigations on the effect of sediment concentration, turbulence, and floe size on the clearing of a suspension column were also undertaken. Results of both field and laboratory investigations show faster clearing in quiescent conditions than in turbulent conditions. Turbulence at low levels disturbs the dewatering microchannels of the fluid mud layer. As turbulence increases the effect of floe breakage and settling retardation also become important.

The effect of variation in suspended sediment properties on reflectance measurements

Laboratory-based studies related to isolation and quantification of sediment and their properties which influence the spectral reflectance of sediment-laden waters were made. Some of these including the effects of sediment concentration, size variation, salinity, etc. have been published elsewhere. Using spectral reflectance measurements, properties of various soil types in a suspension can be inferred. The identification of dominant soil types present in a runoff water may help in the characterisation of the type of catchment area. The source of sediment load carried by the runoffs may also be predicted for future confirmation through the ground and geological surveys. Predictive models for evaluating soil properties alongwith steps to identify the dominant soil type(s) in a suspension are also presented.

The effects of sediment concentration and tube-diameter on particle settling velocity measured beyond Stokes' range; experiment and theory

ABSTRACT The effect of initial sediment concentration on settling velocity distributions measured by the modified bottom withdrawal tube (MBWT) method is presented for a well-aggregated clay soil (a vertisol). Sediment concentrations in the experiments range from 10 to 100 kg m-3 of suspension. Particle Reynolds numbers in the polydisperse suspensions range from less than 0.1 up to 100. Settling velocities of all size classes in the sediment are reduced by an increase in sediment concentration. The empirical equations of Richardson and Zaki appear useful for predicting ratios of settling velocity at different polydisperse concentrations, but absolute velocities predicted are lower than measured. The discrepancy is attributed to the empirical equations being derived for ratios of particle Reynolds numbers much lower than are present in this natural sediment. Hydrodynamic wake capture occurs during this sedimentation, a process not considered in the empirical equations. Settling velocities of all size classes in the sediment are also reduced by a decrease in MBWT diameter, and an incorrect relation between settling velocity and sediment concentration is measured using the small tube originally recommended for this technique. A minimum tube diameter of 45 mm is recommended to avoid such errors.

Effect of Sediment Load on Stable Sand Canal Dimensions

An experimental study was taken up by the writers with the object of providing a clear picture of the effect of sediment load on the dimensions of stable canals. These experiments were carried out in a recirculating sand tray at a constant discharge using sand of median size of 0.27 mm. Variation in sediment load was achieved by suitable changes in the initial cross section and slope given to the channel; the equilibrium sediment concentration could thus be varied from 150 ppm to 2500 ppm by weight. It was found that the final stable cross sectional dimensions of the channel were practically insensitive to sediment concentration, whereas the final slope was strongly dependent on it. It is thus concluded that relations for cross-sectional dimensions of a stable canal may be evolved ignoring the effect of sediment concentration, but the regime slope ought to be related to the sediment concentration apart from the discharge and sediment size.

Effect of Sediment Concentration on Well Recharge in a Fine Sand Aquifer

A model recharge well was constructed to simulate recharge into wells in a fine sand aquifer. The sand in the model aquifer was uniform fine sand and had a uniformity coefficient of 1.25 and an effective diameter of 144 microns. Both clear tap water and sediment laden water were used for recharge. Sediment laden water was obtained by mixing 50% bentonite and 50% kaolinite with tap water. Sediment concentrations were 100, 200, and 500 ppm. The piezometric surfaces near the recharge well were measured during the tests. Migration of sediment into the aquifer was determined by sampling the aquifer sand after the tests at predetermined distances from the well. The sediment in the recharge water highly affected the rate of recharge. During the period of the tests a reduction in hydraulic conductivity of the model aquifer of 15–46% occurred as a result of recharge with sediment laden water. Most of the sediment deposited in the aquifer was retained near the well screen.