Behaviour Of Suspended Sediment Research Articles

Incorporating memory effect into a fractional stochastic diffusion particle tracking model for suspended sediment using Malliavin-Calculus-based fractional Brownian Motion

This study aims to develop a Fractional Stochastic Diffusion Particle Tracking Model (FSDPTM) to illustrate suspended sediment’s long-term dependence (LTD) trajectories immersed in fully developed turbulent flow. Carried by eddies in the open channel, individual suspended sediment behavior exhibits dependence on its past increments. The Fractional Brownian Motion (FBM) is incorporated into the FSDPTM to account for the randomness of turbulent flow and to include the time-dependent increments as a memory effect. Additionally, to enhance the capacity for differentiating FBM, this study introduces Malliavin Calculus, the stochastic calculus of variation, to construct the square -differentiable FBM. For the numerical realizations of square differentiable FBM, the integration of fractional Gaussian white noise and Wiener–Ito Chaos expansion with the Hermite sequence is employed. The FSDPTM offers probabilistic LTD trajectories as solutions to the Ito-type Langevin equation. It also provides particle velocity, acceleration, and ensemble statistics, collectively demonstrating the application of FBM to sediment transport modeling. In conclusion, the key feature of the FSDPTM is its ability to translate LTD derived from FBM into the trajectory of suspended sediment particles in fully developed turbulent flow. Additionally, it expands the solutions from non-differentiable to square-differentiable stochastic processes.

Advances in Monitoring and Understanding the Dynamics of Suspended-Sediment Transport in the River Drava, Slovenia: An Analysis More than a Decade-Long

Managing sediment transport in streams is crucial to the surface water resource development strategy and has several implications for flood risk and water management, hydropower use, and balancing river morphology. This paper summarises the movement and behaviour of suspended sediment within the Slovenian portion of the River Drava, covering a span of thirteen years from 2005 to 2018. An analysis of relevant data collected during this period is also presented. Suspended-sediment dynamics strongly depend on flow velocity, seasonal variations in sediment sources, and human interventions in the riverbed. The transportation of material in the River Drava results in the accumulation of sediments in reservoirs and riverbeds, consequently impeding the natural hydrological cycle by reducing the outflow into aquifers. The 2018 high-water event is analysed in terms of the dependence of concentration of suspended sediments on discharge, where counterclockwise hysteresis was observed, providing an essential clue to the origin of sediment. Sediments from the River Drava in Slovenia are managed with some conventional processes and are mainly deposited or reintegrated into rivers and aquatic ecosystems. Some additional sediment management strategies with long-term solutions for efficient and comprehensive water management, hydropower, and ecological problems are proposed.

Coastal plumes contribution to the suspended sediment transport in the Southwest Atlantic inner continental shelf

Global coastal zones are constantly changing due to the actions of various physical forces. Recent studies show that the supply of suspended sediment of continental origin plays an important role in these changes. Once in the coastal region, this sediment significantly influences the sedimentation process on the inner shelf. Thus, understanding the transport and destination of these suspended sediments is crucial to interpret the morphodynamic evolution of the seabed and biogeochemical processes in the ocean. The Southwest Atlantic Shelf is the largest continental shelf in the Southern Hemisphere and one of the most important in biological production, because of the great continental contribution exercised by both Río de la Plata and Patos Lagoon. Studies in the region showed that these effluents are significantly affected by the El Niño–Southern Oscillation (ENSO) effect, which can interfere with the availability of suspended material inserted into the coastal region. Despite the great efforts of several authors to understand these changes and their interactions with the environment, some questions remain unanswered. Thus, this work aims to fill this gap by answering questions related to the contribution of suspended sediment of continental origin and its behaviour on the Southwest Atlantic Inner Shelf. The behaviour of suspended sediment was investigated in two distinct periods using the hydro-morphodynamic model TELEMAC-3D: one representing normal years, that is, without the effect of ENSO (2005–2006) and the other experiencing the effect of ENSO (2008–2009).The model was calibrated and validated using field data for both studied periods. R esults were based on statistical analysis, such as wavelet and empirical orthogonal function (EOF) analysis, in addition to time series analysis. Results showed that the Southwest Atlantic Inner Shelf is mainly influenced by the fluvial discharge of Río de la Plata and Patos Lagoon, and by the local wind. Río de la Plata is the largest exporter of suspended sediment in the region, with an approximate rate of 1.2 × 108 tons.year-1 in neutral (normal) years and 3.0 × 108 tons.year-1 in years under the influence of ENSO. The Patos Lagoon, on the other hand, exports approximately 1.25 × 107 tons.year-1 in the period without the ENSO effect and 1.35 × 107 tons.year-1 in the period influenced by ENSO. Results also showed that the fluvial discharge interacts with the suspended sediment in seasonal to interannual scales, while the wind contributes to the concentration of suspended sediment on synoptic scales. Still on the wind regime, results show that the local wind regime gains importance particularly when the suspended sediment reaches the coastal region.

Experimental Investigation of Water Temperature Influence on Suspended Sediment Concentration

Health of coastal ecosystems depends on the quantity and quality of suspended sediments brought by the rivers from land to the estuary. Behaviour of suspended sediments depends on water and sediment characteristics. Water temperature affects suspended sediment behaviour but has not been fully understood. Increase in water temperature due to global warming creates ecological issues. In the present study, influence of water temperature rise on suspended sediment concentration (SSC) has been studied under controlled laboratory conditions. Experiments were conducted in an annular flume using kaolin (d50 = 6.9 μm) at different water temperatures (T = 30o, 40o, and 50 °C) and salinities (S = 0, 1, 2, 5, and 10 g/L). Results show that both SSC and particle size increased with an increase in water temperature, but both decreased with an increase in water salinity. For S ≥ 2 g/L, the influence of water temperature on both SSC and settling velocity of suspended sediments was more significant compared to S < 2 g/L. For a unit increase in water temperature (°C), the SSC increased by 0.18%, 0.30%, 0.73%, 0.89%, 2.05% and settling velocity decreased by 1.71%, 2.15%, 3.64%, 3.17%, 3.45%, for water salinities of 0, 1, 2, 5 and 10 g/L, respectively. Empirical equations for determining the SSC at any time t and at any length L along the flow direction have been developed and verified.

The impact of persistent dynamics on suspended sediment load estimation

Fluvial suspended sediment concentration and discharge is most commonly estimated by applying rating curves developed over a given base period of sediment monitoring to longer, continuous records of water discharge. This practice invokes the tacit assumption of stationary suspended sediment concentration–water discharge relationships (i.e. suspended sediment behavior). Here the ramifications of this assumption are explored through an investigation into the temporal dependence of suspended sediment concentration–discharge relationships for all hydrologic stations on small rivers draining the west coast of the continental US that have been monitored for suspended sediment over a period of 10 years or more. Persistent suspended sediment behavior was found to be the norm, with 19 of 24 stations expressing apparent monotonic trends over their base periods, and 21 stations with finer scale (subannual to interdecadal) persistent patterns. The identified persistent periods of suspended sediment behavior corresponded to distinct rating curves that differed significantly from other periods in terms of offset, slope, or both. Assuming stationary suspended sediment behavior resulted in 1% to 63% biasing of suspended sediment load. Applying rating curves developed for single persistent periods to broader discharge records resulted in up to 10× potential error in estimated sediment load. The risk of falsely characterizing the long-term (interannual-scale) suspended sediment behavior of a river through a single persistent period of elevated or depressed behavior may be much higher than expected. The average duration of identified persistent periods was 8.6 years, which is longer than the base period of suspended sediment monitoring for most river stations in the US. Peak discharge (high discharge events 20 to 1000 times mean discharge) was usually followed by periods of increased sediment concentration across US Pacific Coast. Seven rivers in Oregon and northern California displayed the same pattern of decadal- to interdecadal-scale elevated suspended sediment concentrations following the Great Christmas Floods of 1964.

Spatio-temporal monitoring of suspended sediments in the Solimões River (2000–2014)

The Amazon River sediment discharge has been estimated at between 600 and 1200Mt/year, of which more than 50% comes from the Solimões River. Because of the area's inaccessibility, few studies have examined the sediment discharge spatial and temporal pattern in the upper Solimões region. In this study, we use MODIS satellite images to retrieve and understand the spatial and temporal behaviour of suspended sediments in the Solimões River from Peru to Brazil. Six virtual suspended sediment gauging stations were created along the Solimões River on a 2050-km-long transect. At each station, field-derived river discharge estimates were available and field-sampling trips were conducted for validation of remote-sensing estimates during different periods of the annual hydrological cycle between 2007 and 2014. At two stations, 10-day surface suspended sediment data were available from the SO-HYBAM monitoring program (881 field SSS samples). MODIS-derived sediment discharge closely matched the field observations, showing a relative RMSE value of 27.3% (0.48Mtday) overall. Satellite-retrieved annual sediment discharge at the Tamshiyacu (Peru) and Manacapuru (Brazil) stations is estimated at 521 and 825Mt/year, respectively. While upstream the river presents one main sediment discharge peak during the hydrological cycle, a secondary sediment discharge peak is detected downstream during the declining water levels, which is induced by sediment resuspension from the floodplain, causing a 72% increase on average from June to September.

Effects of antecedent hydrologic conditions, time dependence, and climate cycles on the suspended sediment load of the Salinas River, California

summary Previous estimations of sediment flux for the Salinas River of central California were based on data collected in the 1970s and assumptions of time invariant suspended sediment–discharge behavior. The goals of this study were to estimate sediment flux from the Salinas River using data from 1967–2011 by incorporating time dependent behavior and reassess the role of El Nino Southern Oscillation patterns in inter-decadal sediment load. This study builds on previous findings that time-dependent suspended sediment behavior in this system is controlled in part by antecedent hydrologic conditions. The condition of temporal dependence was further tested herein through comparison of flux estimates obtained using time-dependent formulations and a multivariate approach incorporating hydrologic factors. Longer sampling records and incorporation of decadal scale behavior or antecedent hydrologic conditions resulted in average annual load estimates of 2.0–2.9 Mt/yr with 95% confidence intervals of ±25 to 202%, in comparison to earlier estimates of � 3.3 Mt/yr. Previous overestimation of sediment load is due largely to the extrapolation of suspended sediment behavior from a decade of high sediment concentrations to the entire record, and the use of log-linear regression techniques on a non-linear system. The use of LOESS methods lowered QSS estimates and decreased confidence interval size. The inclusion of time-stratified and antecedent flow indices further decreased QSS estimates, but increased confidence interval size. However, temporal dependence of the CSS–Q relationship violates the assumptions of single base period regression, which suggests that time-stratified rating curves provide more realistic estimates of sediment flux means and uncertainty. The majority of suspended sediment was transported by flows of � 25–90 times mean discharge depending on transport constituent (fines or sand) and estimation method. Periods of differential suspended sediment behavior changed the relative importance of rare floods due to changes in the relationship of suspended sediment concentration vs. discharge. El Nino years dominated the sediment budget by producing on average ten times more sediment than non-El Nino years. Sediment load estimates provided further evidence that antecedent hydrologic conditions appear to have caused much of the temporal dependence of suspended sediment behavior.

The effect of El Niño Southern Oscillation cycles on the decadal scale suspended sediment behavior of a coastal dry‐summer subtropical catchment

AbstractRivers display temporal dependence in suspended sediment–water discharge relationships. Although most work has focused on multi‐decadal trends, river sediment behavior often displays sub‐decadal scale fluctuations that have received little attention. The objectives of this study were to identify inter‐annual to decadal scale fluctuations in the suspended sediment–discharge relationship of a dry‐summer subtropical river, infer the mechanisms behind these fluctuations, and examine the role of El Niño Southern Oscillation climate cycles. The Salinas River (California) is a moderate sized (11 000 km2), coastal dry‐summer subtropical catchment with a mean discharge (Qmean) of 11.6 m3 s−1. This watershed is located at the northern most extent of the Pacific coastal North America region that experiences increased storm frequency during El Niño years. Event to inter‐annual scale suspended sediment behavior in this system was known to be influenced by antecedent hydrologic conditions, whereby previous hydrologic activity regulates the suspended sediment concentration–water discharge relationship. Fine and sand suspended sediment in the lower Salinas River exhibited persistent, decadal scale periods of positive and negative discharge corrected concentrations. The decadal scale variability in suspended sediment behavior was influenced by inter‐annual to decadal scale fluctuations in hydrologic characteristics, including: elapsed time since small (~0.1 × Qmean), and moderate (~10 × Qmean) threshold discharge values, the number of preceding days that low/no flow occurred, and annual water yield. El Niño climatic activity was found to have little effect on decadal‐scale fluctuations in the fine suspended sediment–discharge relationship due to low or no effect on the frequency of moderate to low discharge magnitudes, annual precipitation, and water yield. However, sand concentrations generally increased in El Niño years due to the increased frequency of moderate to high magnitude discharge events, which generally increase sand supply. Copyright © 2014 John Wiley &amp; Sons, Ltd.

Suspended sediment behavior in a coastal dry-summer subtropical catchment: Effects of hydrologic preconditions

Variation in fluvial suspended sediment–discharge behavior is generally thought to be the product of changes in processes governing the delivery of sediment and water to the channel. The objective of this study was to infer sediment supply dynamics from the response of suspended sediment behavior to antecedent hydrologic factors. The Salinas River (California) is seasonally active, moderately sized, and potentially susceptible to lasting impacts of hydrologic event history because of aridity, high discharge variability, and in-channel terminating flows. Forty-five years of suspended sediment data from the lower Salinas and 80years of hydrologic data were used to construct hydrologic descriptors of basin preconditioning and to test the effects of these preconditions on suspended sediment behavior. Hydrologic precondition factors — including change in mean daily discharge and increasing elapsed time since the last moderate discharge event (~10–20 times mean discharge (Qmean)) — were found to have significant positive effects on discharge-corrected, fine suspended-sediment concentrations. Conversely, increased elapsed time since the last low discharge event (~0.1–0.4 times Qmean), and the sum of low flow conditions over interannual time scales were found to cause significant negative trends in fine suspended sediment concentration residuals. Suspended sand concentrations are suppressed by increased elapsed time after threshold discharges of ~0.1–2 and 5–100 times Qmean, and increased low to no flow days over time scales from 1 to 2000days. Current and previous year water yield and precipitation magnitudes correlate positively with sand concentration. Addition of fine sediment from lower Salinas hillslope or channel sources on the rising limb of the hydrograph is the major mechanism behind an overall positive hysteretic pattern, which was forensically supported by the annual occurrence of in-channel suspended sediment deposition by early season, channel terminating flows and by the flushing function of moderate hydrologic events found in this study. The importance of hillslope and/or channel fine sediment contributions proximal to the lower Salinas are further highlighted by the lack of control exerted by upper subbasin water provenance on fine suspended sediment concentration, while sand behavior is differentiated by upper basin water provenance. Investigation of suspension of bed-sized sediment showed that the channel bed could exert significant effects on fine and sand-sized suspended sediment dynamics, but this mediation for fine sediment was most likely small in terms of decadal-scale sediment budgets. The magnitude of the effects of hydrologic variables on sediment dynamics remains uncertain, but the factors identified here may play a significant role in water quality, if not long-term sediment flux to the ocean.

Dynamics of Turbid Plumes Generated by Marine Aggregate Dredging: An Example of a Macrotidal Environment (the Bay of Seine, France)

Duclos, P.-A.; Lafite, R.; Le Bot, S.; Rivoalen, E., and Cuvilliez, A., 2013. Dynamics of turbid plumes generated by marine aggregate dredging: an example of a macrotidal environment (the Bay of Seine, France).On the French marine shelf, marine aggregates are currently dredged by trailing suction hopper dredgers (TSHD), without screening, with an overflow process, with or against currents. In the framework of the Groupement d'Interét Scientifique (GIS) Suivi des Impacts de l'Extraction de Granulats Marins (SIEGMA), the dynamics of the turbid plume formed by the overflow was studied at an experimental dredging site (0.6 km2), located in the Bay of Seine (eastern English Channel), a macrotidal environment where the seabed is composed of sandy gravel. An original field strategy based on Lagrangian monitoring, using the back-scattered signal of an Acoustic Doppler Current Profiler (ADCP), Laser In Situ Scattering and Transmissometry (LISST) measurements, water samples, and aerial photographs, has shown good results in describing suspended sediment concentration (SSC) dynamics from a turbid plume. The behaviour of suspended sediment has been studied, for the first time, to our knowledge, from their release at the dredger overflow to their deposition on the seabed. A fluid mixture, overflowed from the TSHD, with a mean concentration of 6 g L−1 of mineral and organic silty sands, induces the formation of a turbid plume at the rear of the TSHD, with an immediate dilution effect about 10–100 on SSC. Then, the SSC decreases through the process of lateral dispersion and sedimentation until the plume disappear in 2 hours. Evolution of the plume characteristics (SSC, particle size and nature, geometry) makes it possible to quantify the processes involved: dilution, advection, dispersion, and settling. The passive and dynamic behaviours of the plume are analysed. Extensions of deposits are calculated for spring tide conditions: 800 m for sand and 6.5 km for silt. This study has been conducted in macrotidal and specific dredging conditions (orientation of the dredging tracks against currents, dredger speed, loading capacity, overflow type), whose effects on plume dispersion have been quantified. Indicators relative to the effect of the plume on the water column (I/R) and to the plume duration (T1.25SSC) are proposed.

Intra-event and inter-seasonal behaviour of suspended sediment in flash floods of the semi-arid northern Negev, Israel

A better understanding of the relation between suspended sediment concentration and water discharge is gained by recognizing, amongst other things, the different impacts of two types of rainfall event: wandering, discrete, convective or convectively-enhanced, high intensity storms; and ubiquitous, multi-celled, low intensity, frontal storms. In the Levant, the first type is characteristic of autumn and spring and the flushing of sediment by the instant onset of high intensity rainfall produces a clockwise hysteresis in the suspended sediment–water discharge relation. The second type is characteristic of winter and can be marked by either anticlockwise or no hysteresis in the suspended sediment–water discharge relation; sedimentary flushing is rarely apparent. Suspended sediment concentrations in flash floods resulting from convective storms are high (typically 10 4–10 5 mg l − 1 ) but correlation with water discharge is low ( r = 0.57). In contrast, frontal storm runoff carries lower suspended sediment concentrations (typically 10 3–10 4 mg l − 1 ) and correlation with water discharge is better ( r = 0.78). This division assists in interpreting the high degree of scatter evident in the overall suspended sediment concentration–water discharge relation, but it reveals that much is yet to be learned about the interplay of the disposition of cellular storm tracks and sediment source areas.

Behaviour of fine suspended sediment at the North passage of the Changjiang Estuary, China

Current velocity, salinity and suspended sediment concentration were measured at spring, moderate and neap tides at two ends (landward and seaward) of the North Passage of the Changjiang Estuary. A turbidity maximum was consistently observed during spring and moderate tides. The data were analyzed for intratidal, spring/neap and seasonal variations in fine suspended sediment transport processes within the turbidity maximum there. The dominant mechanisms responsible for the formation of the turbidity maximum are (1) tidal asymmetry at the landward end of the North Passage, (2) near-bed periodic tidal resuspension and (3) turbulence suppression by suspension/salinity stratifications at the North Passage.

Behaviour of fine suspended sediment at the North passage of the Changjiang Estuary, China

Current velocity, salinity and suspended sediment concentration were measured at spring, moderate and neap tides at two ends (landward and seaward) of the North Passage of the Changjiang Estuary. A turbidity maximum was consistently observed during spring and moderate tides. The data were analyzed for intratidal, spring/neap and seasonal variations in fine suspended sediment transport processes within the turbidity maximum there. The dominant mechanisms responsible for the formation of the turbidity maximum are (1) tidal asymmetry at the landward end of the North Passage, (2) near-bed periodic tidal resuspension and (3) turbulence suppression by suspension/salinity stratifications at the North Passage.

NUMERICAL MODELING OF FLOODWATER INTRUSION AND FINE SUSPENDED SEDIMENT BEHAVIOR IN A STRATIFIED RESERVOIR

This paper presents a development of a numerical model that simulates flood water intrusion into a stratified reservoir and fine suspended sediment behavior. The model is based on laterally averaged vertical 2-dimensional equations and κ-ε turbulence model, which are solved by using SIMPLE scheme.A laboratory experiment was conducted on settlement of fine suspended sediment and a tentative modeling is proposed to estimate settling velocity of fine solid. The model is validated by simulating the flood event on which the field measurement was conducted. Vertical distributions of suspended sediment concentration are well reproduced and effectiveness of the proposed model is demonstrated.

A simple turbulent energy-based model of fine suspended sediments in the Irish Sea

Energy is required to maintain a particle heavier than water in suspension in the sea. In equilibrium, energy must be supplied at a rate equal to the product of the weight of the particle and its sinking velocity. If the energy supply rate is known, it becomes possible to predict the total weight, and hence the concentration of suspended particles in the sea. This principle has been applied to a model of fine suspended sediments in the Irish Sea. The model is used to test the hypothesis that the supply of turbulent kinetic energy (TKE) alone controls both the spatial pattern and seasonal changes in concentration. TKE is supplied by the tide and wind, and a fixed fraction of this energy is used to keep sediment in suspension. There is assumed to be a readily available supply of fine sediments at the sea bed, which rises into suspension as soon as TKE becomes available, and sinks down again when it is not. The model incorporates 2-layer thermal stratification and vertical mixing between layers but there is no horizontal advection or diffusion. The model is driven by smoothly varying wind speeds and heating over the year and spatially varying tidal stirring. The particles have a constant settling velocity of 10 m day −1, and a density twice that of water. A fraction 0.00006 of the total (tide+wind) TKE energy input is used to stir the sediment. The results of the model are in agreement with both the observed spatial pattern and the seasonal variation of fine suspended sediments in the surface waters of the Irish Sea to within the limits of measurement accuracy and natural variability. This energy model performs at least as well as conventional stress-driven models in this regard. We therefore conclude that the general behaviour of fine suspended sediments in the Irish Sea can be explained by TKE supply alone. Other factors, such as changes in particle size and density over the year, can be used for fine tuning but are not necessary to give a broadly correct picture. The result is that we have a simple, physically coherent, method of predicting the turbidity (and hence the light regime) of a shelf sea from physical inputs alone.

Suspended sediment dynamics in a large drainage basin: the River Rhine

The behaviour of suspended sediment in rivers is often a function of energy conditions, i.e. sediment is stored at low flow and transported under high discharge conditions. The timing of maximum sediment transport can, however, also be related to mixing and routing of water and sediment from different sources. In this study suspended sediment transport was studied in the River Rhine between Kaub and the German–Dutch border. As concentrations decrease over a runoff season and as the relationship between water discharge and suspended sediment concentrations during most floods is characterized by clockwise hysteresis, it is concluded that sediment depletion occurs during a hydrological year and during individual floods. However, analyses of the sediment contribution from the River Mosel indicate that clockwise hysteresis may result from sediment depletion as well as from early sediment supply from a tributary. Thus, although the suspended sediment behaviour in the downstream part of the River Rhine is partly a transport phenomenon related to energy conditions, mixing and routing of water from different sources also plays an important role. Suspended sediment transport during floods was modelled using a ‘supply-based’ model. Addition of a sediment supply term to the sediment rating curve leads to a model that produces better estimates of instantaneous suspended sediment concentrations during high discharge events. A major constriction of the model is that it cannot be used to predict suspended sediment concentrations as long as the amount of sediment in storage and the timing of sediment supply are unknown. Copyright © 1999 John Wiley & Sons, Ltd.

The characteristics of composite suspended sediment particles transported during storm events in the river Exe, Devon, U.K

Abstract Particle size is one of the most important factors controlling the behaviour of fluvial suspended sediment and its role in different environmental and geomorphological processes. Primary mineral particles are frequently transported as composite particles or aggregates, which consist of different sized mineral particles combined with organic matter and biogenic material. The formation and behaviour of such aggregates are controlled by physical, chemical and biological factors which act independently and also in combination at different spatial and temporal scales. This paper examines the nature and behaviour of the composite suspended sediment particles transported by the River Exe, Devon, U.K. during several storm events. Effective size (undispersed) fractions were separated in situ using a field-portable water elutriation apparatus. The absolute (chemically dispersed) grain size composition of each effective size class was examined, in order to provide information on the proportion of the sediment transported as aggregates. In addition, the influence of a number of factors in controlling the occurrence and behaviour of aggregates during storm events has been examined. More detailed information concerning the character and structure of the composite particles has been obtained using Scanning Electron Microscope observation and Energy Dispersive X-Ray analysis (SEM/EDAX).

Dynamics and behaviour of suspended sediment in macrotidal estuaries along the south coast of the English Channel : Avoine, Jacques and Claude Larsonneur, 1987. Continent. Shelf Res., 7(11–12):1301–1305. Lab. de Geol. Mar., Univ. de Caen, 14032 Caen Cedex, France

Dynamics and behaviour of suspended sediment in macrotidal estuaries along the south coast of the English Channel : Avoine, Jacques and Claude Larsonneur, 1987. Continent. Shelf Res., 7(11–12):1301–1305. Lab. de Geol. Mar., Univ. de Caen, 14032 Caen Cedex, France

Dynamics and behaviour of suspended sediment in macrotidal estuaries along the south coast of the English Channel

A review is given of suspended sediment dynamics in macrotidal regimes using examples of estuaries situated along the French coast of the English Channel. Characteristic features of estuarine turbidity maxima are described over a range of time-scales, which includes semidiurnal and neap-spring tidal cycles, and seasonal fluctuations of river discharge. The present behaviour of the fluvial sediment influx within these systems is described, taking into account the geological history of estuarine infilling.

The Behaviour of Suspended Sediments and Muds in an Estuary

The fundamental behaviour of suspended sediments and muds was investigated using an annular flume with the condition of cyclically changed shear stress. The results from two series of experiments showed that particle sizes which participate in the variation of suspended sediments were restricted to smaller sizes of the material. It was also found that the cyclically steady state was finally attained with respect to the suspended sediments as the tidal cycle repeated. In that state the suspended sediments were subject to three phenomena: erosion; deposition with dispersed state; and deposition with flocculation. A simple model on the suspended sediments in an estuary was developed and its behaviour in a model estuary was simulated by using the fluxes of erosion and deposition in the experiment. That model well described the variation of the suspended sediments and muds.