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To understand the Holocene sedimentary evolution of the Pearl River associated delta–estuary–shelf system, high‐resolution seismic data were acquired from Lingdingyang Bay to the inner shelf. A Pearl‐derived Holocene subaqueous clinoform developed over the pre‐Holocene incised channel/valley network. Overlying the Holocene ravinement surface, progradational highstand and acoustically semi‐transparent or transparent transgressive system tracts are separated by a maximum flooding surface. Restricted and thick in‐channel/in‐valley retrogressive deposits represent an earlier transgressive deposit. Displaying a westward‐oriented along‐shore extent, the highstand sediment accumulated asymmetrically within 30 m water depths, corresponding to a modern hydrodynamic environment. The wedge‐shaped highstand unit thickened landward with a depocentre (>15 m) located in western Lingdingyang Bay, possibly because of higher sediment trap efficiency inside the salinity front. Preliminary analyses suggest that the Pearl River has been trapping sediment to fill its extensive estuarine system for most of the Holocene and its sediment trap efficiency is greater since the sea‐level highstand. Since ca 7.5 ka bp, the total volume of highstand sediment accumulated in the entire delta‐estuary‐shelf dispersal system was approximately 128.36 × 109 m3. The calculated highstand riverine sediment flux was 16.01 to 16.50 Mt/yr. This value is equivalent to approximately one‐fifth of the flux that occurred prior to widespread dam construction and likely related to late‐Holocene intensified anthropogenic influence in South China. Since ca 7.5 ka bp, only ca 35% of the Pearl‐derived sediment has been dispersed to offshore shelf areas from the delta‐estuary system. With the dramatic decrease in river sediment discharge in recent decades, a larger fraction of Pearl‐derived sediment transported to the shelf might have been interrupted and changed. [ABSTRACT FROM AUTHOR]

Shelf mud patches represent major sinks for fine-grained particles on continental shelves, as well as for carbon and contaminants of continental origin. The West Gironde Mud Patch (WGMP) is an interesting example of such offshore marine systems as it is an active mud deposition area located offshore the Gironde estuarine mouth (France) at depths between 30 and 70 m. It is known to be the trap of fine particles coming from the estuary, but the contribution of this material to the total mass of the depocenter is poorly quantified. In addition, despite the economic and ecological issues at stake, the response of such subtidal sedimentary structure to the combination of tidal currents, waves, and river supply remain poorly understood. Thus, using a realistic 3-D hydrodynamic and mixed (mud/sand) sediment transport model, this study aims at investigating the sediment dynamics of the WGMP under different hydrometeorological conditions. The analysis of the residual fluxes at the estuarine mouth exhibited large discrepancies between the different sediment classes as well as for contrasted hydro-and meteorological conditions induced by different dominant transport mechanisms. During winter, the reinforced density gradients drive strong up-estuary baroclinic circulation at the bottom that dominates the sediment dynamics over the barotropic export of mud particles. The model also reproduced the signature of a subtidal mud accumulation area over the continental shelf around 30–40 m water depth, on the proximal side of the observed WGMP. On average over two years, 26% of the mud mass accumulating on the simulated subtidal mudflat comes from the estuary. The trapping efficiency of this mud patch is negatively correlated with the significant wave height. Moreover, due to the estuarine turbid plume being more concentrated and developed at the surface during high river discharge, the trapping efficiency of the mud body is enhanced compared to lower discharge. This study highlights the sensitivity of mud and sand fluxes to vertical and horizontal residual circulation, and points out the uncertainties associated with the simulation of short-term (i.e., years) fine particle deposits compared to long-term (i.e., centuries) sediment accumulation trends. In addition, these results show the primordial effects of both wave action and riverine sediment supply on the dynamics of such subtidal muddy structures, which raises concern about their fate facing climate change and human activities in the future. • A process-based model simulated mud/sand fluxes along an estuary-shelf continuum. • Density gradients drive up-estuary sand fluxes at the estuarine mouth. • The formation and dynamics of an active shelf mud deposition area are reproduced. • The trapping efficiency of the mudflat is modulated by waves and river turbid plume. • About 26% of the mud mass accumulated on the mudflat originates from the estuary. [ABSTRACT FROM AUTHOR]

Understanding trends in estuarine sediment fluxes is of great interest to sustainable estuarine management addressing anthropogenic interferences and climate change. The long‐term sediment budget of the Western Scheldt estuary, Netherlands, is investigated by a detailed analysis of a unique and long‐term bathymetric data set and data of a three‐dimensional subsurface model ('GeoTop'). Different sediment types show contrasting transport behaviour. The Western Scheldt narrowed and deepened, while the estuary exported sand (1.5 to 2.5 million m3 per year) and imported mud (0.5 to 1.5 million m3 per year) over the 1860 to 1955 period. The eroded sand originated from the channels in the seaward part of the estuary and was dispersed in all directions. A significant amount of mud permanently deposited in the side branches, which were also gradually reclaimed. These results suggest that sediment characteristics potentially play a crucial role in deriving long‐term sediment budgets and morphodynamic behaviour of estuarine environments. Future morphodynamic sand–mud model studies may reproduce and further explain the underlying transport processes of the current study. [ABSTRACT FROM AUTHOR]

The siliciclastic topset of a continental margin, or a shelf‐margin prism in subsiding nonplate‐margin deepwater basins, is the flat‐lying upper part of the margin succession; it is coeval basinwards with deepwater slope clinoforms. Topsets develop by the aggradation of repeated, cross‐shelf, shoreline regressions and transgressions, thereby hosting the shelf portion of stacked, fourth‐order stratigraphic sequences. Sediment spreading downdip and along strike during the cross‐shelf transit of the sediment delivery system, as well as process regime changes of deltas and shorefaces (regressive) and of estuaries, barrier–lagoon systems and shelf ridges (transgressive) are highly variable over short distances, so that correlation within a single stratigraphic sequence is far more difficult than correlation of the cross‐shelf maximum flooding surface boundaries. Thickness of individual regressive–transgressive, fourth‐order sequences is given by shelf accommodation, typically <10 m in embayment or on the inner shelf and up to 200 m on outer shelf. Tectonic subsidence and compaction will enhance this thickness only if rates are very high compared to shelf‐transit time. In very high subsidence rate settings, the transgressive tracts are well preserved and often thickly developed. Topset sequences in an Icehouse climate setting tend to have a high proportion and greater landward development of marine vs nonmarine deposits, compared to Greenhouse sequences, because of the importance of eustatic rise of sea level in the former. Previous numerical experiments show that even for very wide shelves and irrespective of Icehouse or Greenhouse conditions, deltas rarely take more than 10 s of ky to reach their shelf edge, suggesting that it is fourth‐order (or higher) sequences that are the fundamental ones in sequence stratigraphy. [ABSTRACT FROM AUTHOR]

Creeks are essential for salt marshes by conveying water and sediment through this geomorphic system. In this paper, we investigate the mechanisms that determine the residual sediment flux using measurements conducted in tidal creeks in salt marshes of the Yangtze Estuary. A main creek and a secondary creek were studied to explore whether the mechanisms determining residual sediment fluxes through the main creek differ from those in the secondary creek. Measurements in creeks were carried out over 5 years, spanning different months. Sediment import was found during most tides, both in the main creek and the secondary creek, implying that creeks in Chongming generally function as a conveyor belt of sediment into the marsh. However, sediment export can occur during certain overbank tides. When comparing the role of creeks in drainage and sediment delivery, the main creek functions more in delivering sediment while the secondary creek primarily serves as a drainage conduit. To better understand the mechanisms behind sediment fluxes, the residual sediment flux was compared with the residual discharge and the sediment differential (differences in sediment concentration between flood and ebb). Overbank tides generally lead to a net outward discharge as more water from saltmarshes can be concentrated into the marsh creek during ebb tides. This net outward discharge tends to export more sediment during ebb tides. However, due to the sediment abundance during the flood phase in the turbid environment, sediment import can be expected even with the residual export of water. Export of sediment was only found for the few tides with a net outward discharge and a small positive sediment concentration differential. Large negative sediment differentials (larger averaged suspended sediment concentration during ebb tides) have not been observed because the sediment supply during ebb is limited. This paper unravels how the sediment differential and residual discharge contribute to the residual sediment flux, providing a better understanding of sediment dynamics in marsh creek systems. • The relative importance of asymmetries in sediment concentration and in flow for residual sediment fluxes was explored. • The main creek is mainly a conduit for sediment delivery whereas the secondary creek is mainly a drainage conduit. • Sediment supply limitation can even occur in a turbid system like Chongming. [ABSTRACT FROM AUTHOR]

• Combined numerical model and GOCI to improve the ability of sediment flux (SF) estimation. • Multi-timescale SFs at typical cross-sections in YRE are estimated in 2013 and 2015. • Locally morphological changes are further estimated, showing erosions in 2013 and 2015. Sediment flux (SF) in the estuary is vital to the coastal and estuarine environment, especially the morphodynamical and ecological processes. However, its quantitative estimation with high accuracy is difficult because it is controlled by complex mechanisms and multiple processes. This study corrects the seasonal variations of the simulated suspended sediment concentration (SSC) by using GOCI-derived surface SSC and calculates the variations of SFs at the main cross-sections in and out of the Yangtze River Estuary (YRE). The results show that in 2013, 159 Mt and 143 Mt of sediments passed through Xuliujing hydrological station in YRE and estuarine mouth section, respectively. In the inner estuary, the significant seasonal variations of sediment transport are noted that the most seaward transport happens in summer (43.8%) and the least occurs in winter (7.3%). In the outer estuary, the southward transport towards Hangzhou Bay is the most critical pathway, accounting for 109.0% of total transport at mouth section, and is prevalent in autumn and winter. With considerations of sand mining and land reclamation, obviously erosions appear in the whole estuary during both 2013 and 2015. With stronger wind conditions in 2013, severer erosion (161 Mt) happens in outer estuary than that in 2015 (86 Mt). By combining the GOCI-derived surface SSC and the numerical model results, this study can better represent high-frequency hydro- and sediment-dynamical processes to calculate the annual, seasonal, and vertical SFs with improved accuracy. Hence this method may provide a viable way to infer locally averaged morphological changes. [ABSTRACT FROM AUTHOR]

River is a location that is responsible for the main transport of nutrient flow from land to estuary and oceans. The nutrients that are adsorbed by the solid phase can be deposited and stored in the sediment. Sediments in estuaries and beaches have an important role in storing or removing nutrients from or to the water column. The presence of nutrients in porewater interacts with sediment and water column. In general, the nutrients that have a role as limiting factors for life in the waters are nitrogen (N) and phosphorus (P). The release of N and P elements is very important for the estuary and coastal environment, related to the process of regenerating nutrients into the water column. The release mechanism is determined by a diffusion process, based on the difference of concentration between the water column and the porewater. This study aims to determine the concentration of N and P in the porewater and estimate the value of flux. The sediment samples were taken from the Wiso and Serang estuary, Jepara. The components that were analyzed in the pore water are the concentration of N (nitrate, nitrite) and P (phosphate). Nitrite, nitrate and phosphate were determined by using sulphanilamide method and the molybdenum blue method, respectively. Furthermore, the flux value (F) was calculated based on the Fick’s I Law which was corrected by porosity. The results show that the mean concentrations of nitrate (NO3-), nitrite (NO2-) and phosphate (PO42-) in the sediment water of Serang Estuary are 1.96, 1.41, 3.46 μM and in the Wiso estuary are 3.4, 1.85, 8.22 μM. In general, based on the calculation of flux, the sediments in the Serang and Wiso estuaries have a positive flux. Moreover, the sediment in Jepara acts as a source and releases N and P nutrient into the water column. The Wiso estuary has a higher flux than the Serang estuary. [ABSTRACT FROM AUTHOR]

A process-based numerical model is applied to investigate sediment transport dynamics and sediment budget in tide-dominated estuaries under different salt marsh erosion scenarios. Using a typical funnel-shaped estuary (Ribble Estuary, UK) as a study site, it is found that the remobilization of sediments within the estuary is increased as a result of the tidal inundation of the eroded salt marsh. The landward export of the finest sediment is also intensified. The relationship between salt marsh erosion and net landward export of sediments has been found to be non-linear—with the first 30% salt marsh erosion causing most of the predicted export. The presence of vegetation also influences the sediment budget. Results suggest that vegetation reduces the amount of sediment being transported upstream. Again, the trapping effect of salt marsh in terms of plant density is non-linear. Whilst a vegetated surface with a stem density of 64 plants/m2 decreased the net landward export of very fine sand by around 50%, a further increase in stem density from 64 to 512 plants/m2 had a relatively small effect. [ABSTRACT FROM AUTHOR]

Tidal bores are believed to induce significant sediment transport in macrotidal estuaries. However, due to high turbulence and very large suspended sediment concentration (SSC), the measurement of sediment transport induced by a tidal bore is actually a technical challenge. Consequently, very few quantitative data have been published so far. This paper presents SSC measurements performed in the Sée River estuary (Mont-Saint-Michel Bay, northwestern France) during the tidal bore passage with direct and indirect (optical) methods. Both methods are calibrated in laboratory in order to verify the consistency of measurements, to calculate the uncertainties, and to correct the raw data. The SSC measurements coupled with ADCP velocity data are used to calculate the instantaneous sediment transport ( q s ) associated with the tidal bore passage (up to 40 kg/m 2 /s). [ABSTRACT FROM AUTHOR]

To better understand suspended-sediment transport in a tidal slough adjacent to a large wetland restoration project, we deployed continuously measuring temperature, salinity, depth, turbidity, and velocity sensors in 2010 at a near-bottom location in Alviso Slough (Alviso, California, USA). Alviso Slough is the downstream reach of the Guadalupe River and flows into the far southern end of San Francisco Bay. River flow is influenced by the Mediterranean climate, with high flows (∼90 m s) correlated to episodic winter storms and low base flow (∼0.85 m s) during the summer. Storms and associated runoff have a large influence on sediment flux for brief periods, but the annual peak sediment concentrations in the slough, which occur in April and May, are similar to the rest of this part of the bay and are not directly related to peak discharge events. Strong spring tides promote a large upstream sediment flux as a front associated with the passage of a salt wedge during flood tide. Neap tides do not have flood-directed fronts, but a front seen sometimes during ebb tide appears to be associated with the breakdown of stratification in the slough. During neap tides, stratification likely suppresses sediment transport during weaker flood and ebb tides. The slough is flood dominant during spring tides, and ebb dominant during neap tides. Extreme events in landward (salt wedge) and bayward (rainfall events) suspended-sediment flux account for 5.0 % of the total sediment flux in the slough and only 0.55 % of the samples. The remaining 95 % of the total sediment flux is due to tidal transport, with an imbalance in the daily tidal transport producing net landward flux. Overall, net sediment transport during this study was landward indicating that sediment in the sloughs may not be flushed to the bay and are available for sedimentation in the adjacent marshes and ponds. [ABSTRACT FROM AUTHOR]

Flood tide salinity stratification in the presence of an axial convergent front is revealed with new data. The data were collected during sampling campaigns in the Conwy estuary, North Wales, the location of a previous study for axial convergent fronts. The stratification, with a maximum observed vertical density difference of 5 kg m −3 , begins as soon as the saline intrusion arrives and lasts throughout the flood tide. The flood stratification is shown to be caused by a tidal straining-type process. The along-channel shear is modified by cross-channel currents developed during the formation of the convergent front such that surface currents are smaller than those at mid-depth. The modified shear interacts with the horizontal density gradient to form the stratification on the flood tide. Implications for the turbulence and sediment transport regime in the estuary are discussed. [ABSTRACT FROM AUTHOR]

We used high-resolution in situ measurements of turbidity and fluorescent dissolved organic matter (FDOM) to quantitatively estimate the tidally driven exchange of mercury (Hg) between the waters of the San Francisco estuary and Browns Island, a tidal wetland. Turbidity and FDOM-representative of particle-associated and filter-passing Hg, respectively-together predicted 94 % of the observed variability in measured total mercury concentration in unfiltered water samples (UTHg) collected during a single tidal cycle in spring, fall, and winter, 2005-2006. Continuous in situ turbidity and FDOM data spanning at least a full spring-neap period were used to generate UTHg concentration time series using this relationship, and then combined with water discharge measurements to calculate Hg fluxes in each season. Wetlands are generally considered to be sinks for sediment and associated mercury. However, during the three periods of monitoring, Browns Island wetland did not appreciably accumulate Hg. Instead, gradual tidally driven export of UTHg from the wetland offset the large episodic on-island fluxes associated with high wind events. Exports were highest during large spring tides, when ebbing waters relatively enriched in FDOM, dissolved organic carbon (DOC), and filter-passing mercury drained from the marsh into the open waters of the estuary. On-island flux of UTHg, which was largely particle-associated, was highest during strong winds coincident with flood tides. Our results demonstrate that processes driving UTHg fluxes in tidal wetlands encompass both the dissolved and particulate phases and multiple timescales, necessitating longer term monitoring to adequately quantify fluxes. [ABSTRACT FROM AUTHOR]

The flux of cohesive sediment in an estuary is determined by many factors, including tidal asymmetry, wave effect, fluvial influence, phase difference between tidal velocity and tidal level fluctuations, sediment properties, flocculation, bed erodibility, bathymetry effect and other nonlocal effects. Our capability in predicting sediment fluxes in tide-dominant environments is critical to the morphodynamics and water quality of estuaries. Due to the difficulties in carrying out detailed measurement of sediment flux with high spatial and temporal resolutions, an one-dimensional-vertical (1DV) numerical model for cohesive sediment transport, previously verified and calibrated with field measured cohesive sediment concentration data, is utilized here to study some of the aforementioned factors in affecting tidal-driven sediment fluxes in idealized condition. Tidal-averaged sediment flux is shown to be correlated with tidal velocity skewness with a linear relationship. This linear relationship is different from that of non-cohesive sediment and it is demonstrated here to be mainly due to variable critical shear stress implemented for the mud bed in order to parameterize consolidation. The reason that tidal velocity skewness causes tidal-averaged residual sediment transport is shown to be due to nonlinear intra-tidal interactions between flow velocity and sediment concentration. Moreover, the effects of nonlinear intra-tidal interaction between tidal velocity and tidal level fluctuations is shown to mainly cause seaward transport, which is the most significant under progressive wave system (phase difference 90°) and almost negligible for standing wave system (phase difference 0°). [ABSTRACT FROM AUTHOR]

We investigated the spatiotemporal distribution of 137Cs radioactivity in surface sediment of Qinghai Lake, and developed the spatial pattern of sedimentation rate. The 137Cs inventory is higher near the estuary/bank area, but lower at the central lake. On the other hand, the average 137Cs activity is lower near the estuary/bank area, but higher at the central lake. The mass accumulation rate (MAR) and the fluxes and contents of the terrestrial detritus (e.g. SiO2, Fe2O3, and Ti) are higher near the estuary/bank area, but lower at the central lake. The chemical/biogenic deposits (e.g. the autogenic carbonates) take up higher fractions at the central lake. These suggest that the spatial pattern of recent sedimentation rate is dominated by the deposition of terrestrial detritus. The average MAR (0.0337 g cm-2 a-1) was estimated based on those of different cores of Qinghai Lake and was verified by a Ca mass-balance method. The fluxes of total lake sediments, terrestrial detritus, and direct atmospheric deposits were also estimated. [ABSTRACT FROM AUTHOR]

Abstract: Annual suspended-sediment flux estimates through Carquinez Strait (the seaward boundary of Suisun Bay, California) are provided based on surrogate measurements for advective, dispersive, and Stokes drift flux. The surrogates are landward watershed discharge, suspended-sediment concentration at one location in the Strait, and the longitudinal salinity gradient. The first two surrogates substitute for tidally averaged discharge and velocity-weighted suspended-sediment concentration in the Strait, thereby providing advective flux estimates, while Stokes drift is estimated with suspended-sediment concentration alone. Dispersive flux is estimated using the product of longitudinal salinity gradient and the root-mean-square value of velocity-weighted suspended-sediment concentration as an added surrogate variable. Cross-sectional measurements validated the use of surrogates during the monitoring period. During high freshwater flow advective and dispersive flux were in the seaward direction, while landward dispersive flux dominated and advective flux approached zero during low freshwater flow. Stokes drift flux was consistently in the landward direction. Wetter than average years led to net export from Suisun Bay, while dry years led to net sediment import. Relatively low watershed sediment fluxes to Suisun Bay contribute to net export during the wet season, while gravitational circulation in Carquinez Strait and higher suspended-sediment concentrations in San Pablo Bay (seaward end of Carquinez Strait) are responsible for the net import of sediment during the dry season. Annual predictions of suspended-sediment fluxes, using these methods, will allow for a sediment budget for Suisun Bay, which has implications for marsh restoration and nutrient/contaminant transport. These methods also provide a general framework for estimating sediment fluxes in estuarine environments, where temporal and spatial variability of transport are large. [Copyright &y& Elsevier]

The formation and dynamics of turbidity maxima (TM) in the Pearl River estuary (PRE) are not well understood but the existence of TM in the estuary have great potential engineering and environmental impacts. Based on the measurements of two large-scale field surveys conducted in the wet season of 1978 (July of 1978) and the dry season of 1979 (March of 1979), the existence and seasonal variations of TM in the PRE focusing on the two major natural navigation channels have been studied. The sediment transport fluxes over two consecutive tidal cycles have been analyzed in detail. The analysis results reveal that the formation mechanisms of TM in the estuary are rather complex. In general, gravitational circulation, tidal trapping, and sediment resuspension and deposition processes are the primary TM formation mechanisms in the PRE. The clockwise back flow pattern around Lingding Island also leads to the formation of TM in the West channel of the PRE. The occurrence of TM far upstream of the salt water wedge is the result of the complex hydrodynamic and sediment transport processes generated by the runoff of the major rivers. [Copyright &y& Elsevier]

The Nakdong Estuary, Korea, is a dramatic example of an Anthropocene estuary. Over the last century, the construction of two dams has divided the estuary into two discharge energy regimes with the East Nakdong Estuary receiving discharge and the West Nakdong Estuary receiving no discharge. The mean-flow sediment flux gradient during high discharge was the main mechanism for deposition in the East Nakdong Estuary. Because of limited observations, the sediment transport mechanisms for the entire estuary remained unclear. To complement previous observations that were limited to a high discharge event of the East Nakdong Estuary, this study aimed to better understand the spatiotemporal variation of sediment transport and the mechanisms of deposition throughout the Nakdong Estuary. Sediment fluxes and bed level changes were estimated by utilizing the Coupled-Ocean-Atmosphere-Wave-Sediment Transport (COAWST). Results confirmed that the East and West Nakdong Estuaries had different depositional patterns. The East Nakdong Estuary was characterized as a river-dominated environment with a high influence of river discharge that experiences rapid deposition. The West Nakdong Estuary was characterized as an environment mainly influenced by tides and waves that contribute to gradual deposition throughout the year. The mean-flow sediment flux by river discharge was a main mechanism of deposition in the East Nakdong Estuary after the construction of dam. The continuous landward mean-flow flux by tides and waves through the inlets was the dominant mechanism for deposition in the West Nakdong Estuary. These model results suggest that the Nakdong Estuary may serve as an analogue for a microtidal estuary altered by an estuarine dam, particularly those for which there is a monsoonal climate or anthropogenically reduced river discharge. • The spatiotemporal variation of sediment transport in the Anthropocene Nakdong Estuary was explored by numerical modeling. • The East Nakdong Estuary was characterized as a river-dominated environment with a high influence of river discharge. • The mean-flow flux convergence occurred in the East Nakdong Estuary during high discharge, causing rapid deposition. • The West Nakdong Estuary was mainly influenced by tides and waves on sediment transport throughout a year. • The continuous landward mean-flow flux occurred in the West Nakdong Estuary over a year, contributing gradual deposition. [ABSTRACT FROM AUTHOR]

While estuarine dams can develop freshwater resources and block the salt intrusion, they can result in increased sediment deposition in the estuary. The mechanism of increased sediment deposition in an estuary with an estuary dam is not well understood. To fill this knowledge gap, 7 ADCP measurements of flow and suspended sediment concentration (SSC) were collected along-channel in an estuary with an estuarine dam over a neap-spring cycle. Flow and SSC were used to calculate the sediment flux and sediment flux gradients, which in turn were decomposed into mean-flow fluxes (which occur on timescales longer than a tidal cycle) and correlation fluxes (which occur on the tidal timescale). Then the fluxes were compared with the external forcing to determine the relative importance of tides, dam discharge, and waves in driving the fluxes. The results indicated that the cumulative sediment fluxes at all stations were directed landward. The along-channel sediment flux gradient was negative, which indicated deposition along the channel. The landward mean-flow fluxes were dominant in the deep portion of the channel near the estuary mouth, whereas landward correlation fluxes were dominant in the shallow portion of the channel near the estuarine dam. The tides were the dominant forcing driving the sediment fluxes throughout the estuary. Waves and dam discharge were locally important forcing however. In particular, the dam discharge resulted in seaward mean-flow fluxes for 7 km seaward of the estuarine dam. This distance corresponded approximately to a tidal excursion seaward from the dam. It was the distance a freshwater mass discharged during an ebb tide could propagate before the currents returned landward during the following flood tide. Overall, the along-channel sediment flux gradient in an estuary with an estuarine dam was different from a similar estuary without an estuarine dam because the mean-flow fluxes in the inner estuary are forced by episodic dam discharge which was limited in seaward extent by the tidal excursion. This imposed a limitation for the seaward mean-flow fluxes which counteract the landward mean-flow and correlation fluxes due to the tides. With restricted seaward flushing, the tides could dominate, which could in turn result in increased depositional rates for an estuary with an estuarine dam. [ABSTRACT FROM AUTHOR]

An overview of the field work research projects under the LOIS Biological Influences On interTidal Areas (BIOTA) program is presented. The main objective of BIOTA is to characterize and quantify fluxes of sediments and the influence of biological components within the intertidal saltmarsh and mudflat zones of the main LOIS study area. Three studies concerned with sediment dynamics and the biota at a variety ofsites and salt marsh types on the east coast are described, and a saltmarsh flux study at a single site in Norfolk is briefly outlined (Fig. 1). Some examples of the preliminary research findings are shown with reference to selected sites in the Humber estuary. Regular monitoring of sediment levels out on the sand and mudflats showed remarkable stability, with the amplitude of variation rarely exceeding 5 cm over the four years of measurement. Some sites (generally the more cohesive sediments) displayed a seasonal pattern of elevation change. Oscillations of surface level changes decreased towards the marsh and damping continued with increasing vegetation cover. As expected net accretion generally decreases landward under reduced submergence times,particularly on the open coast marshes; however different sedimentation profiles were observed. In the Humber estuary, net accretion was generally greatest in the middle to lower marsh, with periods of erosion at the seaward edge. The role of vegetation in accretion is complex and may be site specific, affected by a variety of physical factors. The cord grass, Spartina anglica appears to have little effect on sediment deposition, but is more important as a sediment stabilizer during periods of erosion. The types of models that can be derived from the BIOTA study are briefly outlined. [ABSTRACT FROM AUTHOR]