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Abstract: Modern sediment deposits on continental margins form a vast reservoir of particulate matter that is regularly affected by resuspension processes. Resuspension by bottom trawling on shelves with strong fishing activity can modify the scale of natural disturbance by waves and currents. Recent field data show that the impact of bottom trawls on fine sediment resuspension per unit surface is comparable with that of the largest storms. We assessed the impact of both natural and anthropogenic processes on the dispersal of riverborne particles and shelf sediments on the Gulf of Lion shelf. We performed realistic numerical simulations of resuspension and transport forced by currents and waves or by a fleet of bottom trawlers. Simulations were conducted for a 16-month period (January 1998–April 1999) to characterise the seasonal variability. The sediment dynamics takes into account bed armoring, ripple geometry and the cohesive and non-cohesive characteristics of the sediments. Essential but uncertain parameters (clay content, erosion fluxes and critical shear stress for cohesive sediment) were set with existing data. Resuspension by waves and currents was controlled by shear stress, whereas resuspension by trawls was controlled by density and distribution of the bottom trawler fleet. Natural resuspension by waves and currents mostly occurred during short seasonal episodes, and was concentrated on the inner shelf. Trawling-induced resuspension, in contrast, occurred regularly throughout the year and was concentrated on the outer shelf. The total annual erosion by trawls (5.6×106 ty−1, t for metric tonnes) was four orders of magnitude lower than the erosion induced by waves and currents (35.3×109 ty−1). However the net resuspension (erosion/deposition budget) for trawling (0.4×106 ty−1) was only one order of magnitude lower than that for waves and currents (9.2×106 ty−1). Off-shelf export concerned the finest fraction of the sediment (clays and fine silts) and took place primarily at the southwestern end of the Gulf. Off-shelf transport was favoured during the winter 1999 by a very intense episode of dense shelf water cascading. Export of sediment resuspended by trawls (0.4×106 ty−1) was one order of magnitude lower than export associated with natural resuspension (8.5×106 ty−1). Trawling-induced resuspension is thought to represent one-third of the total export of suspended sediment from the shelf. A simulation combining both resuspension processes reveals no significant changes in resuspension and export rates compared with the sum of each individual process, suggesting the absence of interference between both processes. [Copyright &y& Elsevier]

Abstract: Multiple canyons incise the continental slope at the seaward edge of the continental shelf in the Gulf of Lions and are actively involved in the transfer of sediment from shelf to deep sea. Two canyons in the southwest region of the Gulf of Lions, Lacaze-Duthiers Canyon and Cap de Creus Canyon, were instrumented with bottom-boundary-layer tripods in their heads to evaluate the processes involved in sediment delivery, resuspension and transport. In both canyons, intense cold, dense-water flows carry sediment across the slope. In the Lacaze-Duthiers canyon head (located ∼35km from the shoreline), dense-water cascading into the canyon was episodic. Currents were highly variable in the canyon head, and responded to interactions between the along-slope Northern Current and the sharp walls of the canyon. Inertial and other high-frequency fluctuations were associated with suspended-sediment concentrations of ∼5mg/l. In Cap de Creus canyon head (located ∼14km from the shoreline), downslope currents were higher in magnitude and more persistent than in Lacaze-Duthiers canyon head. Greater suspended-sediment concentrations (peaks up to 20mg/l) were observed in Cap de Creus Canyon due to resuspension of the canyon seabed during dense-water cascading events. The similarities and contrasts between processes in these two canyon heads emphasize the importance of the interaction of currents with sharp canyon bathymetry. The data also suggest that cold, dense-water flows have more potential to carry sediment to the slope on narrow shelves, and may more efficiently transfer that sediment to the deep sea where a smooth transition between shelf and slope exists. [Copyright &y& Elsevier]

Abstract: In situ observations were combined with 3D modeling to gain understanding of and to quantify the suspended sediment transport in the Gulf of Lions (NW Mediterranean Sea). The outputs of a hydrodynamic–sediment transport coupled model were compared to near-bottom current and suspended sediment concentration measurements collected at the head of seven submarine canyons and at a shallow shelf site, over a 6-month period (November 2003–May 2004). The comparisons provide a reasonable validation of the model that reproduces the observed spatial and time variations. The study period was marked by an unusual occurrence of marine storms and high river inputs. The major water and sediment discharges were supplied by the Rhone, the largest Mediterranean river, during an exceptional flood accompanying a severe marine storm in early December 2003. A second major storm, with moderate flooding, occurred in February 2004. The estimate of river input during the studied period was 5.9Mt. Our study reveals (i) that most of the particulate matter delivered by the Rhone was entrapped on the prodelta, and (ii) that marine storms played a crucial role on the sediment dispersal on the shelf and the off-shelf export. The marine storms occurring in early December 2003 and late February 2004 resuspended a very large amount of shelf sediment (>8Mt). Erosion was controlled by waves on the inner shelf and by energetic currents on the outer shelf. Sediment deposition took place in the middle part of the shelf, between 50 and 100m depth. Resuspended sediments and river-borne particles were transported to the southwestern end of the shelf by a cyclonic circulation induced by these onshore winds and exported towards the Catalan shelf and into the Cap de Creus Canyon which incises the slope close to the shore. Export taking place mostly during marine storms was estimated to reach 9.1Mt during the study period. [Copyright &y& Elsevier]

Abstract: Previous work in the Gulf of Lions (western Mediterranean Sea) has suggested that significant amounts of sediment escape through the western part of this tectonically passive margin, despite it being far removed from the primary sediment source (the Rhone River, ∼160km to the NE). The primary mechanism behind this export is hypothesized to be the interaction of a regional, southwestward sediment-transport path with a canyon deeply incising the southwestern part of the shelf, Cap de Creus Canyon. To understand the pattern of off-shelf sediment export from the western Gulf of Lions, and more specifically, the role of Cap de Creus Canyon in this transport, box cores were collected within the canyon and on the adjacent shelf during five cruises from November 2003 to April 2005. Geochronology (210Pb-derived accumulation rates), grain-size distributions, and sedimentary structures (X-radiography) were analyzed to assess temporal and spatial sedimentation patterns. Results indicate two mid-shelf depocenters (30–90m water depth) in the northern and southern portions of the study area, separated by a zone of bypassing due to current acceleration around a headland (Cap Bear). Estimates of a sediment budget indicate that ∼6–8% of the sediment input to the Gulf is sequestered on the shelf region. Within the Cap de Creus Canyon, there is a significant spatial asymmetry in both grain size and accumulation rates. The northern flank is a modern depocenter of fine-grained sediments, while the southern flank is primarily non-depositional for mud and includes locations of apparent erosion. This suggests the influence of multiple oceanographic processes supplying sediment to the canyon: advection of nepheloid layers from the northern rim that provide a relatively continuous sediment supply (over decadal timescales), and episodic strong currents affecting the southern rim, which can scour sediment from the southern flank. The mid-depth thalweg has an ephemeral mud layer, overlying sand and consolidated mud. The mud layer appears to be flushed down canyon periodically. The canyon head contains coarse material, suggesting reworked sands may be entering. The 100-year sediment budget, based on accumulation rates for the fine-grained fraction in the upper canyon, indicates that ∼1% of the total sediment input to the Gulf is accumulating in upper Cap de Creus Canyon. However, this number may significantly underestimate the total sediment entering the canyon because water-column measurements show that sediment is likely moving through the upper canyon during major dense-water cascading events from the shelf and being deposited deeper in the canyon system. The ephemeral mud layer also indicates rapid deposition and frequent flushing of sediment through the upper canyon. Overall, this study shows that Cap de Creus Canyon is an active conduit of sediment past the shelf break, despite its location distal to the primary sediment source to the Gulf. [Copyright &y& Elsevier]

Abstract: Sediment cores from the western Gulf of Lions France were subject to known bottom shear stresses with the goal of understanding size-specific sediment erodibility. On cruises in October 2004, February and April 2005, cores with an undisturbed sediment–water interface were collected along a transect extending seaward from the Tet river mouth. The cores were exposed to increasing shear stresses (0.01–0.4Pa) onboard the vessel shortly after collection by using a Gust erosion chamber. Samples of the suspensate were collected during the erosion experiments and analyzed for disaggregated inorganic grain size (DIGS) using a Coulter Multisizer IIe. Size-specific mobility plots were generated by dividing the proportion of each grain size in suspension at each shear stress by its proportion in the sediment before erosion. If all grain sizes that make up the bottom sediment are eroded equally from the bed, then mobility equals one for all grain sizes. Values >1 indicate that the suspended sediment is enriched in the size class and values <1 indicate that the size class is enriched in the bed. Results show that in non-cohesive, sandy silts, fine grains (clays and fine silts) are eroded preferentially from the bed at low shear stresses. With increasing bottom stress progressively larger grains are eroded from the bed. In cohesive silts, preferential erosion of the finer sizes no longer occurs, with all sizes up to medium silts eroding at approximately the same rate. Effectively, a sandy silt can be winnowed of its fine grain fraction during erosion while cohesive silts cannot. This difference in the sortability of cohesive and non-cohesive sediment during erosion may control the position and maintenance of the sand–mud transition and the sequestration of surface-adsorbed contaminants. [Copyright &y& Elsevier]

Abstract: In the framework of the European project Eurostrataform, an array of six near-bottom mooring lines was deployed in the heads of the major submarine canyons incising the continental slope of the Gulf of Lions (NW Mediterranean). All moorings were equipped with sediment traps, current meters and turbidity Optical Backscatters Sensors (OBS) situated at few meters above the bottom. Particulate mass fluxes were recorded weekly by the sediment traps between November 2003 and May 2004 and compared with horizontal export fluxes obtained from the turbidity and current meters. Results show that near-bottom vertical particulate mass fluxes generally increase along slope between the northeastern-most and the southwestern region of the Gulf of Lions. Horizontal export fluxes also show some increase southwestward with flux in the southwestern-most canyon up to two-orders of magnitude higher than in northeast canyons. Furthermore, most of the export flux is driven by energetic and short events such as marine storms and dense shelf water cascading. Although the consequence of storms and cascading was obvious from traps and OBS measurements, substantial differences between vertical and horizontal fluxes appeared. While sediment traps recorded the largest vertical flux during the autumn storm (4 December) with contributions from river discharge and resuspended material, horizontal flux as obtained from OBS data was highest in winter (21–24 February). We believe that such discrepancies are partly due to measurement artifacts originating from the particle size effects and/or the different height above the bottom occupied by the traps and OBS which complicate comparisons between vertical and horizontal fluxes. However, different water-column conditions (stratified versus unstratified) together with the hydrodynamic regime during the two periods appear as a likely explanation for the flux differences between fall and winter storms. [Copyright &y& Elsevier]

Abstract: A 1-year survey of sediment dynamics on the Têt inner-shelf in the south-western part of the Gulf of Lions was conducted as part of the EUROSTRATAFORM program (European Margin Strata Formation) from October 2004 to November 2005. Several bottom instruments (ADCP, wave gauge and altimeters) were deployed at 28m water depth on the Têt prodelta to measure forcing responsible for sediment erosion and transport on the inner-shelf. The survey period was characterized by low inputs from the coastal rivers and the absence of severe E–SE marine storms, but intense cold dense shelf water formation along the inner-shelf due to strong and persistent N–NW continental winds. The strong (>20cm/s) and prolonged (4 months) southwards alongshore currents during the preconditioning and formation phases of dense shelf water generated continuous sediment erosion of several centimetres on the Têt prodelta and significant suspended-sediment transport. Hydrodynamical modelling shows that the core of the flow predominantly affects the inner-shelf, but occasionally spreads over the mid-shelf mud belt and the outer-shelf, due to the variable intensity of the NW wind (Tramontane). The impact of this N–NW wind-driven process in terms of resuspension rates and suspended-sediment transport clearly differs from that of extreme E–SE storms observed during the previous winter at the same site [Guillén, J., Bourrin, F., Palanques, A., Durrieu de Madron, X., Puig, P., Buscail, R., 2006. Sediment dynamics during wet and dry storm events on the Têt inner shelf (SW Gulf of Lions). Marine Geology 234 (1–4), 129–142.]. Bottom shear stresses and resuspension rates due to strong dense shelf water flow peaked at 0.7–1Pa and 0.3–0.4g/m2/s, respectively, while they reached values of 6–9Pa and 1.6–1.8g/m2/s, respectively, during the strong E–SE storms events. However, due to differing durations, both led to significant (few centimetres) erosion of the inner-shelf sediment. [Copyright &y& Elsevier]

Abstract: To investigate the role of coastal canyons in the transfer of organic matter from the shelf to the slope and basin, we deployed sediment trap/current meter pairs at the head of five canyons in the Gulf of Lions (GoL) between November 2003 and May 2004. Analysis of organic carbon, biogenic silica, Corg isotopic composition, Corg/total nitrogen, chloropigments, and amino acids clearly shows the seasonal influence and effect of extreme meteorological events on the composition of collected particles. The sampling period was divided into three “scenarios”. The first corresponded to a large easterly storm and flood of the Rhone river during stratified water column conditions; the composition of material collected during this event was influenced by increased transfer of riverine and coastal particulate matter, with a lower Corg content. During the second “fall-winter” scenario, northern and northwestern winds blowing over the shelf caused cooling and homogenization of the shelf water column; particles collected at this time reflected the homogeneous source of particulate matter transported through canyons; particles sitting in the vicinity of canyon heads are most likely swept downslope by the general south-westward circulation. Organic tracers indicate a degraded origin for organic matter transported during this period. A third “spring” scenario corresponded to northern winds alternating with eastward windstorms that triggered and/or enhanced the cascading of dense waters accumulated on the bottom of the shelf due to previous cooling. These conditions occurred in conjunction with increased phytoplankton productivity in shelf surface waters. Organic matter advected mainly by dense shelf water cascading was fresher due to the transport of newly produced particles and a variable terrestrial fraction; this fraction depended on the proportion of resuspended material accumulated during previous high discharge periods that was involved in each transport pulse. The tight link shown between meteorological conditions and organic matter transport is important for continental margin geochemical studies as future changes in climatic conditions may lead to dramatic changes in carbon sequestration capability and in the ecosystems of deep margin environments. [Copyright &y& Elsevier]

Abstract: Simulations of both currents and waves were performed throughout the year 2001 to assess the relative contribution of each to their overall erosive potential on the Gulf of Lions shelf. Statistical analysis of bottom shear stress (BSS) was compared to sediment grain-size distribution on the bottom. The hydrodynamic features of the bottom layer coincide with the distribution of surficial sediments, and three areas with different hydro-sedimentary characteristics were revealed. (i) The sandy inner shelf (<30m) area is a high-energy-wave dominated area but may be subjected to intense current-induced BSS during on-shore winds along the coast and during continental winds mainly in the up-welling cells. (ii) The middle shelf (30–100m) is a low-energy environment characterised by deposition of cohesive sediments, where the wave effect decreases with depth and current-induced BSS cannot reach the critical value for erosion of fine-grained sediments. (iii) The outer shelf, which has a higher bottom sand fraction than the middle shelf, may be affected by strong south-westward currents generated by on-shore winds, which can have an erosive effect on the fine-grained sediments. Particular attention was paid to features of the current that were found to be predominant on the mid-outer shelf. These currents are strongly dependent on wind direction. [Copyright &y& Elsevier]

Abstract: This paper describes an integrated study of a typical Mediterranean flood event in the Gulf of Lions. A flood with a 5-year return interval occurred in the Têt River basin and adjacent inner-shelf in the Gulf of Lions, northwest Mediterranean, during April 2004. Data were collected during this flood as part of event-response investigations of the EU-funded Eurostrataform (European Margin Strata Formation) project. Southeasterly storm winds led to a flood which directly modified the inner-shelf hydrodynamics. Sediment delivery to the coastal zone during this flood represented more than half of the mean annual discharge of the Têt River to the Gulf of Lions. This river transported a large amount of sand in suspension, representing 25% of the total suspended load, and as bedload representing 8% of the total load, during this event. Sand introduced in the nearshore was transported northwards during the peak storm and nourished a small delta. Fine sediments were separated from coarse sediments at the river mouth, and were advected southwards and seawards by the counter-clockwise general circulation. Fine-grained sediments were transported via a hypopycnal plume along the coast towards the southern tip of the Gulf of Lions and the Cap Creus canyon. The along-shore currents, which intensified from north to south of the Gulf of Lions, particularly between the Cap Creus promontory and the Cap Creus canyon, favoured the transfer of fine-grained sediments from the continental shelf of the Gulf of Lions towards the continental slope. Our results show that floods with a few-year return interval in small coastal rivers can play a significant role in the transport of sediments on microtidal continental margins and their export from the shelf through canyons. [Copyright &y& Elsevier]

Abstract: Shelf-to-canyon suspended sediment transport during major storms was studied at the southwestern end of the Gulf of Lions. Waves, near-bottom currents, temperature and water turbidity were measured on the inner shelf at 28-m water depth and in the Cap de Creus submarine canyon head at 300m depth from November 2003 to March 2004. Two major storm events producing waves H s>6m coming from the E–SE sector took place, the first on 3–4 December 2003 (max H s: 8.4m) and the second on 20–22 February 2004 (max H s: 7m). During these events, shelf water flowed downcanyon producing strong near-bottom currents on the canyon head due to storm-induced downwelling, which was enhanced by dense shelf water cascading in February 2004. These processes generated different pulses of downcanyon suspended sediment transport. During the peak of both storms, the highest waves and the increasing near-bottom currents resuspended sediment on the canyon head and the adjacent outer shelf causing the first downcanyon sediment transport pulses. The December event ended just after these first pulses, when the induced downwelling finished suddenly due to restoration of shelf water stratification. This event was too short to allow the sediment resuspended on the shallow shelf to reach the canyon head. In contrast, the February event, reinforced by dense shelf water cascading, was long enough to transfer resuspended sediment from shallow shelf areas to the canyon head in two different pulses at the end of the event. The downcanyon transport during these last two pulses was one order of magnitude higher than those during the December event and during the first pulses of the February event and accounted for more than half of the total downcanyon sediment transport during the fall 2003 and winter 2004 period. Major storm events, especially during winter vertical mixing periods, produce major episodes of shelf-to-canyon sediment transport at the southwestern end of the Gulf of Lions. Hydrographic structure and storm duration are important factors controlling off-shelf sediment transport during these events. [Copyright &y& Elsevier]

The applicability of grain-size trend analysis for determining sediment transport pathways was investigated on two macrotidal shorefaces of the southern North Sea and Dover Strait where sediment transport is strongly controlled by well-defined, shore-parallel, tidal currents. Sediment transport directions were defined following the Gao and Collins (Sedimentary Geology, 80, 47-60) method, using surficial sediment samples collected from 0 to 8 m water depths. Grain-size trend analysis produced results in relatively good agreement with the directions of near-bottom currents measured in the vicinity of the sampling sites in some cases, but also yielded more confused patterns of calculated transport vectors in others. The best results were obtained when using discrete sets of samples collected during a distinct half tide-cycle. Comparison of threshold shear velocity for sediment motion with estimates of bed shear velocity obtained from near-bottom current data recorded simultaneously with sediment sampling indicates that sediment transport was most likely occurring when sediment samples were collected, suggesting that the grain-size trends observed in the surface sediments probably reflect the last transport event. Our results suggest that grain-size trend analysis can be efficient for determining the mean transport direction of the last sediment transport event when applied to small areas and when sampling is limited to the thickness of the active layer of sediment remobilisation. This method may be appropriate, however, for defining time-averaged residual transport directions when applied to larger areas over which progressive variations in surface sediment distribution reflect a longer term adjustment to hydraulic regime. [ABSTRACT FROM AUTHOR]

The article describes a study that compares the concentration of suspended sediment in two small streams in France to discharges. Both suspended sediment and discharges were measured at the outlets on a yearly and monthly basis, with flood and non-flood periods taken into account. Data revealed that the relationship between suspended sediment concentration and discharge varied greatly, leading to the conclusion that cattle trampling and hydraulic erosion of stream banks are the two chief causes of sediment accumulating in stream catchments.

The mouth of the Seine River estuary (France) has undergone marked morphological evolution over several decades mainly due to engineering works aimed at improving access to Rouen and Le Havre harbours. The intertidal areas are decreasing in size and the lower estuary is accumulating sediment and prograding. In order to understand and better describe the major morphological behaviours of the estuary, a morphodynamic numerical model was developed within the Seine-Aval program. At the end of the 1st part of the research program, a validated fine sediment transport model (3D) was available (Le Hir et al., b). As the present morphological study addresses medium-term issues (a few decades), and because of the need to investigate impacts of local structures or events, we chose to use the so-called “process-based approach” starting from the existing model. First, the existing model was upgraded to account for (suspended) sand transport, and to achieve coupling between morphological changes and sediment transport. Erodability of the sediment accounts for the respective proportions of mud and sand. Simulations starting from an arbitrary surficial sediment cover show that the model is able to reproduce realistic sediment patterns. For example, it is able to change the sediment nature on the intertidal flat near Le Havre from sand to mud. Observed structures of suspended sediment are also reproduced: fine particles mainly follow the turbidity maximum whereas significant concentrations of sand grains in suspension are found where the hydrodynamic stresses are intense. Concerning morphodynamics, simulations with real forcing over one year are discussed. The effect of waves on the bathymetric evolution of the mouth is shown and the sensitivity of morphodynamics to the coupling procedure is tested. [ABSTRACT FROM AUTHOR]

Understanding the dynamics of fine sediment transport across the upper intertidal zone is critical in managing the erosion and accretion of intertidal areas, and in managed realignment/estuarine habitat recreation strategies. This paper examines the transfer of sediments between salt marsh and mudflat environments in two contrasting macrotidal estuaries: the Seine (France) and the Medway (UK), using data collected during two joint field seasons undertaken by the Anglo-French RIMEW project (Rives-Manche Estuary Watch). High-resolution ADCP, Altimeter, OBS and ASM measurements from mudflat and marsh surface environments have been combined with sediment trap data to examine short-term sediment transport processes under spring tide and storm flow conditions. In addition, the longer-term accumulation of sediment in each salt marsh system has been examined via radiometric dating of sediment cores. In the Seine, rapid sediment accumulation and expansion of salt marsh areas, and subsequent loss of open intertidal mudflats, is a major problem, and the data collected here indicate a distinct net landward flux of sediments into the marsh interior. Suspended sediment fluxes are much higher than in the Medway estuary (averaging 0.09 g/m3/s), and vertical accumulation rates at the salt marsh/mudflat boundary exceed 3 cm/y. Suspended sediment data collected during storm surge conditions indicate that significant in-wash of fine sediments into the marsh interior can occur during (and following) these high-magnitude events. In contrast to the Seine, the Medway is undergoing erosion and general loss of salt marsh areas. Suspended sediment fluxes are of the order of 0.03 g/m3/s, and the marsh system here has much lower rates of vertical accretion (sediment accumulation rates are ca. 4 mm/y). Current velocity data for the Medway site indicate higher velocities on the ebb tide than occur on the flood tide, which may be sufficient to remobilise sediments deposited on the previous tide and so force net removal of material from the marsh. [ABSTRACT FROM AUTHOR]

A study of the particulate organic carbon (POC) in the estuarine turbidity maxima (ETMs) of the three major French macrotidal estuaries shows that the average contents are 1.5, 3.3 and 3.1% (expressed in % of dry suspended sediment) in the Gironde, Loire and Seine Estuaries, respectively. There is no seasonal variation of POC contents in the Gironde Estuary, whereas, they often increase in the Loire and the Seine Estuaries in spring and summer. The lability of the estuarine particulate organic matter was estimated by two analyses: 1/labile organic matter was measured as the organic carbon loss during incubation tests over one month; 2/ the hydrolysable organic fraction was determined after 6N HCl digestion. The organic fractions of the ETMs are mainly refractory. Any increase in the amount of POC as compared to the background levels (cited above) is always correlated to an increase of organic matter lability. The yearly average fluvial contributions by various particulate organic pools (soil and litter organic matter; organic matter of phytoplanktonic and human origin) that enter the three estuaries were quantified. In the Garonne River, soil and litter are the major (90%) POC sources. In the Loire system, due to the eutrophication of the river water, phytoplankton contributes up to 50% of the total POC load. In the Seine river, soil and litter contribute 70% of the total POC input; POC of human origin is also significant (10%), due to the impact of the City of Paris (10 million inhabitants). The lability of the different types of organic matter ranks as follows: phytoplankton ∼litter > human-origin organic matter >> soil. By combining the POC budgets and the lability of each type of organic fraction, it was possible to explain why the POC of the three ETMs is different and characterizes its refractory vs. labile nature. [ABSTRACT FROM AUTHOR]

Temporal and spatial variability of the Abra alba–Pectinaria koreni and Macoma balthica communities was examined in the northern part of the Seine estuary (North Channel) over different space and time scales in order to assess the role that the hydrologic regime and/or anthropogenic influences play in defining benthic communities over time. Sediment in the North Channel displayed strong spatial and temporal variability, sustained by intense sediment transport episodes. Total macrobenthic abundances ranged widely on the course of the year and there was no evidence of a seasonal signal for the density fluctuations, whatever the spatial scale considered. The bio-sedimentary dynamics can be divided into two periods: the first corresponds to the high flow rate period (January–May) during which fauna is influenced by fine silt/clay deposition, and the second to the low flow rate period (June–December) during which sandy deposits prevail. Despite the absence of significant correlations between sediment composition and abundance, episodes of sediment transport seem to be an important structuring mechanism in the Seine estuary. As a consequence, the faunal composition varied throughout the year. The winter and spring fauna, characterised by species living on muddy fine-sands or muds, were enriched during the summer and autumn by species living in clean fine sand, such as Donax vittatus, Nephtys cirrosa or Spio decoratus, mainly represented by adult individuals. Secondary settlement of drifters may explain the rapid structuration of assemblages a few days after the sandy deposits. Our results suggest the importance of the bentho-pelagic coupling, primarily induced by the sedimentary instability, on the macrobenthic fauna dynamics. The intra-annual variability of assemblages at the mouth of the Seine river and the silted situation of the North Channel might simply be the result of the silting up and alteration of the inner estuary, generated by several decades of man-made modifications and natural processes. [ABSTRACT FROM AUTHOR]

Sediment budget data from an 18-month topographic survey were analysed with data from brief experiments on wind parameters, beach moisture contents, bedforms and sand mobilization in order to monitor conditions and patterns of embryo dune development over a flat 150-1000 m wide accreting upper beach. The surface conditions over the upper beach locally affect aeolian transport, but net dune development over time depends on sustained strong winds and their orientation. Incoming marine sand supplied by storms and onshore winds is reorganized by the dominant offshore to longshore winds into elongated embryo dunes over this upper beach, imprinting a regional morphology of long-term longshore dune ridge development. [ABSTRACT FROM AUTHOR]

River basin metal pollution originates from heavy industries (plating, automobile) and from urban sources (Paris conurbation: 2740 km2, 9. 47 million inhabitants). The natural sources of metal have been found to be limited due to sedimentary nature of this catchment and to the very low river sediment transport (10 t km−2 y−1). Several types of data have been collected to build the metal budget within the whole Seine River basin: field surveys, economical statistics and environmental models. Environmental contamination and related fluxes have been measured on atmospheric fallout, rural streams particles, and Seine River particles upstream and downstream of Paris and at river mouth. Metal pathways and budgets have been set up for (i) a typical cultivated area, (ii) a Paris combined sewer system, (iii) Paris conurbation and (iv) the whole catchment metal retention effect in floodplain and dredged material. Metal fluxes to the estuary have been decomposed into natural, urban domestic and other sources. The latter are within 1–2 orders of magnitude larger than waste water fluxes directly released into rivers according to an industrial census. These fluxes have been further compared to the annual use (1994–2003) of these metals. Metal excess fluxes exported by the river are now a marginal leak of metal inputs to the catchment (i.e. “raw” metals, metals in goods, atmospheric fallout), generally from 0. 2 to 5‰. However, due to the very limited dilution power in this basin, the contamination of particles is still relatively high. The Seine River basin is gradually storing metals, mostly in manufactured products used in construction, but also in various waste dumps, industrial soils, agricultural and flood plain soils. [Copyright &y& Elsevier]

Located in the south-eastern part of the Bay of Biscay, the Capbreton Canyon incises the continental shelf up to the 30 m isobath contour, and acts as a natural conduit for continental and shelf-derived sediments. EM1000 multibeam bathymetry shows two main features characterising the canyon — a deeply entrenched meandering channel, bordered by fluvial-like terraces constituting large sediment traps. A dataset of cores and seismic profiles together with a multibeam bathymetry map has enabled the characterisation of recent sedimentary activity in the axial channel and on the terraces. Data analysis evidenced the major role of the canyon head in recent sediment dynamics. This part of the canyon is a temporary reservoir for sediments, accumulated by coastal hydrodynamic processes. Exceptional climatic, tectonic or hydrodynamic events can mobilise the sediments and generate gravity-driven flows. Under the present-day sea-level highstand conditions, these flows are not powerful enough to bring their bedload to the deep sea, and are confined mainly to the upper part of the canyon. Turbidity currents model the axial channel pathway and are at the origin of terrace formation. Terraces in the Capbreton Canyon are not typical but rather are reduced to confined levees. Three factors control the vertical growth of a terrace: (1) the amount of overspilled sediments brought by turbidity currents, (2) hemipelagic sedimentation and (3) terrace height. The amount of sediment spilling over a terrace decreases with increased terrace elevation. Concurrently, the proportion of hemipelagic fallout depositing on a terrace increases. Terraces are considered to be fossil when the height of the terrace prevents further deposition by overspilling. The terraces studied in this paper are interpreted as having formed during the Holocene, implying that the sediment dynamics of the Capbreton Canyon is continuous through time. Highstand periods differ from lowstand periods because they show a decrease in the energy of erosive processes. Temporal variations in erosive and depositional processes in the canyon are controlled by the Adour River, which delivers large amounts of sediment to the system. [ABSTRACT FROM AUTHOR]

This paper presents continuous field experiments carried out during 4 years in a man-entry egg-shaped combined sewer in Lyon, France in order to contribute to the knowledge and the modelling of sediment accumulation and sediment removal by means of a Hydrass flushing gate. The 250 μm sediments are mainly mineral, and their physical and chemical characteristics appear as rather stable in time and space. Long-term sediment monitoring reveals: i) a regular asymptotic increase of both the sediment mass and the slope of its longitudinal profile, ii) a clear correlation between local sediment profile irregularities and sewer ancillaries but without significant influence on the global and long term accumulation. Simple sediment accumulation modelling shows: i) a good suitability of a three parameters conceptual model to reproduce asymptotic sediment volume accumulation, and ii) a good suitability of the Velikanov model to reproduce sediment profiles. Both models reproduce observations with an acceptable margin of uncertainty for operational management purposes but are very sensitive to input data and parameter values. The Hydrass flushing gate is efficient and it appeared that the mass of sediments moves downstream linearly with the number of flushes. [ABSTRACT FROM AUTHOR]

Abstract: This paper investigates the relative influence of waves, wind-induced current and tidal current on the sediment mobility of a macro-tidal environment belonging to the inner shelf seaward of the ‘pertuis Charentais’ (France). This study, mainly based on three-week hydrodynamic in-situ measurements, shows that, for a water depth of 23 m, the swell (rather than wind waves) orbital velocity is large enough to initiate the motion of medium sands that are then transported by currents. Estimations show that medium sand of 0.2 mm is transported during 92% of the measurements, whereas coarse sand and gravel move sporadically, during storm, synchronously with spring tides. Further more, bedload fluxes appear strongly larger when waves are taken into account (370 times larger for 0.2-mm sands). To cite this article: D. Idier et al., C. R. Geoscience 338 (2006). [Copyright &y& Elsevier]

Forty-nine sediments were sampled along the coast of the Seine bay: 19 from the Port-en-Bessin harbor and 30 from the Bay des Veys. Metallic and polychlorinated biphenyl contaminations were estimated in harbor sediments by their comparison to the OSPAR Convention guidelines. Sediments in Bay des Veys were considered as nonpolluted materials and metal concentrations were chosen as regional reference data to calculate anthropogenic factor and gave human contributions of each metal in harbor sediments. The source of the principal pollutants was principally associated with the careening activities and the use of antifouling paints. A statistical study of data showed strong relationships between metals, organic matter, and fine-grained fraction (<50 μm) of sediments, assuming mobility of metals to water column in case of removal. [ABSTRACT FROM AUTHOR]

The greatest change in particle roundness, sphericity, and size in most fluvial systems generally occurs in the initial first few kilometers of sediment transport. Observations in natural settings and laboratory experiments have shown that changes, such as increased grain rounding and decreased size due to particle breakage, wear, and attrition, tend to be progressive along the dispersal path. In marked contrast, this study records highly variable and poorly developed particle-texture trends downslope along short (<5 km) channels that extend directly from a high-relief carbonate source area down to the shore of Lake Annecy in the western Alps, SE France. The observed inconsistent patterns are measured in both a region-wide analysis using all collected samples and also in a more specific survey of samples in six different channels incised on the steep, topographically irregular mountain flanks that border the lake. The major factor responsible for the irregular downslope patterns of roundness, sphericity, and size in the Annecy study area is the lateral introduction of sediment into the fluvial channels along dispersal paths. Episodic failure of mechanically unstable sediments and their transport down steep valley walls bring less-abraded sediment of variable shape and size along the dispersal paths. The valley wall sediment influx factor warrants further examination to better interpret sedimentation processes in dissected, high-gradient terrains that border coastal areas. [ABSTRACT FROM AUTHOR]

Abstract: The morphology and migration of rhythmic intertidal ridge and runnel systems, and subtidal crescentic bars that border the southwest coast of France were characterized using in situ surveys and maps obtained by remote-sensing methods. The period from 1986 to 2000 was investigated. A total of 35km of coast was mapped. This data set shows several specificities, the origin of which are examined in the present report using hydrodynamic data. A complete analysis of the influence of wave climate on both the shape and the movements of these rhythmic sedimentary patterns was performed. In addition, SWAN and MORPHODYN-coupled numerical models were used to provide quantification of both wave breaking and longshore currents for wave parameters that were representative of the mean values and of the energetic conditions. This study demonstrated the short time response of intertidal systems to the wave forcing. When the offshore significant wave height (H s) was lower than 2.5m, regular coastal ridge and runnel systems developed in the intertidal zone and migrated in the longshore-drift direction at a rate of 1.7–3.1mday−1. By contrast, the ridge and runnel system morphology abruptly changed when the H s exceeded 2.5m, and after the storm, the typical ridge and runnel rhythmic topography was recovered within 5–9 days. The crescentic bars, which had a convex seaward shape, were affected by waves with H s values greater than 3m (slightly less for short waves). Depending on the wave orientation, the crescentic bars moved in the longshore-drift direction at a rate that reached 1mday−1. The data suggested a slight negative correlation between the mean alongshore length of the crescentic bar and the mean H s. Finally, it seemed that increasing the wave obliquity with respect to the coast resulted in the flattening of the crescentic bars. Thus, coupling Spot and in situ mapping to hydrodynamic records allow the characterization of coastal morphology and dynamics, with time and space samplings that are particularly well adapted to the little studied alongshore morphodynamics. This approach should improve the difficult parameterization of morphodynamic models in high-energy environments. [Copyright &y& Elsevier]

For three years (2001-2003), sediment samples were extracted from about 100 silt traps (STs) spread out all over the combined sewer network of Paris. These STs, whose volume varied from 21 to 325m³, were cleaned out as soon as their filling capacities were reached. All these sediment samples were analysed for physicochemical parameters (pH, organic matter (OM) content, grain size distribution), total hydrocarbons (THs), 16 polycyclic aromatic hydrocarbons (PAHs) selected from the priority list of the USEPA, and heavy metals (Al, Ag, As, Cd, Cu, Cr, Sn, Fe, Mn, Hg, Ni, Pb, Zn). For each silt trap, six sediment samples were extracted before the clean out procedure: three samples were extracted from the sediment surface (5-10 cm depth) and three other samples were extracted from a deeper sediment layer (approximately at 1m depth). The location of these sampling points allowed us to take into account the possible spatial fluctuation of pollutant loads in each ST. The first results showed that there were some important inter-site variations of pollutant contents. These variations have to be taken into account by the sewer manager for the fate of the ST sediments. Therefore, we decided to assess the grain size distribution of some pollutants. OM, heavy metals and PAHs have been investigated on the five grain size fractions (>20 mm, 8-20 mm, 0.5-8 mm, 50-500 µm, <50 µm) for 9 STs, which have been selected on their heavy metal content basis. This work aims at understanding the distribution of the pollutant contents and at improving the knowledge of the ST sediment pollution. [ABSTRACT FROM AUTHOR]

The impact of combined sewer overflows on the Seine River was studied for the scientific interest of understanding highly transient situations and for the management challenges they represent.Measurements were made in the Seine River downstream of a combined sewer overflow (CSO) to identify the relevant variables describing the evolution of water quality. The combined effects of various processes influencing oxygen depletion after a rain event were analysed given all the available data. A complete oxygen balance was established to rank the relative importance of the processes.The model ProSe used for these tasks was designed in the framework of a long term multidisciplinary research program devoted to the Seine River catchment. A comparison of the model we used with existing models was done. The conceptual model was especially adapted for this highly impacted urban ecosystem. Apart from usual processes considered in river ecological modelling, sedimentation and erosion of particles, a biologically active and mobile benthic boundary layer (BBL), exchange of particles and diffusion of solutes between this BBL and the water column, detailed descriptions of algal and bacteria physiology were taken into account.To explain the oxygen depletion in the river, the more relevant variables appear to be the quantity of bacteria brought by the overflow and the biodegradable dissolved organic carbon concentrations. Specific contribution to the evolution of water quality of the river of particles that are sedimenting, was investigated, including the micro organisms brought by the overflows.For this highly eutrophicated river, the influence of the reduction of photosynthesis activity due to cloud cover was quantified. The influence of the toxicity of the CSO on the phytoplanktonic photosynthesis was studied experimentally and taken into account in the model. The resulting effect is a delayed oxygen depletion inside the plume of polluted water. [Copyright &y& Elsevier]

The formation and long-term evolution of an estuarine bank of the Gironde mouth, SW France (the Saint-Georges Bank) is studied through the comparison of nine historical bathymetric maps (1677, 1723, 1825, 1874, 1892, 1920, 1.940, 1960, and 1992) and information obtained during a recent bathymetric survey (! 999). The data show that the initial formation of Saint-Georges Bank occurred at the end of the 17th or the beginning of the 18th century and it could be related to the other morphological changes which took place at the estuarine inlet and particularly to the gradual destruction of the downstream estuarine shoal of Grande Barre, which (a) changed the inshore hydrodynamic regime, (b) allowed large quantities of marine sediments to move further upstream along the coast and (c) made large quantities of sand-sized sediments available. The Saint Georges Bank growth during the past centuries can be differentiated into 3 stages: Stage 1 (1723–1892), which has been characterized by a vertical and lateral (down-stream) bank .growth (with an average rate of accretion of about 0.3 ⊗ 106 m³ yr-1); Stage II (1892–1960), which is characterized by a relatively slow development (with an average growth rate of about 0.15 ⊗ 106 m³ yr-1); and Stage III (1960–1999), which is characterized by a rapid bank growth (with an accretion rate of about 0.7 ⊗ 106 m³ yr-1) and a anticlockwise rotation of the crest. The morphological and sedimentological data (side-scan sonar and sub-bottom profiling data and surficial sediment samples) which were collected during the present investigation suggest that Saint Georges Bank is likely to be maintained by a complex hydrodynamic/sediment dynamic regime consisting of a clockwise residual tidal circulation, headland associated secondary flows and trapping of sediments in a zone contained between mutually evasive sediment transport paths. [ABSTRACT FROM AUTHOR]

Investigates a large debris flow on the fan of the Chalance torrent system, a tributary of the Séveraisse river, French Alps. Details of fieldwork to assess the magnitude and frequency of such debris flows on this fan; Results revealing that several debris flows have occurred in the past 200 years; Dating technique used to obtain the frequency of these debris-flow events; Data indicating the relationship of magnitude and frequency; Data indicating a debris flow of such a volume appears to have a recurrence interval of approximately 34 years.

Wave dynamics contribute significantly to coastal hazards and were thus investigated at Vougot Beach by simulating both historical and projected future waves considering climate change impacts. The historical period included a major storm event. This period was projected to the future using three globally averaged sea level rise (SLR) scenarios for 2100, and combined SLR and wave climate scenarios for A1B, A2, and B1 emissions paths of the IPCC. The B1 wave climate predicts an increase in the occurrence of storm events. The simulated waves in all scenarios showed larger relative changes at the beach than in the nearshore area. The maximum increase of wave energy for the combined SLR and wave scenarios was 95%, while only 50% for the SLR-only scenarios. The effective bed shear stress from waves and currents showed different spatial variability than that of the wave height, emphasizing the importance of interactions between nearshore waves and currents. Increases in the effective bed shear stress (combined scenarios: up to 190%, and SLR-only scenarios: 35%) indicate that the changes in waves and currents will likely have significant impacts on the nearshore sediment transport. This work emphasizes that combined SLR and future wave climate scenarios need to be used to evaluate future changes in local hydrodynamics and their impacts. These results provide preliminary insights into potential future wave dynamics at Vougot Beach under different climate change scenarios. Further studies are necessary to generalize the results by investigating the wave dynamics during storm events with different hydrodynamical conditions and to evaluate potential changes in sediment transport and morphological evolution due to climate change. [ABSTRACT FROM AUTHOR]

The domain of Chantilly (Oise, France) includes a castle and a garden, both dating from the eighteenth century, which are seen as important legacies of France's history. Nowadays, the 2.5 km canal that runs through the domain is subject to the phenomenon of silting, leading to the accumulation of sediments within the canal linked to the proliferation of algae, which has a dissuasive effect among visitors. HEC-RAS software (Hydrologic Engineering Centers River Analysis System, US army corps of Engineers, Washington, D.C., USA) was used to model and understand sediment accumulation within the canal. This model is widely used in the literature tackling sediment transport and accumulation, and allows the forecasting of which stretches of the canal are most susceptible to sediment accumulation. The simulation results highlight an accumulation of sediment near the entrance of the Nonette stream into the canal and a propagation through the canal. The total accumulated volume assessed by the model between 2001 and 2010 equals 3901 m3, when the reconnaissance of the catchment showed the sediment was not a limiting factor. However, the volumes determined are underestimated, as matter brought by vegetation or other systems different from the river (e.g., wind, rainfall) is not considered in the calculation. The quantity of sediment is also subject to uncertainties, as the bathymetry of the canal is not available. [ABSTRACT FROM AUTHOR]

This special issue of Geo-Marine Letters presents selected contributions from the international conference Particles in Europe (PiE) 2010 organized by Sequoia Scientific, Inc., and the Laboratoire d'Océanographie de Villefranche (LOV) on 15-17 November 2010 in Villefranche-sur-Mer, France, and guest-edited by Ole Mikkelsen, Malik Chami and David Doxaran. PiE was initiated in 2008, in order to promote and further our understanding of the importance of suspended particulate matter (SPM) for a very wide range of processes in the aquatic environment-from optics and acoustics, over sediment transport, to the global carbon balance. The papers in this special issue are in particular concerned with the interaction between SPM and water optical properties, as well as how to use optical proxy measurements to understand SPM processes. The next PiE conference is scheduled for 17-19 October 2012 in Barcelona, Spain. [ABSTRACT FROM AUTHOR]

• Low and high bar modes originate from water discharge variations. • In turn, this induces complex compound bar formation. • Sediment sorting patterns differ between unit and compound bar patterns. • Sediment sorting does not modify bar morphodynamics if sediment mobility is high. • Floods decrease the degree of sediment sorting. Bars are large sediment deposits alternating with deeper areas that arise from alluvial river bed instability and forcing. The present study aimed at investigating the combined influence of flow and longitudinal width variations on the co-evolution between bar pattern and sediment sorting in a sandy-gravel river reach. To this goal, a fully non-linear 2D numerical model was developed to reproduce the morphodynamic behavior of bars in a reach of the Loire River consisting in a typical channel expansion/contraction. Numerical results showed that varying water discharge promoted a competition between low and high bar modes: i.e., from alternate to multiple bar patterns. Low bar modes were associated with coarse sediment over bar tops and fine sediment in pools, and this sorting pattern was inverted for higher bar modes. Surface sediment was coarser and the degree of sediment sorting was greater after periods of low than high flow. Due to high sediment mobility, sediment sorting did not significantly modify bar morphodynamics. [ABSTRACT FROM AUTHOR]

An increasing number of scientific studies are tackling the management of discharges downstream of dams for environmental objectives. Such management is generally complex, and experiments are required for proper implementation. This article present the main lessons from a silt sand removal experiment on a bypassed reach of a dam on the Selves River (164 km²), France. Three four-hour operational tests at maximum discharge (10, 15, and 20 m3/s) were carried out in September 2016 to determine the discharge required for transporting as much silt and sand as possible without remobilizing coarser sediments. In September 2017, an additional flow release was performed over 34 h at 15 m3/s. Suspended sediment concentration and water level were recorded throughout the releases. Monitoring at the reach scale was supplemented by morphological measurements. The results demonstrate that a discharge of approximately 10 m3/s enables significant transport of suspended sediments (SS), whereas a discharge of 15 m3/s enables significant sand transport. The results provide operational information on silt and sand transport applicable to other small rivers. This study represents an important contribution to the relatively sparse existing body of literature regarding the effects of water releases and sediment state. Our study also demonstrates that it is possible to successfully undertake water releases in small rivers with an adaptive management approach. [ABSTRACT FROM AUTHOR]

The presence of F-specific RNA phages (FRNAPH) in stream waters indicate faecalpollution, and its occurrence and propagation constitute a major public health issue.FRNAPH are considered as water colloids, they can be transported in suspension, attached tosuspended sediment particles and flocs, or be deposed in the channel bed. For instance,several studies have shown a higher persistence of viruses in sediment than in the watercolumn. However, the exchanges between water and sediment are not well understood, andfurther studies are needed in catchment with varying physiographical characteristics andanthropogenic disturbances. Accordingly, whereas laboratory experiments have shown thattemperature and sunlight are among the most important factors responsible for the virusinactivation, we still lack a general understanding on how the virus are transported, itsdynamics and persistence under natural conditions. Here, we present a 2-years dataset(2015-2017) of weekly FRNAPH concentrations in the Orne River (northeastern France),which drains around 1,270 km2 and flows into the Moselle River. Our underlyinghypothesis is that the fate and transport of FRNAPH might be explained by catchmenthydrologic processes, suspended sediment transport and meteorological variables. Wehypothesize that if we are able to decipher the controlling factors, we might better predictconcentration downstream of the faecal sources and better understand the relationshipbetween FRNAPH and suspended sediment dynamics. We collected stream watersamples weekly at two sampling sites, upstream and downstream a wastewatertreatment plant, and quantified FRNAPH concentrations using infectivity assays. Inparallel, we measured hydrological and meteorological parameters, including watertemperature, conductivity, turbidity, flow rate, suspended sediment concentration, solarradiation, rainfall and air temperature. We also investigated the occurrence of FRNAPHon suspended sediment particles. Our results showed a higher concentration ofFRNAPH at the upstream site (Haropré), what might be associated to faecal pollutionpoint sources. A seasonal variability on phage concentrations was only observedat the downstream site (Beth), what could be associated with water temperatureannual fluctuations. Correlations between FRNAPH and suspended solids werenon-significant, indicating a low implication of suspended sediment transport on the phagetransport and settling in our study site. A multivariate statistical analysis will bepresented, together with an estimation of the FRNAPH fluxes at the two study sites. [ABSTRACT FROM AUTHOR]

The shoreface is an important transitional zone between the beach and the inner shelf. Significant change on the shoreface occurs at long temporal time scales and over large spatial domains, making its study challenging. The shoreface's contribution to nearshore dynamics is also usually complex, acting as both a sediment source and a sediment sink, as well as facilitating or impeding sediment transport. To date, no universal agreement exists for the definition of the shoreface nor its exact spatial extent.When considering the longer term and larger-scale evolution of coastal systems, the morphodynamics of the shoreface appears to be a determining factor in coastal and shoreline evolution. Along high-energy coastal areas, for instance western Ireland and North-western France, dominated by geomorphological features such as embayments, pocket beaches, sea cliffs and rock outcrops, the geological background plays a major role in the control of the coastal morphodynamics. This geological control acts to limit accommodation space, sediment availability and longshore sediment transport thus helping constrain the shape of the shoreface and therefore its dynamics and evolution.The study of shoreface morphodynamics requires the combination of multiple datasets at variable temporal and spatial scales. In this study, the west coast of Ireland provides spatially extensive bathymetry (multi-beam) datasets to allow the study of shoreface morphology and extent. Furthermore, the existence of wave data from offshore buoys and reanalysis wave models, also allows the analysis of hydrodynamic behaviour (using SWAN modelling) and the identification of the seaward shoreface limit. The overall aim of the work is to advance our understanding of the morphodynamics of the shoreface in complex regions. [ABSTRACT FROM AUTHOR]

Along the Northern coast of France, bathymetric surveys were carried out since the early 19th century, and were stored in the French Hydrographic Service (Shom) archives. These hydrographic field sheets were made for mapping the seabed of the coastal zone where tidal sand banks are common, forming linear shore-parallel or slightly oblique massive sand bodies. Digitization of these historical records was undertaken in the course of this study, enabling to assess changes in sand bank morphology and position. Our analyses of bathymetry changes show significant morphological variations across the shoreface since the 19th century, which are largely due to sand bank mobility. Alongshore migration and elongation of sand banks can be related to tidal asymmetry directed to the east-north-east. Shore-perpendicular movement can be related to the action of storm waves that can be responsible for onshore-directed sediment transport. One of the objectives of this study is to attempt to relate the observed changes in coastal and nearshore morphology with possible changes in hydrodynamic processes. A simulation of tidal circulation and of wave propagation over bathymetry grids based on historical bathymetric soundings will enable to compare coastal hydrodynamics during distinct time periods and assess their possible effects on nearshore morphology change. This could lead to a better understanding of the long-term mechanisms responsible for coastal zone evolution. [ABSTRACT FROM AUTHOR]

In the last two centuries, many areas have undergone a rather fast demographic, industrial andurban development. This intense land occupancy affected the quality of surface waters, whichbecome the receptacle of anthropogenic effluents from various origins. In this context, severalrivers in North-Eastern France were strongly modified (rectification of river bed, dambuilding) and received high amounts of industrial and domestic effluents due to paststeel-making activities installed nearby water resources. As a consequence of these pasteffluent inputs in the river, and although part of the settled material was dredged andremoved from the riverbeds, these often remain contaminated. During flood events, theremobilization of these riverbed sediments can strongly impact water and evensoil quality. In this context, there is consequently a clear need for predicting thepotential resuspension and transport of sediment in these heavily polluted riversystems. Hydromorphodynamic models are powerful tools for predicting the potential mobilizationand transport of sediment in river ecosystems. Recent studies even showed that they are ableto predict suspended sediment matter concentration in small river systems satisfyingly.However, modelling exercises often neglect suspended sediment properties (e.g.particle site distribution and density), even though such properties are known todirectly control the sediment particle dynamics in the water column during floodevents. This study has two objectives. On the one hand, it aims to further develop an existinghydromorphodynamic model based on the dynamic coupling of TELEMAC-3D (v7p1) andSISYPHE (v7p1) in order to enable an enhanced parameterization of the sediment grain-sizeand density distributions. On the other hand, it evaluates and discusses the added-value of thenew development for improving sediment transport and riverbed evolution predictions. Tothis end, we evaluate the sensitivity of the model to the parameterization of sedimentgrain-size distribution, sediment density and suspended sediment concentration at theupstream boundary. As a test case, the model is used to simulate a flood event in asmall-scale river, the Orne River in north-eastern France. The results show substantialdiscrepancies in bathymetry evolution depending on the model setup. Moreover,the sediment model based on an enhanced sediment grain-size distribution (10classes) and with distributed sediment density outperforms the model with only twosediment grain-size classes in terms of simulated suspended sediment concentration. [ABSTRACT FROM AUTHOR]

In the classic Wilson plate-tectonic cycle, plate convergence and orogenesis follow plate divergence. This results in an asymmetric doubly vergent collisional orogen with pro- and retro-wedge/foreland basin systems (lower and upper plate, respectively). Conceptual models propose that an orogen evolves as a single dynamic system from an early, non-equilibrated, growth stage to a late, mature, steady-state stage. Yet, early convergence processes and mechanisms responsible for the transition from rift to collision are, as yet, little known and quantified. In particular, most of our understanding of wedge/foreland dynamics comes from the pro-wedge, where mainly late orogenesis is well preserved. In contrast, the retro-foreland basin is believed to preserve the full orogen history due to lower shortening and translation values. This is the case in the NE Pyrenean retro-wedge, where recent studies suggest that during early orogenesis the Pyrenees never reached a steady-state configuration.Our work aims to constrain the timing and rates of orogenic episodes as well as timescales for sediment transport from source to sink in the Eastern Pyrenees. We apply coordinated U-Pb and (U-Th)/He dating methods on detrital zircon to ten samples through the syn-orogenic Upper Cretaceous to Eocene succession. We use the recently developed in situ double dating approach to address firstly, a two-fold shortcoming in quantifying syn-orogenic denudation and secondly, an issue with recognising the signature of early Pyrenean convergence in source-to-sink processes. Firstly, most previous regional exhumation studies have focused on reconstructing thermal histories for currently exposed bedrock, which has led to sparse constraints on the initiation and early phase of convergence. Moreover, regional detrital double dating has until recent years been performed either on distinct batches of grains or statistically non-representative numbers of grains or samples. Secondly, in the Pyrenees, the delay between the end of rifting (and associated HT metamorphism, early Cenomanian) and the onset of convergence (end Santonian) is short, leading to difficulties in recognising a clear thermal signature of early orogenesis.Our results show that lag times (the difference between the age of apparent cooling and deposition, assuming instantaneous transport) sharply decrease during the Maastrichtian, passing from >50 Myrs to <20 Myrs. This indicates a significant increase in denudation rates. Around this time we also note a marked increase in the proportion of Early Cretaceous rifting and Hercynian source signals, indicating a change in source area(s) and/or progressive unroofing of thermally reset rifted Pyrenean crust. All these changes are recorded over <2 Myrs and are synchronous with changes in paleo-current directions. We interpret these results as recording the sedimentary response to the onset of Pyrenean orogenesis. Our data suggest that the early orogen and the Early Cretaceous rift extended further east, in an area which has since been destroyed by the Oligo-Miocene opening of the Gulf of Lion. Our work clarifies early growth in the Pyrenees, providing new evidence for dynamic coupling between range and foreland basin(s), and contributing to the debate on the role of rift inheritance into early orogenic processes. [ABSTRACT FROM AUTHOR]

Abstract: Sediment–turbulence interactions near the bed are still poorly understood in highly turbid estuaries, especially in the presence of fluid mud layers. This results primarily from the difficulty in measuring co-located velocity and suspended sediment concentration (SSC) at sufficiently high rate to resolve small turbulent flow scales. In this paper, we show how a set of commercial acoustic and optical backscattering systems known as ADCPs, ADVs and OBSs, can be deployed and used in a complementary way to perform large-scale profilings of tidal current and SSC combined with high-resolution velocity and SSC measurements in the highly turbid near-bed zone. The experiment was done in the Gironde estuary (France) which is well known for its turbidity maximum zone characterized by high SSC values, above 1gl−1 near the surface. A first simple inversion method is proposed to convert the backscattered acoustic intensity measured with ADV into SSC data in the highly turbid near-bed zone. Near-bed SSC data from the OBS are used to compensate for the important acoustic sediment attenuation effect at an acoustic frequency of 6MHz. No a priori knowledge of acoustic backscattering properties of mud suspensions is required with this calibration procedure. We obtain an attenuation coefficient for mud suspensions of 0.28m2/kg at 6MHz leading to a good agreement between the SSC timeseries from the three ADV receivers and the OBS over the entire tidal cycle. The obtained SSC data are then analyzed with respect to the near-bed velocity, Reynolds shear stress and turbulent kinetic energy (TKE) timeseries in order to identify the relevant sediment transport processes during the tidal cycle. Significant differences in bed shear stress and TKE levels are found between ebb and flood stages with effects on near-bed sediment dynamics. During the ebb, maximum levels of tidal current, bed shear stress and TKE are associated with a reduction of near-bed sediment concentration (from 400kgm−3 down to 100kgm−3). Bed liquefaction process is assumed to occur at this moment with the presence of highly concentrated mud layer and a possible lutocline at a distance of less than 20cm above the bed. During the first 1.5h of flood, turbulent activity remains moderate. The near-bed flood current is then inhibited very abruptly while a sudden increase in SSC occurred above the bed. Assuming that the ADV is able to estimate relevant turbulent erosion fluxes, the co-located velocity and SSC are multiplied and compared with settling flux measurements made onboard under quiescent water conditions. The mean sediment settling fluxes (averaged over 3min) increase with SSC and are in relative good coherence with fluxes in quiescent water below the hindered regime, for SSC below 15gl−1. Reducing averaging time from 3min to 30s allows to increase the range of turbulent fluxes and SSC values, up to 99gl−1. At this scale, fluxes keep increasing quasi-linearly at higher SSC, suggesting the inhibition (delay or reduction) of the hindered settling regime as previously shown by from laboratory experiments. However, the 3-min averaged concentration field remained too low to conclude definitively on the effectiveness of such a process. Further analysis conducted at higher SSC regimes and under fully verified equilibrium are necessary. [Copyright &y& Elsevier]

During the 19th century oblique groynes were built in the bed of theLoire River, with the aim of channelling the river during low flow in order to maintain sufficient navigation conditions on a permanent basis. The long-term effect of these structures, in combination with massive sediment extraction over the past 50 years, has been to deepenthe minor bed and aggrade old flood-prone areas. The goal of the present study was to restore the original flood conveyance properties ofthe river bed. The methodological approach combined refined flow modelling using the TELEMAC-2D program with traditional morphological expertise. Justifications for making this choice over alternative methods are given. Constraints and objectives for site correction were determined by multidisciplinary analysis. In particular, this included an environmental analysis aimed at preserving the area's fauna and flora and at restoring its former ecological diversity. The analysis also concerned the hydromorphological behaviour of the system. Proposalsfor site corrections are described. These essentially involved modifying the structures and dredging in order to recover flow conditions whereby the secondary branches of the river bed would be self-maintaining. The main objective of lowering flood levels was thus achieved, together with some restoration of the ecological diversity of the river system. The study was an opportunity to compare a now well-established method for 1-D fluvial modelling with specific 2-D modelling aspects. It is an example of the progress that can be made by combining advanced modelling results with more traditional approaches. [ABSTRACT FROM AUTHOR]