Caractéristiques hydrodynamiques d'un estran à forte sédimentation

1990 ◽  
Vol 17 (2) ◽  
pp. 148-155 ◽  
Author(s):  
Jean-Pierre Troude ◽  
Jean-Baptiste Sérodes
Keyword(s):  
Tidal Marsh ◽  
Drainage System ◽  
High Energy ◽  
Tidal Flats ◽  
Tidal Creeks ◽  
Lawrence Estuary ◽  
Strong Winds ◽  
St Lawrence Estuary ◽  
The Impact ◽  
The Mathematical Model

In the St. Lawrence estuary (Canada), tidal flats localized in the area of saline intrusion are covered with up to 30 cm of fine sedimentation during July, August, and September. This sedimentation is the result of waters coming from the turbidity zone. The upper half of the tidal flats are covered with a tidal marsh. This vegetation is very important in preventing the sediments from eroding. In the tidal marsh, measurements with automatic current meters were taken during periods longer than a month. These showed that, among the vegetation, currents are weak and steady during spring tides and neap tides, whereas next to the drainage systems, currents are heavily dependant on the range of the tide. Close to the shore, currents decrease significantly, thus helping fine sedimentation to occur. A mathematical simulation of the currents made on a line perpendicular to the shore shows the impact of the vegetation on the formation of the drainage system in the tidal flats. Water entrapment by the vegetation at the end of the flood initiates the creation of creeks and insures their continuity throughout the summer. As soon as the vegetation is destroyed, creeks fill up with sediments and disappear from the surface of the tidal marsh. Contrary to what could be assumed, the mathematical model also shows that spring tides, even though associated with strong currents, promote a very active sedimentation on the tidal marsh. In the St. Lawrence estuary, erosion of the mud flats deposits is observed during short periods of strong winds in summer. This high energy and high variability do explain the strong year to year variation in sedimentation observed in the tidal flats. Key words: currents, intertidal sedimentation, tidal creeks, tidal flats.

Tsunami modelling of the 7250 cal years BP Betsiamites submarine landslide

2018 ◽  
Vol 477 (1) ◽  
pp. 293-301 ◽  
Author(s):  
Dominique Turmel ◽  
Jacques Locat ◽  
Jonathan Leblanc ◽  
Geneviève Cauchon-Voyer
Keyword(s):  
Tsunami Wave ◽  
Submarine Landslide ◽  
Lawrence Estuary ◽  
Runout Distance ◽  
Tsunami Modelling ◽  
The North ◽  
St Lawrence Estuary ◽  
Short Time ◽  
The Impact ◽  
Very High

AbstractOn the north shore of the St Lawrence Estuary (Québec, Canada), near the Betsiamites river delta, a large sub-aerial submarine landslide complex was mapped using multi-beam bathymetry and light detection and ranging (LiDAR) data. Previous analysis of this landslide complex revealed that, since 7250 cal years BP, at least four different landsliding events occurred to form the present morphology, in which over 2 km3 of material have been mobilized. The 7.25 cal ka BP landslide is of particular interest here: this landslide is entirely submarine and mobilized about 1.3 km3 of material, deposited over an area of 54 km2, which make this landslide the largest identified on the St Lawrence estuary seafloor. This landslide showed a runout distance of about 15 km. Landslide-generated tsunamis may be triggered by such a landslide, where a large volume of material is mobilized in a short time. Kinematic analysis of this landslide was previously performed, and here we use these analyses in order to perform tsunami wave generation and propagation modelling. It is shown in this analysis that, even if the mobilized volume is very high and there is a long runout, the tsunami generated is small with tsunami wave amplitudes of <1.5 m, except in the vicinity of the landslide. The highest tide elevation in this part of the St Lawrence Estuary is about 5.5 m, so the impact of such a tsunami wave may be limited.

Mud Cracks and Polygons on Ice Push Ridges, in Tidal Flats of the St. Lawrence Estuary

1974 ◽  
Vol 11 (3) ◽  
pp. 489-494 ◽  
Author(s):  
Jean-Claude Dionne
Keyword(s):  
Water Level ◽  
Tidal Flats ◽  
The South ◽  
Lawrence Estuary ◽  
Waves And Currents ◽  
South Shore ◽  
Break Up ◽  
St Lawrence Estuary

Mud cracks and polygons form during summer in tidal flats of the south shore of the St. Lawrence Estuary. They occur near mean low water level at the top surface of ice push mud ridges formed during winter and break-up. They are a source of mud clasts which settle in the surroundings when carried away by waves and currents.

Forty Years of Change in the Bulrush Marshes of the St. Lawrence Estuary and The Impact of the Greater Snow Goose

Wetlands ◽  
2012 ◽  
Vol 32 (6) ◽  
pp. 1175-1188 ◽  
Author(s):  
Matthieu Allard ◽  
Richard A. Fournier ◽  
Marcelle Grenier ◽  
Josée Lefebvre ◽  
Jean-François Giroux
Keyword(s):  
Lawrence Estuary ◽  
Snow Goose ◽  
Greater Snow Goose ◽  
St Lawrence Estuary ◽  
The Impact

scholarly journals Tidally induced variations of pH at the head of the Laurentian Channel

2018 ◽  
Vol 75 (7) ◽  
pp. 1128-1141 ◽  
Author(s):  
Alfonso Mucci ◽  
Maurice Levasseur ◽  
Yves Gratton ◽  
Chloé Martias ◽  
Michael Scarratt ◽  
...  
Keyword(s):  
Water Column ◽  
Surface Waters ◽  
Field Measurements ◽  
Tidal Mixing ◽  
Lawrence Estuary ◽  
Saguenay Fjord ◽  
Physical And Chemical Variables ◽  
The Difference ◽  
St Lawrence Estuary ◽  
The Impact

The head of the Laurentian Channel is a very dynamic region of exceptional biological richness. To evaluate the impact of freshwater discharge, tidal mixing, and biological activity on the pH of surface waters in this region, a suite of physical and chemical variables was measured throughout the water column over two tidal cycles. The relative contributions to the water column of the four source-water types that converge in this region were evaluated using an optimum multiparameter algorithm (OMP). Results of the OMP analysis were used to reconstruct the water column properties assuming conservative mixing, and the difference between the model properties and field measurements served to identify factors that control the pH of the surface waters. These surface waters are generally undersaturated with respect to aragonite, mostly due to the intrusion of waters from the Upper St. Lawrence Estuary and the Saguenay Fjord. The presence of a cold intermediate layer impedes the upwelling of the deeper, hypoxic, lower pH and aragonite-undersaturated waters of the Lower St. Lawrence Estuary to depths shallower than 50 m.

Polished and Striated Mud Surfaces in the St. Lawrence Tidal Flats, Quebec

1974 ◽  
Vol 11 (6) ◽  
pp. 860-866 ◽  
Author(s):  
Jean-Claude Dionne
Keyword(s):  
Shallow Water ◽  
Sedimentary Rocks ◽  
Tidal Flats ◽  
Tidal Currents ◽  
Cold Environment ◽  
Current Direction ◽  
Lawrence Estuary ◽  
St Lawrence Estuary

Drift ice polishes and striates the surface of mud tidal flats along the St. Lawrence Estuary. Drag marks are due to tidal currents dragging ice cakes on the bottom. Striated and polished mud surfaces can be fossilized and preserved. If found in consolidated sedimentary rocks, they would be indicators of: the top of a bed, current direction, shallow water, and a cold environment.

scholarly journals Impact of anthropogenic pH perturbation on dimethyl sulfide cycling

Elem Sci Anth ◽  
2021 ◽  
Vol 9 (1) ◽  
Author(s):  
Robin Bénard ◽  
Martine Lizotte ◽  
Maurice Levasseur ◽  
Michael Scarratt ◽  
Sonia Michaud ◽  
...  
Keyword(s):  
Chlorophyll A ◽  
Atmospheric Chemistry ◽  
Dimethyl Sulfide ◽  
Phytoplankton Bloom ◽  
Lawrence Estuary ◽  
Chlorophyll A Concentration ◽  
Pco2 Treatment ◽  
St Lawrence Estuary ◽  
Scavenging Efficiency ◽  
The Impact

The objective of this study was to assess experimentally the potential impact of anthropogenic pH perturbation (ApHP) on concentrations of dimethyl sulfide (DMS) and dimethylsulfoniopropionate (DMSP), as well as processes governing the microbial cycling of sulfur compounds. A summer planktonic community from surface waters of the Lower St. Lawrence Estuary was monitored in microcosms over 12 days under three pCO2 targets: 1 × pCO2 (775 µatm), 2 × pCO2 (1,850 µatm), and 3 × pCO2 (2,700 µatm). A mixed phytoplankton bloom comprised of diatoms and unidentified flagellates developed over the course of the experiment. The magnitude and timing of biomass buildup, measured by chlorophyll a concentration, changed in the 3 × pCO2 treatment, reaching about half the peak chlorophyll a concentration measured in the 1 × pCO2 treatment, with a 2-day lag. Doubling and tripling the pCO2 resulted in a 15% and 40% decline in average concentrations of DMS compared to the control. Results from 35S-DMSPd uptake assays indicated that neither concentrations nor microbial scavenging efficiency of dissolved DMSP was affected by increased pCO2. However, our results show a reduction of the mean microbial yield of DMS by 34% and 61% in the 2 × pCO2 and 3 × pCO2 treatments, respectively. DMS concentrations correlated positively with microbial yields of DMS (Spearman’s ρ = 0.65; P &lt; 0.001), suggesting that the impact of ApHP on concentrations of DMS in diatom-dominated systems may be strongly linked with alterations of the microbial breakdown of dissolved DMSP. Findings from this study provide further empirical evidence of the sensitivity of the microbial DMSP switch under ApHP. Because even small modifications in microbial regulatory mechanisms of DMSP can elicit changes in atmospheric chemistry via dampened efflux of DMS, results from this study may contribute to a better comprehension of Earth’s future climate.

Sign in / Sign up

Export Citation Format

Share Document