scholarly journals Effects of storm events on the shelf-to-basin sediment transport in the southwestern end of the Gulf of Lions (Northwestern Mediterranean)

2011 ◽  
Vol 11 (3) ◽  
pp. 843-850 ◽  
Author(s):  
A. Palanques ◽  
P. Puig ◽  
J. Guillén ◽  
X. Durrieu de Madron ◽  
M. Latasa ◽  
...  
Keyword(s):  
Sediment Transport ◽  
Mediterranean Basin ◽  
Sediment Flux ◽  
Shelf Water ◽  
Storm Events ◽  
Deep Basin ◽  
Gulf Of Lions ◽  
Bottom Currents ◽  
Sediment Fluxes ◽  
Northwestern Mediterranean

Abstract. Shelf-to-basin sediment transport during storms was studied at the southwestern end of the Gulf of Lions from November 2003 to March 2004. Waves, near-bottom currents, temperature and sediment fluxes were measured on the inner shelf at 28-m depth, in the Cap de Creus submarine canyon head at 300-m depth and in the northwestern Mediterranean basin at 2350-m depth. This paper is a synthesis of results published separately in different papers; it includes some new data and focusses on the subject of storms. It is the first paper in which simultaneous data about the effect of storms on the shelf, the slope and in the basin are shown together. During the winter studied, there were two severe E-SE storms with significant wave heights ≥ 7 m: one in December 2003 and one in February 2004. During these storms, coastal water was exported off-shelf producing strong near-bottom currents (up to 82 cm s−1) at the canyon head that resuspended sediment and increased the downcanyon sediment fluxes by several orders of magnitude. The suspended sediment flux increase in the canyon head was much larger during the February storm than during the December storm. At the deep basin site, particle fluxes also increased drastically (1–2 orders of magnitude) immediately after the February storm but not after the December storm. The reason was that the February storm was reinforced by dense shelf water cascading and was long enough (43 h) to transfer large amounts of resuspended sediment from shallow shelf areas to the canyon head and from there to the northwestern Mediterranean basin. Thus, in the western Gulf of Lions, severe winter E-SE storms occurring during the dense shelf water cascading period can significantly increase the transfer to deep-sea (> 2000 m) environments of shelf and slope resuspended material, including anthropogenic contaminants and organic matter.

scholarly journals Sediment transport along the Cap de Creus Canyon flank during a mild, wet winter

2012 ◽  
Vol 9 (12) ◽  
pp. 18211-18252 ◽  
Author(s):  
J. Martín ◽  
X. Durrieu de Madron ◽  
P. Puig ◽  
F. Bourrin ◽  
A. Palanques ◽  
...  
Keyword(s):  
Particulate Matter ◽  
Sediment Transport ◽  
Transport Processes ◽  
Depth Range ◽  
Shelf Water ◽  
Head Region ◽  
Deep Basin ◽  
Remarkable Feature ◽  
The Impact ◽  
Southern Flank

Abstract. Cap de Creus Canyon (CCC) is known as a preferential conduit for particulate matter leaving the Gulf of Lion continental shelf towards the slope and the deep basin, particularly in winter when storms and dense shelf water cascading coalesce to enhance the seaward export of shelf waters. During the CASCADE (CAscading, Storm, Convection, Advection and Downwelling Events) cruise in March 2011, deployments of recording instruments within the canyon and vertical profiling of the water column properties were conducted to study with high spatial-temporal resolution the impact of such processes on particulate matter fluxes. In the context of a mild and wet 2010–2011 winter, no remarkable dense shelf water formation was observed. On the other hand, the experimental setup allowed to study the impact of E-SE storms on the hydrographical structure and the particulate matter fluxes in the CCC. The most remarkable feature in terms of sediment transport was a period of dominant E-SE winds from 12 to 16 March, including two moderate storms of significant wave heights = 4–4.5 m. During this period, a plume of freshened, relatively cold and turbid water flowed at high speeds along the southern flank of CCC in an approximate depth range of 150–350 m. The density of this water mass only reached ~ 28.78 kg m−3, indicating that it did not cascade into the canyon and that merely downwelled into it forced by the accumulation of seawater along the coast during the storms and by the subsequent strong cyclonic circulation induced over the shelf. Suspended sediment load in this turbid intrusion was comparable at three heights above bottom where turbidimeters were installed (10, 75 and 115 m above bottom) on the southern canyon flank and oscillated between 10 and 50 mg L−1. Current speeds were also comparable in the depth range profiled by ADCPs (40 to 150 mab) and reached values up to 90 cm s−1 during the peak of the strongest storm (13 March, Hs = 4.5 m). Sediment transport at 75 mab on the southern canyon flank was estimated at 1–1.5 t m−2 for the entire deployment while very close to the bottom (5 m above) in the canyon head it was less than 0.6 t m−2 during the same period. We provide a rough estimation of 105 t of sediment transported through the canyon along its southern wall during a 3 day-long period of storm-induced downwelling. Following the veering of the wind direction (from SE to NW) on 16 March, downwelling ceased, currents inside the canyon reversed from down to up-canyon, and the turbid shelf plume was evacuated from the canyon, most probably flowing along the southern canyon flank and being entrained by the general SW circulation after leaving the canyon confinement. This study highlights that remarkable sediment transport occurs in the CCC, and particularly along its southern flank, even during mild and wet winters, in absence of cascading and under limited external forcing. The sediment transport associated to eastern storms like the ones described in this paper tends to enter the canyon by its downstream flank, partially affecting the canyon head region. Sediment transport during these events is not constrained near the seafloor but distributed in a depth range of 200–300 m above the bottom. Our paper broadens the understanding of the complex set of atmosphere-driven sediment transport processes acting in this highly dynamic area of the northwestern Mediterranean Sea.

scholarly journals Tidal Asymmetry in Ocean-Boundary Flux and In-Estuary Trapping of Suspended Sediment Following Watershed Storms: San Francisco Estuary, California, USA

2021 ◽  
Author(s):  
Maureen A. Downing-Kunz ◽  
Paul A. Work ◽  
David H. Schoellhamer
Keyword(s):  
Suspended Sediment ◽  
San Francisco ◽  
Sediment Resuspension ◽  
San Francisco Estuary ◽  
Sediment Flux ◽  
Golden Gate ◽  
Storm Events ◽  
Suspended Sediment Flux ◽  
Field Campaigns ◽  
Ocean Boundary

AbstractSuspended-sediment flux at the ocean boundary of the San Francisco Estuary—the Golden Gate—was measured over a tidal cycle following peak watershed runoff from storms to the estuary in two successive years to investigate sediment transport through the estuary. Observations were repeated during low-runoff conditions, for a total of three field campaigns. Boat-based measurements of velocity and acoustic backscatter were used to calculate water and suspended-sediment flux at a location 1 km landward of the Golden Gate. Suspended-sediment concentration (SSC) and salinity data from up-estuary sensors were used to track watershed-sourced sediment plumes through the estuary. Estimates of suspended-sediment load from the watershed and net suspended-sediment flux for one up-estuary subembayment were used to infer in-estuary trapping of sediment. For both post-storm field campaigns, observations at the ocean boundary were conducted on the receding limb of the watershed hydrograph. At the ocean boundary, peak instantaneous suspended-sediment flux was tidally asymmetric and was greater on flood tides than on ebb tides for all three field campaigns, due to higher average SSC in the cross-section on flood tides. Shear-induced sediment resuspension was greater on flood tides and suggests the presence of an erodible pool outside the estuary. The storms in 2016 led to less export of discharge and sediment from the watershed and greater sediment trapping within one up-estuary subembayment compared to that observed in 2017. Results suggest that substantial trapping of watershed sediments occurred during both storm events, likely due to the formation of estuarine turbidity maxima (ETM) at different locations in the estuary. ETM locations were forced nearer the ocean boundary in 2017. Additional measurements and modeling are required to quantify the long-term sediment flux at the Golden Gate.

Mass balance controls on sediment scour and bedrock erosion in waterfall plunge pools

Geology ◽  
2021 ◽  
Author(s):  
Joel S. Scheingross ◽  
Michael P. Lamb
Keyword(s):  
Sediment Transport ◽  
Mass Balance ◽  
River Discharge ◽  
Sediment Load ◽  
Sediment Flux ◽  
Habitat Availability ◽  
Flux Divergence ◽  
Plunge Pool ◽  
Bedrock Erosion ◽  
Recurrence Intervals

Waterfall plunge pools experience cycles of sediment aggradation and scour that modulate bedrock erosion, habitat availability, and hazard potential. We calculate sediment flux divergence to evaluate the conditions under which pools deposit and scour sediment by comparing the sediment transport capacities of waterfall plunge pools (Qsc_pool) and their adjacent river reaches (Qsc_river). Results show that pools fill with sediment at low river discharge because the waterfall jet is not strong enough to transport the supplied sediment load out of the pool. As discharge increases, the waterfall jet strengthens, allowing pools to transport sediment at greater rates than in adjacent river reaches. This causes sediment scour from pools and bar building at the downstream pool boundary. While pools may be partially emptied of sediment at modest discharge, floods with recurrence intervals >10 yr are typically required for pools to scour to bedrock. These results allow new constraints on paleodischarge estimates made from sediment deposited in plunge pool bars and suggest that bedrock erosion at waterfalls with plunge pools occurs during larger floods than in river reaches lacking waterfalls.

scholarly journals Sediment transport to the deep canyons and open-slope of the western Gulf of Lions during the 2006 intense cascading and open-sea convection period

2012 ◽  
Vol 106 ◽  
pp. 1-15 ◽  
Author(s):  
A. Palanques ◽  
P. Puig ◽  
X. Durrieu de Madron ◽  
A. Sanchez-Vidal ◽  
C. Pasqual ◽  
...  
Keyword(s):  
Sediment Transport ◽  
Gulf Of Lions ◽  
Open Sea

Fluvial sediment fluxes response to modern climate change and human activities in the Tibetan Plateau and its margins

2021 ◽  
Author(s):  
Dongfeng Li ◽  
Xixi Lu ◽  
Ting Zhang
Keyword(s):  
Climate Change ◽  
Water Resources ◽  
Tibetan Plateau ◽  
Air Temperature ◽  
Human Activities ◽  
Sediment Flux ◽  
The Tibetan Plateau ◽  
Fluvial Sediment ◽  
Sediment Fluxes ◽  
Cold Environments

<p>Sediment flux in cold environments is a crucial proxy to link glacial, periglacial, and fluvial systems and highly relevant to hydropower operation, water quality, and the riverine carbon cycle. However, the long-term impacts of climate change and multiple human activities on sediment flux changes in cold environments remain insufficiently investigated due to the lack of monitoring and the complexity of the sediment cascade. Here we examine the multi-decadal changes in the in-situ observed fluvial sediment fluxes from two types of basins, namely, pristine basins and disturbed basins, in the Tibetan Plateau and its margins. The results show that the fluvial sediment fluxes in the pristine Tuotuohe headwater have substantially increased over the past three decades (i.e., a net increase of 135% from 1985–1997 to 1998–2017) due to the warming and wetting climate. We also quantify the relative impacts of air temperature and precipitation on the increases in the sediment fluxes with a novel attribution approach and finds that climate warming and intensified glacier-snow-permafrost melting is the primary cause of the increased sediment fluxes in the pristine cold environment (Tuotuohe headwater), with precipitation increase and its associated pluvial processes being the secondary driver. By contrast, the sediment fluxes in the downstream disturbed Jinsha River (southeastern margin of the Tibetan Plateau) exhibit a net increase of 42% from 1966-1984 to 1985-2010 mainly due to human activities such as deforestation and mineral extraction (contribution of 82%) and secondly because of climate change (contribution of 18%). Then the sediment fluxes dropped by 76% during the period of 2011-2015 because of the operations of six cascade reservoirs since 2010. In an expected warming and wetting climate for the region, we predict that the sediment fluxes in the pristine headwaters of the Tibetan Plateau will continue to increase throughout the 21st century, but the rising sediment fluxes from the Tibetan Plateau would be mostly trapped in its marginal reservoirs.</p><p>Overall, this work has provided the sedimentary evidence of modern climate change through robust observational sediment flux data over multiple decades. It demonstrates that sediment fluxes in pristine cold environments are more sensitive to air temperature and thermal-driven geomorphic processes than to precipitation and pluvial-driven processes. It also provides a guide to assess the relative impacts of human activities and climate change on fluvial sediment flux changes and has significant implications for water resources stakeholders to better design and manage the hydropower dams in a changing climate. Such findings may also have implications for other cold environments such as the Arctic, Antarctic, and other high mountainous basins.</p><p>Furthermore, this research is under the project of "Water and Sediment Fluxes Response to Climate Change in the Headwater Rivers of Asian Highlands" (supported by the IPCC and the Cuomo Foundation) and the project of "Sediment Load Responses to Climate Change in High Mountain Asia" (supported by the Ministry of Education of Singapore). Part of the results are also published in Li et al., 2018 Geomorphology, Li et al., 2020 Geophysical Research Letters, and Li et al., 2021 Water Resources Research.</p>

scholarly journals Theoretical Interpretation of the Exceptional Sediment Transport of Fine-grained Dispersal Systems Associated with Bedform Categories

2018 ◽  
Author(s):  
Tian Zhao ◽  
Qian Yu ◽  
Yunwei Wang ◽  
Shu Gao
Keyword(s):  
Sediment Transport ◽  
Regime Shift ◽  
Sedimentary Environment ◽  
Sediment Flux ◽  
Theoretical Interpretation ◽  
Fine Grained ◽  
Transport Regime ◽  
Source To Sink ◽  
Bed Roughness ◽  
Set Up

Abstract. Being a widespread source-to-sink sedimentary environment, the fine-grained dispersal system (FGDS) features remarkably high sediment flux, interacting closely with local morphology and ecosystem. Such exceptional transport is believed to be associated with changes in bedform geometry, which further demands theoretical interpretation. Using van Rijn (2007a) bed roughness predictor, we set up a simple numerical model to calculate sediment transport, classify sediment transport behaviors into dune and (mega-)ripple dominant regimes, and discuss the causes of the sediment transport regime shift linked with bedform categories. Both regimes show internally consistent transport behaviors, and the latter, associated with FGDSs, exhibits considerably higher sediment transport rate than the previous. Between lies the coexistence zone, the sediment transport regime shift accompanied by degeneration of dune roughness, which can considerably reinforce sediment transport and is further highlighted under greater water depth. This study can be applied to modeling of sediment transport and morphodynamics.

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