An introduction to the geological significance of sediment transport and accumulation on the Amazon continental shelf

Nittrouer, Charles A.; Kuehl, Steven A.; Sternberg, Richard W.; Figueiredo, Alberto G.; Faria, L. Ercilio C.

doi:10.1016/0025-3227(95)00075-a

Cited by 132 publications

(75 citation statements)

References 30 publications

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“…About 200-300 Mt yr -1 of muddy Amazon sediment is transported northwestward along the Atlantic continental shelf toward the Guyana and Venezuela coast 33 . These sediments provide substrate and nutrients for the largest preserved mangrove region of South America that spans Marajo Island, the coastline of Pará and Amapá states, Brazil, and the Guianas.…”

Section: The Main-stem Amazon System and The Amazon Sediment Plumementioning

confidence: 99%

Damming the rivers of the Amazon basin

Latrubesse

Arima

Dunne

et al. 2017

Nature

638

473

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SummaryMore than 100 hydropower dams have already been built in the Amazon basin and numerous proposals for further dam constructions are under consideration. The accumulated negative environmental effects of built and proposed dams, if constructed, will trigger massive hydrophysical and biotic disturbances that will impact the Amazon basin's floodplains, estuary, and sediment plume. By introducing a Dam Environmental Vulnerability Index (DEVI) we quantify the current and potential impacts of dams in the basin. The scale of foreseeable environmental degradation indicates the need for collective action among nations and states to avoid cumulative, far-field impacts. We suggest institutional innovations to assess and avoid the likely impoverishment of Amazon rivers.

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Section: The Main-stem Amazon System and The Amazon Sediment Plumementioning

confidence: 99%

Damming the rivers of the Amazon basin

Latrubesse

Arima

Dunne

et al. 2017

Nature

638

473

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show abstract

“…The ungauged regions, which include tidal rivers (i.e., freshwater but tidally varying) and their floodplains, deltas, estuaries, and nearshore zones, likely trap great amounts of sediment [Milliman and Farnsworth, 2011]. In large rivers, these areas may sequester about one third of the reported sediment discharge (Amazon [Nittrouer et al, 1995;Mertes et al, 1996;Dunne et al, 1998]; Ganges-Brahmaputra [Goodbred and Kuehl, 1998]; Changjiang [Milliman et al, 1985]). These ungauged environments are extensive, and a considerable portion of sediment transported in them does not reach the continental shelf.…”

Section: Introductionmentioning

confidence: 99%

Sediment dynamics in the lowerMekongRiver: Transition from tidal river to estuary

et al. 2015

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A better understanding of flow and sediment dynamics in the lowermost portions of large‐tropical rivers is essential to constraining estimates of worldwide sediment delivery to the ocean. Flow velocity, salinity, and suspended‐sediment concentration were measured for 25 h at three cross sections in the tidal Song Hau distributary of the Mekong River, Vietnam. Two campaigns took place during comparatively high‐seasonal and low‐seasonal discharge, and estuarine conditions varied dramatically between them. The system transitioned from a tidal river with ephemeral presence of a salt wedge during high flow to a partially mixed estuary during low flow. The changing freshwater input, sediment sources, and estuarine characteristics resulted in seaward sediment export during high flow and landward import during low flow. The Dinh An channel of the Song Hau distributary exported sediment to the coast at a rate of about 1 t s−1 during high flow and imported sediment in a spatially varying manner at approximately 0.3 t s−1 during low flow. Scaling these values results in a yearly Mekong sediment discharge estimate about 65% smaller than a generally accepted estimate of 110 Mt yr−1, although the limited temporal and spatial nature of this study implies a relatively high degree of uncertainty for the new estimate. Fluvial advection of sediment was primarily responsible for the high‐flow sediment export. Exchange‐flow and tidal processes, including local resuspension, were principally responsible for the low‐flow import. The resulting bed‐sediment grain size was coarser and more variable during high flow and finer during low, and the residual flow patterns support the maintenance of mid‐channel islands.

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“…Studies of modem clinoforms in deltaic depositional systems [e.g., Kuehl et al, 1986Kuehl et al, , 1989Wright et al, 1988Wright et al, , 1990Alexander et al, 1991;Nittrouer et al, 1995Nittrouer et al, , 1996Nittrouer and DeMaster, 1996] revealed that clinoform shape and growth patterns are determined to a large extent by the spatial and temporal distribution of energy in the water column. The hydrodynamic characteristics of the water column and the resulting sediment dispersal patterns ultimately determine the shape of the sedimentation rate profile across the clinoform surface.…”

mentioning

confidence: 99%

Clinoform development by advection‐diffusion of suspended sediment: Modeling and comparison to natural systems

Pirmez¹,

Pratson²,

Steckler³

1998

J. Geophys. Res.

198

228

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Abstract. Clinoforms are the building blocks of prograding stratigraphic sequences. These sigmoid-shaped surfaces can be found forming today on modem deltas. Sedimentation rate profiles over the clinoform surface of these deltas show low rates of sediment accumulation on both topset and bottomset regions, with a maximum accumulation rate on the upper foreset region. We present a model for the formation of clinoforms that relies on the interpretation of modem clinoform sedimentation as a result of the distribution of shear stresses at the mouth of a river. Model clinoform surfaces are generated using an equation for the conservation of suspended sediment concentration, together with a conservation of fluid equation for simple time-averaged flow velocity fields. In the model, suspended sediment is advected horizontally into a basin, and gravitational settling of sediment particles is counteracted by vertical turbulent diffusion. In shallow water, shear stresses are too large to allow deposition, and sediment bypasses the topset region. With increasing water depth, near-bed shear stresses decrease, and sediment is allowed to deposit at the foreset region, with gradually decreasing rates toward deeper water. This sedimentation pattern leads to progradation of the clinoform surfaces through time. The clinoform surfaces produced by the model capture the fundamental morphological characteristics of natural clinoforms. These include the gradual slope rollover at the topset and bottomset, steeper foreset slopes with increased grain size, and an increase in foreset slope through time as clinoforms prograde into deeper water. Because the parameters controlling the model clinoforms have a direct relation to physical quantities that can be measured in natural systems, the model is an important step toward unraveling the physical processes associated with these deposits.

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An introduction to the geological significance of sediment transport and accumulation on the Amazon continental shelf

Cited by 132 publications

References 30 publications

Damming the rivers of the Amazon basin

Damming the rivers of the Amazon basin

Sediment dynamics in the lowerMekongRiver: Transition from tidal river to estuary

Clinoform development by advection‐diffusion of suspended sediment: Modeling and comparison to natural systems

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