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sediment
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{{short description|Particulate solid matter that is deposited on the surface of land}}File:Cobbles Nash Point.jpg|thumb|{{center|Cobbles on a beach}}]]File:Leman img 0573.jpg|thumb|upright|River Rhône flowing into Lake Geneva. Sediments make the water appear brownish-grey; they are an indicator of increased water runoff, land degradation, erosionerosionSediment is a naturally occurring material that is broken down by processes of weathering and erosion, and is subsequently transported by the action of wind, water, or ice or by the force of gravity acting on the particles. For example, sand and silt can be carried in suspension in river water and on reaching the sea bed deposited by sedimentation. If buried, they may eventually become sandstone and siltstone (sedimentary rocks) through lithification.Sediments are most often transported by water (fluvial processes), but also wind (aeolian processes) and glaciers. Beach sands and river channel deposits are examples of fluvial transport and deposition, though sediment also often settles out of slow-moving or standing water in lakes and oceans. Desert sand dunes and loess are examples of aeolian transport and deposition. Glacial moraine deposits and till are ice-transported sediments.

Classification

File:Sediment in the Gulf of Mexico.jpg|thumb|Sediment in the Gulf of MexicoGulf of MexicoFile:Sediment off the Yucatan Peninsula.jpg|thumb|Sediment off the Yucatán PeninsulaYucatán PeninsulaSediment can be classified based on its grain size or composition.

Grain size

{{see also|soil texture|Unified Soil Classification System}}Sediment size is measured on a log base 2 scale, called the "Phi" scale, which classifies particles by size from "colloid" to "boulder". {| class="wikitable"! φ scale !! Size range(metric) !! Size range(inches) !! Aggregate class(Wentworth) !! Other names
256 mm > 10.1 in >| Boulder
Cobble (geology)>Cobble
gravel >| Pebble
| Pebble
| Pebble
| Pebble
Granule (geology)>Granule
| Very coarse sand
| Coarse sand
| Medium sand
micrometre>µm 0.0049–0.010 in Fine sand
| Very fine sand
Silt >| Mud
8 >Clay >| Mud
10 >Colloid >| Mud

Composition

Composition of sediment can be measured in terms of: This leads to an ambiguity in which clay can be used as both a size-range and a composition (see clay minerals).

Sediment transport

(File:StoneFormationInWater.jpg|thumb|Sediment builds up on human-made breakwaters because they reduce the speed of water flow, so the stream cannot carry as much sediment load.)(File:Glacial Transportation and Deposition.jpg|thumb|Glacial transport of boulders. These boulders will be deposited as the glacier retreats.){{see also|Rouse number}}Sediment is transported based on the strength of the flow that carries it and its own size, volume, density, and shape. Stronger flows will increase the lift and drag on the particle, causing it to rise, while larger or denser particles will be more likely to fall through the flow.

Fluvial processes: rivers, streams, and overland flow

Particle motion

Rivers and streams carry sediment in their flows. This sediment can be in a variety of locations within the flow, depending on the balance between the upwards velocity on the particle (drag and lift forces), and the settling velocity of the particle. These relationships are shown in the following table for the Rouse number, which is a ratio of sediment fall velocity to upwards velocity.textbf{Rouse}=frac{text{Settling velocity}}{text{Upwards velocity from lift and drag}}=frac{w_s}{kappa u_*}where File:Hjulströms diagram en.PNG|thumb|{{center|(Hjulström curve]]: The velocities of currents required for erosion, transportation, and deposition (sedimentation) of sediment particles of different sizes.}}){| class="wikitable" style="background:#efefef;"!Mode of Transport!Rouse Number
|Bed load|>2.5
|Suspended load: 50% Suspended|>1.2, 0.8,

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- time: 9:28pm EDT - Tue, Aug 20 2019
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