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Encyclopedia > Sediment

Sediment is any particulate matter that can be transported by fluid flow and which eventually is deposited as a layer of solid particles on the bed or bottom of a body of water or other liquid. Sedimentation is the deposition by settling of a suspended material. This article or section should be merged with Fluid mechanics Fluid dynamics is the study of fluids (liquids and gases) in motion, and the effect of the fluid motion on fluid boundaries, such as solid containers or other fluids. ... Settling is the process by which particulates settle to the bottom of a liquid and form a sediment. ... This article or section is in need of attention from an expert on the subject. ...

Sediment builds up on human-made breakwaters because they reduce the speed of water flow, so the stream cannot carry as much sediment load.
Glacial transport of boulders. These boulders will be deposited as the glacier retreats.

Seas, oceans, and lakes accumulate sediment over time. These materials can be terrestrial (deposited on the land) or marine (deposited in the ocean); terrigenous deposits originate on land, but may be deposited in either terrestrial, marine, or lacustrine (lake) environments. Deposited sediments are the source of sedimentary rocks, which can contain fossils of the inhabitants of the body of water that were, upon death, covered by accumulating sediment. Lake bed sediments that have not solidified into rock can be used to determine past climatic conditions. Sea as seen from jetty in Frankston, Australia Look up maritime in Wiktionary, the free dictionary. ... Animated map exhibiting the worlds oceanic waters. ... A man-made lake in Keukenhof, Netherlands A lake is a body of water or other liquid of considerable size contained on a body of land. ... This article or section does not cite any references or sources. ... FOSSIL is a standard for allowing serial communication for telecommunications programs under DOS. FOSSIL is an acronym for Fido Opus Seadog Standard Interface Layer. ...

### Rivers and streams

For a fluid to begin transporting sediment, the bed shear stress exerted by the fluid must exceed the critical shear stress of the bed. Once this critical stress is exceeded, the way in which the sediment is transported depends on the characteristics of the sediment and the fluid. If a fluid, such as water, is flowing, it can carry suspended particles. The settling velocity is the minimum velocity a flow must have in order to transport, rather than deposit, sediments, and (for a dilute suspension) is given by Stoke's Law: Impact from a water drop causes an upward rebound jet surrounded by circular capillary waves. ... This article or section is in need of attention from an expert on the subject. ... Settling is the process by which particulates settle to the bottom of a liquid and form a sediment. ...

$w=frac{2(rho_p-rho_f)gr^2}{9mu}$

where w is the settling velocity, ρ is density (the subscripts p and f indicate particle and fluid respectively), g is the acceleration due to gravity, r is the radius of the particle and μ is the dynamic viscosity of the fluid. This equation is only valid for particle Reynold's numbers <1. The Reynolds number is the most important dimensionless number in fluid dynamics and provides a criterion for determining dynamic similitude. ...

If the flow velocity is greater than the settling velocity, sediment will be transported downstream as suspended load. As there will always be a range of different particle sizes in the flow, some will have sufficiently large diameters that they settle on the river or stream bed, but still move downstream. This is known as bed load and the particles are transported via such mechanisms as saltation (jumping up into the flow, being transported a short distance then settling again), rolling and sliding. Saltation marks are often preserved in solid rocks and can be used to estimate the flow rate of the rivers that originally deposited the sediments.

Early applications of mathematical modeling of sediment transport in riverine systems were observed in the late 1970s. One such application was conducted by Santa Cruz County for the San Lorenzo River to study erosion from surface runoff and the resulting turbidity and bedload transport to downstream reaches. This work was used to analyze effects of land use practices in this drainage basin. Note: The term model is also given a formal meaning in model theory, a part of axiomatic set theory. ... Santa Cruz County is a county located on the Pacific coast of the U.S. state of California, just south of the San Francisco Bay Area, it forms the northern coast of the Monterey Bay. ... The San Lorenzo River is the main river running through Santa Cruz, California. ... Severe soil erosion in a wheat field near Washington State University, USA. For erosion as an operation of Mathematical morphology, see Erosion (morphology) Erosion is displacement of solids (soil, mud, rock and other particles) by the agents of ocean currents, wind, water, or ice by downward or down-slope movement... Runoff flowing into a stormwater drain Surface runoff is water, from rain, snowmelt, or other sources, that flows over the land surface, and is a major component of the water cycle[1][2]. Runoff that occurs on surfaces before reaching a channel is also called overland flow. ... Turbidity standards of 5, 50, and 500 NTU Turbidity is a cloudiness or haziness of water (or other fluid) caused by individual particles (suspended solids) that are generally invisible to the naked eye, thus being much like smoke in air. ...

One of the main causes of riverine sediment load siltation stems from slash and burn treatment of tropical forests. When the ground surface is stripped of vegetation and then seared of all living organisms, the upper soils are vulnerable to both wind and water erosion. In a number of regions of the earth, entire sectors of a country have been rendered erosive; for example, on the Madagascar high central plateau, comprising approximately ten percent of that country's land area, virtually the entire landscape is sterile of vegetation, with gully erosive furrows typically in excess of 50 meters deep and one kilometer wide. Shifting cultivation is a farming system which sometimes incorporates the slash and burn method in some regions of the world. The resulting sediment load in rivers flowing to the west is ongoing, with most rivers a dark red brown colour, also leading to massive fish kills. Assarting in Finland in 1892 Slash and burn (a specific practice that may be part of shifting cultivation or swidden-fallow agriculture) is an agricultural procedure widely used in forested areas. ... The tropics are the geographic region of the Earth centered on the equator and limited in latitude by the two tropics: the Tropic of Cancer in the north and the Tropic of Capricorn in the southern hemisphere. ... Temperate rainforest on Northern Slopes of the Alborz mountain ranges, Iran A dense growth of softwoods (a conifer forest) in the Sierra Nevada Range of Northern California A deciduous broadleaf (Beech) forest in Slovenia. ... Image:NONE Monte Roraima In geology and earth science, a plateau, also called a high plateau or tableland, is an area of highland, usually consisting of relatively flat rural area. ... Vegetation is a general term for the plant life of a region; it refers to the ground cover provided by plants, and is, by far, the most abundant biotic element of the biosphere. ... Shifting cultivation is an agricultural system in which a person uses a piece of land, only to abandon or alter the initial use a short time later. ... Assarting in Finland in 1892 Slash and burn (a specific practice that may be part of shifting cultivation or swidden-fallow agriculture) is an agricultural procedure widely used in forested areas. ...

### Surface runoff

Surface runoff water can pick up soil particles and transport them in overland flow for deposition at a lower land elevation or deliver that sediment to receiving waters. In this case the sediment is usually deemed to result from erosion. If the initial impact of rain droplets dislodges soil, the phenomenon is called splash erosion". If the effects are diffuse for a larger area and the velocity of moving runoff is responsible for sediment pickup, the effect is called "sheet erosion". If there are massive gouges in the earth from high velocity flow for uncovered soil, then "gully erosion" may result. Runoff flowing into a stormwater drain Surface runoff is water, from rain, snowmelt, or other sources, that flows over the land surface, and is a major component of the water cycle[1][2]. Runoff that occurs on surfaces before reaching a channel is also called overland flow. ...

#### Fluvial bedforms

Any particle that is larger in diameter than approximately 0.7 mm will form visible topographic features on the river or stream bed. These are known as and include ripples, dunes, plane beds and antidunes. See bedforms for more detail. Again, bedforms are often preserved in sedimentary rocks and can be used to estimate the direction and magnitude of the depositing flow. The bed of this stream is made up of rocks, some very rounded (having had a longer life in the stream) and some not. ...

#### Key depositional environments

The major fluvial (river and stream) environments for deposition of sediments include:

1. Deltas (arguably an intermediate environment between fluvial and marine)
2. Point-bars
3. Alluvial fans
4. Braided rivers
5. Oxbow lakes
6. Levees

Nile River delta, as seen from Earth orbit. ... Alluvial Fan in Death Valley An alluvial fan is a fan-shaped deposit formed where a fast flowing stream flattens, slows, and spreads typically at the exit of a canyon onto a flatter plain. ... The speedy deletion of this page is contested. ... Songhua River, northeast China. ... It has been suggested that this article or section be merged with Dike (construction). ...

## Shores and shallow seas

The second major environment where sediment may be suspended in a fluid is in seas and oceans. The sediment could consist of terrigenous material supplied by nearby rivers and streams or reworked marine sediment (e.g. sand). In the mid-ocean, living organisms are primarily responsible for the sediment accumulation, their shells sinking to the ocean floor upon death. Patterns in the sand Sand is a granular material made up of fine rock particles. ...

#### Key depositional environments

The major areas for deposition of sediments in the marine environment include:

1. Littoral sands (e.g. beach sands, runoff river sands, coastal bars and spits, largely clastic with little faunal content)
2. The continental shelf (silty clays, increasing marine faunal content).
3. The shelf margin (low terrigenous supply, mostly calcareous faunal skeletons)
4. The shelf slope (much more fine-grained silts and clays)
5. Beds of estuaries with the resultant deposits called "bay mud".

One other depositional environment which is a mixture of fluvial and marine is the turbidite system, which is a major source of sediment to the deep sedimentary and abyssal basins as well as the deep oceanic trenches. A littoral is the region near the shoreline of a body of fresh or salt water. ... This article or section does not cite any references or sources. ... Silt is soil or rock derived granular material of a specific grain size. ... The Gay Head cliffs in Marthas Vineyard are made almost entirely of clay. ... Doubly refracting Calcite from Iceberg claim, Dixon, New Mexico. ... Richardson Bay mudflats of are exposed layers of bay mud Bay mud consists of thick deposits of soft, unconsolidated silty clay, which is saturated with water; these soil layers are situated at the bottom of certain estuaries, which are normally in temperate regions that have experienced cyclical glacial cycles. ... USGS image Turbidite geological formations have their origins in turbidity current deposits, deposits from a form of underwater avalanche that are responsible for distributing vast amounts of clastic sediment into the deep ocean. ... The term sedimentary basin is used to refer to any geographical feature exhibiting subsidence and consequent infilling by sedimentation. ... Abyssal plains are flat or very gently sloping areas of the deep ocean basin floor. ... The oceanic trenches are hemispheric-scale long but narrow topographic depressions of the sea floor. ...

Results from FactBites:

 Sediment - Wikipedia, the free encyclopedia (944 words) Sediment is any particulate matter that can be transported by fluid flow and which eventually is deposited as a layer of solid particles on the bed or bottom of a body of water or other liquid. Deposited sediments are the source of sedimentary rocks, which can contain fossils of the inhabitants of the body of water that were, upon death, covered by accumulating sediment. One other depositional environment which is a mixture of fluvial and marine is the turbidite system, which is a major source of sediment to the deep sedimentary and abyssal basins as well as the deep oceanic trenches.
 Water Resource Characterization DSS - Sediment (2198 words) Sediments are classified into four broad categories, according to their origin in relation to the basin of water in which they are deposited: extrabasinal, carbonaceous, pyroclastic, and intrabasinal. Sediment introduced into surface water is either deposited on the bed of the stream or lake or suspended in the water column (suspended load). Sediment may also be eroded from stream banks during high flows or resuspended from the substrate by changes of speed or direction of the water current.
More results at FactBites »

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