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. Fluid dynamics is the sub-discipline of Fluid mechanics dealing with fluid flow: Fluids ( Liquids and Gases in motion Sedimentation is the deposition by settling of a suspended material. Settling is the process by which particulates settle to the bottom of a liquid and form a Sediment. In Chemistry, A suspension is a Heterogenous fluid containing Solid particles that are sufficiently large for Sedimentation.
Sediments are also transported by wind (aeolian processes) and glaciers. Aeolian (or Eolian or Æolian) processes pertain to the activity of the Winds and more specifically to the winds' ability to shape the surface of the "Glacial" and "Glaciation" redirect here For the geological periods see Glacial period. Desert sand dunes and loess are examples of aeolian transport and deposition. A desert is a Landscape or region that receives very little precipitation. In physical Geography, a dune is a Hill of Sand built by Aeolian processes. Loess is a homogeneous typically non stratified porous Friable,slightly coherent often calcareous fine-grained Silty pale yellow or buff windblown ( aeolian Glacial moraine deposits and till are ice transported sediments. "Glacial" and "Glaciation" redirect here For the geological periods see Glacial period. Moraine refers to any glacially formed accumulation of unconsolidated glacial debris (soil and rock which can occur in currently glaciated and formerly glaciated regions such as those Till is unsorted glacial sediment Glacial drift is a general term for the coarsely graded and extremely heterogeneous Sediments of glacial origin Simple gravitational collapse also creates sediments such as talus and mountainslide deposits as well as karst collapse features. Karst topography is a landscape shaped by the dissolution of a layer or layers of soluble Bedrock, usually Carbonate rock such as Limestone Each sediment type has different settling velocities, depending on size, volume, density, and shape.
Seas, oceans, and lakes accumulate sediment over time. This article is about the body of water For other uses see SEA and Seas. An ocean (from Greek, ''Okeanos'' (Oceanus) is a major body of saline water, and a principal component of the Hydrosphere. A lake (from Latin lacus) is a Terrain feature (or Physical feature) a body of Liquid on the surface of a world that is localized to the 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. Sedimentary rock is one of the three main rock types (the others being igneous and Metamorphic rock) FOSSIL is a standard protocol for allowing serial communication for Telecommunications programs under the DOS Operating system. Lake bed sediments that have not solidified into rock can be used to determine past climatic conditions. Climate encompasses the temperatures humidity rainfall atmospheric particle count and numerous other meteorogical factors in a given region over long periods of
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Sediment transport
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. Water is a common Chemical substance that is essential for the survival of all known forms of Life. In Chemistry, A suspension is a Heterogenous fluid containing Solid particles that are sufficiently large for Sedimentation. 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 Stokes' Law:
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. Settling is the process by which particulates settle to the bottom of a liquid and form a Sediment. This equation is only valid for particle Reynold's numbers <1. In Fluid mechanics and Heat transfer, the Reynolds number \mathrm{Re} is a Dimensionless number that gives a measure of the Ratio
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.
The overall balance between sediment in transport and sediment being deposited on the bed is given by the Exner equation. Introduction The Exner equation is a statement of Conservation of mass that applies to Sediment in a Fluvial system such as a This equation is important in that changes in flow depth and slope (see: depth-slope product) will change the basal shear stress, thus causing local areas of erosion and deposition. A shear stress, denoted \tau\ ( Tau) is defined as a stress which is applied Parallel or tangential to a face of a material More large-scale changes such as dam emplacement and removal and sea-level variation change Base level and cause the river to either pool (and deposit its entire load) or rapidly erode into its underlying substrate. The base level of a River or Stream is the lowest point to which it can flow often referred to as the 'mouth' of the river
Early applications of mathematical modeling of sediment transport in riverine systems were observed in the late 1970s. Note The term model has a different meaning in Model theory, a branch of Mathematical logic. 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. Santa Cruz County is a county located on the Pacific coast of the U The San Lorenzo River drains a large watershed in Santa Cruz County California. Erosion is the carrying away or displacement of solids ( Sediment, Soil, rock and other particles usually by the agents of currents such as wind Surface runoff is a term used to describe when soil is infiltrated to full capacity and excess Water, from Rain, Snowmelt, or other sources flows Turbidity is the cloudiness or haziness of a fluid caused by individual particles ( suspended solids) that are generally invisible to the Naked eye This work was used to analyze effects of land use practices in this drainage basin.
One of the main causes of riverine sediment load siltation stems from slash and burn treatment of tropical forests. Slash and burn consists of cutting and burning of Forests or Woodlands to create fields for Agriculture or Pasture for Livestock, or The Tropics are centered on the Equator and limited in Latitude by the Tropic of Cancer in the northern hemisphere at approximately 23°26' (23 A forest is an area with a high density of Trees There are many definitions of a forest based on various criteria 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. Madagascar, or Republic of Madagascar (older name Malagasy Republic) is an Island nation in the Indian Ocean off the southeastern In Geology and Earth science, a plateau, also called a high plateau or tableland, is an area of highland, usually consisting Vegetation is a general term for the plant life of a region it refers to the Ground cover provided by plants Shifting cultivation is a farming system which sometimes incorporates the slash and burn method in some regions of the world. For methods see Slash and burn Shifting cultivation is an Agricultural system in which plots of land are cultivated temporarily then abandoned Slash and burn consists of cutting and burning of Forests or Woodlands to create fields for Agriculture or Pasture for Livestock, or 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.
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. Surface runoff is a term used to describe when soil is infiltrated to full capacity and excess Water, from Rain, Snowmelt, or other sources flows 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.
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. A stream bed is the channel bottom of a Stream or River or creek the physical confine of the normal water flow 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.
Key depositional environments
The major fluvial (river and stream) environments for deposition of sediments include:
- Deltas (arguably an intermediate environment between fluvial and marine)
- Point-bars
- Alluvial fans
- Braided rivers
- Oxbow lakes
- Levees
Shores and shallow seas
The second major environment where sediment may be suspended in a fluid is in seas and oceans. A delta is a Landform where the mouth of a River flows into an Ocean, Sea, Estuary, Lake or another river 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 Not to be confused with the River Braid Ballymena, Northern Ireland. An oxbow lake is a U-shaped lake water body formed when a wide Meander from the mainstem of a River is cut off to create a lake Dike (constructionEmbankmentA levee, levée, dike (or dyke) embankment, floodbank or stopbank is a natural or artificial The sediment could consist of terrigenous material supplied by nearby rivers and streams or reworked marine sediment (e. g. sand). Sand is a naturally occurring Granular material composed of finely divided rock and Mineral particles In the mid-ocean, living organisms are primarily responsible for the sediment accumulation, their shells sinking to the ocean floor upon death.
Marine bedforms
Marine environments also see the formation of bedforms, whose characteristics are influenced by the tides or currents. Characteristics A tide is a repeated cycle of sea level changes in the following stages Over several hours the water rises or advances up a beach in the flood
Key depositional environments
The major areas for deposition of sediments in the marine environment include:
- Littoral sands (e. Littoral refers to the coast of an ocean or sea or to the banks of a river lake or estuary g. beach sands, runoff river sands, coastal bars and spits, largely clastic with little faunal content)
- The continental shelf (silty clays, increasing marine faunal content). Sedimentary rock is one of the three main rock types (the others being igneous and Metamorphic rock) Silt is Soil or rock derived Granular material of a Grain size between sand and clay Clay is a naturally occurring material composed primarily of fine-grained Minerals which show plasticity through a variable range of Water content, and
- The shelf margin (low terrigenous supply, mostly calcareous faunal skeletons)
- The shelf slope (much more fine-grained silts and clays)
- Beds of estuaries with the resultant deposits called "bay mud". Calcite is a carbonate mineral and the most stable polymorph of Calcium carbonate ( Ca[[carbon C]] O 3 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
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. Turbidite Geological formations have their origins in Turbidity current deposits, which are deposits from a form of underwater Avalanche that 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
See also
- Beach cusps
- Biorhexistasy
- Bioswale
- Decantation
- Erosion
- Exner equation
- Gravel bar
- Particle size
- Regolith
- Sand
- Sedimentary depositional environment
- Settling
- Surface runoff
References
Donald R. The Theory of Biorhexistasy describes climatic conditions necessary for periods of soil formation ( Pedogenesis) separated by periods of Soil erosion. Bioswales are landscape elements designed to remove Silt and Pollution from Surface runoff water Decantation is a process for the Separation of mixtures carefully pouring a solution from a container leaving the Precipitate ( Sediments in the bottom Erosion is the carrying away or displacement of solids ( Sediment, Soil, rock and other particles usually by the agents of currents such as wind Introduction The Exner equation is a statement of Conservation of mass that applies to Sediment in a Fluvial system such as a A gravel bar is a hydrogeologic Sediment composed of Gravel, and is prone to continuous Erosion and Meandering due to Fluid dynamics Regolith ( Greek: "blanket rock" is a layer of loose Heterogeneous material covering solid rock. Sand is a naturally occurring Granular material composed of finely divided rock and Mineral particles In geology sedimentary depositional environment describes the combination of physical chemical and biological processes associated with the deposition of a particular type of sediment Settling is the process by which particulates settle to the bottom of a liquid and form a Sediment. Surface runoff is a term used to describe when soil is infiltrated to full capacity and excess Water, from Rain, Snowmelt, or other sources flows Prothero and Fred Schwab, Sedimentary Geology: An Introduction to Sedimentary Rocks and Stratigraphy, W. H. Freeman (1996), ISBN 0 7167 2726 9.
Raymond Siever, Sand, Scientific American Library, New York (1988), ISBN 0 7167 5021 X.
Gary Nichols, Sedimentology & Stratigraphy, Wiley-Blackwell, Malden, MA (1999), ISBN 0 6320 3578 1.
Dictionary
sediment
-noun
- A collection of small particles, particularly dirt, that precipitates from a river or other body of water.
-verb
- (transitive) To deposit material as a sediment
- (intransitive) To be deposited as a sediment
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