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Sedimentation is the deposition ofsediments.[1] It takes place whenparticles insuspension settle out of thefluid in which they areentrained and come to rest against a barrier. This is due to their motion through the fluid in response to theforces acting on them: these forces can be due togravity,centrifugal acceleration, orelectromagnetism.Settling is the falling of suspended particles through the liquid, whereas sedimentation is the final result of the settling process.
Ingeology, sedimentation is thedeposition of sediments which results in the formation ofsedimentary rock. The term is broadly applied to the entire range of processes that result in the formation of sedimentary rock, from initialerosion throughsediment transport and settling to thelithification of the sediments. However, the strict geological definition of sedimentation is the mechanical deposition of sediment particles from an initial suspension in air or water.
Sedimentation may pertain to objects of various sizes, ranging from large rocks in flowing water, to suspensions of dust and pollen particles, tocellular suspensions, tosolutions of singlemolecules such asproteins andpeptides. Even small molecules supply a sufficiently strong force to produce significant sedimentation.
Settling is the process by which particulates move towards the bottom of a liquid and form asediment. Particles that experience a force, either due to gravity or due tocentrifugal motion will tend to move in a uniform manner in the direction exerted by that force. For gravity settling, this means that the particles will tend to fall to the bottom of the vessel, formingsludge orslurry at the vessel base.Settling is an important operation in many applications, such asmining,wastewater anddrinking water treatment, biological science,spacepropellant reignition,[2] and scooping.
Classification of sedimentation:[3]
When particles settling from a suspension reach a hard boundary, the concentration of particles at the boundary is opposed by thediffusion of the particles. The distribution of sediment near the boundary comes intosedimentation equilibrium. Measurements of the distribution yields information on the nature of the particles.[4][5]
Ingeology, the termsedimentation is broadly applied to the entire range of processes that result in the formation of sedimentary rock, from initial formation of sediments byerosion of particles from rock outcrops, throughsediment transport and settling, to thelithification of the sediments. However, the term is more particularly applied to the deposition of sediments, and in the strictest sense, it applies only to the mechanical deposition of sediment particles from an initial suspension in air or water. Sedimentation results in the formation of depositionallandforms and the rocks that constitute thesedimentary record.[6] The building up of land surfaces by sedimentation, particularly in river valleys, is calledaggradation.[7]
Therate of sedimentation is the thickness of sediment accumulated per unit time.[8] Forsuspended load, this can be expressed mathematically by theExner equation.[9] Rates of sedimentation vary from less than 3 millimeters (0.12 in) per thousand years forpelagic sediment to several meters per thousand years in portions of majorriver deltas. However, long-term accumulation of sediments is determined less by rate of sedimentation than by rate of subsidence, which createsaccommodation space for sediments to accumulate over geological time scales.
Most sedimentation in thegeologic record occurred in relative briefdepositional episodes separated by long intervals of nondeposition or even erosion.[10]
Inestuarine environments, settling can be influenced by the presence or absence of vegetation. Trees such as mangroves are crucial to theattenuation of waves or currents, promoting the settlement of suspended particles.[11]
An undesired increased transport and sedimentation of suspended material is calledsiltation, and it is a major source of pollution in waterways in some parts of the world.[12][13] High sedimentation rates can be a result of poor land management and a high frequency of flooding events. If not managed properly, it can be detrimental to fragile ecosystems on the receiving end, such as coral reefs.[14]Climate change also affects siltation rates.[15]
Sedimentation enhancing strategies areenvironmental management projects aiming to restore and facilitate land-building processes indeltas.[16]Sediment availability and deposition are important because deltas naturallysubside and therefore need sediment accumulation to maintain their elevation, particularly considering increasing rates ofsea-level rise.[17][18] Sedimentation enhancing strategies aim to increase sedimentation on the delta plain primarily by restoring the exchange of water and sediments betweenrivers and low-lying delta plains. Sedimentation enhancing strategies can be applied to encourageland elevation gain to offset sea-level rise.[19] Interest in sedimentation enhancing strategies has recently increased due to their ability to raise land elevation, which is important for the long-termsustainability of deltas.[16]
In chemistry, sedimentation has been used to measure the size of large molecules (macromolecule), where the force of gravity is augmented withcentrifugal force in anultracentrifuge.
The physical process ofsedimentation (the act of depositingsediment) has applications inwater treatment, wherebygravity acts to removesuspended solids from water.[20] Solid particles entrained by theturbulence of moving water may be removed naturally by sedimentation in the still water of lakes and oceans.Settling basins are ponds constructed for the purpose of removing entrained solids by sedimentation.[21]Clarifiers are tanks built with mechanical means for continuous removal of solids being deposited by sedimentation;[22] however, clarification does not removedissolved solids.[23]
It consumes waste hydrogen and oxygen to produce power, generate settling and attitude control thrust.
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