Sedimentation

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Sedimentation is the deposition of sediments. [1] It takes place when particles in suspension settle out of the fluid in which they are entrained and come to rest against a barrier. This is due to their motion through the fluid in response to the forces acting on them: these forces can be due to gravity, centrifugal acceleration, or electromagnetism. Settling is the falling of suspended particles through the liquid, whereas sedimentation is the final result of the settling process.

Contents

In geology, sedimentation is the deposition of sediments which results in the formation of sedimentary rock. The term is broadly applied to the entire range of processes that result in the formation of sedimentary rock, from initial erosion through sediment transport and settling to the lithification 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, to cellular suspensions, to solutions of single molecules such as proteins and peptides. Even small molecules supply a sufficiently strong force to produce significant sedimentation.

Principles

Settling

Settling pond for iron particles at water works Kalova laguna Sojovice.jpg
Settling pond for iron particles at water works

Settling is the process by which particulates move towards the bottom of a liquid and form a sediment. Particles that experience a force, either due to gravity or due to centrifugal 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, forming sludge or slurry at the vessel base. Settling is an important operation in many applications, such as mining, wastewater and drinking water treatment, biological science, space propellant reignition, [2]

and scooping.

Classification

Classification of sedimentation: [3]

Sedimentation equilibrium

When particles settling from a suspension reach a hard boundary, the concentration of particles at the boundary is opposed by the diffusion of the particles. The distribution of sediment near the boundary comes into sedimentation equilibrium. Measurements of the distribution yields information on the nature of the particles. [4] [5]

In geology

Siltation Siltation or Sedimentation.jpg
Siltation

In geology, the term sedimentation is broadly applied to the entire range of processes that result in the formation of sedimentary rock, from initial formation of sediments by erosion of particles from rock outcrops, through sediment transport and settling, to the lithification 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 depositional landforms and the rocks that constitute the sedimentary record. [6] The building up of land surfaces by sedimentation, particularly in river valleys, is called aggradation . [7]

The rate of sedimentation is the thickness of sediment accumulated per unit time. [8] For suspended load, this can be expressed mathematically by the Exner equation. [9] Rates of sedimentation vary from less than 3 millimeters (0.12 in) for pelagic sediment to several meters per year in portions of major river deltas. However, long-term accumulation of sediments is determined less by rate of sedimentation than by rate of subsidence, which creates accommodation space for sediments to accumulate over geological time scales. Most sedimentation in the geologic record occurred in relative brief depositional episodes separated by long intervals of nondeposition or even erosion. [10]

In estuarine environments, settling can be influenced by the presence or absence of vegetation. Trees such as mangroves are crucial to the attenuation of waves or currents, promoting the settlement of suspended particles. [11]

Siltation

An undesired increased transport and sedimentation of suspended material is called siltation, 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]

Human-enhanced sedimentation

Gediz delta, showing a typical natural delta landscape Bright Afternoon at Gediz Delta.jpg
Gediz delta, showing a typical natural delta landscape
Sedimentation enhancing strategies are environmental management projects aiming to restore and facilitate land-building processes in deltas. [16] Sediment availability and deposition are important because deltas naturally subside and therefore need sediment accumulation to maintain their elevation, particularly considering increasing rates of sea-level rise. [17] [18] Sedimentation enhancing strategies aim to increase sedimentation on the delta plain primarily by restoring the exchange of water and sediments between rivers and low-lying delta plains. Sedimentation enhancing strategies can be applied to encourage land 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-term sustainability of deltas. [16]

In chemistry

In chemistry, sedimentation has been used to measure the size of large molecules (macromolecule), where the force of gravity is augmented with centrifugal force in an ultracentrifuge.

In water treatment

The physical process of sedimentation (the act of depositing sediment) has applications in water treatment, whereby gravity acts to remove suspended solids from water. [20] Solid particles entrained by the turbulence 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 remove dissolved solids. [23]

See also

Notes

  1. "sedimentation" . Oxford English Dictionary (Online ed.). Oxford University Press.(Subscription or participating institution membership required.)
  2. Zegler, Frank; Bernard Kutter (2010-09-02). "Evolving to a Depot-Based Space Transportation Architecture" (PDF). AIAA SPACE 2010 Conference & Exposition. AIAA. Archived from the original (PDF) on 2013-05-10. Retrieved 2011-01-25. It consumes waste hydrogen and oxygen to produce power, generate settling and attitude control thrust.
  3. Coe, H.S.; Clevenger, G.H. (1916). "Methods for determining the capacities of slime-settling tanks". Transactions of the American Institute of Mining and Metallurgical Engineers. 55: 356.
  4. "The Nobel Prize in Physics 1926". NobelPrize.org. 27 Nov 2021. Retrieved 27 November 2021.
  5. Piazza, Roberto; Buzzaccaro, Stefano; Secchi, Eleonora (2012-06-27). "The unbearable heaviness of colloids: facts, surprises, and puzzles in sedimentation". Journal of Physics: Condensed Matter. 24 (28): 284109. Bibcode:2012JPCM...24B4109P. doi:10.1088/0953-8984/24/28/284109. ISSN   0953-8984. PMID   22738878. S2CID   23309333.
  6. Jackson, Julia A., ed. (1997). "sedimentation". Glossary of geology (Fourth ed.). Alexandria, Virginia: American Geological Institute. ISBN   0922152349.
  7. Jackson 1997, "aggradation".
  8. Jackson 1997, "rate of sedimentation".
  9. Paola, C.; Voller, V. R. (2005). "A generalized Exner equation for sediment mass balance". Journal of Geophysical Research. 110: F04014. Bibcode:2005JGRF..11004014P. doi:10.1029/2004JF000274.
  10. Blatt, Harvey; Middleton, Gerard; Murray, Raymond (1980). Origin of sedimentary rocks (2d ed.). Englewood Cliffs, N.J.: Prentice-Hall. pp. 30–31, 122–123. ISBN   0136427103.
  11. Van Santen, P.; Augustinus, P. G. E. F.; Janssen-Stelder, B. M.; Quartel, S.; Tri, N. H. (2007-02-15). "Sedimentation in an estuarine mangrove system". Journal of Asian Earth Sciences. Morphodynamics of the Red River Delta, Vietnam. 29 (4): 566–575. Bibcode:2007JAESc..29..566V. doi:10.1016/j.jseaes.2006.05.011.
  12. "Siltation & Sedimentation". blackwarriorriver.org. Archived from the original on 2009-12-21. Retrieved 2009-11-16.
  13. "Siltation killed fish at Batang Rajang - Digest on Malaysian News". malaysiadigest.blogspot.com. Retrieved 2009-11-16.
  14. Victor, Steven; Neth, Leinson; Golbuu, Yimnang; Wolanski, Eric; Richmond, Robert H. (2006-02-01). "Sedimentation in mangroves and coral reefs in a wet tropical island, Pohnpei, Micronesia". Estuarine, Coastal and Shelf Science. 66 (3–4): 409–416. Bibcode:2006ECSS...66..409V. doi:10.1016/j.ecss.2005.07.025.
  15. U.D. Kulkarni; et al. "The International Journal of Climate Change: Impacts and Responses » Rate of Siltation in Wular Lake, (Jammu and Kashmir, India) with Special Emphasis on its Climate & Tectonics". The International Journal of Climate Change: Impacts and Responses. Archived from the original on 2017-03-18. Retrieved 2009-11-16.
  16. 1 2 Nicholls, R. J.; Hutton, C. W.; Adger, W. N.; Hanson, S. E.; Rahman, Md. M.; Salehin, M., eds. (2018). Ecosystem Services for Well-Being in Deltas: Integrated Assessment for Policy Analysis. Cham: Springer International Publishing. doi:10.1007/978-3-319-71093-8. ISBN   978-3-319-71092-1. S2CID   135458360.
  17. Syvitski, J. P. (2008). "Deltas at risk". Sustainability Science. 3 (1): 23–32. doi:10.1007/s11625-008-0043-3. ISSN   1862-4065. S2CID   128976925.
  18. Giosan, L.; Constantinescu, S.; Filip, F.; Deng, B. (2013). "Maintenance of large deltas through channelization: Nature vs. humans in the Danube delta". Anthropocene. 1: 35–45. Bibcode:2013Anthr...1...35G. doi:10.1016/j.ancene.2013.09.001.
  19. Paola, C.; Twilley, R. R.; Edmonds, D. A.; Kim, W.; Mohrig, D.; Parker, G.; Viparelli, E.; Voller, V. R. (2011). "Natural Processes in Delta Restoration: Application to the Mississippi Delta". Annual Review of Marine Science. 3 (1): 67–91. Bibcode:2011ARMS....3...67P. doi:10.1146/annurev-marine-120709-142856. ISSN   1941-1405. PMID   21329199.
  20. Omelia, C (1998). "Coagulation and sedimentation in lakes, reservoirs and water treatment plants". Water Science and Technology. 37 (2): 129. doi:10.1016/S0273-1223(98)00018-3.
  21. Goldman, Steven J., Jackson, Katharine & Bursztynsky, Taras A. Erosion & Sediment Control Handbook. McGraw-Hill (1986). ISBN   0-07-023655-0. pp. 8.2, 8.12.
  22. Hammer, Mark J. Water and Waste-Water Technology. John Wiley & Sons (1975). ISBN   0-471-34726-4. pp. 223–225.
  23. Reinsel, M., Apex Engineering. 'Industrial Water Treatment For Inorganic Contaminants: Physical Treatment Processes' Water Online; Accessed 15 October 2018

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Shale is a fine-grained, clastic sedimentary rock formed from mud that is a mix of flakes of clay minerals (hydrous aluminium phyllosilicates, e.g. kaolin, Al2Si2O5(OH)4) and tiny fragments (silt-sized particles) of other minerals, especially quartz and calcite. Shale is characterized by its tendency to split into thin layers (laminae) less than one centimeter in thickness. This property is called fissility. Shale is the most common sedimentary rock.

<span class="mw-page-title-main">Sedimentary rock</span> Rock formed by the deposition and cementation of particles

Sedimentary rocks are types of rock that are formed by the accumulation or deposition of mineral or organic particles at Earth's surface, followed by cementation. Sedimentation is the collective name for processes that cause these particles to settle in place. The particles that form a sedimentary rock are called sediment, and may be composed of geological detritus (minerals) or biological detritus. The geological detritus originated from weathering and erosion of existing rocks, or from the solidification of molten lava blobs erupted by volcanoes. The geological detritus is transported to the place of deposition by water, wind, ice or mass movement, which are called agents of denudation. Biological detritus was formed by bodies and parts of dead aquatic organisms, as well as their fecal mass, suspended in water and slowly piling up on the floor of water bodies. Sedimentation may also occur as dissolved minerals precipitate from water solution.

<span class="mw-page-title-main">Sediment</span> Particulate solid matter that is deposited on the surface of land

Sediment 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 through lithification.

<span class="mw-page-title-main">River delta</span> Silt deposition landform at the mouth of a river

A river delta is a landform shaped like a triangle, created by the deposition of sediment that is carried by a river and enters slower-moving or stagnant water. This occurs when a river enters an ocean, sea, estuary, lake, reservoir, or another river that cannot carry away the supplied sediment. It is so named because its triangle shape resembles the Greek letter Delta. The size and shape of a delta are controlled by the balance between watershed processes that supply sediment, and receiving basin processes that redistribute, sequester, and export that sediment. The size, geometry, and location of the receiving basin also plays an important role in delta evolution.

<span class="mw-page-title-main">Silt</span> Classification of soil or sediment

Silt is granular material of a size between sand and clay and composed mostly of broken grains of quartz. Silt may occur as a soil or as sediment mixed in suspension with water. Silt usually has a floury feel when dry, and lacks plasticity when wet. Silt also can be felt by the tongue as granular when placed on the front teeth.

<span class="mw-page-title-main">Deposition (geology)</span> Geological process in which sediments, soil and rocks are added to a landform or landmass

Deposition is the geological process in which sediments, soil and rocks are added to a landform or landmass. Wind, ice, water, and gravity transport previously weathered surface material, which, at the loss of enough kinetic energy in the fluid, is deposited, building up layers of sediment.

Retrogradation is the landward change in position of the front of a river delta with time. This occurs when the mass balance of sediment into the delta is such that the volume of incoming sediment is less than the volume of the delta that is lost through subsidence, sea-level rise, and/or erosion. As a result, retrogradation is most common:

Detritus is particles of rock derived from pre-existing rock through weathering and erosion. A fragment of detritus is called a clast. Detrital particles can consist of lithic fragments, or of monomineralic fragments. These particles are often transported through sedimentary processes into depositional systems such as riverbeds, lakes or the ocean, forming sedimentary successions. Diagenetic processes can transform these sediments into rock through cementation and lithification, forming sedimentary rocks such as sandstone. These rocks can then in turn again be weathered and eroded to form a second generation of sediment. Detrital grains commonly weather at different rates, according to the Goldich dissolution series, which dictates that early crystallizing minerals are less stable at the earth's surface than late crystallizing minerals.

<span class="mw-page-title-main">Mudrock</span> Type of sedimentary rock

Mudrocks are a class of fine-grained siliciclastic sedimentary rocks. The varying types of mudrocks include siltstone, claystone, mudstone, slate, and shale. Most of the particles of which the stone is composed are less than 116 mm and are too small to study readily in the field. At first sight, the rock types appear quite similar; however, there are important differences in composition and nomenclature.

<span class="mw-page-title-main">Particle aggregation</span> Clumping of particles in suspension

Particle agglomeration refers to the formation of assemblages in a suspension and represents a mechanism leading to the functional destabilization of colloidal systems. During this process, particles dispersed in the liquid phase stick to each other, and spontaneously form irregular particle assemblages, flocs, or agglomerates. This phenomenon is also referred to as coagulation or flocculation and such a suspension is also called unstable. Particle agglomeration can be induced by adding salts or other chemicals referred to as coagulant or flocculant.

<span class="mw-page-title-main">Clastic rock</span> Sedimentary rocks made of mineral or rock fragments

Clastic rocks are composed of fragments, or clasts, of pre-existing minerals and rock. A clast is a fragment of geological detritus, chunks, and smaller grains of rock broken off other rocks by physical weathering. Geologists use the term clastic to refer to sedimentary rocks and particles in sediment transport, whether in suspension or as bed load, and in sediment deposits.

The physical process of sedimentation has applications in water treatment, whereby gravity acts to remove suspended solids from water. Solid particles entrained by the turbulence 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. Clarifiers are tanks built with mechanical means for continuous removal of solids being deposited by sedimentation; however, clarification does not remove dissolved solids.

<span class="mw-page-title-main">Siltation</span> Water pollution caused by particulate terrestrial clastic material

Siltation is water pollution caused by particulate terrestrial clastic material, with a particle size dominated by silt or clay. It refers both to the increased concentration of suspended sediments and to the increased accumulation of fine sediments on bottoms where they are undesirable. Siltation is most often caused by soil erosion or sediment spill.

<span class="mw-page-title-main">Graded bedding</span> Type of layering in sediment or sedimentary rock

In geology, a graded bed is a bed characterized by a systematic change in grain or clast size from bottom to top of the bed. Most commonly this takes the form of normal grading, with coarser sediments at the base, which grade upward into progressively finer ones. Such a bed is also described as fining upward. Normally graded beds generally represent depositional environments which decrease in transport energy as time passes, but these beds can also form during rapid depositional events. They are perhaps best represented in turbidite strata, where they indicate a sudden strong current that deposits heavy, coarse sediments first, with finer ones following as the current weakens. They can also form in terrestrial stream deposits.

<span class="mw-page-title-main">Depositional environment</span> Processes associated with the deposition of a particular type of sediment

In geology, depositional environment or sedimentary environment describes the combination of physical, chemical, and biological processes associated with the deposition of a particular type of sediment and, therefore, the rock types that will be formed after lithification, if the sediment is preserved in the rock record. In most cases, the environments associated with particular rock types or associations of rock types can be matched to existing analogues. However, the further back in geological time sediments were deposited, the more likely that direct modern analogues are not available.

<span class="mw-page-title-main">Avulsion (river)</span> Rapid abandonment of a river channel and formation of a new channel

In sedimentary geology and fluvial geomorphology, avulsion is the rapid abandonment of a river channel and the formation of a new river channel. Avulsions occur as a result of channel slopes that are much less steep than the slope that the river could travel if it took a new course.

In sedimentary geology and geomorphology, the term progradation refers to the growth of a river delta farther out into the sea over time. This occurs when the volume of incoming sediment is greater than the volume of the delta that is lost through subsidence, sea-level rise, or erosion.

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<span class="mw-page-title-main">Sedimentation enhancing strategy</span>

Sedimentation enhancing strategies are environmental management projects aiming to restore and facilitate land-building processes in deltas. Sediment availability and deposition are important because deltas naturally subside and therefore need sediment accumulation to maintain their elevation, particularly considering increasing rates of sea-level rise. Sedimentation enhancing strategies aim to increase sedimentation on the delta plain primarily by restoring the exchange of water and sediments between rivers and low-lying delta plains. Sedimentation enhancing strategies can be applied to encourage land elevation gain to offset sea-level rise. Interest in sedimentation enhancing strategies has recently increased due to their ability to raise land elevation, which is important for the long-term sustainability of deltas.