Base level

In geology and geomorphology a base level is the lower limit for an erosion process.[1] The modern term was introduced by John Wesley Powell in 1875.[1] The term was subsequently appropriated by William Morris Davis who used it in his cycle of erosion theory.[1][2] The "ultimate base level" is the plane that results from projection of the sea level under landmasses.[1] It is to this base level that topography tends to approach due to erosion, eventually forming a peneplain close to the end of a cycle of erosion.[3][4][5][6]

There are also lesser structural base levels where erosion is delayed by resistant rocks.[1] Examples of this include karst regions underlain by insoluble rock.[7] Base levels may be local when large landmasses are far from the sea or disconnected from it, as in the case of endorheic basins.[1] An example of this is the Messinian salinity crisis, in which the Mediterranean Sea dried up making the base level drop more than 1000 m below sea level.[8][9]

The height of a base level also influences the position of deltas and river terraces.[1] Together with river discharge and sediment flux the position of the base level influences the gradient, width and bed conditions in rivers.[10] A relative drop in base level can trigger re-adjustments in river profiles including knickpoint migration and abandonment of terraces leaving them "hanging".[11] Base level fall is also known to result in progradation of deltas and river sediment at lakes or sea.[12] If the base level falls below the continental shelf, rivers may form a plain of braided rivers until headward erosion penetrates enough inland from the shelfbreak.[12]

When base levels are stable or rising rivers may aggrade.[12] Rising base levels may also drown the lower courses of rivers creating rias. This happened in the Nile during the Zanclean flood when its lower course became, in a relatively short time, a large estuary extending up to 900 km inland from the Mediterranean coast.[9]

Base level change may be related to the following factors:

  1. Sea level change[1]
  2. Tectonic movement[1]
  3. River capture[1]
  4. Extensive sedimentation[13]
Desembocadura del Ebro
Aerial picture of the Ebro river as it reaches the Mediterranean sea by the Ebro Delta

References

  1. ^ a b c d e f g h i j Goudie, A.S. (2004). "Base level". In Goudie, A.S. (ed.). Encyclopedia of Geomorphology. Routledge. p. 62.
  2. ^ Orme, Anthony R. (2007). "The Rise and Fall of the Davisian Cycle of Erosion: Prelude, Fugue, Coda, and Sequel". Physical Geography. 28 (6): 474–506. doi:10.2747/0272-3646.28.6.474.
  3. ^ Phillips, Jonathan D. (2002), "Erosion, isostatic response, and the missing peneplains", Geomorphology, Vol. 45, No. 3-4. Elsevier, 15 June 2002, pp. 225-241. doi:10.1016/S0169-555X(01)00156-8.
  4. ^ Chorley, R.J. (1973). The History and Study of Landforms or The Development of Geomorphology. Vol. Two: The Life and Work of William Morris Davis, Methuen.
  5. ^ Green, Paul F.; Lidmar-Bergström, Karna; Japsen, Peter; Bonow, Johan M.; Chalmers, James A. (2013). "Stratigraphic landscape analysis, thermochronology and the episodic development of elevated, passive continental margins". Geological Survey of Denmark and Greenland Bulletin. 30: 18. Archived from the original on 2015-09-24. Retrieved 30 April 2015.
  6. ^ Lidmar-Bergström, Karna; Bonow, Johan M.; Japsen, Peter (2013). "Stratigraphic Landscape Analysis and geomorphological paradigms: Scandinavia as an example of Phanerozoic uplift and subsidence". Global and Planetary Change. 100: 153–171. doi:10.1016/j.gloplacha.2012.10.015.
  7. ^ Ford, Derek C. (2004). "Cave". In Goudie, A.S. (ed.). Encyclopedia of Geomorphology. Routledge. pp. 124–128.
  8. ^ Fairbridge, Rhodes W.; Finkl Jr., Charles W. (1980). "Cratonic erosion unconformities and peneplains". The Journal of Geology. 88 (1): 69–86. doi:10.1086/628474.
  9. ^ a b Goudie, A.S. (2005). "The drainage of Africa since the Cretaceous". Geomorphology. 67 (3–4): 437–456. doi:10.1016/j.geomorph.2004.11.008.
  10. ^ Whipple, Kelin X. (2004). "Bedrock channel". In Goudie, A.S. (ed.). Encyclopedia of Geomorphology. Routledge. pp. 81–82.
  11. ^ Spotila, James A. (2004). "Crustal deformation". In Goudie, A.S. (ed.). Encyclopedia of Geomorphology. Routledge. pp. 201–203.
  12. ^ a b c Koss, John E.; Ethridge, Frank G.; Schumm, S.A. (1994). "An Experimental Study of the Effects of Base-Level Change on Fluvial, Coastal Plain and Shelf Systems". Journal of Sedimentary Research. 64B (2): 90–98. doi:10.1306/D4267F64-2B26-11D7-8648000102C1865D.
  13. ^ Babault, Julien; Van Den Driessche, Jean; Bonnet, Stephanie; Castelltort, Sébastien; Crave, Alain (2005). "Origin of the highly elevated Pyrenean peneplain". Tectonics. 24 (2): n/a. doi:10.1029/2004TC001697.
Backwater (river)

A backwater is a part of a river in which there is little or no current. It can refer to a branch of a main river, which lies alongside it and then rejoins it, or to a body of water in a main river, backed up by the tide or by an obstruction such as a dam. Manmade restrictions to natural stream flow or temporary natural obstructions such as ice jams, vegetation blockage, or flooding of a lower stream can create backwater.

Cycle of erosion

The geographic cycle or cycle of erosion is an idealized model that explains the development of relief in landscapes. The model starts with the erosion that follows uplift of land above a base level and ends – if conditions allow – in the formation of a peneplain. Landscapes that show evidence of more than one cycle of erosion are termed "polycyclical". The cycle of erosion and some of its associated concepts have, despite popularity, been a subject of much criticism.

District Councils of India

Zila Panchayats are Panchayats at Apex or District Level in Panchayat Raj Institutions (or PRIs).

The 73rd Amendment is about Governments' (which are also known as Panchayati Raj Institutions or PRIs) [1]

Panchayat at District (or apex) Level

Panchayat at Intermediate Level

Panchayat at Base LevelThe Zila Panchayat or District Council or Zilla Parishad or District Panchayat

, is the third tier of the Panchayati Raj system. Zila Parishad is an elected body. Block Pramukh of Block Panchayat are also represented in Zila Parishad. The members of the State Legislature and the members of the Parliament of India are members of the Zila Parishad.

Dodge Custom Royal

The Dodge Custom Royal is an automobile which was produced by Dodge in the United States for the 1955 through 1959 model years. In each of these years the Custom Royal was the top trim level of the Dodge line, above the mid level Dodge Royal and the base level Dodge Coronet. 2 Door and 4 Door Hardtop Models, along with the convertible were referred to as "Custom Royal Lancers" only the 4 Door Sedan was known as strictly a "Custom Royal"

Downcutting

Downcutting, also called erosional downcutting, downward erosion or vertical erosion is a geological process by hydraulic action that deepens the channel of a stream or valley by removing material from the stream's bed or the valley's floor. The speed of downcutting depends on the stream's base level, the lowest point to which the stream can erode. Sea level is the ultimate base level, but many streams have a higher "temporary" base level because they empty into another body of water that is above sea level or encounter bedrock that resists erosion. A concurrent process called lateral erosion refers to the widening of a stream channel or valley. When a stream is high above its base level, downcutting will take place faster than lateral erosion; but as the level of the stream approaches its base level, the rate of lateral erosion increases. This is why streams in mountainous areas tend to be narrow and swift, forming V-shaped valleys, while streams in lowland areas tend to be wide and slow-moving, with valleys that are correspondingly wide and flat-bottomed. The term gradient refers to the elevation of a stream relative to its base level. The steeper the gradient, the faster the stream flows. Sometimes geological uplift will increase the gradient of a stream even while the stream downcuts toward its base level, a process called "rejuvenation." This happened in the case of the Colorado River in the western United States, resulting in the process that created the Grand Canyon.

Fluvial terrace

Fluvial terraces are elongated terraces that flank the sides of floodplains and fluvial valleys all over the world. They consist of a relatively level strip of land, called a “tread,” separated from either an adjacent floodplain, other fluvial terraces, or uplands by distinctly steeper strips of land called “risers.” These terraces lie parallel to and above the river channel and its floodplain. Because of the manner in which they form, fluvial terraces are underlain by fluvial sediments of highly variable thickness.Fluvial terraces are the remnants of earlier floodplains that existed at a time when either a stream or river was flowing at a higher elevation before its channel downcut to create a new floodplain at a lower elevation. Changes in elevation can be due to changes in the base level (elevation of the lowest point in the fluvial system, usually the drainage basin) of the fluvial system, which leads to headward erosion along the length of either a stream or river, gradually lowering its elevation. For example, downcutting by a river can lead to increased velocity of a tributary, causing that tributary to erode toward its headwaters. Terraces can also be left behind when the volume of the fluvial flow declines due to changes in climate, typical of areas which were covered by ice during periods of glaciation, and their adjacent drainage basins.

Juggling competition

Competitive or sport juggling may range from friendly and silly games to competitive sports. Most juggling conventions include friendly games such as endurance and gladiators. Since 1969, the International Jugglers' Association (IJA) has held annual stage championships, judged both on technique and presentation. The stage championships have three categories: Individuals, Teams and Juniors (individuals under 17 years old). First, second and third-place winners in the Stage Championships are awarded medals and money prizes. In addition the Numbers Championships awards Gold medals to those who demonstrate that they can juggle the most balls, clubs or rings for the most catches.

In recent times there has been a move to more competitive and technical juggling events. The most notable example of this is the annual World Juggling Federation (WJF) Championships. Other competitions include those produced by the International Sport Juggling Federation, and the Atlanta Jugglers Association Groundhog Day competition.

One type of competition is called combat, often known as Gladiators in Europe, is a "last man standing" competition, with the participating jugglers agree to maintain a base level of juggling, normally a three club cascade, within a certain area. Participants who drop a club, or go out of bounds, have lost the round and are expected to remove themselves (and their clubs if necessary) from the competition area. Although participants are not allowed to deliberately come into body to body contact with each other unless previously specified, they are allowed to use their clubs to interfere with other participants' cascades through juggling tricks. Stealing a club out of another participant's cascade, in order to replace one's own dropped or discarded club, is a common tactic. Multiple rounds may be played, with the winner being the first to win a set number of rounds, or the person with the most wins by a set end time.

Knickpoint

In geomorphology, a knickpoint or nickpoint is part of a river or channel where there is a sharp change in channel slope, such as a waterfall or lake. Knickpoints reflect different conditions and processes on the river, often caused by previous erosion due to glaciation or variance in lithology. In the cycle of erosion model, knickpoints advance one cycle upstream, or inland, replacing an older cycle.

Moulin (geomorphology)

A moulin or glacier mill is a roughly circular, vertical to nearly vertical well-like shaft within a glacier or ice sheet which water enters from the surface. The term is derived from the French word for mill.They can be up to 10 meters wide and are typically found on ice sheets and flat areas of a glacier in a region of transverse crevasses. Moulins can reach the bottom of the glacier, hundreds of meters deep, or may only reach the depth of common crevasse formation (about 10–40 m) where the stream flows englacially. They are the most typical cause for the formation of a glacier cave.

Moulins are parts of the internal structure of glaciers, that carry meltwater from the surface down to wherever it may go. Water from a moulin often exits the glacier at base level, sometimes into the sea, and occasionally the lower end of a moulin may be exposed in the face of a glacier or at the edge of a stagnant block of ice.

Water from moulins may help lubricate the base of the glacier, affecting glacial motion. Given an appropriate relationship between an ice sheet and the terrain, the head of water in a moulin can provide the power and medium with which a tunnel valley may be formed. The role of this water in lubricating the base of ice sheets and glaciers is complex and it is implicated in accelerating the speed of glaciers and thus the rate of glacial calving.

Multilevel feedback queue

In computer science, a multilevel feedback queue is a scheduling algorithm. Solaris 2.6 Time-Sharing (TS) scheduler implements this algorithm. The MacOS and Microsoft Windows schedulers can both be regarded as examples of the broader class of multilevel feedback queue schedulers.

This scheduling algorithm is intended to meet the following design requirements for multimode systems:

Give preference to short jobs.

Give preference to I/O bound processes.

Separate processes into categories based on their need for the processor.The Multi-level Feedback Queue scheduler was first developed by Fernando J. Corbató et al. in 1962, and this work, along with other work on Multics, led the ACM to award Corbató the Turing Award.

Nair Service Society

The Nair Service Society (NSS) is an organisation created for the social advancement and welfare of the Nair community that is found primarily in the state of Kerala in South India. It was established under the leadership of Mannathu Padmanabha Pillai. The NSS is a three-tier organisation with Karayogams at the base level, Taluk Unions at the intermediate level and a central headquarters operating from Perunna, Changanassery in Kerala.Gopurathinkal Sukumaran Nair(G Sukumaran Nair) is the present General Secretary.

The Society owns and manages a large number of educational institutions and hospitals.

OBIX

oBIX (for Open Building Information Exchange) is a standard for RESTful Web Services-based interfaces to building control systems. oBIX is about reading and writing data over a network of devices using XML and URIs, within a framework specifically designed for building automation.

Building control systems include those electrical and mechanical systems that operate inside a building, including Heating and Cooling (HVAC), Security, Power Management, and Life/Safety Alarms that are in nearly all buildings as well as the myriad of special purpose systems that may be tied to particular buildings such as A/V Event Management, Theatre Lighting, Medical Gas Distribution, Fume Hoods, and many others.

oBIX is a web services interface because it does not necessarily allow deep interactions with the underlying control systems. This interface can enable communications between enterprise applications and embedded building systems as well as between two embedded building systems. Facilities and their operations to be managed as full participants in knowledge-based businesses.

oBIX is being developed within OASIS[1], the Organization for the Advancement of Structured Information Standards. Version 1.0 was completed as a committee standard in December 2006.

Panchayat samiti (block)

Mandals, taluka panchayats, block panchayats, or panchayat samiti are rural local governments (panchayats) at the intermediate level in panchayat raj institutions (PRI).

It has been said to be the "panchayat of panchayats".The 73rd Amendment defines the levels of panchayati raj institution as :

District (or apex) level

Intermediate level

Base levelThey operate at the tehsil (taluka) level and govern the villages of the tehsil that together are called a development block. The panchayat samiti is the link between the gram panchayat (village council) and the zila parishad (district board). The name varies across states: mandal praja parishad in Andhra Pradesh, taluka panchayat in Gujarat, and mandal panchayat in Karnataka.

Peneplain

In geomorphology and geology, a peneplain is a low-relief plain formed by protracted erosion. This is the definition in the broadest of terms, albeit with frequency the usage of peneplain is meant to imply the representation of a near-final (or penultimate) stage of fluvial erosion during times of extended tectonic stability. Peneplains are sometimes associated with the cycle of erosion theory of William Morris Davis, but Davis and other workers have also used the term in a purely descriptive manner without any theory or particular genesis attached.The existence of some peneplains, and peneplanation as a process in nature, is not without controversy, due to a lack of contemporary examples and uncertainty in identifying relic examples. By some definitions, peneplains grade down to a base level represented by sea level, yet in other definitions such a condition is ignored. Geomorphologist Karna Lidmar-Bergström and co-workers consider the base level criterion crucial and above the precise mechanism of formation of peneplains, including this way some pediplains among peneplains.While peneplains are usually assumed to form near sea level it has also been posited that peneplains can form at height if extensive sedimentation raises the local base level sufficiently or if river networks are continuously obstructed by tectonic deformation. The peneplains of the Pyrenees and Tibetan Plateau may exemplify these two cases respectively.A common misconception about peneplains is that they ought to be so plain they are featureless. In fact, some peneplains may be hilly as they reflect irregular deep weathering, forming a plain grading to a base level only at a grand-scale.

Ringle Crouch Green Mill

Ringle Crouch Green Mill is a smock mill in Sandhurst, Kent, England, that was demolished to base level in 1945, and now has a new smock tower built on it as residential accommodation and an electricity generator.

River rejuvenation

In geomorphology a river is said to be rejuvenated when it is eroding the landscape in response to a lowering of its base level. The process is often a result of a sudden fall in sea level or the rise of land. The disturbance enables a rise in the river's potential energy, increasing its riverbed erosion rate. The erosion occurs as a means for the river to adjust to its new base level.

Security testing

Security testing is a process intended to reveal flaws in the security mechanisms of an information system that protect data and maintain functionality as intended. Due to the logical limitations of security testing, passing security testing is not an indication that no flaws exist or that the system adequately satisfies the security requirements.

Typical security requirements may include specific elements of confidentiality, integrity, authentication, availability, authorization and non-repudiation. Actual security requirements tested depend on the security requirements implemented by the system. Security testing as a term has a number of different meanings and can be completed in a number of different ways. As such a Security Taxonomy helps us to understand these different approaches and meanings by providing a base level to work from.

Stream

A stream is a body of water with surface water flowing within the bed and banks of a channel. The stream encompasses surface and groundwater fluxes that respond to geological, geomorphological, hydrological and biotic controls.Depending on its location or certain characteristics, a stream may be referred to by a variety of local or regional names. Long large streams are usually called rivers.

Streams are important as conduits in the water cycle, instruments in groundwater recharge, and corridors for fish and wildlife migration. The biological habitat in the immediate vicinity of a stream is called a riparian zone. Given the status of the ongoing Holocene extinction, streams play an important corridor role in connecting fragmented habitats and thus in conserving biodiversity. The study of streams and waterways in general is known as surface hydrology and is a core element of environmental geography.

Stream pool

A stream pool, in hydrology, is a stretch of a river or stream in which the water depth is above average and the water velocity is below average.

Large-scale features
Alluvial rivers
Bedrock river
Bedforms
Regional processes
Mechanics

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