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35-460: Artificial rills are channels constructed to carry a water supply from a distant water source. In landscape or garden design, constructed rills are an aesthetic water feature . Rills are narrow and shallow channels which are eroded into unprotected soil by hillslope runoff . Since soil is regularly left bare during agricultural operations , rills may form on farmland during these vulnerable periods. Rills may also form when bare soil

70-410: A shear velocity between 3 and 3.5 cm/s. After rills begin forming, they are subjected to variety of other erosional forces which may increase their size and output volume. Up to 37% of erosion in a rill-ridden area may derive from mass movement, or collapse, of rill sidewalls. As water flows through a rill, it will undercut into the walls, triggering collapse. Also, as water seeps into the soil of

105-749: A carrying capacity of nearly ten times that of non-rill, or interrill, areas. In a moderate rainfall, rill flow can carry rock fragments up to 9 cm in diameter downslope. In 1987, scientist J. Poesen conducted an experiment on the Huldenberg field in Belgium which revealed that during a moderate rainfall, rill erosion removed as much as 200 kg (in submerged weight) of rock. Unfortunately, rills' considerable effect on landscapes often negatively impacts human activity. Rills have been observed washing away archaeological sites. They are also very common in agricultural areas because sustained agriculture depletes

140-487: A constant flux. Channel heads associated with hollows in steep terrain frequently migrate up and down hillslopes depending on sediment supply and precipitation. Natural channels are formed by fluvial process and are found across the Earth . These are mostly formed by flowing water from the hydrological cycle , though can also be formed by other fluids such as flowing lava can form lava channels . Channels also describe

175-471: A point where shear stress can overcome erosion resistance of the ground surface. Channel heads are often associated with colluvium , hollows and landslides . Overland flow is a primary factor in channel initiation where saturation overland flow deepens to increase shear stress and begin channel incision. Overland flows converge in topographical depressions where channel initiation begins. Soil composition, vegetation, precipitation, and topography dictate

210-435: A similar artificial structure. Channels are important for the functionality of ports and other bodies of water used for navigability for shipping . Naturally, channels will change their depth and capacity due to erosion and deposition processes. Humans maintain navigable channels by dredging and other engineering processes. By extension, the term also applies to fluids other than water, e.g., lava channels . The term

245-420: Is a difference between low gradient streams (less than a couple of percent in gradient or slightly sloped) and high gradient streams (steeply sloped). A wide variety of stream channel types can be distinguished (e.g. braided rivers , wandering rivers, single-thread sinuous rivers etc.). During floods , water flow may exceed the capacity of the channel and flood waters will spill out of the channel and across

280-538: Is also traditionally used to describe the waterless surface features on Venus . Channel initiation refers to the site on a mountain slope where water begins to flow between identifiable banks. This site is referred to as the channel head and it marks an important boundary between hillslope processes and fluvial processes. The channel head is the most upslope part of a channel network and is defined by flowing water between defined identifiable banks. A channel head forms as overland flow and/or subsurface flow accumulate to

315-403: Is an open-air none recycled water hydroponics relationship. The below described circumstances are not in perspective, have limited duration, and have a tendency to accumulate trace materials in soil that either there or elsewhere cause deoxygenation. The use of vast amounts of fertilizer may have unintended consequences for the environment by devastating rivers, waterways, and river endings through

350-462: Is frequently called a canal , with the Panama Canal providing an example. The term not only includes the deep-dredged   ship-navigable parts of an estuary or river leading to port facilities, but also to lesser channels accessing boat port-facilities such as marinas . When dredged channels traverse bay mud or sandy bottoms, repeated dredging is often necessary because of

385-455: Is left exposed following deforestation , or during construction activities. Rills are fairly easily visible when first incised, so they are often the first indication of an ongoing erosion problem. Unless soil conservation measures are put into place, rills on regularly eroding areas may eventually develop into larger erosional features such as gullies or even (in semi-arid regions) into badlands . Rills are created when fire erodes

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420-462: Is not arable according to the FAO definition above includes: Other non-arable land includes land that is not suitable for any agricultural use. Land that is not arable, in the sense of lacking capability or suitability for cultivation for crop production, has one or more limitations – a lack of sufficient freshwater for irrigation, stoniness, steepness, adverse climate, excessive wetness with

455-574: Is not included in this category. Data for 'Arable land' are not meant to indicate the amount of land that is potentially cultivable. A more concise definition appearing in the Eurostat glossary similarly refers to actual rather than potential uses: "land worked (ploughed or tilled) regularly, generally under a system of crop rotation ". In Britain, arable land has traditionally been contrasted with pasturable land such as heaths , which could be used for sheep-rearing but not as farmland . Arable land

490-434: Is the seawater greenhouse , which desalinates water through evaporation and condensation using solar energy as the only energy input. This technology is optimized to grow crops on desert land close to the sea. The use of artifices does not make the land arable. Rock still remains rock, and shallow – less than 6 feet (1.8 metres) – turnable soil is still not considered toilable. The use of artifice

525-416: Is unsuitable for cultivation, yet such land has value for grazing of livestock. In British Columbia, Canada, 41 percent of the provincial Agricultural Land Reserve area is unsuitable for the production of cultivated crops, but is suitable for uncultivated production of forage usable by grazing livestock. Similar examples can be found in many rangeland areas elsewhere. Land incapable of being cultivated for

560-558: Is vulnerable to land degradation and some types of un-arable land can be enriched to create useful land. Climate change and biodiversity loss , are driving pressure on arable land. According to the Food and Agriculture Organization of the United Nations, in 2013, the world's arable land amounted to 1.407 billion hectares, out of a total of 4.924 billion hectares of land used for agriculture. Agricultural land that

595-581: The Latin : arabilis , "able to be ploughed ") is any land capable of being ploughed and used to grow crops. Alternatively, for the purposes of agricultural statistics, the term often has a more precise definition: Arable land is the land under temporary agricultural crops (multiple-cropped areas are counted only once), temporary meadows for mowing or pasture , land under market and kitchen gardens and land temporarily fallow (less than five years). The abandoned land resulting from shifting cultivation

630-586: The valley bottom, floodplain or drainage area . Examples of rivers that are trapped in their channels: Grand Canyon and Black Canyon of the Gunnison . In a larger nautical context, as a geographical place name, the term channel is another word for strait , which is defined as a relatively narrow body of water that connects two larger bodies of water. In this nautical context, the terms strait , channel , sound , and passage are synonymous and usually interchangeable. For example, in an archipelago ,

665-437: The accumulation of non-degradable toxins and nitrogen-bearing molecules that remove oxygen and cause non-aerobic processes to form. Examples of infertile non-arable land being turned into fertile arable land include: One of the impacts of land degradation is that it can diminish the natural capacity of the land to store and filter water leading to water scarcity . Human-induced land degradation and water scarcity are increasing

700-545: The amount and rate of overland flow. The composition of a soil determines how quickly saturation occurs and cohesive strength retards the entrainment of material from overland flows. Vegetation slows infiltration rates during precipitation events and plant roots anchor soil on hillslopes. Subsurface flow destabilizes soil and resurfaces on hillslopes where channel heads are often formed. This often results in abrupt channel heads and landslides. Hollows form due to concentrated subsurface flows where concentrations of colluvium are in

735-567: The deeper course through a reef , sand bar , bay , or any shallow body of water. An example of a river running through a sand bar is the Columbia Bar —the mouth of the Columbia River . A stream channel is the physical confine of a stream ( river ) consisting of a bed and stream banks . Stream channels exist in a variety of geometries. Stream channel development is controlled by both water and sediment movement. There

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770-436: The desert, hydroponics , fertilizer, nitrogen fertilizer, pesticides , reverse osmosis water processors, PET film insulation or other insulation against heat and cold, digging ditches and hills for protection against the wind, and installing greenhouses with internal light and heat for protection against the cold outside and to provide light in cloudy areas. Such modifications are often prohibitively expensive. An alternative

805-489: The formation of rills is primarily controlled by the slope of the hillside. Slope controls the depth of the rills, while the length of the slope and the soil's permeability control the number of incisions in an area. Each type of soil has a threshold value, a slope angle below which water velocity cannot produce sufficient force to dislodge enough soil particles for rills to form. For instance, on many non-cohesive slopes, this threshold value hovers around an angle of 2 degrees with

840-405: The impracticality of drainage, excessive salts, or a combination of these, among others. Although such limitations may preclude cultivation, and some will in some cases preclude any agricultural use, large areas unsuitable for cultivation may still be agriculturally productive. For example, United States NRCS statistics indicate that about 59 percent of US non-federal pasture and unforested rangeland

875-400: The product of the sediment load and bed Bukhara size is proportional to the product of discharge and channel slope. A term " navigable channel " is used as a nautical term to mean a lane for ship travel, frequently marked (cf. Buoy ) and sometimes dredged . Thoresen distinguishes few categories of channels, from A (suitable for day and night navigation with guaranteed fairway depth ) all

910-402: The production of crops can sometimes be converted to arable land. New arable land makes more food and can reduce starvation . This outcome also makes a country more self-sufficient and politically independent, because food importation is reduced. Making non-arable land arable often involves digging new irrigation canals and new wells, aqueducts, desalination plants, planting trees for shade in

945-433: The slope. These forces explain why sandy, loamy soils are especially susceptible to the formation of rills, whereas dense clays tend to resist rill formation. Rills cannot form on every surface and their formation is intrinsically connected to the steepness of the hillside slope. Gravity determines the force of the water, which provides the power required to start the erosional environment necessary to create rills. Therefore,

980-456: The soil topsoil on hillsides and so are significantly affected by seasonal weather patterns. They tend to appear more often in rainier months. Rills begin to form when the runoff shear stress , the ability of surface runoff to detach soil particles, overcomes the soil's shear strength, the ability of soil to resist force working parallel to the soil's surface. This begins the erosion process as water breaks soil particles free and carries them down

1015-490: The soil of much of its organic content, increasing the erodibility of the soil. Agricultural machines, such as tractors, compact the soil to the point where water flows over the surface rather than seeping into the soil. Tractor wheel impressions often channel water, providing a perfect environment for generating rills. These rills may erode considerable amounts of arable soil if left alone. Under proper field management, rills are small and are easily repaired by contour tilling

1050-421: The soil. This will prevent, for a time at least, the rills from growing and eroding the landscape more rapidly with time. Channel (geography) In physical geography and hydrology , a channel is a landform on which a relatively narrow body of water is situated, such as a river , river delta or strait . While channel typically refers to a natural formation, the cognate term canal denotes

1085-688: The unstable subsequent movement of benthic soils. Responsibility for monitoring navigability conditions of navigation channels to various port facilities varies, and the actual maintenance work is frequently performed by a third party. Storms, sea-states, flooding, and seasonal sedimentation adversely affect navigability . In the U.S., navigation channels are monitored and maintained by the United States Army Corps of Engineers (USACE), although dredging operations are often carried out by private contractors (under USACE supervision). USACE also monitors water quality and some remediation. This

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1120-479: The walls, they weaken, amplifying the chance of wall collapse. The erosion created by these forces increases the size of the rill while also swelling its output volume. Less commonly, dissolution of limestone and other soluble rocks by slightly acidic rainfall and runoff also results in the formation of rill-like features on the surface of the rock. Although rills are small, they transport significant amounts of soil each year. Some estimates claim rill flow has

1155-512: The water between islands is typically called a channel or passage . The English Channel is the strait between England and France. The channel form is described in terms of geometry (plan, cross-sections, profile) enclosed by the materials of its bed and banks. This form is under influence of two major forces: water discharge and sediment supply. For erodible channels the mutual dependence of its parameters may be qualitatively described by Lane's Principle (also known as Lane's relationship ):

1190-400: The way to D with no navigational aids and only estimated depths provided to the shipmaster . With regard to the dredging , channels can be unrestricted (wide enough to accommodate 10-15 widths of a largest ship used in this channel, semi-restricted with limited dredging in shallow waters, and fully restricted , where the entire channel is dredged. The latter, entirely human-made, channel

1225-1326: Was first established under the Rivers and Harbors Act of 1899 and modified under acts of 1913, 1935, and 1938. For example, the USACE developed the Intracoastal Waterway , and has the Mississippi Valley Division responsible for the Mississippi River from the Gulf to Cairo, Illinois , the North Atlantic Division for New York Harbor and Port of Boston , and the South Pacific Division for Port of Los Angeles and Port of Long Beach . Waterways policing as well as some emergency spill response falls under United States Coast Guard jurisdiction, including inland channels serving ports like Saint Louis hundreds of miles from any coast. The various state or local governments maintain lesser channels, for example former Erie Canal . Arable land Arable land (from

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