Mining is the extraction of valuable minerals or other geological materials from the earth from an ore body, vein, reef or placer deposit. These deposits form a mineralized package, of economic interest to the miner. Ores recovered by mining include metals, oil shale, limestone, dimension stone, rock salt, potash and clay. Mining is required to obtain any material that cannot be grown through agricultural processes, or feasibly created artificially in a laboratory or factory. Mining in a wider sense includes extraction of any non-renewable resource such as petroleum, natural gas, or water. Mining of stones and metal has been a human activity since pre-historic times. Modern mining processes involve prospecting for ore bodies, analysis of the profit potential of a proposed mine, extraction of the desired materials, final reclamation of the land after the mine is closed. De Re Metallica, Georgius Agricola, 1550, Book I, Para. 1Mining operations create a negative environmental impact, both during the mining activity and after the mine has closed.
Hence, most of the world's nations have passed regulations to decrease the impact. Work safety has long been a concern as well, modern practices have improved safety in mines. Levels of metals recycling are low. Unless future end-of-life recycling rates are stepped up, some rare metals may become unavailable for use in a variety of consumer products. Due to the low recycling rates, some landfills now contain higher concentrations of metal than mines themselves. Since the beginning of civilization, people have used stone and metals found close to the Earth's surface; these were used to make early weapons. Flint mines have been found in chalk areas where seams of the stone were followed underground by shafts and galleries; the mines at Grimes Graves and Krzemionki are famous, like most other flint mines, are Neolithic in origin. Other hard rocks mined or collected for axes included the greenstone of the Langdale axe industry based in the English Lake District; the oldest-known mine on archaeological record is the Ngwenya Mine in Swaziland, which radiocarbon dating shows to be about 43,000 years old.
At this site Paleolithic humans mined hematite to make the red pigment ochre. Mines of a similar age in Hungary are believed to be sites where Neanderthals may have mined flint for weapons and tools. Ancient Egyptians mined malachite at Maadi. At first, Egyptians used the bright green malachite stones for ornamentations and pottery. Between 2613 and 2494 BC, large building projects required expeditions abroad to the area of Wadi Maghareh in order to secure minerals and other resources not available in Egypt itself. Quarries for turquoise and copper were found at Wadi Hammamat, Tura and various other Nubian sites on the Sinai Peninsula and at Timna. Mining in Egypt occurred in the earliest dynasties; the gold mines of Nubia were among the largest and most extensive of any in Ancient Egypt. These mines are described by the Greek author Diodorus Siculus, who mentions fire-setting as one method used to break down the hard rock holding the gold. One of the complexes is shown in one of the earliest known maps.
The miners crushed the ore and ground it to a fine powder before washing the powder for the gold dust. Mining in Europe has a long history. Examples include the silver mines of Laurium. Although they had over 20,000 slaves working them, their technology was identical to their Bronze Age predecessors. At other mines, such as on the island of Thassos, marble was quarried by the Parians after they arrived in the 7th century BC; the marble was shipped away and was found by archaeologists to have been used in buildings including the tomb of Amphipolis. Philip II of Macedon, the father of Alexander the Great, captured the gold mines of Mount Pangeo in 357 BC to fund his military campaigns, he captured gold mines in Thrace for minting coinage producing 26 tons per year. However, it was the Romans who developed large scale mining methods the use of large volumes of water brought to the minehead by numerous aqueducts; the water was used for a variety of purposes, including removing overburden and rock debris, called hydraulic mining, as well as washing comminuted, or crushed and driving simple machinery.
The Romans used hydraulic mining methods on a large scale to prospect for the veins of ore a now-obsolete form of mining known as hushing. They built numerous aqueducts to supply water to the minehead. There, the water stored in large tanks; when a full tank was opened, the flood of water sluiced away the overburden to expose the bedrock underneath and any gold veins. The rock was worked upon by fire-setting to heat the rock, which would be quenched with a stream of water; the resulting thermal shock cracked the rock, enabling it to be removed by further streams of water from the overhead tanks. The Roman miners used similar methods to work cassiterite deposits in Cornwall and lead ore in the Pennines; the methods had been developed by the Romans in Spain in 25 AD to exploit large alluvial gold deposits, the largest site being at Las Medulas, where seven long aqueducts tapped local rivers and sluiced the deposits. Spain was one of the most important mining regions, but all regions of the Roman Empire were exploited.
In Great Britain the natives had mined minerals for millennia, but after the Roman conquest, the scale of the operations increased as the Romans needed Britannia's resources gold, silver
Human impact on the environment
Human impact on the environment or anthropogenic impact on the environment includes changes to biophysical environments and ecosystems and natural resources caused directly or indirectly by humans, including global warming, environmental degradation, mass extinction and biodiversity loss, ecological crisis, ecological collapse. Modifying the environment to fit the needs of society is causing severe effects, which become worse as the problem of human overpopulation continues; some human activities that cause damage to the environment on a global scale include human reproduction, overexploitation and deforestation, to name but a few. Some of the problems, including global warming and biodiversity loss pose an existential risk to the human race, overpopulation causes those problems; the term anthropogenic object resulting from human activity. The term was first used in the technical sense by Russian geologist Alexey Pavlov, it was first used in English by British ecologist Arthur Tansley in reference to human influences on climax plant communities.
The atmospheric scientist Paul Crutzen introduced the term "Anthropocene" in the mid-1970s. The term is sometimes used in the context of pollution emissions that are produced from human activity but applies broadly to all major human impacts on the environment. David Attenborough described the level of human population on the planet as a multiplier of all other environmental problems. In 2013, he described humanity as "a plague on the Earth" that needs to be controlled by limiting population growth; some deep ecologists, such as the radical thinker and polemicist Pentti Linkola, see human overpopulation as a threat to the entire biosphere. In 2017, over 15,000 scientists around the world issued a second warning to humanity which asserted that rapid human population growth is the "primary driver behind many ecological and societal threats." Overconsumption is a situation where resource use has outpaced the sustainable capacity of the ecosystem. It can be measured by the ecological footprint, a resource accounting approach which compares human demand on ecosystems with the amount of planet matter ecosystems can renew.
Estimates indicate that humanity's current demand is 70% higher than the regeneration rate of all of the planet's ecosystems combined. A prolonged pattern of overconsumption leads to environmental degradation and the eventual loss of resource bases. Humanity's overall impact on the planet is affected by many factors, not just the raw number of people, their lifestyle and the pollution they generate are important. In 2008, The New York Times stated that the inhabitants of the developed nations of the world consume resources like oil and metals at a rate 32 times greater than those of the developing world, who make up the majority of the human population; the effects of overpopulation are compounded by overconsumption. According to Paul R. Ehrlich: Rich western countries are now siphoning up the planet’s resources and destroying its ecosystems at an unprecedented rate. We want to build highways across the Serengeti to get more rare earth minerals for our cellphones. We wreck the coral reefs and put carbon dioxide into the atmosphere.
We have triggered a major extinction event A world population of around a billion would have an overall pro-life effect. This could be supported for many millennia and sustain many more human lives in the long term compared with our current uncontrolled growth and prospect of sudden collapse If everyone consumed resources at the US level –, what the world aspires to – you will need another four or five Earths. We are wrecking our planet’s life support systems. Humanity has caused the loss of 83% of all wild mammals and half of plants The world’s chickens are triple the weight of all the wild birds, while domesticated cattle and pigs outweigh all wild mammals by 14 to 1; the applications of technology result in unavoidable and unexpected environmental impacts, which according to the I = PAT equation is measured as resource use or pollution generated per unit GDP. Environmental impacts caused by the application of technology are perceived as unavoidable for several reasons. First, given that the purpose of many technologies is to exploit, control, or otherwise “improve” upon nature for the perceived benefit of humanity while at the same time the myriad of processes in nature have been optimized and are continually adjusted by evolution, any disturbance of these natural processes by technology is to result in negative environmental consequences.
Second, the conservation of mass principle and the first law of thermodynamics dictate that whenever material resources or energy are moved around or manipulated by technology, environmental consequences are inescapable. Third, according to the second law of thermodynamics, order can be increased within a system only by increasing disorder or entropy outside the system. Thus, technologies can create “order” in the human economy only at the expense of increasing “disorder” in the environment. According to a number of studies, increased entropy is to be correlated to negative environmental impacts; the environmental impact of agriculture varies based on the wide variety of agricultural practices employed around the world. The environmental impact depends on the production practices of the system used by farmers; the connection between emissions into th
Coppicing is a traditional method of woodland management which exploits the capacity of many species of trees to put out new shoots from their stump or roots if cut down. In a coppiced wood, called a copse, young tree stems are cut down to near ground level, known as a stool. New growth emerges and after a number of years, the coppiced tree is harvested and the cycle begins anew. Pollarding is a similar process carried out at a higher level on the tree. Many silviculture practices involve regrowth; the widespread and long-term practice of coppicing as a landscape-scale industry is something that remains of special importance in southern England. Many of the English-language terms referenced in this article are relevant to historic and contemporary practice in that area. A coppiced woodland is harvested in sections or coups on a rotation. In this way, a crop is available each year somewhere in the woodland. Coppicing has the effect of providing a rich variety of habitats, as the woodland always has a range of different-aged coppice growing in it, beneficial for biodiversity.
The cycle length depends upon the species cut, the local custom, the use to which the product is put. Birch can be coppiced for faggots on a three- or four-year cycle, whereas oak can be coppiced over a fifty-year cycle for poles or firewood. Coppicing maintains trees at a juvenile stage, a coppiced tree will never die of old age; the age of a stool may be estimated from its diameter, some are so large—perhaps as much as 5.4 metres across—that they are thought to have been continually coppiced for centuries. Evidence suggests. Coppiced stems are characteristically curved at the base; this curve occurs as the competing stems grow out from the stool in the early stages of the cycle up towards the sky as the canopy closes. The curve may allow the identification of coppice timber in archaeological sites. Timber in the Sweet Track in Somerset has been identified as coppiced lime; the silvicultural system now called coppicing was practiced for small wood production. In German this is called Niederwald.
On in Mediaeval times farmers encouraged pigs to feed from acorns and so some trees were allowed to grow bigger. This different silvicultural system is called in English coppice with standards. In German this is called Mittelwald; as modern forestry seeks to harvest timber mechanically, pigs are no longer fed from acorns, both systems have declined. However, there are cultural and wildlife benefits from these 2 silvicultural systems so both can be found where timber production or some other main forestry purpose is not the sole management objective of the woodland. In the 16th and 17th centuries the technology of charcoal iron production became established in England, continuing in some areas until the late 19th century Along with the growing need for oak bark for tanning, this required large amounts of coppice wood. With this coppice management, wood could be provided for those growing industries in principle indefinitely; this was regulated by a statute of 1544 of Henry VIII, which required woods to be enclosed after cutting and 12 standels to be left in each acre, to be grown into timber.
Coppice with standards has been used throughout most of Europe as a means of giving greater flexibility in the resulting forest product from any one area. The woodland provides not only the small material from the coppice but a range of larger timber for jobs like house building, bridge repair, cart-making and so on. In the 18th century coppicing in Britain began a long decline; this was brought about by the erosion of its traditional markets. Firewood was no longer needed for domestic or industrial uses as coal and coke became obtained and transported, wood as a construction material was replaced by newer materials. Coppicing died out first in the north of Britain and contracted towards the south-east until by the 1960s active commercial coppice was concentrated in Kent and Sussex; the shoots may be used either in their young state for interweaving in wattle fencing or the new shoots may be allowed to grow into large poles, as was the custom with trees such as oaks or ashes. This creates long, straight poles which do not have the bends and forks of grown trees.
Coppicing may be practiced to encourage specific growth patterns, as with cinnamon trees which are grown for their bark. Another, more complicated system is called compound coppice. Here some of the standards would be left; some of the coppice would be allowed to grow into new standards and some regenerated coppice would be there. Thus there would be three age classes. Coppiced hardwoods were used extensively in carriage and shipbuilding, they are still sometimes grown for making wooden buildings and furniture. Withies for wicker-work are grown in coppices of various willow species, principally osier. In France, chestnut trees are coppiced for use as canes and bâtons for the martial art Canne de combat; some Eucalyptus species are coppiced in a number of countries. The Sal tree is coppiced in India, the Moringa oleifera tree is
Pollution is the introduction of contaminants into the natural environment that cause adverse change. Pollution can take the form such as noise, heat or light. Pollutants, the components of pollution, can be either foreign substances/energies or occurring contaminants. Pollution is classed as point source or nonpoint source pollution. In 2015, pollution killed 9 million people in the world. Major forms of pollution include: Air pollution, light pollution, noise pollution, plastic pollution, soil contamination, radioactive contamination, thermal pollution, visual pollution, water pollution. Air pollution has always accompanied civilizations. Pollution started from prehistoric times. According to a 1983 article in the journal Science, "soot" found on ceilings of prehistoric caves provides ample evidence of the high levels of pollution, associated with inadequate ventilation of open fires." Metal forging appears to be a key turning point in the creation of significant air pollution levels outside the home.
Core samples of glaciers in Greenland indicate increases in pollution associated with Greek and Chinese metal production. The burning of coal and wood, the presence of many horses in concentrated areas made the cities the primary sources of pollution; the Industrial Revolution brought an infusion of untreated chemicals and wastes into local streams that served as the water supply. King Edward I of England banned the burning of sea-coal by proclamation in London in 1272, after its smoke became a problem, it was the industrial revolution. London recorded one of the earlier extreme cases of water quality problems with the Great Stink on the Thames of 1858, which led to construction of the London sewerage system soon afterward. Pollution issues escalated as population growth far exceeded viability of neighborhoods to handle their waste problem. Reformers began to clean water. In 1870, the sanitary conditions in Berlin were among the worst in Europe. August Bebel recalled conditions before a modern sewer system was built in the late 1870s: "Waste-water from the houses collected in the gutters running alongside the curbs and emitted a fearsome smell.
There were no public toilets in the squares. Visitors women became desperate when nature called. In the public buildings the sanitary facilities were unbelievably primitive.... As a metropolis, Berlin did not emerge from a state of barbarism into civilization until after 1870."The primitive conditions were intolerable for a world national capital, the Imperial German government brought in its scientists and urban planners to not only solve the deficiencies, but to forge Berlin as the world's model city. A British expert in 1906 concluded that Berlin represented "the most complete application of science and method of public life," adding "it is a marvel of civic administration, the most modern and most organized city that there is."The emergence of great factories and consumption of immense quantities of coal gave rise to unprecedented air pollution and the large volume of industrial chemical discharges added to the growing load of untreated human waste. Chicago and Cincinnati were the first two American cities to enact laws ensuring cleaner air in 1881.
Pollution became a major issue in the United States in the early twentieth century, as progressive reformers took issue with air pollution caused by coal burning, water pollution caused by bad sanitation, street pollution caused by the 3 million horses who worked in American cities in 1900, generating large quantities of urine and manure. As historian Martin Melosi notes, The generation that first saw automobiles replacing the horses saw cars as "miracles of cleanliness.". By the 1940s, automobile-caused smog was a major issue in Los Angeles. Other cities followed around the country until early in the 20th century, when the short lived Office of Air Pollution was created under the Department of the Interior. Extreme smog events were experienced by the cities of Los Angeles and Donora, Pennsylvania in the late 1940s, serving as another public reminder. Air pollution would continue to be a problem in England later during the industrial revolution, extending into the recent past with the Great Smog of 1952.
Awareness of atmospheric pollution spread after World War II, with fears triggered by reports of radioactive fallout from atomic warfare and testing. A non-nuclear event – the Great Smog of 1952 in London – killed at least 4000 people; this prompted some of the first major modern environmental legislation: the Clean Air Act of 1956. Pollution began to draw major public attention in the United States between the mid-1950s and early 1970s, when Congress passed the Noise Control Act, the Clean Air Act, the Clean Water Act, the National Environmental Policy Act. Severe incidents of pollution helped increase consciousness. PCB dumping in the Hudson River resulted in a ban by the EPA on consumption of its fish in 1974. National news stories in the late 1970s – the long-term dioxin contamination at Love Canal starting in 1947 and uncontrolled dumping in Valley of the Drums – led to the Superfund legislation of 1980; the pollution of industrial land gave rise to the name brownfield, a term now common in city planning.
The development of nuclear science introduced radioactive contamination, which can remain lethally radioactive for hundreds of thousands of years. Lake Karachay – named by the Worldwatch Institute as the "most polluted
A quarry is a type of open-pit mine in which dimension stone, construction aggregate, sand, gravel, or slate is excavated from the ground. The word quarry can include the underground quarrying for stone, such as Bath stone. Types of rock extracted from quarries include: Chalk China clay Cinder Clay Coal Construction aggregate Coquina Diabase Gabbro Granite Gritstone Gypsum Limestone Marble Ores Phosphate rock Quartz Sandstone Slate Many quarry stones such as marble, granite and sandstone are cut into larger slabs and removed from the quarry; the surfaces finished with varying degrees of sheen or luster. Polished slabs are cut into tiles or countertops and installed in many kinds of residential and commercial properties. Natural stone quarried from the earth is considered a luxury and tends to be a durable surface, thus desirable. Quarries in level areas with shallow groundwater or which are located close to surface water have engineering problems with drainage; the water is removed by pumping while the quarry is operational, but for high inflows more complex approaches may be required.
For example, the Coquina quarry is excavated to more than 60 feet below sea level. To reduce surface leakage, a moat lined with clay was constructed around the entire quarry. Ground water entering the pit is pumped up into the moat; as a quarry becomes deeper, water inflows increase and it becomes more expensive to lift the water higher during removal. Some water-filled quarries are worked by dredging. Many people and municipalities consider quarries to be eyesores and require various abatement methods to address problems with noise and appearance. One of the more effective and famous examples of successful quarry restoration is Butchart Gardens in Victoria, BC, Canada. A further problem is pollution of roads from trucks leaving the quarries. To control and restrain the pollution of public roads, wheel washing systems are becoming more common. Many quarries fill with water after abandonment and become lakes. Others are made into landfills. Water-filled quarries can be deep 50 ft or more, cold, so swimming in quarry lakes is not recommended.
Unexpectedly cold water can cause a swimmer's muscles to weaken. Though quarry water is very clear, submerged quarry stones and abandoned equipment make diving into these quarries dangerous. Several people drown in quarries each year. However, many inactive quarries are converted into safe swimming sites; such lakes lakes within active quarries, can provide important habitat for animals. Clay pit Coal mining Collecting fossils Gravel pit List of minerals List of rock types List of stones Miner Mountaintop removal mining Opencast mining Quarry lake Quarries
Lumber or timber is a type of wood, processed into beams and planks, a stage in the process of wood production. Lumber is used for structural purposes but has many other uses as well. There are two main types of lumber, it may be surfaced on one or more of its faces. Besides pulpwood, rough lumber is the raw material for furniture-making and other items requiring additional cutting and shaping, it is available in many species hardwoods. Finished lumber is supplied in standard sizes for the construction industry – softwood, from coniferous species, including pine and spruce, hemlock, but some hardwood, for high-grade flooring, it is more made from softwood than hardwoods, 80% of lumber comes from softwood. In the United States milled boards of wood are referred to as lumber. However, in Britain and other Commonwealth nations, the term timber is instead used to describe sawn wood products, like floor boards. In the United States and Canada timber describes standing or felled trees. In Canada, lumber describes cut and surfaced wood.
In the United Kingdom, the word lumber is used in relation to wood and has several other meanings, including unused or unwanted items. Referring to wood, Timber is universally used instead. Remanufactured lumber is the result of secondary or tertiary processing/cutting of milled lumber, it is lumber cut for industrial or wood-packaging use. Lumber is cut by ripsaw or resaw to create dimensions that are not processed by a primary sawmill. Resawing is the splitting of 1-inch through 12-inch hardwood or softwood lumber into two or more thinner pieces of full-length boards. For example, splitting a ten-foot 2×4 into two ten-foot 1×4s is considered resawing. Structural lumber may be produced from recycled plastic and new plastic stock, its introduction has been opposed by the forestry industry. Blending fiberglass in plastic lumber enhances its strength and fire resistance. Plastic fiberglass structural lumber can have a "class 1 flame spread rating of 25 or less, when tested in accordance with ASTM standard E 84," which means it burns slower than all treated wood lumber.
Logs are converted into timber by being hewn, or split. Sawing with a rip saw is the most common method, because sawing allows logs of lower quality, with irregular grain and large knots, to be used and is more economical. There are various types of sawing: Plain sawn – A log sawn through without adjusting the position of the log and the grain runs across the width of the boards. Quarter sawn and rift sawn – These terms have been confused in history but mean lumber sawn so the annual rings are reasonably perpendicular to the sides of the lumber. Boxed heart – The pith remains within the piece with some allowance for exposure. Heart center – the center core of a log. Free of heart center – A side-cut timber without any pith. Free of knots – No knots are present. Dimensional lumber is lumber, cut to standardized width and depth, specified in inches. Carpenters extensively use dimensional lumber in framing wooden buildings. Common sizes include 2×4, 2×6, 4×4; the length of a board is specified separately from the width and depth.
It is thus possible to find 2×4s that are four and twelve feet in length. In Canada and the United States, the standard lengths of lumber are 6, 8, 10, 12, 14, 16, 18, 20, 22 and 24 feet. For wall framing, "stud" or "precut" sizes are available, are used. For an eight-, nine-, or ten-foot ceiling height, studs are available in 92 5⁄8 inches, 104 5⁄8 inches, 116 5⁄8 inches; the term "stud" is used inconsistently to specify length. Under the prescription of the Method of Construction issued by the Southern Song government in the early 12th century, timbers were standardized to eight cross-sectional dimensions. Regardless of the actual dimensions of the timber, the ratio between width and height was maintained at 1:1.5. Units are in Song Dynasty inches. Timber smaller than the 8th class were called "unclassed"; the width of a timber is referred to as one "timber", the dimensions of other structural components were quoted in multiples of "timber". The dimensions of timbers in similar application show a gradual diminution from the Sui Dyansty to the modern era.
The length of a unit of dimensional lumber is limited by the height and girth of the tree it is milled from. In general the maximum length is 24 ft. Engineered wood products, manufactured by binding the strands, fibers, or veneers of wood, together with adhesives, to form composite materials, offer more flexibility and greater structural strength than typical wood building materials. Pre-cut studs save a framer much time, because they are pre-cut by the manufacturer for use in 8-, 9-
In earth science, erosion is the action of surface processes that removes soil, rock, or dissolved material from one location on the Earth's crust, transports it to another location. This natural process is caused by the dynamic activity of erosive agents, that is, ice, air, plants and humans. In accordance with these agents, erosion is sometimes divided into water erosion, glacial erosion, snow erosion, wind erosion, zoogenic erosion, anthropogenic erosion; the particulate breakdown of rock or soil into clastic sediment is referred to as physical or mechanical erosion. Eroded sediment or solutes may be transported just a few millimetres, or for thousands of kilometres. Natural rates of erosion are controlled by the action of geological weathering geomorphic drivers, such as rainfall; the rates at which such processes act control. Physical erosion proceeds fastest on steeply sloping surfaces, rates may be sensitive to some climatically-controlled properties including amounts of water supplied, wind speed, wave fetch, or atmospheric temperature.
Feedbacks are possible between rates of erosion and the amount of eroded material, carried by, for example, a river or glacier. Processes of erosion that produce sediment or solutes from a place contrast with those of deposition, which control the arrival and emplacement of material at a new location. While erosion is a natural process, human activities have increased by 10-40 times the rate at which erosion is occurring globally. At well-known agriculture sites such as the Appalachian Mountains, intensive farming practices have caused erosion up to 100x the speed of the natural rate of erosion in the region. Excessive erosion causes both "on-site" and "off-site" problems. On-site impacts include decreases in agricultural productivity and ecological collapse, both because of loss of the nutrient-rich upper soil layers. In some cases, the eventual end result is desertification. Off-site effects include sedimentation of waterways and eutrophication of water bodies, as well as sediment-related damage to roads and houses.
Water and wind erosion are the two primary causes of land degradation. Intensive agriculture, roads, anthropogenic climate change and urban sprawl are amongst the most significant human activities in regard to their effect on stimulating erosion. However, there are many prevention and remediation practices that can curtail or limit erosion of vulnerable soils. Rainfall, the surface runoff which may result from rainfall, produces four main types of soil erosion: splash erosion, sheet erosion, rill erosion, gully erosion. Splash erosion is seen as the first and least severe stage in the soil erosion process, followed by sheet erosion rill erosion and gully erosion. In splash erosion, the impact of a falling raindrop creates a small crater in the soil, ejecting soil particles; the distance these soil particles travel can be as much as 0.6 m vertically and 1.5 m horizontally on level ground. If the soil is saturated, or if the rainfall rate is greater than the rate at which water can infiltrate into the soil, surface runoff occurs.
If the runoff has sufficient flow energy, it will transport loosened soil particles down the slope. Sheet erosion is the transport of loosened soil particles by overland flow. Rill erosion refers to the development of small, ephemeral concentrated flow paths which function as both sediment source and sediment delivery systems for erosion on hillslopes. Where water erosion rates on disturbed upland areas are greatest, rills are active. Flow depths in rills are of the order of a few centimetres or less and along-channel slopes may be quite steep; this means that rills exhibit hydraulic physics different from water flowing through the deeper, wider channels of streams and rivers. Gully erosion occurs when runoff water accumulates and flows in narrow channels during or after heavy rains or melting snow, removing soil to a considerable depth. Valley or stream erosion occurs with continued water flow along a linear feature; the erosion is both downward, deepening the valley, headward, extending the valley into the hillside, creating head cuts and steep banks.
In the earliest stage of stream erosion, the erosive activity is dominantly vertical, the valleys have a typical V cross-section and the stream gradient is steep. When some base level is reached, the erosive activity switches to lateral erosion, which widens the valley floor and creates a narrow floodplain; the stream gradient becomes nearly flat, lateral deposition of sediments becomes important as the stream meanders across the valley floor. In all stages of stream erosion, by far the most erosion occurs during times of flood when more and faster-moving water is available to carry a larger sediment load. In such processes, it is not the water alone