Shunning

From Wikipedia, the free encyclopedia

https://en.wikipedia.org/wiki/Shunning 

Shunning can be the act of social rejection, or emotional distance. In a religious context, shunning is a formal decision by a denomination or a congregation to cease interaction with an individual or a group, and follows a particular set of rules. It differs from, but may be associated with, excommunication.

Social rejection occurs when a person or group deliberately avoids association with, and habitually keeps away from an individual or group. This can be a formal decision by a group, or a less formal group action which will spread to all members of the group as a form of solidarity. It is a sanction against association, often associated with religious groups and other tightly knit organizations and communities. Targets of shunning can include persons who have been labeled as apostates, whistleblowers, dissidents, strikebreakers, or anyone the group perceives as a threat or source of conflict. Social rejection has been established to cause psychological damage and has been categorized as torture or punishment. Mental rejection is a more individual action, where a person subconsciously or willfully ignores an idea, or a set of information related to a particular viewpoint. Some groups are made up of people who shun the same ideas.

Social rejection was and is a punishment in many customary legal systems. Such sanctions include the ostracism of ancient Athens and the still-used kasepekang in Balinese society.

Overview

Shunning can be broken down into behaviours and practices that seek to accomplish either or both of two primary goals.

1. To modify the behaviour of a member. This approach seeks to influence, encourage, or coerce normative behaviours from members, and may seek to dissuade, provide disincentives for, or to compel avoidance of certain behaviours. Shunning may include disassociating from a member by other members of the community who are in good standing. It may include more antagonistic psychological behaviours (described below). This approach may be seen as either corrective or punitive (or both) by the group membership or leadership, and may also be intended as a deterrent.
2. To remove or limit the influence of a member (or former member) over other members in a community. This approach may seek to isolate, to discredit, or otherwise dis-empower such a member, often in the context of actions or positions advocated by that member. For groups with defined membership criteria, especially based on key behaviours or ideological precepts, this approach may be seen as limiting damage to the community or its leadership. This is often paired with some form of excommunication.

Some less often practiced variants may seek to:

• Remove a specific member from general external influence to provide an ideological or psychological buffer against external views or behaviour. The amount can vary from severing ties to opponents of the group up to and including severing all non-group-affiliated intercourse.

Shunning is usually approved of (if sometimes with regret) by the group engaging in the shunning, and usually highly disapproved of by the target of the shunning, resulting in a polarization of views. Those subject to the practice respond differently, usually depending both on the circumstances of the event, and the nature of the practices being applied. Extreme forms of shunning have damaged some individuals' psychological and relational health. Responses to the practice have developed, mostly around anti-shunning advocacy; such advocates highlight the detrimental effects of many of such behaviors, and seek to limit the practice through pressure or law. Such groups often operate supportive organizations or institutions to help victims of shunning to recover from damaging effects, and sometimes to attack the organizations practicing shunning, as a part of their advocacy.

In many civil societies, kinds of shunning are practiced de facto or de jure, to coerce or avert behaviours or associations deemed unhealthy. This can include:

• restraining orders or peace bonds (to avoid abusive relationships)
• court injunctions to disassociate (to avoid criminal association or temptation)
• medical or psychological instructing to avoid associating (to avoid hazardous relations, i.e. alcoholics being instructed to avoid friendship with non-recovering alcoholics, or asthmatics being medically instructed to keep to smoke-free environs)
• using background checks to avoid hiring people who have criminal records (to avoid association with felons, even when the crimes have nothing to do with the job description)

Stealth shunning

See also: Stealth banning

Stealth shunning is a practice where a person or an action is silently banned. When a person is silently banned, the group they have been banned from does not interact with them. This can be done by secretly distributing a blacklist announcing the person's wrongdoing.

It can happen informally when all people in a group or email list each conclude that they do not want to interact with the person. When an action is silently banned, requests for that action are either ignored or refused with faked explanations.

Effects

Shunning is often used as a pejorative term to describe any organizationally mandated disassociation, and has acquired a connotation of abuse and relational aggression. This is due to the sometimes extreme damage caused by its disruption to normal relationships between individuals, such as friendships and family relations. Disruption of established relationships certainly causes pain, which is at least an unintended consequence of the practices described here, though it may also in many cases be an intended, coercive consequence. This pain, especially when seen as unjustly inflicted, can have secondary general psychological effects on self-worth and self-confidence, trust and trustworthiness, and can, as with other types of trauma, impair psychological function.

Shunning often involves implicit or explicit shame for a member who commits acts seen as wrong by the group or its leadership. Such shame may not be psychologically damaging if the membership is voluntary and the rules of behavior were clear before the person joined. However, if the rules are arbitrary, if the group membership is seen as essential for personal security, safety, or health, or if the application of the rules is inconsistent, such shame can be highly destructive. This can be especially damaging if perceptions are attacked or controlled, or certain tools of psychological pressure applied. Extremes of this cross over the line into psychological torture and can be permanently scarring.

A key detrimental effect of some of the practices associated with shunning relate to their effect on relationships, especially family relationships. At its extremes, the practices may destroy marriages, break up families, and separate children and their parents. The effect of shunning can be very dramatic or even devastating on the shunned, as it can damage or destroy the shunned member's closest familial, spousal, social, emotional, and economic bonds.

Shunning contains aspects of what is known as relational aggression in psychological literature. When used by church members and member-spouse parents against excommunicant parents it contains elements of what psychologists call parental alienation. Extreme shunning may cause traumas to the shunned (and to their dependents) similar to what is studied in the psychology of torture.

Shunning is also a mechanism in family estrangement. When an adult child, sibling, or parent physically and/or emotionally cuts himself off from the family without proper justification, the act traumatizes the family.

Civil rights implications

Some aspects of shunning may also be seen as being at odds with civil rights or human rights, especially those behaviours that coerce and attack. When a group seeks to have an effect through such practices outside its own membership, for instance when a group seeks to cause financial harm through isolation and disassociation, they can come at odds with their surrounding civil society, if such a society enshrines rights such as freedom of association, conscience, or belief. Many civil societies do not extend such protections to the internal operations of communities or organizations so long as an ex-member has the same rights, prerogatives, and power as any other member of the civil society.

In cases where a group or religion is state-sanctioned, a key power, or in the majority (e.g. in Singapore), a shunned former member may face severe social, political, and/or financial costs.

In religion

Christianity

Main article: Excommunication

Passages in the New Testament, such as 1 Corinthians 5:11–13 and Matthew 18:15–17, suggest shunning as an internal practice of early Christians and are cited as such by its modern-day practitioners within Christianity. However, not all Christian scholars or denominations agree on this interpretation of these verses. Douglas A. Jacoby interprets 1 Corinthians 5:11 and Titus 3:9–11 as evidence that members can be excluded from fellowship for matters perceived within the church as grave sin without a religiously acceptable repentance.

Amish

Certain sects of the Amish practice shunning or meidung.

Catholicism

Prior to the Code of Canon Law of 1983, in rare cases (known as excommunication vitandi) the Catholic Church expected adherents to shun an excommunicated member in secular matters.

In 1983, the distinction between vitandi and others (tolerandi) was abolished, and thus the expectation is not made anymore.

Jehovah's Witnesses

Main article: Jehovah's Witnesses and congregational discipline

See also: Jehovah's Witnesses practices § Discipline

Jehovah's Witnesses practise a form of shunning which they refer to as "disfellowshipping". A disfellowshipped person is not to be greeted either socially or at their meetings. Disfellowshipping follows a decision of a judicial committee established by a local congregation that a member is unrepentantly guilty of a "serious sin".

Sociologist Andrew Holden's research indicates that many Witnesses who would otherwise defect because of disillusionment with the organization and its teachings retain affiliation out of fear of being shunned and losing contact with friends and family members.

Judaism

Main article: Herem (censure)

Cherem is the highest ecclesiastical censure in the Jewish community. It is the total exclusion of a person from the Jewish community. It is still used in the Ultra-Orthodox and Chassidic community. In the 21st century, sexual abuse victims and their families who have reported abuse to civil authorities have experienced shunning in the Orthodox communities of New York and Australia.

Baháʼí faith

Main article: Covenant breaker

Members of the Baháʼí Faith are expected to shun those that have been declared Covenant-breakers, and expelled from the religion, by the head of their faith. Covenant-breakers are defined as leaders of schismatic groups that resulted from challenges to legitimacy of Baháʼí leadership, as well as those who follow or refuse to shun them. Unity is considered the highest value in the Baháʼí Faith, and any attempt at schism by a Baháʼí is considered a spiritual sickness, and a negation of that for which the religion stands.

Church of Scientology

Further information: Disconnection (Scientology)

The Church of Scientology asks its members to quit all communication with Suppressive Persons (those whom the Church deems antagonistic to Scientology). The practice of shunning in Scientology is termed disconnection. Members can disconnect from any person they already know, including existing family members. Many examples of this policy's application have been established in court. It used to be customary to write a "disconnection letter" to the person being disconnected from, and to write a public disconnection notice, but these practices have not continued. The Church states that typically only people with "false data" about Scientology are antagonistic, so it encourages members to first attempt to provide "true data" to these people. According to official Church statements, disconnection is only used as a last resort and only lasts until the antagonism ceases. Failure to disconnect from a Suppressive Person is itself labelled a Suppressive act. In the United States, the Church has tried to argue in court that disconnection is a constitutionally protected religious practice. However, this argument was rejected because the pressure put on individual Scientologists to disconnect means it is not voluntary.

Uncertainty

From Wikipedia, the free encyclopedia

https://en.wikipedia.org/wiki/Uncertainty 

 

Situations often arise wherein a decision must be made when the results of each possible choice are uncertain.

Uncertainty refers to epistemic situations involving imperfect or unknown information. It applies to predictions of future events, to physical measurements that are already made, or to the unknown. Uncertainty arises in partially observable or stochastic environments, as well as due to ignorance, indolence, or both. It arises in any number of fields, including insurance, philosophy, physics, statistics, economics, finance, medicine, psychology, sociology, engineering, metrology, meteorology, ecology and information science.

Concepts

Although the terms are used in various ways among the general public, many specialists in decision theory, statistics and other quantitative fields have defined uncertainty, risk, and their measurement as:

Uncertainty

The lack of certainty, a state of limited knowledge where it is impossible to exactly describe the existing state, a future outcome, or more than one possible outcome.

Measurement of uncertainty

A set of possible states or outcomes where probabilities are assigned to each possible state or outcome – this also includes the application of a probability density function to continuous variables.

Second order uncertainty

In statistics and economics, second-order uncertainty is represented in probability density functions over (first-order) probabilities.

Opinions in subjective logic carry this type of uncertainty.

Risk

A state of uncertainty where some possible outcomes have an undesired effect or significant loss.

Measurement of risk

A set of measured uncertainties where some possible outcomes are losses, and the magnitudes of those losses – this also includes loss functions over continuous variables.

Uncertainty versus Variability

There is a difference between uncertainty and variability. Uncertainty is quantified by a probability distribution which depends upon our state of information about the likelihood of what the single, true value of the uncertain quantity is. Variability is quantified by a distribution of frequencies of multiple instances of the quantity, derived from observed data.

Knightian uncertainty

In economics, in 1921 Frank Knight distinguished uncertainty from risk with uncertainty being lack of knowledge which is immeasurable and impossible to calculate. Because of the absence of clearly defined statistics in most economic decisions where people face uncertainty, he believed that we cannot measure probabilities in such cases; this is now referred to as Knightian uncertainty.

Uncertainty must be taken in a sense radically distinct from the familiar notion of risk, from which it has never been properly separated.... The essential fact is that 'risk' means in some cases a quantity susceptible of measurement, while at other times it is something distinctly not of this character; and there are far-reaching and crucial differences in the bearings of the phenomena depending on which of the two is really present and operating.... It will appear that a measurable uncertainty, or 'risk' proper, as we shall use the term, is so far different from an unmeasurable one that it is not in effect an uncertainty at all.

— Frank Knight (1885–1972), Risk, Uncertainty, and Profit (1921), University of Chicago.

There is a fundamental distinction between the reward for taking a known risk and that for assuming a risk whose value itself is not known. It is so fundamental, indeed, that … a known risk will not lead to any reward or special payment at all.

— Frank Knight

Knight pointed out that the unfavorable outcome of known risks can be insured during the decision-making process because it has a clearly defined expected probability distribution. Unknown risks have no known expected probability distribution, which can lead to extremely risky company decisions.

Other taxonomies of uncertainties and decisions include a broader sense of uncertainty and how it should be approached from an ethics perspective:

A taxonomy of uncertainty

There are some things that you know to be true, and others that you know to be false; yet, despite this extensive knowledge that you have, there remain many things whose truth or falsity is not known to you. We say that you are uncertain about them. You are uncertain, to varying degrees, about everything in the future; much of the past is hidden from you; and there is a lot of the present about which you do not have full information. Uncertainty is everywhere and you cannot escape from it.

Dennis Lindley, Understanding Uncertainty (2006)

For example, if it is unknown whether or not it will rain tomorrow, then there is a state of uncertainty. If probabilities are applied to the possible outcomes using weather forecasts or even just a calibrated probability assessment, the uncertainty has been quantified. Suppose it is quantified as a 90% chance of sunshine. If there is a major, costly, outdoor event planned for tomorrow then there is a risk since there is a 10% chance of rain, and rain would be undesirable. Furthermore, if this is a business event and $100,000 would be lost if it rains, then the risk has been quantified (a 10% chance of losing $100,000). These situations can be made even more realistic by quantifying light rain vs. heavy rain, the cost of delays vs. outright cancellation, etc.

Some may represent the risk in this example as the "expected opportunity loss" (EOL) or the chance of the loss multiplied by the amount of the loss (10% × $100,000 = $10,000). That is useful if the organizer of the event is "risk neutral", which most people are not. Most would be willing to pay a premium to avoid the loss. An insurance company, for example, would compute an EOL as a minimum for any insurance coverage, then add onto that other operating costs and profit. Since many people are willing to buy insurance for many reasons, then clearly the EOL alone is not the perceived value of avoiding the risk.

Quantitative uses of the terms uncertainty and risk are fairly consistent from fields such as probability theory, actuarial science, and information theory. Some also create new terms without substantially changing the definitions of uncertainty or risk. For example, surprisal is a variation on uncertainty sometimes used in information theory. But outside of the more mathematical uses of the term, usage may vary widely. In cognitive psychology, uncertainty can be real, or just a matter of perception, such as expectations, threats, etc.

Vagueness is a form of uncertainty where the analyst is unable to clearly differentiate between two different classes, such as 'person of average height.' and 'tall person'. This form of vagueness can be modelled by some variation on Zadeh's fuzzy logic or subjective logic.

Ambiguity is a form of uncertainty where even the possible outcomes have unclear meanings and interpretations. The statement "He returns from the bank" is ambiguous because its interpretation depends on whether the word 'bank' is meant as "the side of a river" or "a financial institution". Ambiguity typically arises in situations where multiple analysts or observers have different interpretations of the same statements.

Uncertainty may be a consequence of a lack of knowledge of obtainable facts. That is, there may be uncertainty about whether a new rocket design will work, but this uncertainty can be removed with further analysis and experimentation.

At the subatomic level, uncertainty may be a fundamental and unavoidable property of the universe. In quantum mechanics, the Heisenberg uncertainty principle puts limits on how much an observer can ever know about the position and velocity of a particle. This may not just be ignorance of potentially obtainable facts but that there is no fact to be found. There is some controversy in physics as to whether such uncertainty is an irreducible property of nature or if there are "hidden variables" that would describe the state of a particle even more exactly than Heisenberg's uncertainty principle allows.

Measurements

Main article: Measurement uncertainty

See also: Uncertainty quantification and Uncertainty propagation

The most commonly used procedure for calculating measurement uncertainty is described in the "Guide to the Expression of Uncertainty in Measurement" (GUM) published by ISO. A derived work is for example the National Institute of Standards and Technology (NIST) Technical Note 1297, "Guidelines for Evaluating and Expressing the Uncertainty of NIST Measurement Results", and the Eurachem/Citac publication "Quantifying Uncertainty in Analytical Measurement". The uncertainty of the result of a measurement generally consists of several components. The components are regarded as random variables, and may be grouped into two categories according to the method used to estimate their numerical values:

• Type A, those evaluated by statistical methods
• Type B, those evaluated by other means, e.g., by assigning a probability distribution

By propagating the variances of the components through a function relating the components to the measurement result, the combined measurement uncertainty is given as the square root of the resulting variance. The simplest form is the standard deviation of a repeated observation.

In metrology, physics, and engineering, the uncertainty or margin of error of a measurement, when explicitly stated, is given by a range of values likely to enclose the true value. This may be denoted by error bars on a graph, or by the following notations:

• measured value ± uncertainty
• measured value ^+uncertainty
  _{−uncertainty}
• measured value (uncertainty)

In the last notation, parentheses are the concise notation for the ± notation. For example, applying 10 1⁄2 meters in a scientific or engineering application, it could be written 10.5 m or 10.50 m, by convention meaning accurate to within one tenth of a meter, or one hundredth. The precision is symmetric around the last digit. In this case it's half a tenth up and half a tenth down, so 10.5 means between 10.45 and 10.55. Thus it is understood that 10.5 means 10.5±0.05, and 10.50 means 10.50±0.005, also written 10.50(5) and 10.500(5) respectively. But if the accuracy is within two tenths, the uncertainty is ± one tenth, and it is required to be explicit: 10.5±0.1 and 10.50±0.01 or 10.5(1) and 10.50(1). The numbers in parentheses apply to the numeral left of themselves, and are not part of that number, but part of a notation of uncertainty. They apply to the least significant digits. For instance, 1.00794(7) stands for 1.00794±0.00007, while 1.00794(72) stands for 1.00794±0.00072. This concise notation is used for example by IUPAC in stating the atomic mass of elements.

The middle notation is used when the error is not symmetrical about the value – for example 3.4+0.3
−0.2. This can occur when using a logarithmic scale, for example.

Uncertainty of a measurement can be determined by repeating a measurement to arrive at an estimate of the standard deviation of the values. Then, any single value has an uncertainty equal to the standard deviation. However, if the values are averaged, then the mean measurement value has a much smaller uncertainty, equal to the standard error of the mean, which is the standard deviation divided by the square root of the number of measurements. This procedure neglects systematic errors, however.

When the uncertainty represents the standard error of the measurement, then about 68.3% of the time, the true value of the measured quantity falls within the stated uncertainty range. For example, it is likely that for 31.7% of the atomic mass values given on the list of elements by atomic mass, the true value lies outside of the stated range. If the width of the interval is doubled, then probably only 4.6% of the true values lie outside the doubled interval, and if the width is tripled, probably only 0.3% lie outside. These values follow from the properties of the normal distribution, and they apply only if the measurement process produces normally distributed errors. In that case, the quoted standard errors are easily converted to 68.3% ("one sigma"), 95.4% ("two sigma"), or 99.7% ("three sigma") confidence intervals.

In this context, uncertainty depends on both the accuracy and precision of the measurement instrument. The lower the accuracy and precision of an instrument, the larger the measurement uncertainty is. Precision is often determined as the standard deviation of the repeated measures of a given value, namely using the same method described above to assess measurement uncertainty. However, this method is correct only when the instrument is accurate. When it is inaccurate, the uncertainty is larger than the standard deviation of the repeated measures, and it appears evident that the uncertainty does not depend only on instrumental precision.

In the media

Uncertainty in science, and science in general, may be interpreted differently in the public sphere than in the scientific community. This is due in part to the diversity of the public audience, and the tendency for scientists to misunderstand lay audiences and therefore not communicate ideas clearly and effectively. One example is explained by the information deficit model. Also, in the public realm, there are often many scientific voices giving input on a single topic. For example, depending on how an issue is reported in the public sphere, discrepancies between outcomes of multiple scientific studies due to methodological differences could be interpreted by the public as a lack of consensus in a situation where a consensus does in fact exist. This interpretation may have even been intentionally promoted, as scientific uncertainty may be managed to reach certain goals. For example, climate change deniers took the advice of Frank Luntz to frame global warming as an issue of scientific uncertainty, which was a precursor to the conflict frame used by journalists when reporting the issue.

"Indeterminacy can be loosely said to apply to situations in which not all the parameters of the system and their interactions are fully known, whereas ignorance refers to situations in which it is not known what is not known." These unknowns, indeterminacy and ignorance, that exist in science are often "transformed" into uncertainty when reported to the public in order to make issues more manageable, since scientific indeterminacy and ignorance are difficult concepts for scientists to convey without losing credibility. Conversely, uncertainty is often interpreted by the public as ignorance. The transformation of indeterminacy and ignorance into uncertainty may be related to the public's misinterpretation of uncertainty as ignorance.

Journalists may inflate uncertainty (making the science seem more uncertain than it really is) or downplay uncertainty (making the science seem more certain than it really is). One way that journalists inflate uncertainty is by describing new research that contradicts past research without providing context for the change. Journalists may give scientists with minority views equal weight as scientists with majority views, without adequately describing or explaining the state of scientific consensus on the issue. In the same vein, journalists may give non-scientists the same amount of attention and importance as scientists.

Journalists may downplay uncertainty by eliminating "scientists' carefully chosen tentative wording, and by losing these caveats the information is skewed and presented as more certain and conclusive than it really is". Also, stories with a single source or without any context of previous research mean that the subject at hand is presented as more definitive and certain than it is in reality. There is often a "product over process" approach to science journalism that aids, too, in the downplaying of uncertainty. Finally, and most notably for this investigation, when science is framed by journalists as a triumphant quest, uncertainty is erroneously framed as "reducible and resolvable".

Some media routines and organizational factors affect the overstatement of uncertainty; other media routines and organizational factors help inflate the certainty of an issue. Because the general public (in the United States) generally trusts scientists, when science stories are covered without alarm-raising cues from special interest organizations (religious groups, environmental organizations, political factions, etc.) they are often covered in a business related sense, in an economic-development frame or a social progress frame. The nature of these frames is to downplay or eliminate uncertainty, so when economic and scientific promise are focused on early in the issue cycle, as has happened with coverage of plant biotechnology and nanotechnology in the United States, the matter in question seems more definitive and certain.

Sometimes, stockholders, owners, or advertising will pressure a media organization to promote the business aspects of a scientific issue, and therefore any uncertainty claims which may compromise the business interests are downplayed or eliminated.

Applications

• Uncertainty is designed into games, most notably in gambling, where chance is central to play.
• In scientific modelling, in which the prediction of future events should be understood to have a range of expected values
• In optimization, uncertainty permits one to describe situations where the user does not have full control on the final outcome of the optimization procedure, see scenario optimization and stochastic optimization.
  • In weather forecasting, it is now commonplace to include data on the degree of uncertainty in a weather forecast.
• Uncertainty or error is used in science and engineering notation. Numerical values should only have to be expressed in those digits that are physically meaningful, which are referred to as significant figures. Uncertainty is involved in every measurement, such as measuring a distance, a temperature, etc., the degree depending upon the instrument or technique used to make the measurement. Similarly, uncertainty is propagated through calculations so that the calculated value has some degree of uncertainty depending upon the uncertainties of the measured values and the equation used in the calculation.
• In physics, the Heisenberg uncertainty principle forms the basis of modern quantum mechanics.
• In metrology, measurement uncertainty is a central concept quantifying the dispersion one may reasonably attribute to a measurement result. Such an uncertainty can also be referred to as a measurement error. In daily life, measurement uncertainty is often implicit ("He is 6 feet tall" give or take a few inches), while for any serious use an explicit statement of the measurement uncertainty is necessary. The expected measurement uncertainty of many measuring instruments (scales, oscilloscopes, force gages, rulers, thermometers, etc.) is often stated in the manufacturers' specifications.
• In engineering, uncertainty can be used in the context of validation and verification of material modeling.
• Uncertainty has been a common theme in art, both as a thematic device (see, for example, the indecision of Hamlet), and as a quandary for the artist (such as Martin Creed's difficulty with deciding what artworks to make).
• Uncertainty is an important factor in economics. According to economist Frank Knight, it is different from risk, where there is a specific probability assigned to each outcome (as when flipping a fair coin). Knightian uncertainty involves a situation that has unknown probabilities.
• Investing in financial markets such as the stock market involves Knightian uncertainty when the probability of a rare but catastrophic event is unknown.

Philosophy

Main article: Philosophical skepticism

In Western philosophy the first philosopher to embrace uncertainty was Pyrrho resulting in the Hellenistic philosophies of Pyrrhonism and Academic Skepticism, the first schools of philosophical skepticism. Aporia and acatalepsy represent key concepts in ancient Greek philosophy regarding uncertainty.

Surface runoff

From Wikipedia, the free encyclopedia

https://en.wikipedia.org/wiki/Surface_runoff 

 

Runoff flowing into a stormwater drain

Pollution

Air pollution

Biological pollution

Electromagnetic pollution

Natural pollution

Noise pollution

Radiation pollution

Soil pollution

Solid waste pollution

Space pollution

Thermal pollution

Visual pollution

War pollution

Water pollution

Surface runoff (also known as overland flow) is the flow of water occurring on the ground surface when excess rainwater, stormwater, meltwater, or other sources, can no longer sufficiently rapidly infiltrate in the soil. This can occur when the soil is saturated by water to its full capacity, and that the rain arrives more quickly than the soil can absorb it. Surface runoff often occurs because impervious areas (such as roofs and pavement) do not allow water to soak into the ground. Furthermore, runoff can occur either through natural or man-made processes. Surface runoff is a major component of the water cycle. It is the primary agent of soil erosion by water. The land area producing runoff that drains to a common point is called a drainage basin.

Runoff that occurs on the ground surface before reaching a channel can be a nonpoint source of pollution, as it can carry man-made contaminants or natural forms of pollution (such as rotting leaves). Man-made contaminants in runoff include petroleum, pesticides, fertilizers and others.

In addition to causing water erosion and pollution, surface runoff in urban areas is a primary cause of urban flooding, which can result in property damage, damp and mold in basements, and street flooding.

Generation

Surface runoff from a hillside after soil is saturated

Surface runoff is defined as precipitation (rain, snow, sleet, or hail) that reaches a surface stream without ever passing below the soil surface. It is distinct from direct runoff, which is runoff that reaches surface streams immediately after rainfall or melting snowfall and excludes runoff generated by the melting of snowpack or glaciers.

Snow and glacier melt occur only in areas cold enough for these to form permanently. Typically snowmelt will peak in the spring and glacier melt in the summer, leading to pronounced flow maxima in rivers affected by them. The determining factor of the rate of melting of snow or glaciers is both air temperature and the duration of sunlight. In high mountain regions, streams frequently rise on sunny days and fall on cloudy ones for this reason.

In areas where there is no snow, runoff will come from rainfall. However, not all rainfall will produce runoff because storage from soils can absorb light showers. On the extremely ancient soils of Australia and Southern Africa, proteoid roots with their extremely dense networks of root hairs can absorb so much rainwater as to prevent runoff even when substantial amounts of rainfall. In these regions, even on less infertile cracking clay soils, high amounts of rainfall and potential evaporation are needed to generate any surface runoff, leading to specialised adaptations to extremely variable (usually ephemeral) streams.

Infiltration excess overland flow

Play media

Stormwater management using trees (animation)

This occurs when the rate of rainfall on a surface exceeds the rate at which water can infiltrate the ground, and any depression storage has already been filled. This is also called Hortonian overland flow (after Robert E. Horton), or unsaturated overland flow. This more commonly occurs in arid and semi-arid regions, where rainfall intensities are high and the soil infiltration capacity is reduced because of surface sealing, or in urban areas where pavements prevent water from infiltrating.

Saturation excess overland flow

When the soil is saturated and the depression storage filled, and rain continues to fall, the rainfall will immediately produce surface runoff. The level of antecedent soil moisture is one factor affecting the time until soil becomes saturated. This runoff is called saturation excess overland flow, saturated overland flow, or Dunne runoff.

Antecedent soil moisture

Soil retains a degree of moisture after a rainfall. This residual water moisture affects the soil's infiltration capacity. During the next rainfall event, the infiltration capacity will cause the soil to be saturated at a different rate. The higher the level of antecedent soil moisture, the more quickly the soil becomes saturated. Once the soil is saturated, runoff occurs. Therefore, surface runoff is a significantly factor in the controlling of soil moisture after medium and low intensity storms.

Subsurface return flow

After water infiltrates the soil on an up-slope portion of a hill, the water may flow laterally through the soil, and exfiltrate (flow out of the soil) closer to a channel. This is called subsurface return flow or throughflow.

As it flows, the amount of runoff may be reduced in a number of possible ways: a small portion of it may evapotranspire; water may become temporarily stored in microtopographic depressions; and a portion of it may infiltrate as it flows overland. Any remaining surface water eventually flows into a receiving water body such as a river, lake, estuary or ocean.

Human influence

Precipitation washing contaminates into local streams

 

Urban surface water runoff

Urbanization increases surface runoff by creating more impervious surfaces such as pavement and buildings that do not allow percolation of the water down through the soil to the aquifer. It is instead forced directly into streams or storm water runoff drains, where erosion and siltation can be major problems, even when flooding is not. Increased runoff reduces groundwater recharge, thus lowering the water table and making droughts worse, especially for agricultural farmers and others who depend on the water wells.

When anthropogenic contaminants are dissolved or suspended in runoff, the human impact is expanded to create water pollution. This pollutant load can reach various receiving waters such as streams, rivers, lakes, estuaries and oceans with resultant water chemistry changes to these water systems and their related ecosystems.

A 2008 report by the United States National Research Council identified urban stormwater as a leading source of water quality problems in the U.S.

As humans continue to alter the climate through the addition of greenhouse gases to the atmosphere, precipitation patterns are expected to change as the atmospheric capacity for water vapor increases. This will have direct consequences on runoff amounts.

See also: Urban runoff and Rainwater harvesting

Effects of surface runoff

Erosion and deposition

Surface runoff can cause erosion of the Earth's surface; eroded material may be deposited a considerable distance away. There are four main types of soil erosion by water: splash erosion, sheet erosion, rill erosion and gully erosion. Splash erosion is the result of mechanical collision of raindrops with the soil surface: soil particles which are dislodged by the impact then move with the surface runoff. Sheet erosion is the overland transport of sediment by runoff without a well defined channel. Soil surface roughness causes may cause runoff to become concentrated into narrower flow paths: as these incise, the small but well-defined channels which are formed are known as rills. These channels can be as small as one centimeter wide or as large as several meters. If runoff continue to incise and enlarge rills, they may eventually grow to become gullies. Gully erosion can transport large amounts of eroded material in a small time period.

Soil erosion by water on intensively-tilled farmland.

Willow hedge strengthened with fascines for the limitation of runoff, north of France.

Reduced crop productivity usually results from erosion, and these effects are studied in the field of soil conservation. The soil particles carried in runoff vary in size from about .001 millimeter to 1.0 millimeter in diameter. Larger particles settle over short transport distances, whereas small particles can be carried over long distances suspended in the water column. Erosion of silty soils that contain smaller particles generates turbidity and diminishes light transmission, which disrupts aquatic ecosystems.

Entire sections of countries have been rendered unproductive by erosion. On the high central plateau of Madagascar, approximately ten percent of that country's land area, virtually the entire landscape is devoid of vegetation, with erosive gully furrows typically in excess of 50 meters deep and one kilometer wide. Shifting cultivation is a farming system which sometimes incorporates the slash and burn method in some regions of the world. Erosion causes loss of the fertile top soil and reduces its fertility and quality of the agricultural produce.

Modern industrial farming is another major cause of erosion. Over a third of the U.S. Corn Belt has completely lost its topsoil. Switching to no-till practices would reduce soil erosion from U.S. agricultural fields by more than 70 percent.

Environmental effects

The principal environmental issues associated with runoff are the impacts to surface water, groundwater and soil through transport of water pollutants to these systems. Ultimately these consequences translate into human health risk, ecosystem disturbance and aesthetic impact to water resources. Some of the contaminants that create the greatest impact to surface waters arising from runoff are petroleum substances, herbicides and fertilizers. Quantitative uptake by surface runoff of pesticides and other contaminants has been studied since the 1960s, and early on contact of pesticides with water was known to enhance phytotoxicity. In the case of surface waters, the impacts translate to water pollution, since the streams and rivers have received runoff carrying various chemicals or sediments. When surface waters are used as potable water supplies, they can be compromised regarding health risks and drinking water aesthetics (that is, odor, color and turbidity effects). Contaminated surface waters risk altering the metabolic processes of the aquatic species that they host; these alterations can lead to death, such as fish kills, or alter the balance of populations present. Other specific impacts are on animal mating, spawning, egg and larvae viability, juvenile survival and plant productivity. Some research shows surface runoff of pesticides, such as DDT, can alter the gender of fish species genetically, which transforms male into female fish.

Surface runoff occurring within forests can supply lakes with high loads of mineral nitrogen and phosphorus leading to eutrophication. Runoff waters within coniferous forests are also enriched with humic acids and can lead to humification of water bodies. Additionally, high standing and young islands in the tropics and subtropics can undergo high soil erosion rates and also contribute large material fluxes to the coastal ocean. Such land derived runoff of sediment nutrients, carbon, and contaminants can have large impacts on global biogeochemical cycles and marine and coastal ecosystems.

In the case of groundwater, the main issue is contamination of drinking water, if the aquifer is abstracted for human use. Regarding soil contamination, runoff waters can have two important pathways of concern. Firstly, runoff water can extract soil contaminants and carry them in the form of water pollution to even more sensitive aquatic habitats. Secondly, runoff can deposit contaminants on pristine soils, creating health or ecological consequences.

Agricultural issues

The other context of agricultural issues involves the transport of agricultural chemicals (nitrates, phosphates, pesticides, herbicides, etc.) via surface runoff. This result occurs when chemical use is excessive or poorly timed with respect to high precipitation. The resulting contaminated runoff represents not only a waste of agricultural chemicals, but also an environmental threat to downstream ecosystems. Pine straws are often used to protect soil from soil erosion and weed growth. However, harvesting these crops may result in the increase of soil erosion.

Economic Issues

Farmland runoff

Surface run-off results in a significant amount of economic effects. Pine straws are cost effective ways of dealing with surface run-off. Moreover, Surface run-off can be reused through the growth of elephant mass. In Nigeria, elephant grass is considered to be an economical way in which surface run-off and erosion can be reduced. Also, China has suffered significant impact from surface run-off to most of their economical crops such as vegetables. Therefore, they are known to have implemented a system which reduced loss of nutrients (nitrogen and phosphorus) in soil.

Flooding

Flooding occurs when a watercourse is unable to convey the quantity of runoff flowing downstream. The frequency with which this occurs is described by a return period. Flooding is a natural process, which maintains ecosystem composition and processes, but it can also be altered by land use changes such as river engineering. Floods can be both beneficial to societies or cause damage. Agriculture along the Nile floodplain took advantage of the seasonal flooding that deposited nutrients beneficial for crops. However, as the number and susceptibility of settlements increase, flooding increasingly becomes a natural hazard. In urban areas, surface runoff is the primary cause of urban flooding, known for its repetitive and costly impact on communities. Adverse impacts span loss of life, property damage, contamination of water supplies, loss of crops, and social dislocation and temporary homelessness. Floods are among the most devastating of natural disasters. The use of supplemental irrigation is also recognized as a significant way in which crops such as maize can retain nitrogen fertilizers in soil, resulting in improvement of crop water availability.

Mitigation and treatment

Runoff holding ponds (Uplands neighborhood of North Bend, Washington)

Mitigation of adverse impacts of runoff can take several forms:

• Land use development controls aimed at minimizing impervious surfaces in urban areas
• Erosion controls for farms and construction sites
• Flood control and retrofit programs, such as green infrastructure
• Chemical use and handling controls in agriculture, landscape maintenance, industrial use, etc.

Land use controls. Many world regulatory agencies have encouraged research on methods of minimizing total surface runoff by avoiding unnecessary hardscape. Many municipalities have produced guidelines and codes (zoning and related ordinances) for land developers that encourage minimum width sidewalks, use of pavers set in earth for driveways and walkways and other design techniques to allow maximum water infiltration in urban settings. An example land use control program can be seen in the city of Santa Monica, California.

Further information: Low-impact development (Canada/US)

Further information: Rainwater harvesting

Erosion controls have appeared since medieval times when farmers realized the importance of contour farming to protect soil resources. Beginning in the 1950s these agricultural methods became increasingly more sophisticated. In the 1960s some state and local governments began to focus their efforts on mitigation of construction runoff by requiring builders to implement erosion and sediment controls (ESCs). This included such techniques as: use of straw bales and barriers to slow runoff on slopes, installation of silt fences, programming construction for months that have less rainfall and minimizing extent and duration of exposed graded areas. Montgomery County, Maryland implemented the first local government sediment control program in 1965, and this was followed by a statewide program in Maryland in 1970.

Flood control programs as early as the first half of the twentieth century became quantitative in predicting peak flows of riverine systems. Progressively strategies have been developed to minimize peak flows and also to reduce channel velocities. Some of the techniques commonly applied are: provision of holding ponds (also called detention basins or balancing lakes) to buffer riverine peak flows, use of energy dissipators in channels to reduce stream velocity and land use controls to minimize runoff.

Chemical use and handling. Following enactment of the U.S. Resource Conservation and Recovery Act (RCRA) in 1976, and later the Water Quality Act of 1987, states and cities have become more vigilant in controlling the containment and storage of toxic chemicals, thus preventing releases and leakage. Methods commonly applied are: requirements for double containment of underground storage tanks, registration of hazardous materials usage, reduction in numbers of allowed pesticides and more stringent regulation of fertilizers and herbicides in landscape maintenance. In many industrial cases, pretreatment of wastes is required, to minimize escape of pollutants into sanitary or stormwater sewers.

The U.S. Clean Water Act (CWA) requires that local governments in urbanized areas (as defined by the Census Bureau) obtain stormwater discharge permits for their drainage systems. Essentially this means that the locality must operate a stormwater management program for all surface runoff that enters the municipal separate storm sewer system ("MS4"). EPA and state regulations and related publications outline six basic components that each local program must contain:

• Public education (informing individuals, households, businesses about ways to avoid stormwater pollution)
• Public involvement (support public participation in implementation of local programs)
• Illicit discharge detection & elimination (removing sanitary sewer or other non-stormwater connections to the MS4)
• Construction site runoff controls (i.e. erosion & sediment controls)
• Post-construction (i.e. permanent) stormwater management controls
• Pollution prevention and "good housekeeping" measures (e.g. system maintenance).

Other property owners which operate storm drain systems similar to municipalities, such as state highway systems, universities, military bases and prisons, are also subject to the MS4 permit requirements.

Measurement and mathematical modeling

Runoff is analyzed by using mathematical models in combination with various water quality sampling methods. Measurements can be made using continuous automated water quality analysis instruments targeted on pollutants such as specific organic or inorganic chemicals, pH, turbidity etc. or targeted on secondary indicators such as dissolved oxygen. Measurements can also be made in batch form by extracting a single water sample and conducting any number of chemical or physical tests on that sample.

In the 1950s or earlier hydrology transport models appeared to calculate quantities of runoff, primarily for flood forecasting. Beginning in the early 1970s computer models were developed to analyze the transport of runoff carrying water pollutants, which considered dissolution rates of various chemicals, infiltration into soils and ultimate pollutant load delivered to receiving waters. One of the earliest models addressing chemical dissolution in runoff and resulting transport was developed in the early 1970s under contract to the United States Environmental Protection Agency (EPA). This computer model formed the basis of much of the mitigation study that led to strategies for land use and chemical handling controls.

Increasingly, stormwater practitioners have recognized the need for Monte Carlo models to simulate stormwater processes because of natural variations in multiple variables that affect the quality and quantity of runofff. The benefit of the Monte Carlo analysis is not to decrease uncertainty in the input statistics, but to represent the different combinations of the variables that determine potential risks of water-quality excursions. One example of this type of stormwater model is the stochastic empirical loading and dilution model (SELDM) is a stormwater quality model. SELDM is designed to transform complex scientific data into meaningful information about the risk of adverse effects of runoff on receiving waters, the potential need for mitigation measures, and the potential effectiveness of such management measures for reducing these risks. SELDM provides a method for rapid assessment of information that is otherwise difficult or impossible to obtain because it models the interactions among hydrologic variables (with different probability distributions) that result in a population of values that represent likely long-term outcomes from runoff processes and the potential effects of different mitigation measures. SELDM also provides the means for rapidly doing sensitivity analyses to determine the potential effects of different input assumptions on the risks for water-quality excursions.

Other computer models have been developed (such as the DSSAM Model) that allow surface runoff to be tracked through a river course as reactive water pollutants. In this case the surface runoff may be considered to be a line source of water pollution to the receiving waters.