Surface runoff (also known as ground flow ) is the flow of water that occurs when excessive rainwater, meltwater, or other sources flow over the Earth's surface. This may be because the soil is saturated with full capacity, because the rain arrives faster than the soil can absorb it, or because the watertight areas (roofs and sidewalks) send their runoff to the surrounding soil that can not absorb it. Surface overtopping is a major component of the water cycle. This is the main agent in soil erosion by water.
The runoff that occurs on the ground before reaching the channel is also called a nonpoint source. If nonpoint sources contain man-made contaminants, or other forms of natural pollution (such as decomposing leaves) their runoff is called non-point source pollution. Land that produces runoff that flows to a common point is called drainage basin. When the flow of the surface flows on the ground, it can take contaminants of the soil including petroleum, pesticides, or fertilizers that become pollution sources of disposal or nonpoin.
In addition to causing water erosion and pollution, surface runoff in urban areas is a major cause of city flooding that can lead to property damage, damp and fungi in the basement, and street flooding.
Video Surface runoff
Generation
Surface runoff can be generated either by rainfall, snowfall or by melting snow, or glaciers.
Snow melting and glaciers only occur in areas cool enough to form permanently. Usually the snow melt will reach its peak in spring and the melting of glaciers in summer, causing maximum flow in the affected river. Factors determining the rate of melting snow or glaciers are the air temperature and the duration of sunlight. In high mountain areas, rivers often rise on sunny days and fall on cloudy for this reason.
In areas where there is no snow, runoff will come from rain. However, not all rainfall will result in runoff because storage from the soil can absorb light rain. In the very ancient lands of Australia and South Africa, the roots of proteoids with their very dense hair roots can absorb so much rainwater to prevent runoff even when rain falls in large quantities. In these areas, even in less fertile clays, high rainfall and potential evaporation are required to produce surface runoff, leading to a particular adaptation to a very variable flow (usually ephemeral).
Flow of overland infiltration
This occurs when the level of precipitation on the surface exceeds the rate at which water can infiltrate the soil, and any storage of depression has been filled. This is called overflow flooding, Horten's inland flow (after Robert E. Horton), or an unsaturated ground flow. This is more common in dry and semi-arid regions, where high rainfall intensity and soil infiltration capacity are reduced due to surface sealing, or in paved areas. This happens in most areas of the city where the sidewalks prevent water from flooding.
Saturation overland overflow
When the soil is saturated and the storage of depression fills up, and the rain continues to fall, rainfall will soon produce surface runoff. The antecedent soil moisture level is one of the factors that affect the time until the soil becomes saturated. This runoff is called overland overland overflow or overland saturated flow.
Previous moisture
Ground maintains moisture level after rain. This residual moisture affects the capacity of soil infiltration. During the ensuing rainfall, infiltration capacity will cause the soil to become saturated at different levels. The higher the moisture level of the antecedent soil, the faster the soil becomes saturated. After the soil is saturated, runoff occurs.
Undercurrent stream
Once the water infiltrated the soil at the top of the hillside, water can flow laterally through the soil, and infiltrate (drain out of the ground) closer to the channel. This is called backflow or subsurface backflow.
When flowing, the amount of runoff may be reduced in a number of possible ways: a small fraction of it may evapotranspiration; water may be stored temporarily in micro-topography deposition; and some of it can infiltrate as it flows overland. The remaining surface water eventually flows into the receiving water body such as rivers, lakes, estuaries or oceans.
Maps Surface runoff
Human influence
Urbanization increases surface runoff by creating more watertight surfaces such as sidewalks and buildings that do not allow percolation of water down through the soil into the aquifer. Instead of being forced directly into a stream or rainwater stream, where erosion and sediment can be a major problem, even when flooding does not occur. Increased runoff reduces soil water infiltration, thus lowering water levels and making droughts worse, especially for farmers and others dependent on water wells.
When anthropogenic contaminants are dissolved or suspended in runoff, human impact is extended to create water pollution. These pollutant loads can reach the various recipient waters such as rivers, rivers, lakes, estuaries and oceans with chemical changes of water produced to the water system and associated ecosystems.
A 2008 report by the US National Research Council identified flash floods as the main source of water quality problems in the US.
As humans continue to change climate through the addition of greenhouse gases to the atmosphere, rainfall patterns are expected to change as atmospheric capacity for water vapor increases. This will have a direct consequence on the amount of runoff.
Surface runoff effect
Erosion and deposition
Surface runoff can cause the erosion of the earth's surface; eroded material can be stored far enough away. There are four main types of soil erosion by water: spark erosion, sheet erosion, rill erosion and bolster erosion. Splash erosion is the result of a mechanical collision of raindrops with soil surface: soil particles released by collision then move with surface runoff. The sheet erosion is the transport of sediments through a well-defined non-channel runoff. The cause of surface soil roughness can cause runoff to be concentrated into narrower flow paths: since it is incised, a well-defined, well-defined channel is known as rills. This channel can be as small as one centimeter or as many as several meters. If runoff continues to incise and enlarge rills, they can eventually grow into a trench. Erosion of bolsters can transport large amounts of eroded material in a short period of time.
Decreased plant productivity is usually the result of erosion, and this effect is studied in the soil conservation field. The ground particles carried in runoff vary in size from about 0.001 millimeter to 1.0 millimeter in diameter. Larger particles settle in short transport distances, whereas small particles can be done with long distances that depend on the water column. The muddy soil erosion that contains smaller particles produces turbidity and reduces light transmission, which disrupts aquatic ecosystems.
All parts of the country have become unproductive due to erosion. In the high plains of Madagascar, approximately ten percent of the country's land area, almost all landscapes have no vegetation, with erosion-shaped grooves usually more than 50 meters wide and 1 kilometer wide. Shifting cultivation is an agricultural system that sometimes combines slash and burn methods in several regions of the world. Erosion causes the loss of fertile soil and reduces the fertility and quality of agricultural produce.
Modern industrial agriculture is another major cause of erosion. In some areas of the American corn belt, more than 50 percent of the original topsoil has been carried over in the last 100 years.
Environmental effects
The major environmental problems associated with runoff are impacts on surface water, groundwater and soil by transporting water pollutants to this system. Ultimately these consequences translate into human health risks, ecosystem disturbances and the aesthetic impact on water resources. Some of the contaminants that create the greatest impact to the surface water that arises from runoff are petroleum, herbicide and fertilizer substances. Quantitative uptake by pesticide surface runoff and other contaminants has been studied since the 1960s, and initial contact of pesticides with water is known to increase phytotoxicity. In the case of surface water, the impact is translated into water pollution, since rivers and streams have received runoff that carries various chemicals or sediments. When surface water is used as a drinking water supply, they can be compromised on health risks and aesthetic drinking water (ie, smell, color and turbidity effects). Contaminated surface water is at risk of altering the metabolic processes of the water species they host; these changes can lead to death, such as killing fish, or altering the balance of the population. Another specific impact is on the viability of animal mating, spawning, eggs and larvae, adolescent survival and crop productivity. Some studies show that pesticide surface runoff, such as DDT, may alter the sex of genetically modified fish species, which convert male fish into female fish.
Surface runoffs occurring within forests can supply lakes with high nitrogen loads and mineral phosphorus leading to eutrophication. Water runoff in coniferous forest is also enriched with humic acid and can cause water body softening. In addition, high and young islands in the tropics and subtropics can experience high levels of soil erosion and also contribute large material fluctuations to the coastal seas. Land derived from sediments from nutrients, carbon, and sediment contaminants can have a major impact on the global biogeochemical cycles and marine and coastal ecosystems.
In the case of ground water, the main problem is the contamination of drinking water, if the aquifer is abstracted for human use. Regarding soil contamination, runoff water can have two important channels of concern. First, water runoff can extract soil contaminants and carry them in the form of water pollution into more sensitive aquatic habitats. Second, runoff can deposit contaminants on pure soils, creating health or ecological consequences.
Agriculture issues
The other context of the agricultural problem involves the transport of agricultural chemicals (nitrates, phosphates, pesticides, herbicides, etc.) through surface runoff. This result occurs when the use of chemicals is excessive or timed poorly with respect to high rainfall. The resulting contaminated runoff is not only agricultural chemical waste, but also environmental threats to the downstream ecosystem.
Flooding
Flooding occurs when a water stream can not convey the amount of runoff flowing downstream. This frequency is explained by the return period. Flooding is a natural process, which retains the composition and process of ecosystems, but can also be altered by land use changes such as river techniques. Floods can benefit the community or cause damage. Farming along the Nile flood plains takes advantage of the seasonal floods that store nutrients that are beneficial to crops. However, as the number and vulnerability of settlements increases, floods are increasingly becoming a natural hazard. In urban areas, surface runoff is a major cause of urban flooding, known for its repeated and costly impacts on society. Adverse effects include loss of life, property damage, water supply contamination, loss of food crops, and social dislocation as well as temporary homelessness. Flooding is one of the most devastating natural disasters.
Mitigation and care
Mitigation of the adverse effects of runoff can take several forms:
- Control of land use development that aims to minimize waterproof surface in urban areas
- Erosion control for agricultural land and construction sites
- Flood control and retrofit programs, such as green infrastructure
- Control of use and handling of chemicals in agriculture, landscape maintenance, industrial use, etc.
Land use control. Many world governing bodies have encouraged research on methods of minimizing total surface runoff by avoiding unnecessary hardscape. Many cities have produced guidelines and codes (zoning and related ordinances) for land developers pushing minimum sidewalk widths, use of earth-arranged pavers for driveways and walkways and other design techniques to allow maximum water infiltration in urban settings. Examples of land use control programs can be seen in the city of Santa Monica, California.
Erosion control has emerged since the middle ages when farmers realized the importance of contour farming to protect soil resources. Beginning in the 1950s, this farming method became increasingly sophisticated. In the 1960s several state and local governments began to focus their efforts on reducing run-off construction by requiring builders to implement erosion and sediment control (ESC). These include techniques such as: the use of straw and obstacles to slow runoff on the slopes, the installation of silt hedges, months of programming constructs that have less rainfall and minimize the level and duration of open 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.
The flood control program as early as the first half of the twentieth century became quantitative in predicting the peak flow of the river system. Progressive strategies have been developed to minimize peak flow and also to reduce channel speed. Some commonly applied techniques are: the provision of a holding pool (also called a place of detention) to support stream flow, use of energy drainage in the canal to reduce flow velocity and control of land use to minimize runoff.
Chemical usage and handling. Following the introduction of the US Conservation and Recovery Act (RCRA) in 1976, and then the 1987 Water Quality Act, states and towns became more vigilant in controlling the storage and storage of toxic chemicals, preventing release and leakage. Commonly used methods are: requirements for double storage of underground storage tanks, registration of use of hazardous materials, reduction of the number of permitted pesticides and stricter regulation of fertilizers and herbicides in landscape maintenance. In many industrial cases, waste pre-treatment is required, to minimize the release of pollutants into sanitary sewers or stormwater.
The US Water Supply Act (CWA) requires that local governments in urban areas (as defined by the Census Bureau) obtain permits for the release of rainwater discharge for their drainage systems. Basically this means that the locality must operate a stormwater management program for all surface runoffs entering the city's separate storm sewer system ("MS4"). The EPA and state regulations and related publications outline six basic components that each must include local programs:
- Public education (informing individuals, households, businesses on how to avoid stormwater pollution)
- Public engagement (supporting public participation in local program implementation)
- Unintentional control of debit & amp; elimination (removing sanitary or other non-stormwater connections to MS4)
- Construction site overrun control (ie erosion control & sediment deposition)
- Stormwater management controls post-construction (ie permanent)
- Pollution prevention and "good spatial" measurement (eg system maintenance).
Other property owners who operate a storm drain system are similar to municipalities, such as state highway systems, universities, military bases and prisons, are also subject to the MS4 license requirements.
Mathematical measurement and modeling
Runoff was analyzed using mathematical models in combination with various water quality sampling methods. Measurements can be made using continuous automatic water quality analysis instruments targeted at pollutants such as certain organic or inorganic chemicals, pH, turbidity etc. Or targeted at secondary indicators such as dissolved oxygen. Measurements can also be done in batch form by extracting a single water sample and performing a number of chemical or physical tests on the sample.
In the 1950s or earlier hydrological transport models appeared to account for the amount of runoff, especially for flood estimates. Beginning in the early 1970s computer models were developed to analyze the transport of runoff carrying water pollutants, which are considered the degree of dissolution of various chemicals, infiltration to soil and final pollutant loads sent to the receiving waters. One of the earliest models to discuss chemical dissolution in runoff and transportation generated was developed in the early 1970s under a contract to the United States Environmental Protection Agency (EPA). This computer model forms the basis of many mitigation studies that lead to strategies for land use and chemical handling control.
Other computer models have been developed (such as the DSSAM Model) that allow surface runoff to be traced through river streams as a reactive water polluter. In this case surface runoff may be considered as a source of water pollution line to the receiving water.
See also
- Agricultural waste
- Farm nutrient abatement
- Catchwater
- Flood forecast
- Hydrological modeling
- National Urban Runoff Program (NURP) - US Research Program
- Nonpoint source pollution
- The runoff curve number
- Reservoir model
- Soil conservation
- Soil contamination
- Stormwater
- Trophic status index
- Urban flooding
- Water pollution
References
External links
- USDA NRCS National Engineering Handbook, Stage Discharge Link, Ch. 14
- http://www.waterlog.info/software.htm provides free downloads of the conceptual model (RainOff) on rainfall-runoff relationships based on nonlinear reservoirs.
- NutrientNet, an online nutrition trading tool developed by the World Resources Institute, designed to address water quality issues related to surface runoff and other pollution. See also PA NutrientNet website designed for the Pennsylvania nutrition trade program.
- Bioretention as a low impact development method for treating surface runoff
- EPA Storm Water Permit Program
- EPA - Stormwater Menu Best Management Practices
- Automatic Rainfall-Runoff Seal Calibration Using Swarm Algorithms Fast Multi-purpose and Elitist Particles
- Automatic calibration of fast flood deployment models using multiobjective optimizations
- Automatic sensitivity and calibration analysis of rainfall models with multi-purpose runoff
- Hurricane Water License: Status of Research Service EPA Congress, Research Services
Source of the article : Wikipedia
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