Surface runoff

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Runoff flowing into a stormwater drain
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Surface runoff (also known as overland flow or terrestrial runoff) is the unconfined flow of

channel runoff (or stream flow). It occurs 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 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 human-made processes.[1]

Surface runoff is a major component of the water cycle. It is the primary agent of soil erosion by water.[2][3] 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 human-made contaminants or natural forms of pollution (such as rotting leaves). Human-made contaminants in runoff include petroleum, pesticides, fertilizers and others.[4] Much agricultural pollution is exacerbated by surface runoff, leading to a number of down stream impacts, including nutrient pollution that causes eutrophication.

In addition to causing water erosion and pollution, surface

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[5]) that reaches a surface stream without ever passing below the soil surface.[6] 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.[7]

Snow and glacier melt occur only in areas cold enough for these to form permanently. Typically snowmelt will peak in the spring[8] and glacier melt in the summer,[9] leading to pronounced flow maxima in rivers affected by them.[10] The determining factor of the rate of melting of snow or glaciers is both air temperature and the duration of sunlight.[11] 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

proteoid roots with their extremely dense networks of root hairs can absorb so much rainwater as to prevent runoff even with 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

Stormwater management using trees (animation)

This occurs when the rate of

surface sealing, or in urban areas where pavements prevent water from infiltrating.[15]

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,[15] saturated overland flow,[16] or Dunne runoff.[17]

Antecedent soil moisture

Soil retains a degree of moisture after a

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.[18]

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.[19]

Human influence

Precipitation washing contaminates into local streams
Urban surface water runoff

water wells.[20]

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.[21]

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.[22]

Urban runoff

This section is an excerpt from Urban runoff.[edit]
Urban runoff flowing into a storm drain

storm drains, instead of allowing the water to percolate through soil.[24] This causes lowering of the water table (because groundwater recharge is lessened) and flooding since the amount of water that remains on the surface is greater.[25][26] Most municipal storm sewer systems discharge untreated stormwater to streams, rivers, and bays
. This excess water can also make its way into people's properties through basement backups and seepage through building wall and floors.

Urban runoff can be a major source of urban flooding and water pollution in urban communities worldwide.
Willow hedge strengthened with fascines for the limitation of runoff, north of France
Soil erosion by water on intensively-tilled farmland

Industrial runoff

This section is an excerpt from Industrial stormwater.[edit]
Industrial stormwater is runoff from precipitation (rain, snow, sleet, freezing rain, or hail) that lands on industrial sites (e.g. manufacturing facilities, mines, airports). This runoff is often polluted by materials that are handled or stored on the sites, and the facilities are subject to regulations to control the discharges.[27][28]

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.

Reduced crop productivity usually results from erosion, and these effects are studied in the field of

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

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.[29] Switching to no-till practices would reduce soil erosion from U.S. agricultural fields by more than 70 percent.[30]

Environmental effects

The principal environmental issues associated with runoff are the impacts to surface water,

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.[32]

Surface runoff occurring within forests can supply lakes with high loads of mineral nitrogen and phosphorus leading to

humic acids and can lead to humification of water bodies [33] 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.[34]

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

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.[35]
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.[36] 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.[37]

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.[38] 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.[39]

Mitigation and treatment

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

Mitigation of adverse impacts of runoff can take several forms:

Land use controls. Many world regulatory agencies have encouraged research on methods of minimizing total surface runoff by avoiding unnecessary

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

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.[42]

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.[43]

stormwater sewers
.

The U.S.

storm sewer
system ("MS4"). EPA and state regulations and related publications outline six basic components that each local program must contain:

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

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
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 runoff. 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)[47][48] 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.[49]

See also

References

  1. ^ "runoff". National Geographic Society. 2011-01-21. Archived from the original on 2021-01-28. Retrieved 2021-02-19.
  2. ^ Ronnie Wilson, The Horton Papers (1933)
  3. ^ Keith Beven, Robert E. Horton's perceptual model of infiltration processes, Hydrological Processes, Wiley Intersciences DOI 10:1002 hyp 5740 (2004)
  4. ISBN 0-07-235053-9
  5. ISBN 0922152349
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  6. ^ Jackson 1997, "surface runoff".
  7. ^ Jackson 1997, "direct runoff".
  8. ^ "Snowmelt Runoff and the Water Cycle". United States Geological Survey. Archived from the original on 6 November 2021. Retrieved 5 November 2021.
  9. S2CID 129207404
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  10. ^ Huston, Mike. "Snowmelt and Peak Streamflow Relationships for the Big Wood River in Southeast Idaho" (PDF). National Weather Service. Archived (PDF) from the original on 6 November 2021. Retrieved 5 November 2021.
  11. ^ Van Mullem, Joseph A.; Garen, David. "Snowmelt". National Engineering Handbook. Vol. 630. U.S. Department of Agriculture. Archived from the original on 6 November 2021. Retrieved 5 November 2021.
  12. ISBN 3-923381-27-1
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    (PDF) from the original on 19 January 2022. Retrieved 6 November 2021.
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  23. ^ "Impact of Water Runoff from Streets and Yards". Highlands Ranch, CO: Highlands Ranch Metro District. Retrieved 30 August 2021.
  24. ^ "Runoff (surface water runoff)". USGS Water Science School. Reston, VA: U.S. Geological Survey (USGS). 2018-06-06.
  25. ISBN 1-57278-039-8
    . Chapter 1.
  26. ^ Schueler, Thomas R. (2000) [initial publ. 1995]. "The Importance of Imperviousness". In Schueler; Holland, Heather K. (eds.). The Practice of Watershed Protection. Ellicott City, MD: Center for Watershed Protection. pp. 1–12. Archived from the original (pdf) on 2014-03-27. Retrieved 2014-12-24.
  27. PMID 31905584
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  28. ^ "Stormwater Discharges from Industrial Activities". Washington, D.C.: United States Environmental Protection Agency (EPA). 2022-11-28.
  29. ^ "Study: Over a third of U.S. Corn Belt has lost its carbon-rich topsoil". AGDAILY. 2021-02-16. Archived from the original on 2021-03-08. Retrieved 2021-02-26.
  30. S2CID 227077676
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  31. ^ W.F. Spencer, Distribution of Pesticides between Soil, Water and Air, International symposium on Pesticides in the Soil, February 25–27, 1970, Michigan State University, East Lansing, Michigan
  32. ^ Science News. "DDT treatment turns male fish into mothers." Archived 2012-09-26 at the Wayback Machine 2000-02-05. (By subscription only.)
  33. ^ Klimaszyk Piotr, Rzymski Piotr "Surface Runoff as a Factor Determining Trophic State of Midforest Lake" Polish Journal of Environmental Studies, 2011, 20(5), 1203-1210
  34. ^ Renee K. Takesue,Curt D. Storlazzi. Sources and dispersal of land-based runoff from small Hawaiian drainages to a coral reef: Insights from geochemical signatures. Estuarine, Coastal and Shelf Science Journal. 2/13/17
  35. ^ Pote, D.H.; Grigg, B.C.; Blanche, C.A.; Daniel, T.C. (September–October 2004). "Effects of pine straw harvesting on quantity and quality of surface runoff". Journal of Soil and Water Conservation. 59 (5): 197+. Archived from the original on 2021-01-27. Retrieved 2021-04-07.
  36. PMID 16678407. Archived
    from the original on 2022-03-03. Retrieved 2021-04-07.
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  38. ^ Center for Neighborhood Technology, Chicago IL “The Prevalence and Cost of Urban Flooding.” Archived 2013-10-04 at the Wayback Machine May 2013
  39. ISSN 0378-3774
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  40. ^ U.S. Environmental Protection Agency (EPA). "Impervious Cover." Ecosystems Research Division, Athens, GA. 2009-02-24. Archived May 9, 2009, at the Wayback Machine
  41. ^ "City of Santa Monica Urban Runoff Management Program" (PDF). Santa Monica, CA: City of Santa Monica Environmental & Public Works Management. 2001. Brochure. Archived (PDF) from the original on 2022-03-20. Retrieved 2022-02-12.
  42. ^ Maryland Department of Environment. Baltimore, MD. "Erosion and Sediment Control and Stormwater Management in Maryland." 2007. Archived September 12, 2008, at the Wayback Machine
  43. ISBN 0-7844-0201-9
  44. ^ United States. Code of Federal Regulations, 40 CFR 122.26 Archived 2007-11-07 at the Wayback Machine
  45. ^ EPA. Washington, D.C. "Stormwater Discharges From Municipal Separate Storm Sewer Systems (MS4s)." Archived 2007-10-11 at the Wayback Machine 2009-03-11.
  46. ESL Inc.
    , Sunnyvale, California (1973)
  47. ^ Granato, G.E., 2013, Stochastic empirical loading and dilution model (SELDM) version 1.0.0: U.S. Geological Survey Techniques and Methods, book 4, chap. C3, 112 p. http://pubs.usgs.gov/tm/04/c03/ Archived 2020-08-24 at the Wayback Machine
  48. ^ Granato, G.E., 2014, SELDM: Stochastic Empirical Loading and Dilution Model version 1.0.3 Software support page available at https://doi.org/10.5066/F7TT4P3G
  49. ^ C.M.Hogan, Marc Papineau et al. Development of a dynamic water quality simulation model for the Truckee River, Earth Metrics Inc., Environmental Protection Agency Technology Series, Washington D.C. (1987)

Further reading

  • Gebert, W. A., D.J. Graczyk, and W.R. Krug. (1987). Average annual runoff in the United States, 1951-80 [Hydrologic Investigations Atlas HA-710]. Reston, Va.: U.S. Department of the Interior, U.S. Geological Survey.
  • Shodor Education Foundation (1998)."Surface Water Runoff Modeling." Archived 2019-04-05 at the Wayback Machine

External links

Look up surface runoff in Wiktionary, the free dictionary.
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