Surface runoff (also known as overland flow) is the flow of
water
Water (chemical formula ) is an inorganic, transparent, tasteless, odorless, and nearly colorless chemical substance, which is the main constituent of Earth's hydrosphere and the fluids of all known living organisms (in which it acts as a ...
occurring on the ground surface when excess
rain
Rain is water droplets that have condensed from atmospheric water vapor and then fall under gravity. Rain is a major component of the water cycle and is responsible for depositing most of the fresh water on the Earth. It provides water f ...
water,
stormwater
Stormwater, also spelled storm water, is water that originates from precipitation (storm), including heavy rain and meltwater from hail and snow. Stormwater can soak into the soil ( infiltrate) and become groundwater, be stored on depressed la ...
,
meltwater
Meltwater is water released by the melting of snow or ice, including glacial ice, tabular icebergs and ice shelves over oceans. Meltwater is often found in the ablation zone of glaciers, where the rate of snow cover is reducing. Meltwater can be ...
, or other sources, can no longer sufficiently rapidly infiltrate in the
soil
Soil, also commonly referred to as earth or dirt, is a mixture of organic matter, minerals, gases, liquids, and organisms that together support life. Some scientific definitions distinguish ''dirt'' from ''soil'' by restricting the former te ...
. This can occur when the
soil
Soil, also commonly referred to as earth or dirt, is a mixture of organic matter, minerals, gases, liquids, and organisms that together support life. Some scientific definitions distinguish ''dirt'' from ''soil'' by restricting the former te ...
is
saturated
Saturation, saturated, unsaturation or unsaturated may refer to:
Chemistry
* Saturation, a property of organic compounds referring to carbon-carbon bonds
** Saturated and unsaturated compounds
**Degree of unsaturation
** Saturated fat or fatty ac ...
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
roof
A roof ( : roofs or rooves) is the top covering of a building, including all materials and constructions necessary to support it on the walls of the building or on uprights, providing protection against rain, snow, sunlight, extremes of temper ...
s 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
The water cycle, also known as the hydrologic cycle or the hydrological cycle, is a biogeochemical cycle that describes the continuous movement of water on, above and below the surface of the Earth. The mass of water on Earth remains fairly cons ...
. 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
A drainage basin is an area of land where all flowing surface water converges to a single point, such as a river mouth, or flows into another body of water, such as a lake or ocean. A basin is separated from adjacent basins by a perimeter, t ...
.
Runoff that occurs on the ground surface before reaching a
channel
Channel, channels, channeling, etc., may refer to:
Geography
* Channel (geography), in physical geography, a landform consisting of the outline (banks) of the path of a narrow body of water.
Australia
* Channel Country, region of outback Austral ...
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
Petroleum, also known as crude oil, or simply oil, is a naturally occurring yellowish-black liquid mixture of mainly hydrocarbons, and is found in geological formations. The name ''petroleum'' covers both naturally occurring unprocessed crud ...
,
pesticide
Pesticides are substances that are meant to control pests. This includes herbicide, insecticide, nematicide, molluscicide, piscicide, avicide, rodenticide, bactericide, insect repellent, animal repellent, microbicide, fungicide, and lampri ...
s,
fertilizer
A fertilizer (American English) or fertiliser (British English; see spelling differences) is any material of natural or synthetic origin that is applied to soil or to plant tissues to supply plant nutrients. Fertilizers may be distinct from ...
s and others.
In addition to causing water erosion and pollution, surface
runoff in urban areas is a primary cause of
urban flooding
Urban flooding is the inundation of land or property in a built environment, particularly in more densely populated areas, caused by rainfall overwhelming the capacity of drainage systems, such as storm sewers. Although sometimes triggered by even ...
, which can result in property damage, damp and mold in
basements
A basement or cellar is one or more floors of a building that are completely or partly below the ground floor. It generally is used as a utility space for a building, where such items as the furnace, water heater, breaker panel or fuse box, ...
, and street flooding.
Generation
![Runoffrazorback](https://upload.wikimedia.org/wikipedia/commons/e/e6/Runoffrazorback.jpg)
Surface runoff is defined as
precipitation
In meteorology, precipitation is any product of the condensation of atmospheric water vapor that falls under gravitational pull from clouds. The main forms of precipitation include drizzle, rain, sleet, snow, ice pellets, graupel and hail. ...
(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
Snowpack forms from layers of snow that accumulate in geographic regions and high elevations where the climate includes cold weather for extended periods during the year. Snowpacks are an important water resource that feed streams and rivers as th ...
or glaciers.
Snow
Snow comprises individual ice crystals that grow while suspended in the atmosphere—usually within clouds—and then fall, accumulating on the ground where they undergo further changes.
It consists of frozen crystalline water throughout ...
and
glacier
A glacier (; ) is a persistent body of dense ice that is constantly moving under its own weight. A glacier forms where the accumulation of snow exceeds its Ablation#Glaciology, ablation over many years, often Century, centuries. It acquires dis ...
melt occur only in areas cold enough for these to form permanently. Typically
snowmelt
In hydrology, snowmelt is surface runoff produced from melting snow. It can also be used to describe the period or season during which such runoff is produced. Water produced by snowmelt is an important part of the annual water cycle in many part ...
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
Australia, officially the Commonwealth of Australia, is a Sovereign state, sovereign country comprising the mainland of the Australia (continent), Australian continent, the island of Tasmania, and numerous List of islands of Australia, sma ...
and
Southern Africa
Southern Africa is the southernmost subregion of the African continent, south of the Congo and Tanzania. The physical location is the large part of Africa to the south of the extensive Congo River basin. Southern Africa is home to a number of ...
,
proteoid root
Cluster roots, also known as proteoid roots, are plant roots that form clusters of closely spaced short lateral rootlets. They may form a two- to five-centimetre-thick mat just beneath the leaf litter. They enhance nutrient uptake, possibly by ch ...
s 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
This occurs when the rate of
rainfall
Rain is water droplets that have condensed from atmospheric water vapor and then fall under gravity. Rain is a major component of the water cycle and is responsible for depositing most of the fresh water on the Earth. It provides water f ...
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
Robert Elmer Horton (May 18, 1875 – April 22, 1945) was an American hydrologist, geomorphologist, civil engineer, and soil scientist, considered by many to be the father of modern American hydrology. An eponymous medal is awarded by the Ameri ...
),
or unsaturated overland flow.
This more commonly occurs in
arid
A region is arid when it severely lacks available water, to the extent of hindering or preventing the growth and development of plant and animal life. Regions with arid climates tend to lack vegetation and are called xeric or desertic. Most ar ...
and
semi-arid
A semi-arid climate, semi-desert climate, or steppe climate is a dry climate sub-type. It is located on regions that receive precipitation below potential evapotranspiration, but not as low as a desert climate. There are different kinds of semi-ar ...
regions, where rainfall intensities are high and the
soil
Soil, also commonly referred to as earth or dirt, is a mixture of organic matter, minerals, gases, liquids, and organisms that together support life. Some scientific definitions distinguish ''dirt'' from ''soil'' by restricting the former te ...
infiltration capacity
Infiltration is the process by which water on the ground surface enters the soil. It is commonly used in both hydrology and soil sciences. The infiltration capacity is defined as the maximum rate of infiltration. It is most often measured in meter ...
is reduced because of
surface sealing, or in urban areas where pavements prevent water from infiltrating.
Saturation excess overland flow
When the
soil
Soil, also commonly referred to as earth or dirt, is a mixture of organic matter, minerals, gases, liquids, and organisms that together support life. Some scientific definitions distinguish ''dirt'' from ''soil'' by restricting the former te ...
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
Rain is water droplets that have condensed from atmospheric water vapor and then fall under gravity. Rain is a major component of the water cycle and is responsible for depositing most of the fresh water on the Earth. It provides water f ...
. This residual water moisture affects the soil's
infiltration capacity
Infiltration is the process by which water on the ground surface enters the soil. It is commonly used in both hydrology and soil sciences. The infiltration capacity is defined as the maximum rate of infiltration. It is most often measured in meter ...
. 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 In hydrology, throughflow, a subtype of interflow (percolation), is the lateral unsaturated flow of water in the soil zone, typically through a highly permeable geologic unit overlying a less permeable one. Water thus returns to the surface, as ret ...
.
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
A river is a natural flowing watercourse, usually freshwater, flowing towards an ocean, sea, lake or another river. In some cases, a river flows into the ground and becomes dry at the end of its course without reaching another body of wate ...
,
lake
A lake is an area filled with water, localized in a basin, surrounded by land, and distinct from any river or other outlet that serves to feed or drain the lake. Lakes lie on land and are not part of the ocean, although, like the much large ...
,
estuary
An estuary is a partially enclosed coastal body of brackish water with one or more rivers or streams flowing into it, and with a free connection to the open sea. Estuaries form a transition zone between river environments and maritime environment ...
or
ocean
The ocean (also the sea or the world ocean) is the body of salt water that covers approximately 70.8% of the surface of Earth and contains 97% of Earth's water. An ocean can also refer to any of the large bodies of water into which the wo ...
.
Human influence
Urbanization
Urbanization (or urbanisation) refers to the population shift from rural to urban areas, the corresponding decrease in the proportion of people living in rural areas, and the ways in which societies adapt to this change. It is predominantly t ...
increases surface runoff by creating more
impervious surface
Impervious surfaces are mainly artificial structures—such as pavements (roads, sidewalks, driveways and parking lots, as well as industrial areas such as airports, ports and logistics and distribution centres, all of which use considerable p ...
s such as
pavement and buildings that do not allow
percolation
Percolation (from Latin ''percolare'', "to filter" or "trickle through"), in physics, chemistry and materials science, refers to the movement and filtering of fluids through porous materials.
It is described by Darcy's law.
Broader applicatio ...
of the water down through the soil to the
aquifer
An aquifer is an underground layer of water-bearing, permeable rock, rock fractures, or unconsolidated materials (gravel, sand, or silt). Groundwater from aquifers can be extracted using a water well. Aquifers vary greatly in their characterist ...
. It is instead forced directly into streams or
storm water runoff drains, where
erosion
Erosion is the action of surface processes (such as water flow or wind) that removes soil, rock, or dissolved material from one location on the Earth's crust, and then transports it to another location where it is deposited. Erosion is distin ...
and
siltation
Siltation, is water pollution caused by particulate terrestrial clastic material, with a particle size dominated by silt or clay. It refers both to the increased concentration of suspended sediments and to the increased accumulation (temporary or ...
can be major problems, even when flooding is not. Increased runoff reduces
groundwater
Groundwater is the water present beneath Earth's surface in rock and soil pore spaces and in the fractures of rock formations. About 30 percent of all readily available freshwater in the world is groundwater. A unit of rock or an unconsolidate ...
recharge, thus lowering the
water table
The water table is the upper surface of the zone of saturation. The zone of saturation is where the pores and fractures of the ground are saturated with water. It can also be simply explained as the depth below which the ground is saturated.
T ...
and making
drought
A drought is defined as drier than normal conditions.Douville, H., K. Raghavan, J. Renwick, R.P. Allan, P.A. Arias, M. Barlow, R. Cerezo-Mota, A. Cherchi, T.Y. Gan, J. Gergis, D. Jiang, A. Khan, W. Pokam Mba, D. Rosenfeld, J. Tierney, an ...
s worse, especially for agricultural farmers and others who depend on the
water well
A well is an excavation or structure created in the ground by digging, driving, or drilling to access liquid resources, usually water. The oldest and most common kind of well is a water well, to access groundwater in underground aquifers. Th ...
s.
When anthropogenic contaminants are dissolved or suspended in runoff, the human impact is expanded to create
water pollution
Water pollution (or aquatic pollution) is the contamination of water bodies, usually as a result of human activities, so that it negatively affects its uses. Water bodies include lakes, rivers, oceans, aquifers, reservoirs and groundwater. Water ...
. 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.
As humans continue to alter the climate through the addition of
greenhouse gases
A greenhouse gas (GHG or GhG) is a gas that absorbs and emits radiant energy within the thermal infrared range, causing the greenhouse effect. The primary greenhouse gases in Earth's atmosphere are water vapor (), carbon dioxide (), methane ...
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.
Urban runoff
![Fascine49](https://upload.wikimedia.org/wikipedia/commons/d/d3/Fascine49.jpg)
Industrial runoff
Effects of surface runoff
Erosion and deposition
Surface runoff can cause
erosion
Erosion is the action of surface processes (such as water flow or wind) that removes soil, rock, or dissolved material from one location on the Earth's crust, and then transports it to another location where it is deposited. Erosion is distin ...
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
In hillslope geomorphology, a rill is a shallow channel (no more than a few inches/decimeters deep) cut into soil by the erosive action of flowing surface water. Similar but smaller incised channels are known as microrills; larger incised ch ...
erosion and
gully
A gully is a landform created by running water, mass movement, or commonly a combination of both eroding sharply into soil or other relatively erodible material, typically on a hillside or in river floodplains or terraces. Gullies resemble lar ...
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
Sediment is a naturally occurring material that is broken down by processes of weathering and erosion, and is subsequently transported by the action of wind, water, or ice or by the force of gravity acting on the particles. For example, sand an ...
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
rill
In hillslope geomorphology, a rill is a shallow channel (no more than a few inches/decimeters deep) cut into soil by the erosive action of flowing surface water. Similar but smaller incised channels are known as microrills; larger incised ch ...
s. 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
A gully is a landform created by running water, mass movement, or commonly a combination of both eroding sharply into soil or other relatively erodible material, typically on a hillside or in river floodplains or terraces. Gullies resemble lar ...
. 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
soil conservation
Soil conservation is the prevention of loss of the topmost layer of the soil from erosion or prevention of reduced fertility caused by over usage, acidification, salinization or other chemical soil contamination.
Slash-and-burn and other uns ...
. The soil particles carried in runoff vary in size from about .001 millimeter to 1.0 millimeter in diameter. Larger particles
settle
Settle or SETTLE may refer to:
Places
* Settle, Kentucky, United States
* Settle, North Yorkshire, a town in England
** Settle Rural District, a historical administrative district
Music
* Settle (band), an indie rock band from Pennsylvania
* ''S ...
over short transport distances, whereas small particles can be carried over long distances suspended in the
water column
A water column is a conceptual column of water from the surface of a sea, river or lake to the bottom sediment.Munson, B.H., Axler, R., Hagley C., Host G., Merrick G., Richards C. (2004).Glossary. ''Water on the Web''. University of Minnesota-D ...
. Erosion of silty soils that contain smaller particles generates
turbidity
Turbidity is the cloudiness or haziness of a fluid caused by large numbers of individual particles that are generally invisible to the naked eye, similar to smoke in air. The measurement of turbidity is a key test of water quality.
Fluids can ...
and diminishes light transmission, which disrupts
aquatic ecosystem
An aquatic ecosystem is an ecosystem formed by surrounding a body of water, in contrast to land-based terrestrial ecosystems. Aquatic ecosystems contain communities of organisms that are dependent on each other and on their environment. The tw ...
s.
Entire sections of countries have been rendered unproductive by erosion. On the high central
plateau
In geology and physical geography, a plateau (; ; ), also called a high plain or a tableland, is an area of a highland consisting of flat terrain that is raised sharply above the surrounding area on at least one side. Often one or more sides ha ...
of
Madagascar
Madagascar (; mg, Madagasikara, ), officially the Republic of Madagascar ( mg, Repoblikan'i Madagasikara, links=no, ; french: République de Madagascar), is an island country in the Indian Ocean, approximately off the coast of East Africa ...
, approximately ten percent of that country's land area, virtually the entire landscape is devoid of
vegetation
Vegetation is an assemblage of plant species and the ground cover they provide. It is a general term, without specific reference to particular taxa, life forms, structure, spatial extent, or any other specific botanical or geographic character ...
, with erosive gully furrows typically in excess of 50 meters deep and one kilometer wide.
Shifting cultivation
Shifting cultivation is an agricultural system in which plots of land are cultivated temporarily, then abandoned while post-disturbance fallow vegetation is allowed to freely grow while the cultivator moves on to another plot. The period of cul ...
is a farming system which sometimes incorporates the
slash and burn
Slash-and-burn agriculture is a farming method that involves the cutting and burning of plants in a forest or woodland to create a field called a swidden. The method begins by cutting down the trees and woody plants in an area. The downed veget ...
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
Agriculture or farming is the practice of cultivating plants and livestock. Agriculture was the key development in the rise of sedentary human civilization, whereby farming of domesticated species created food surpluses that enabled people to ...
is another major cause of erosion. Over a third of the U.S.
Corn Belt
The Corn Belt is a region of the Midwestern United States that, since the 1850s, has dominated corn production in the United States. In the United States, ''corn'' is the common word for maize. More generally, the concept of the Corn Belt con ...
has completely lost its
topsoil
Topsoil is the upper layer of soil. It has the highest concentration of organic matter and microorganisms and is where most of the Earth's biological soil activity occurs.
Description
Topsoil is composed of mineral particles and organic matt ...
. Switching to
no-till
No-till farming (also known as zero tillage or direct drilling) is an agricultural technique for growing crops or pasture without disturbing the soil through tillage. No-till farming decreases the amount of soil erosion tillage causes in certai ...
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
Groundwater is the water present beneath Earth's surface in rock and soil pore spaces and in the fractures of rock formations. About 30 percent of all readily available freshwater in the world is groundwater. A unit of rock or an unconsolidate ...
and
soil
Soil, also commonly referred to as earth or dirt, is a mixture of organic matter, minerals, gases, liquids, and organisms that together support life. Some scientific definitions distinguish ''dirt'' from ''soil'' by restricting the former te ...
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
Petroleum, also known as crude oil, or simply oil, is a naturally occurring yellowish-black liquid mixture of mainly hydrocarbons, and is found in geological formations. The name ''petroleum'' covers both naturally occurring unprocessed crud ...
substances,
herbicide
Herbicides (, ), also commonly known as weedkillers, are substances used to control undesired plants, also known as weeds.EPA. February 201Pesticides Industry. Sales and Usage 2006 and 2007: Market Estimates. Summary in press releasMain page fo ...
s and
fertilizer
A fertilizer (American English) or fertiliser (British English; see spelling differences) is any material of natural or synthetic origin that is applied to soil or to plant tissues to supply plant nutrients. Fertilizers may be distinct from ...
s. 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
Phytotoxicity describes any adverse effects on plant growth, physiology, or metabolism caused by a chemical substance, such as high levels of fertilizers, herbicides, heavy metals, or nanoparticles. General phytotoxic effects include altered plan ...
. In the case of surface waters, the impacts translate to
water pollution
Water pollution (or aquatic pollution) is the contamination of water bodies, usually as a result of human activities, so that it negatively affects its uses. Water bodies include lakes, rivers, oceans, aquifers, reservoirs and groundwater. Water ...
, 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
Aesthetics, or esthetics, is a branch of philosophy that deals with the nature of beauty and taste, as well as the philosophy of art (its own area of philosophy that comes out of aesthetics). It examines aesthetic values, often expressed thr ...
(that is, odor, color and
turbidity
Turbidity is the cloudiness or haziness of a fluid caused by large numbers of individual particles that are generally invisible to the naked eye, similar to smoke in air. The measurement of turbidity is a key test of water quality.
Fluids can ...
effects). Contaminated surface waters risk altering the metabolic processes of the aquatic
species
In biology, a species is the basic unit of classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of the appropriate s ...
that they host; these alterations can lead to death, such as
fish kill
The term fish kill, known also as fish die-off, refers to a localized die-off of fish populations which may also be associated with more generalized mortality of aquatic life.University of Florida. Gainesville, FL (2005) ''Plant Management in Fl ...
s, or alter the balance of populations present. Other specific impacts are on animal mating, spawning,
egg
An egg is an organic vessel grown by an animal to carry a possibly fertilized egg cell (a zygote) and to incubate from it an embryo within the egg until the embryo has become an animal fetus that can survive on its own, at which point the a ...
and
larva
A larva (; plural larvae ) is a distinct juvenile form many animals undergo before metamorphosis into adults. Animals with indirect development such as insects, amphibians, or cnidarians typically have a larval phase of their life cycle.
The ...
e viability, juvenile survival and plant productivity. Some research shows surface runoff of pesticides, such as
DDT
Dichlorodiphenyltrichloroethane, commonly known as DDT, is a colorless, tasteless, and almost odorless crystalline chemical compound, an organochloride. Originally developed as an insecticide, it became infamous for its environmental impacts. ...
, 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
Eutrophication is the process by which an entire body of water, or parts of it, becomes progressively enriched with minerals and nutrients, particularly nitrogen and phosphorus. It has also been defined as "nutrient-induced increase in phytopla ...
. Runoff waters within
coniferous forests
Conifers are a group of cone-bearing seed plants, a subset of gymnosperms. Scientifically, they make up the division Pinophyta (), also known as Coniferophyta () or Coniferae. The division contains a single extant class, Pinopsida. All exta ...
are also enriched with
humic acid Humic substances (HS) are organic compounds that are important components of humus, the major organic fraction of soil, peat, and coal (and also a constituent of many upland streams, dystrophic lakes, and ocean water). For a long era in the 19th ...
s and can lead to
humification
In classical soil science, humus is the dark organic matter in soil that is formed by the decomposition of plant and animal matter. It is a kind of soil organic matter. It is rich in nutrients and retains moisture in the soil. Humus is the Lati ...
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 cycle
A biogeochemical cycle (or more generally a cycle of matter) is the pathway by which a chemical substance cycles (is turned over or moves through) the biotic and the abiotic compartments of Earth. The biotic compartment is the biosphere and the ...
s and marine and coastal ecosystems.
In the case of groundwater, the main issue is contamination of drinking water, if the
aquifer
An aquifer is an underground layer of water-bearing, permeable rock, rock fractures, or unconsolidated materials (gravel, sand, or silt). Groundwater from aquifers can be extracted using a water well. Aquifers vary greatly in their characterist ...
is abstracted for human use. Regarding
soil contamination
Soil contamination, soil pollution, or land pollution as a part of land degradation is caused by the presence of xenobiotic (human-made) chemicals or other alteration in the natural soil environment. It is typically caused by industrial activity ...
, 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
![Runoff of soil & fertilizer](https://upload.wikimedia.org/wikipedia/commons/9/95/Runoff_of_soil_%26_fertilizer.jpg)
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
Nigeria ( ), , ig, Naìjíríyà, yo, Nàìjíríà, pcm, Naijá , ff, Naajeeriya, kcg, Naijeriya officially the Federal Republic of Nigeria, is a country in West Africa. It is situated between the Sahel to the north and the Gulf o ...
,
elephant grass The term Elephant grass may refer to the following grass species:
* The Asian '' Miscanthus giganteus'', also known as giant miscanthus, commonly used as a biomass crop
* The African '' Cenchrus purpureus'', also known as Napier grass, Uganda grass ...
is considered to be an economical way in which surface run-off and
erosion
Erosion is the action of surface processes (such as water flow or wind) that removes soil, rock, or dissolved material from one location on the Earth's crust, and then transports it to another location where it is deposited. Erosion is distin ...
can be reduced. Also,
China
China, officially the People's Republic of China (PRC), is a country in East Asia. It is the world's most populous country, with a population exceeding 1.4 billion, slightly ahead of India. China spans the equivalent of five time zones and ...
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
Flood
A flood is an overflow of water ( or rarely other fluids) that submerges land that is usually dry. In the sense of "flowing water", the word may also be applied to the inflow of the tide. Floods are an area of study of the discipline hydrol ...
ing 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 A return period, also known as a recurrence interval or repeat interval, is an average time or an estimated average time between events such as earthquakes, floods, landslides, or river discharge flows to occur.
It is a statistical measurement typ ...
. Flooding is a natural process, which maintains ecosystem composition and processes, but it can also be altered by
land use
Land use involves the management and modification of natural environment or wilderness into built environment such as settlements and semi-natural habitats such as arable fields, pastures, and managed woods. Land use by humans has a long h ...
changes such as river engineering. Floods can be both beneficial to societies or cause damage. Agriculture along the
Nile
The Nile, , Bohairic , lg, Kiira , Nobiin language, Nobiin: Áman Dawū is a major north-flowing river in northeastern Africa. It flows into the Mediterranean Sea. The Nile is the longest river in Africa and has historically been considered ...
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
A fertilizer (American English) or fertiliser (British English; see spelling differences) is any material of natural or synthetic origin that is applied to soil or to plant tissues to supply plant nutrients. Fertilizers may be distinct from ...
in soil, resulting in improvement of crop water availability.
Mitigation and treatment
![North-Bend-Uplands-Runoff-pond-3942](https://upload.wikimedia.org/wikipedia/commons/4/4b/North-Bend-Uplands-Runoff-pond-3942.jpg)
Mitigation of adverse impacts of runoff can take several forms:
*
Land use
Land use involves the management and modification of natural environment or wilderness into built environment such as settlements and semi-natural habitats such as arable fields, pastures, and managed woods. Land use by humans has a long h ...
development controls aimed at minimizing
impervious surface
Impervious surfaces are mainly artificial structures—such as pavements (roads, sidewalks, driveways and parking lots, as well as industrial areas such as airports, ports and logistics and distribution centres, all of which use considerable p ...
s in urban areas
*
Erosion control
Erosion control is the practice of preventing or controlling wind or water erosion in agriculture, land development, coastal areas, river banks and construction. Effective erosion controls handle surface runoff and are important techniques in ...
s for
farm
A farm (also called an agricultural holding) is an area of land that is devoted primarily to agricultural processes with the primary objective of producing food and other crops; it is the basic facility in food production. The name is used fo ...
s and
construction
Construction is a general term meaning the art and science to form objects, systems, or organizations,"Construction" def. 1.a. 1.b. and 1.c. ''Oxford English Dictionary'' Second Edition on CD-ROM (v. 4.0) Oxford University Press 2009 and com ...
sites
* Flood control and retrofit programs, such as
green infrastructure
Green infrastructure or blue-green infrastructure refers to a network that provides the “ingredients” for solving urban and climatic challenges by building with nature.Hiltrud Pötz & Pierre Bleuze (2011). Urban green-blue grids for sustainab ...
* Chemical use and handling controls in
agriculture
Agriculture or farming is the practice of cultivating plants and livestock. Agriculture was the key development in the rise of sedentary human civilization, whereby farming of domesticated species created food surpluses that enabled people to ...
,
landscape maintenance
Landscape maintenance (or groundskeeping) is the art and vocation of keeping a landscape healthy, clean, safe and attractive, typically in a garden, yard, park, institutional setting or estate. Using tools, supplies, knowledge, physical exerti ...
, industrial use, etc.
Land use controls. Many world regulatory agencies have encouraged research on methods of minimizing total surface runoff by avoiding unnecessary
hardscape
Hardscape refers to hard landscape materials in the built environment structures that are incorporated into a landscape. This can include paved areas, driveways, retaining walls, sleeper walls, stairs, walkways, and any other landscaping mad ...
. Many municipalities have produced guidelines and codes (
zoning
Zoning is a method of urban planning in which a municipality or other tier of government divides land into areas called zones, each of which has a set of regulations for new development that differs from other zones. Zones may be defined for a si ...
and related
ordinances) for
land developer
Land development is the alteration of landscape in any number of ways such as:
* Changing landforms from a natural or semi-natural state for a purpose such as agriculture or housing
* Subdividing real estate into lots, typically for the purpose ...
s that encourage minimum width sidewalks, use of
pavers set in earth for
driveway
A driveway (also called ''drive'' in UK English) is a type of private road for local access to one or a small group of structures, and is owned and maintained by an individual or group.
Driveways rarely have traffic lights, but some that bear ...
s and
walkway
In American English, walkway is a composite or umbrella term for all engineered surfaces or structures which support the use of trails.
''The New Oxford American Dictionary'' also defines a walkway as "a passage or path for walking along, esp. a ...
s and other design techniques to allow maximum water
infiltration
Infiltration may refer to:
Science, medicine, and engineering
*Infiltration (hydrology), downward movement of water into soil
*Infiltration (HVAC), a heating, ventilation, and air conditioning term for air leakage into buildings
*Infiltration (me ...
in urban settings. An example of a local program specifying design requirements, construction practices and maintenance requirements for buildings and properties is in
Santa Monica, California
Santa Monica (; Spanish language, Spanish: ''Santa Mónica'') is a city in Los Angeles County, California, Los Angeles County, situated along Santa Monica Bay on California's South Coast (California), South Coast. Santa Monica's 2020 United Sta ...
.
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
State may refer to:
Arts, entertainment, and media Literature
* ''State Magazine'', a monthly magazine published by the U.S. Department of State
* ''The State'' (newspaper), a daily newspaper in Columbia, South Carolina, United States
* ''Our S ...
and
local government
Local government is a generic term for the lowest tiers of public administration within a particular sovereign state. This particular usage of the word government refers specifically to a level of administration that is both geographically-loca ...
s began to focus their efforts on mitigation of construction runoff by requiring builders to implement
erosion
Erosion is the action of surface processes (such as water flow or wind) that removes soil, rock, or dissolved material from one location on the Earth's crust, and then transports it to another location where it is deposited. Erosion is distin ...
and
sediment control
A sediment control is a practice or device designed to keep eroded soil on a construction site, so that it does not wash off and cause water pollution to a nearby stream, river, lake, or sea. Sediment controls are usually employed together with e ...
s (ESCs). This included such techniques as: use of
straw bales and barriers to slow runoff on slopes, installation of
silt fence
A silt fence, sometimes (misleadingly) called a "filter fence," is a temporary sediment control device used on construction sites to protect water quality in nearby streams, rivers, lakes and seas from sediment (loose soil) in stormwater runof ...
s, programming construction for months that have less rainfall and minimizing extent and duration of exposed graded areas.
Montgomery County,
Maryland
Maryland ( ) is a state in the Mid-Atlantic region of the United States. It shares borders with Virginia, West Virginia, and the District of Columbia to its south and west; Pennsylvania to its north; and Delaware and the Atlantic Ocean to ...
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
A river is a natural flowing watercourse, usually freshwater, flowing towards an ocean, sea, lake or another river. In some cases, a river flows into the ground and becomes dry at the end of its course without reaching another body of wate ...
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 basin
A detention basin or retarding basin is an excavated area installed on, or adjacent to, tributaries of rivers, streams, lakes or bays to protect against flooding and, in some cases, downstream erosion by storing water for a limited period of time. ...
s or
balancing lake
A balancing lake (also flood basin or Sustainable urban drainage scheme) is a term used in the U.K. describing an element of an urban drainage system used to control flooding by temporarily storing flood waters. The term balancing pond is also ...
s) to buffer riverine peak flows, use of energy dissipators in channels to reduce stream velocity and land use controls to minimize runoff.
Chemical
A chemical substance is a form of matter having constant chemical composition and characteristic properties. Some references add that chemical substance cannot be separated into its constituent elements by physical separation methods, i.e., wi ...
use and handling. Following enactment of the U.S.
Resource Conservation and Recovery Act
The Resource Conservation and Recovery Act (RCRA), enacted in 1976, is the principal federal law in the United States governing the disposal of solid waste and hazardous waste.United States. Resource Conservation and Recovery Act. , , ''et seq ...
(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 tank
An underground storage tank (UST) is, according to United States federal regulations, a storage tank, including any underground piping connected to the tank, that has at least 10 percent of its volume underground.
Definition & Regulation in U.S. ...
s, registration of
hazardous materials
Dangerous goods, abbreviated DG, are substances that when transported are a risk to health, safety, property or the environment. Certain dangerous goods that pose risks even when not being transported are known as hazardous materials ( syllabi ...
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
Sanitation refers to public health conditions related to clean drinking water and treatment and disposal of human excreta and sewage. Preventing human contact with feces is part of sanitation, as is hand washing with soap. Sanitation systems ...
or
stormwater sewers.
The U.S.
Clean Water Act
The Clean Water Act (CWA) is the primary federal law in the United States governing water pollution. Its objective is to restore and maintain the chemical, physical, and biological integrity of the nation's waters; recognizing the responsibiliti ...
(CWA) requires that local governments in
urbanized areas
An urban area, built-up area or urban agglomeration is a human settlement with a high population density and infrastructure of built environment. Urban areas are created through urbanization and are categorized by urban morphology as cities, ...
(as defined by the
Census Bureau
The United States Census Bureau (USCB), officially the Bureau of the Census, is a principal agency of the U.S. Federal Statistical System, responsible for producing data about the American people and economy. The Census Bureau is part of the ...
) obtain
stormwater
Stormwater, also spelled storm water, is water that originates from precipitation (storm), including heavy rain and meltwater from hail and snow. Stormwater can soak into the soil ( infiltrate) and become groundwater, be stored on depressed la ...
discharge permits for their drainage systems. Essentially this means that the locality must operate a
stormwater management
Stormwater, also spelled storm water, is water that originates from precipitation (storm), including heavy rain and meltwater from hail and snow. Stormwater can soak into the soil ( infiltrate) and become groundwater, be stored on depressed la ...
program for all surface runoff that enters the municipal separate
storm sewer
A storm drain, storm sewer (United Kingdom, U.S. and Canada), surface water drain/sewer (United Kingdom), or stormwater drain ( Australia and New Zealand) is infrastructure designed to drain excess rain and ground water from impervious surface ...
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
A sanitary sewer is an underground pipe or tunnel system for transporting sewage from houses and commercial buildings (but not stormwater) to a sewage treatment plant or disposal. Sanitary sewers are a type of gravity sewer and are part of an o ...
or other non-stormwater connections to the MS4)
*
Construction
Construction is a general term meaning the art and science to form objects, systems, or organizations,"Construction" def. 1.a. 1.b. and 1.c. ''Oxford English Dictionary'' Second Edition on CD-ROM (v. 4.0) Oxford University Press 2009 and com ...
site runoff controls (i.e. erosion & sediment controls)
* Post-construction (i.e. permanent) stormwater management controls
* Pollution prevention (e.g. improved chemical handling, including management of motor fuels & oil, fertilizers, pesticides and
roadway deicers) 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 model
A mathematical model is a description of a system using mathematical concepts and language. The process of developing a mathematical model is termed mathematical modeling. Mathematical models are used in the natural sciences (such as physics, ...
s in combination with various
water quality
Water quality refers to the chemical, physical, and biological characteristics of water based on the standards of its usage. It is most frequently used by reference to a set of standards against which compliance, generally achieved through tr ...
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
Oxygen saturation (symbol SO2) is a relative measure of the concentration of oxygen that is dissolved or carried in a given medium as a proportion of the maximal concentration that can be dissolved in that medium at the given temperature. It ca ...
. 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 model
An hydrological transport model is a mathematical model used to simulate the flow of rivers, streams, groundwater movement or drainage front displacement, and calculate water quality parameters. These models generally came into use in the 1960s a ...
s 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
Dissolution may refer to:
Arts and entertainment Books
* ''Dissolution'' (''Forgotten Realms'' novel), a 2002 fantasy novel by Richard Lee Byers
* ''Dissolution'' (Sansom novel), a 2003 historical novel by C. J. Sansom Music
* Dissolution, in mu ...
rates of various chemicals,
infiltration
Infiltration may refer to:
Science, medicine, and engineering
*Infiltration (hydrology), downward movement of water into soil
*Infiltration (HVAC), a heating, ventilation, and air conditioning term for air leakage into buildings
*Infiltration (me ...
into soils and ultimate pollutant load delivered to
receiving waters
Receiving may refer to:
* ''Kabbalah'', "receiving" in Hebrew
* Receiving department (or receiving dock), in a distribution center
* Receiving house, a theater
* Receiving line, in a wedding reception
* Receiving mark, postmark
* Receiving par ...
.
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
The Environmental Protection Agency (EPA) is an independent executive agency of the United States federal government tasked with environmental protection matters. President Richard Nixon proposed the establishment of EPA on July 9, 1970; it be ...
(EPA). This
computer model
Computer simulation is the process of mathematical modelling, performed on a computer, which is designed to predict the behaviour of, or the outcome of, a real-world or physical system. The reliability of some mathematical models can be deter ...
formed the basis of much of the mitigation study that led to strategies for
land use
Land use involves the management and modification of natural environment or wilderness into built environment such as settlements and semi-natural habitats such as arable fields, pastures, and managed woods. Land use by humans has a long h ...
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'')
[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/] is a
stormwater
Stormwater, also spelled storm water, is water that originates from precipitation (storm), including heavy rain and meltwater from hail and snow. Stormwater can soak into the soil ( infiltrate) and become groundwater, be stored on depressed la ...
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
The DSSAM Model (Dynamic Stream Simulation and Assessment Model) is a computer simulation developed for the Truckee River to analyze water pollution, water quality impacts from land use and wastewater management decisions in the Truckee River Bas ...
) 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
A line source, as opposed to a point source, area source, or volume source, is a source of air, noise, water contamination or electromagnetic radiation that emanates from a linear (one-dimensional) geometry. The most prominent linear sources a ...
of
water pollution
Water pollution (or aquatic pollution) is the contamination of water bodies, usually as a result of human activities, so that it negatively affects its uses. Water bodies include lakes, rivers, oceans, aquifers, reservoirs and groundwater. Water ...
to the receiving waters.
[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)]
See also
*
*
*
*
Flash flood
A flash flood is a rapid flooding of low-lying areas: washes, rivers, dry lakes and depressions. It may be caused by heavy rain associated with a severe thunderstorm, hurricane, or tropical storm, or by meltwater from ice or snow flowing o ...
*
*
* – U.S. Research program
*
*
*
*
*
*
*
*
*
*
*
References
Further reading
*Gebert, W. A., D.J. Graczyk, and W.R. Krug. (1987). ''Average annual runoff in the United States, 1951-80''
ydrologic Investigations Atlas HA-710 Reston, Va.: U.S. Department of the Interior, U.S. Geological Survey.
* Shodor Education Foundation (1998
"Surface Water Runoff Modeling."
External links
*USDA NRCS National Engineering Handbook
Stage Discharge Relationships, Ch. 14NutrientNet an online nutrient trading tool developed b
the World Resources Institute designed to address water quality issues related to surface runoff and other pollution. See also th
PA NutrientNetwebsite designed for Pennsylvania's nutrient trading program.
Bioretentionas a
low impact development method of treating surface runoff
*
*
*
Stormwater ModelUSGS
Stochastic Empirical Loading and Dilution Model (SELDM)
{{Rivers, streams and springs
Aquatic ecology
Earth phenomena
Environmental chemistry
Soil erosion
Hydrology
Irrigation
Soil contamination
Water pollution
Ocean pollution