First flush
Encyclopedia
First flush is the initial surface runoff
of a rainstorm. During this phase, water pollution
entering storm drain
s in areas with high proportions of impervious surface
s is typically more concentrated
compared to the remainder of the storm. Consequently these high concentrations of urban runoff
result in high levels of pollutants discharged from storm sewers to surface water
s.
The term first flush effect refers to rapid changes in water quality
(pollutant concentration or load) that occur after early season rains. Soil
and vegetation particles wash into streams; sediment
s and other accumulated organic
particles on the river bed are re-suspended, and dissolved substances from soil and shallow groundwater can be flushed into streams. Recent research has shown that this effect has not been observed in relatively pervious areas.
The term is often also used to address the first flood after a dry period, which is supposed to contain higher concentrations than a subsequent one. This is referred to as "first flush flood." There are various definitions of the first flush phenomenon.
Apart from this definition, there are a number of rating parameters in literature to determine the occurrence of a first flush.
Surface runoff
Surface runoff is the water flow that occurs when soil is infiltrated to full capacity and excess water from rain, meltwater, or other sources flows over the land. This is a major component of the water cycle. Runoff that occurs on surfaces before reaching a channel is also called a nonpoint source...
of a rainstorm. During this phase, water pollution
Water pollution
Water pollution is the contamination of water bodies . Water pollution occurs when pollutants are discharged directly or indirectly into water bodies without adequate treatment to remove harmful compounds....
entering storm drain
Storm drain
A storm drain, storm sewer , stormwater drain or drainage well system or simply a drain or drain system is designed to drain excess rain and ground water from paved streets, parking lots, sidewalks, and roofs. Storm drains vary in design from small residential dry wells to large municipal systems...
s in areas with high proportions of impervious surface
Impervious surface
Impervious surfaces are mainly artificial structures--such as pavements that are covered by impenetrable materials such as asphalt, concrete, brick, and stone--and rooftops...
s is typically more concentrated
Concentration
In chemistry, concentration is defined as the abundance of a constituent divided by the total volume of a mixture. Four types can be distinguished: mass concentration, molar concentration, number concentration, and volume concentration...
compared to the remainder of the storm. Consequently these high concentrations of urban runoff
Urban runoff
Urban runoff is surface runoff of rainwater created by urbanization. This runoff is a major source of water pollution in many parts of the United States and other urban communities worldwide.-Overview:...
result in high levels of pollutants discharged from storm sewers to surface water
Surface water
Surface water is water collecting on the ground or in a stream, river, lake, wetland, or ocean; it is related to water collecting as groundwater or atmospheric water....
s.
The term first flush effect refers to rapid changes in water quality
Water quality
Water quality is the physical, chemical and biological characteristics of water. It is a measure of the condition of water relative to the requirements of one or more biotic species and or to any human need or purpose. It is most frequently used by reference to a set of standards against which...
(pollutant concentration or load) that occur after early season rains. Soil
Soil
Soil is a natural body consisting of layers of mineral constituents of variable thicknesses, which differ from the parent materials in their morphological, physical, chemical, and mineralogical characteristics...
and vegetation particles wash into streams; sediment
Sediment
Sediment is naturally occurring material that is broken down by processes of weathering and erosion, and is subsequently transported by the action of fluids such as wind, water, or ice, and/or by the force of gravity acting on the particle itself....
s and other accumulated organic
Organic compound
An organic compound is any member of a large class of gaseous, liquid, or solid chemical compounds whose molecules contain carbon. For historical reasons discussed below, a few types of carbon-containing compounds such as carbides, carbonates, simple oxides of carbon, and cyanides, as well as the...
particles on the river bed are re-suspended, and dissolved substances from soil and shallow groundwater can be flushed into streams. Recent research has shown that this effect has not been observed in relatively pervious areas.
The term is often also used to address the first flood after a dry period, which is supposed to contain higher concentrations than a subsequent one. This is referred to as "first flush flood." There are various definitions of the first flush phenomenon.
Related terms
Because the reference of the first flush is not always clear, the terms "concentration-based first flush" (CBFF) and "mass-based first flush" (MBFF) have been introduced.Apart from this definition, there are a number of rating parameters in literature to determine the occurrence of a first flush.
See also
- Combined sewer
- Nationwide Urban Runoff Program - U.S. research project
- Nonpoint source pollutionNonpoint source pollutionNonpoint source pollution refers to both water and air pollution from diffuse sources. Nonpoint source water pollution affects a water body from sources such as polluted runoff from agricultural areas draining into a river, or wind-borne debris blowing out to sea. Nonpoint source air pollution...
- Sanitary sewer overflowSanitary sewer overflowSanitary sewer overflow is a condition whereby untreated sewage is discharged into the environment prior to reaching treatment facilities thereby escaping wastewater treatment. When caused by rainfall it is also known as wet weather overflow. It is primarily meaningful in developed countries,...
- StormwaterStormwaterStormwater is water that originates during precipitation events. It may also be used to apply to water that originates with snowmelt that enters the stormwater system...
- Urban runoffUrban runoffUrban runoff is surface runoff of rainwater created by urbanization. This runoff is a major source of water pollution in many parts of the United States and other urban communities worldwide.-Overview:...
Further reading
- Hager, Mary Catherine (2001). "Evaluating First-Flush Runoff." Stormwater: September-October 2001.
- Alex Maestre, Robert Pitt, and Derek Williamson (2004). "Nonparametric Statistical Tests Comparing First Flush and Composite Samples from the National Stormwater Quality Database." In Models and Applications to Urban Water Systems, Vol. 12 (edited by W. James). Computational Hydraulics Int., Guelph, Ontario. pp. 317 – 338.
External links
- Stormwater first flush pollution - Department of Environment & Climate Change, New South Wales, Australia
- tempQsim - Research project supported by the European Commission and the Swiss Government under the Fifth Framework Programme,