Weather events cause stormwater runoff
Precipitation events, such as rain events, and temperature events, such as snowmelt events, cause stormwater runoff. The EPA defines stormwater runoff as “rain or snowmelt that flows over land and does not percolate into the soil,” occurring naturally from most land surfaces, and distinctly during storm events.
Typical erosion rates from stormwater runoff
Typical erosion rates from stormwater runoff for land-based activities vary from less than one ton of sediment per acre each year on forest land, to one ton of sediment per acre each year on active pasture farm land, to about 4.7 tons of sediment per acre each year on row crop farm land — one tenth of construction.
Erosion rates on unmanaged construction sites
Runoff from an unstabilized and unmanaged construction site can result in the loss of approximately 35 to 45 tons of sediment per acre each year!
However, erosion rates for bare soil, e.g. on unmanaged construction sites, can result in the loss of approximately 35 to 45 tons of sediment per acre each year, jeopardizing biological habitats. Further, sediment from unmanaged construction sites can lower ground water levels and affect drinking water supplies.
Primary stormwater pollutant
The primary stormwater pollutant at an unmanaged construction site is sediment.
The primary stormwater pollutant at a unmamnaged construction site is sediment. In a very short time period, unmanaged construction sites, without an effective stormwater pollution prevention plan (SWPPP), can contribute more sediment to our streams than deposited by mother nature over the course of several decades.
Five basic types of erosion
To control erosion at a construction site with an effective stormwater pollution prevention plan (SWPPP) and comply with stormwater discharge requirements, it is important for construction site operators and HSE (health, safety, environment) managers to understand the five basic types of erosion:
- Raindrop erosion: dislodging of soil particles by raindrops;
- Sheet erosion: the uniform removal of soil without the development of visible water channels;
- Rill erosion: soil removal through the formation of concentrated runoff that creates many small channels;
- Gully erosion: the result of highly concentrated runoff that cuts down into the soil along the line of flow, and;
- Streambank erosion: flowing water that erodes unstable streambanks.
Keywords
BMPs, Best Management Practices, Developing Your Stormwater Pollution Prevention Plan, EPA, EPA fines, HSE, SWPPP, United States Environmental Protection Agency, construction, construction site, construction site operators, environment, environmental protection, erosion, erosion control, gully erosion, health, pollutant, pollution, raindrop erosion, rill erosion, runoff, safety, sediment, sediment control, sediment loss, sediment per acre, sheet erosion, site assessment, site planning, storm water, stormwater management, stormwater pollutant, stormwater runoff, streambank erosion
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(Source: Developing Your Stormwater Pollution Prevention Plan: A Guide for Construction Sites. Washington, DC: U.S. Environmental Protection Agency, 2007. Print.)