BMP owners and operators who are interested in using data obtained from Levels 2 and 3 should consult with the MPCA or other regulatory agency to determine if the results are appropriate for credit calculations. Level 1 activities do not produce numerical performance data that could be used to obtain a stormwater management credit (stormwater credit).
#Water drawdown definition manual
The manual advises on a four-level process to assess the performance of a Best Management Practice. This time period has also been called the period of inundation.Īn online manual for assessing BMP treatment performance was developed in 2010 by Andrew Erickson, Peter Weiss, and John Gulliver from the University of Minnesota and St. This criterion was established to provide the following: wet-dry cycling between rainfall events unsuitable mosquito breeding habitat suitable habitat for vegetation aerobic conditions and storage for back-to-back precipitation events. The drawdown period is therefore defined as the time from the high water level in the practice to 1 to 2 inches above the bottom of the facility. This residual water may be associated with reduced head, water gathered in depressions within the practice, water trapped by vegetation, and so on. Note: experience has demonstrated that, although the drawdown period is 48 hours, there is often some residual water pooled in the infiltration practice after 48 hours.
The drawdown time is typically 48 hours, meaning water captured by an infiltration BMP should completely infiltrate into the underlying soil or media within 48 hours. This time is called the drawdown time or period of inundation. Performance of an infiltration BMP is determined by the length of time needed for captured water to infiltrate. It is difficult to assess the performance of these BMPs, although considering only potential impacts to surface waters, a properly functioning infiltration system is considered to be highly performing. Infiltration trenches and infiltration basins are designed to infiltrate runoff and remove pollutants from the surface water stream through attenuation in soil or media or transport into underlying groundwater at concentrations below drinking water standards. If the practice utilizes vegetation, additional benefits may include cleaner air, carbon sequestration, improved biological habitat, and aesthetic value. EffectsĪquifer drawdown or overdrafting and the pumping of fossil water may be a contributing factor to sea-level rise.Green Infrastructure: Infiltration practices can be an important tool for retention and detention of stormwater runoff and treatment of pollutants in stormwater runoff. In either case, drawdown is the change in head or water level relative to background condition, indicating the difference in head which has occurred at a given location relative an initial time at the same location.Ī record of hydraulic head through time is more generally called a hydrograph (in both groundwater and surface water). In surface water hydrology and civil engineering, drawdown refers to the lowering of the water level in a man-made reservoir or tank.In subsurface hydrogeology, drawdown is the change in hydraulic head observed at a well in an aquifer, typically due to pumping a well as part of an aquifer test or well test.In water-related science and engineering there are two similar but distinct definitions in use for drawdown. Unsourced material may be challenged and removed. Please help improve this article by adding citations to reliable sources. This article needs additional citations for verification.
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