In the last blog I wrote about the catch basin, the workhorse of the stormwater system. Often the next item we find downstream of our catch basins is a water quality or water quantity system. In stormwater facilities present on most every commercial, industrial, or housing development site, there are 2 types of major design systems intended to protect the quality of our waterways – water quality and water quantity.
Water quantity denotes a system put in place to restrict the rate that stormwater drains from a constructed site to approximately the rate that it flowed off the site before the site was constructed. The idea here is that the trees and underbrush that were on the site before the site was constructed would have been able to convert much more rainfall into infiltrated, evaporated, and/or transpirated water and the amount of stormwater runoff would have been comparatively small. A water quantity system is put in place, then, to mimic this condition as closely as possible. Why is that valuable? The reason is that the additional water that would be discharged from a site if these methods were not employed would burden man-made conveyance systems as well as scour rivers and streams and cause soil transport and sediment pollution downstream.
Water quality systems are different from water quantity systems in that they are designed to treat the quality of the stormwater generated on the site prior to its release. Every developed site generates pollutants, some as benign as soil material from car tires, others more serious such as copper from brakes, oil from engines, and even chemical agents used in industrial processes. Water quality systems such as filters, settling facilities, and oil/water separators are designed to clean the stormwater prior to its release.
Both water quantity systems and water quality systems can really be considered to be in the water quality classification. As stated above, water quantity systems are beneficial because they keep down river scour and soil transport, thus improving the clarity of our water supplies – definitely a water quality issue. However, for the purpose of stormwater design and maintenance, we classify them separately and provide different requirements for each.
Now you know a little about the broad classifications that stormwater features fall into. As we continue this series on types and function of various stormwater components, we will look into several different types of water quantity and water quality systems and discuss their pros and cons and the maintenance requirements for each.
– See more at: http://www.catchallenvironmental.com/blog/stormwater-quality-and-water-quantity-systems#sthash.nXQt78KM.dpuf