Drainage & Retention Information
Detention and Retention Basins
A common conventional method for managing storm water is a storm water basin. Basins are meant to collect storm water and slowly release it at a controlled rate so that downstream areas are not flooded or eroded. While effective for flood control, these practices have significant limitations for water quality treatment and for preventing impacts to stream systems.
The main difference between a detention and a retention basin is whether or not it has a permanent pool of water – like a traditional “pond”. The water level is established by the low flow orifice. Most of the time the orifice is part of a metal or concrete structure called a riser. A detention, or dry, basin has an orifice level with the bottom of the basin so that all of the water eventually drains out and it remains dry between storms – hence, a dry basin. Retention basins have a riser with an orifice at a higher point so that it retains a permanent pool of water.
The basins themselves are important for storing and slowing (attenuating) the runoff from impervious surfaces such as rooftops or pavement. The amount of treatment, or cleaning, of the water is limited. Dry detention basins control flood flows only. A retention basin can also provide water quality benefits by reducing sediments and attached pollutants.
One of the most important elements of maintaining basins is making sure the low flow orifice is not blocked or clogged. Other maintenance activities include repairing erosion, removing sediment, and managing the vegetation. Repairing erosion early can save significant costs, both in the erosion and the resulting sedimentation that can end up needing to be removed from the basin.
Vegetation should be kept to heights that allow inspection for animal burrows, sinkholes, wet areas, etc. along the fill embankments. Common mistakes are not mowing important areas because they are too steep or ignoring mowing completely.
These basins are one of the most popular means of providing storm water management throughout most of the United States.
Southbridge Water Quality Basin
The general location of the above mentioned basin is between Southbridge Circle and Blossom Lane on the Westlake/North Olmsted border. In 2012, the City applied for and was granted a SWIF grant through the Ohio EPA. In 2013, the City hired Mark Haynes Construction Inc. to retrofit two existing city-owned detention basins to improve water quality. They restored the aquatic habitat and the riparian corridor in the Cahoon Creek and Columbia Creek watersheds through 1,800lf of floodplain restoration and bank stabilization. With this job there was also, 1.2 acres of riparian vegetation and native grasses planted. In the summer of 2016, we had the opportunity to fly a drone over the basin to show the result of this restoration work.
Watch video of Water Quality Basin