Post Construction Stormwater Management is a permit requirement because the increased impervious surface associated with development may increase stormwater volume and degrade water quality. Post construction stormwater controls are permanent, and are designed to treat, store, and infiltrate the increased stormwater runoff from new development and redevelopment projects.
Under the Post Construction Stormwater Management control measure, the City of Ann Arbor has a program requiring new and redevelopment projects to implement on-site controls that will reduce pollutant loads in stormwater run-off. The City of Ann Arbor follows the rules of the Washtenaw County Water Resources Commissioner for post construction controls. These rules are incorporated by reference into Chapter 63 of the City Code - Stormwater Management and Erosion and Sedimentation Control (pdf).
City staff review site plans for compliance with regulations governing stormwater management.
Chapter 63 (5:658) requires all site plans to include a plan for the long-term maintenance of stormwater controls.
"A program proposal for the continued maintenance of all permanent soil erosion
and sedimentation control measures that remain after project completion, including the designation of the person or party responsible for the maintenance. Maintenance responsibilities shall become a part of any sales or exchange agreement for the land on which the permanent soil erosion and sedimentation control measures are located."
The Washtenaw County Water Resources Commissioner has a sample maintenance plan (pdf) that may be helpful in developing a plan for your site.
Utilizing Low Impact Development (LID)
Low impact development (LID) is is the industry standard for green infrastructure. The LID Manual for Michigan provides the latest tools for implementing post construction stormwater controls.
What is LID? In short, it is a type of development that uses a basic principle modeled after nature - to manage rainfall using design techniques that infiltrate, filter, store, evaporate, and detain runoff close to its source. LID provides a host of stormwater benefits, including groundwater recharge and cleaner streams.
Keep the following in mind if you are implementing a LID project:
- Plan for stormwater management during initial phases of site design
- Manage stormwater close to where it falls
- Conserve and restore natural areas
- Minimize impervious surface
- Manage runoff with structural controls
- Provide maintenance and education
Examples of LID Practices for Stormwater
Implementing LID practices can:
Reduce the volume of stormwater flows
Improve the quality of stormwater runoff
Reduce the need for future capital improvements to maintain or repair stormwater systems
- Practices designed to facilitate the percolation of runoff through the soil to groundwater
- Result in reduced stormwater runoff quantity and reduced mobilization of pollutants
- Examples: infiltration basins/trenches, dry wells, permeable pavement (shown)
- Control stormwater by gathering runoff in wet ponds, dry basins, or multichamber catch basins and slowly releasing it to receiving waters or drainage systems
- Can be designed to both control stormwater volume and settle out particulates for pollutant removal
- Landscaping features that, with optimal design and good soil conditions, remove pollutants and facilitate percolation of runoff
- Maintain natural site hydrology, promote healthier habitats, and increase aesthetic appeal
- Examples: grassy swales, filter strips, artificial wetlands, and rain gardens (shown)
Resources for Implementing Stormwater Controls
Updated March 23, 2010