ALTERNATIVE DESIGN FOR LOW RISK DETENTION FACILITIES

As an alternative to conventional Retention Basin design, the Drain Commissioner's Office will allow the use of Bioretention for storm water management commonly known as "Rain Gardens". Bioretention is an alternative stormwater management practice that utilizes shallow depressions containing native plantings consisting of an assortment of ground cover (grasses) middle story (shrub) and canopy (trees). These landscaped gardens manage stormwater through a combination of physical, biological, and chemical processes to maximize pollutant removal. Typically each lot will contain a Rain Garden, with the use of larger "Community" raingardens utilized to accept overflow during heavy rains and run off from low points in the development.

General design for the use of Rain Gardens will need to include the following:

1. Road slopes not greater than 2.0 percent

2. Under highly permeable soil conditions, soil shall be classified utilizing the USGS Soil Triangle (see Appendix K) as sand, loamy sand & sandy loam.

3. Individual Rain Gardens shall be located in an easement to the Drain Commissioner's Office.

4. Creation of a home owners association responsible for the oversite of individual lot owners maintenance of the raingardens.

5. A homeowners education program outlining proper maintenance of the rain garden.

6. See Appendix M for design criteria and typical layout for a large commercial Rain Garden Design.

7. The Kalamazoo County Drain Office has modified the State of Maryland's design criteria to utilize each Rain Garden as an individual retention area. However, consideration would be given to the staged design methodology outlined in the State of Maryland guidebook, which is available in the Kalamazoo County Drain Office for review. The concept of Rain Gardens originated in Prince George's County, Maryland.