Parking Lot Detention

Technical Standards for Rain Gardens

1. Site VUA detentions as close to the site outfall point as practical.  SA

2. Size the detention to capture ninety (90) percent  of the rainfall that originates within the VUA.

3. Size the area of the detention to be a minimum of 1/12 the size of the VUA. The formula to use shall be A/.08= Detention size.

4. The detention shall have appropriate inflow, outflow and overflow  points with water ramps a minimum of thirty-six (36) inches wide.

5. Detentions should be no deeper than twenty-four inches to minimize the amount of water depth.

6. Side slopes shall not exceed a fifteen (15) percent slope and planted with a combination of large and medium evergreen and deciduous shrubs and small flowering trees.

7. The interior of the facility shall not exceed the slope of three (3) percent but can be molded with a surface similar to golf course rough for added visual interest.

8. Side slopes facing public streets and lower intensity land uses shall be planted with one (1) small tree for each twenty feet, thirty-two (32) large shrubs and sixteen (16) medium shrubs for each one hundred linear feet of perimeter.  Large Class A wetland or facultative may be used in compositional groves throughout the interior of the detention.   All shrub plantings must be in an informal composition in staggered rows. Preference is given for trees plants in composition of groves consisting of 3, 5 or 7 trees in a grouping.

9. The interior of the detention may be surfaced with various materials based upon the proposed ancillary use of the facility. Common surfaces used include turf grass, meadow grass, grasscrete type porous paving, gravel, sand. The space can be used for overflow parking if permitted. Asphalt and concrete can not be used.

10. A grading plan, planting plan and drainage plan stamped by a landscape architect must be submitted for this comprehensively designed storm water facility.