VUA Detention
Technical Standards for VUA Detentions 
General- parking lot detentions must be designed to manage on-site storm water flows directly form vehicular use areas in order to trap non-point pollutants, filter, clean, evaporate or infiltrate storm water. Parking lot detentions must be designed using graded and contoured earth, slotted curbs, rip rap water ramps, an interior swaled collection point, inflow point, emergency spillway, outflow point with filter plants, a grassed filter edge, and a planted screening edge and optional contributing catch basins and underground pipe.The most important parts of a parking lot detention include the containment slope, outflow points, inflow points, the capture area, surface material and the edge filter and landscape screen. These will all be designed using generally accepted practices.
Minimum Length- Shall be one hundred (100) linear feet
Minimum Width- Shall be fifty (50) linear feet to allow for proper maintenance by equipment
Maximum Depth -Shall be twenty-four (24) inches
Minimum Volume -Shall be calculated using the one (1) inch design storm over the area of the VUA.
Containment Slope. Shall not exceed 3:1 and be bordered by a high cut grass filter strip no less than twelve (12) inches in width surrounding any edge exposed to overland inflow.
Outflow Points. Shall consist of a controlled pipe and headwall control point at the low point (LP) of the facility. A secondary outflow shall be located at the high point (HP) of the site and shall consist of an emergency spillway at least ten (10) feet in width. This overflow must release into an authorized public drainage way. Outflow points must be planted with wetland filter plants such as rushes, reeds, iris, pickerelweed, native grasses.
Inflow Points. Locate these along the edge of the VUA through a six (6) slotted curb into a paved concrete water ramp reinforced with 6” rip rap armoring. Space no closer than ten (10) feet on center. Inflow can also arrive by 6” PVC contributing pipe from drop inlets or curb inlets within the VUA or catch basins exterior to the detention.
The capture area. The areas between the containment slopes shall collect run off to be released at a proscribed run off rate controlled by the size of the pipe. The capture area shall be graded at a one (1) percent slope to drain to the out flow point. This area must be porous paved and covered with a filtering layer of turf grass or meadow grass. In some instances, wetland plants and a drivable porous surface may be used.
Landscape Planted Screen. A landscaped planted screen shall be designed at any location facing a public street or a low intensity land use district. Minimum width of the landscape bed shall be six (6) feet in width and shall occur at the edge of the rough cut grass filter strip. Minimum plantings for this screen shall be one (1) class A tree each two hundred (200) feet of detention edge and two class B trees for each one hundred (100) linear feet of edge. Twenty-one (21) seven gallon evergreen screening and wildlife supporting shrubs shall be planted for each one hundred (100) feet of perimeter. Ten (10) three gallon accent and wildlife supporting shrubs shall be planted forty-eight inches on center per 100 linear feet of perimeter. This screen and its planting need not exceed sixty (60) percent of the perimeter length of the detention.
