Low Impact Development Manual for Michigan - OSEH - University ...

7. Planting periods will vary but, in general, trees
and shrubs should be planted from mid-April
through early June, or mid-September through
mid-November. Native seed should be installed
between October 1 and June 1. Live plant
material (plugs or gallon pots) should be installed
between May 1 and June 15. Planting dates may
be lengthened if a regular water source can be
provided. Likewise, planting should be ceased at
an earlier date in the event of a drought year.
8. A maximum of 2-3 inches of shredded hardwood
mulch aged at least six months to one year or leaf
compost (or other comparable product) should be
uniformly applied immediately after shrubs and
trees are planted to prevent erosion, enhance metal
removals, and simulate leaf litter in a natural forest
system. Wood chips should be avoided as they
tend to float during inundation periods. Mulch or
compost should not exceed three inches in depth
or be placed directly against the stems or trunks of
plants to maintain oxygen flow.
9. When working in areas with steeper slopes,
bioretention areas should be terraced laterally
along slope contours to minimize earthwork and
provide level areas for infiltration.
Recycled asphalt product (RAP) used
throughout parking lot and left behind curb
to give structural support.
Source: City of Rochester Hills
10. A subsurface storage/infiltration bed, if used,
should be at least six inches deep and constructed
of clean gravel with a significant void space for
runoff storage (typically 40 percent) and wrapped
in geotextile fabric.
11. Underdrains are often not needed unless in-situ
soils are expected to cause ponding lasting longer
than 48 hours. If used, underdrains are typically
small diameter (6-12-inches) perforated pipes in
a clean gravel trench wrapped in geotextile fabric
(or in the storage/infiltration bed). Underdrains
should have a flow capacity greater than the total
planting soil infiltration rate and should have at
least 18 inches of soil/gravel cover. They can
daylight to the surface or connect to another
stormwater system. A method to inspect and clean
underdrains should be provided (via cleanouts,
inlet, overflow structure, etc.)
Underdrain in trench
Source: City of Rochester Hills
Underdrain excavation, three feet
wide, six inches deep. Peastone was
placed in excavation.
Four-foot-diameter catch basins, used as
overflows. Rim elevation set nine inches
above mulch layer to allow nine inches of
ponding before overflow occurs. Two catch
basins used to ensure stormwater doesn’t
overflow to parking lot.
LID Manual for Michigan – Chapter 7 Page 142