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

oulders only in excavation area.
° Excavate bottom of basin to desired elevation (if
necessary).
• Install surrounding embankments and inlet and
outlet control structures.
• Grade and prepare subsoil in bottom of basin.
For dry ponds, take care to prevent compaction.
Equipment that will apply pressure to the basin
bottom of less than or equal to four pounds per
square inch is recommended. Compact only the
surrounding embankment areas and around inlet
and outlet structures. Compact bottom of basin in
wet ponds and constructed wetlands.
° Apply and grade planting soil. Matching design
grades is crucial especially in wet ponds and
constructed wetlands because aquatic plants can
be very sensitive to depth.
° Apply geo-textiles and other erosion-control
measures.
• Seed, plant, and mulch according to landscaping
plan.
• Install any safety or anti-grazing measures, if
necessary.
• Follow required maintenance and monitoring
guidelines.
Maintenance
Detention facilities must have a maintenance plan and
privately owned facilities should have an easement,
deed restriction, or other legal measure to prevent
neglect or removal.
Maintenance activities required for underground detention
systems focus on regular sediment and debris
removal. All catch basins, inlets, and pretreatment
devices draining to the underground bed should be
inspected and cleaned at least two times per year. The
underground bed and its outlet should be inspected
at least once per year and cleaned as needed. A basin
maintenance plan should be developed which includes
the following measures:
• All basin structures should be inspected for
clogging and excessive debris and sediment
accumulation at least four times per year, as well as
after every storm greater than one inch. Structures
that should be inspected include basin bottoms,
trash racks, outlets structures, riprap or gabion
structures, and inlets.
• Sediment should be removed from the forebay
before it occupies 50 percent of the forebay,
typically every three to 10 years. Sediment removal
should be conducted when the basin is completely
dry.
Wet ponds and constructed wetlands should be
drained prior to sediment removal. Sediment should
be disposed of properly and once sediment is
removed, disturbed areas need to be immediately
stabilized and revegetated. Proper disposal of
removed material depends on the nature of the
drainage area and the intent and function of the
detention basin. Material removed from detention
basins that treat hot spots such as fueling stations or
areas with high pollutant concentrations should be
disposed according to Michigan DEQ regulations
for solid waste. Detention basins that primarily
catch sediment from areas such as lawns may
redistribute the waste on site.
• The pond drain should be inspected and tested four
times per year.
• The embankment should be inspected for evidence
of tunneling or burrowing wildlife at least twice
during the growing season. If damage is found, the
damage should be repaired and remove the animals.
• Mowing and/or trimming of vegetation should
be performed as necessary to sustain the system,
but all detritus must be removed from the basin.
Embankment should be mowed 1–2 times per year
to prevent the establishment of woody vegetation.
• Inspections should assess the vegetation, erosion,
flow channelization, bank stability, inlet/outlet
conditions, embankment, and sediment/debris
accumulation.
• Vegetated areas should be inspected annually for
unwanted growth of invasive species.
• Vegetative cover should be maintained at a
minimum of 85 percent.
Winter Considerations
Dry ponds should be inspected and maintained during
winter months. Application of sand, ash, cinders, or
other anti-skid materials may cause sediment forebays
to fill more quickly. Otherwise, dry ponds should function
as intended in cold weather.
One of the biggest problems associated with proper
LID Manual for Michigan – Chapter 7 Page 183