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

Research in the Saginaw River valley has shown (for
the winter of 1996-1997) that soils in cultivated areas
with little to no snow cover froze to depths of up to
eight inches, while in areas with forest cover, leaf litter,
and thin but persistent snow cover, frost depths only
reached about an inch (Schaetzl and Tomczak, 2002).
One conclusion that can be drawn from this is that plant
material should be left in applicable stormwater BMPs
to provide insulation through the winter. The ability of
persistent snow cover to act as insulation also suggests
that some BMPs such as bioretention areas, infiltration
basins, and vegetated swales can be used for snow storage
(as long as it does not cause physical damage to the
vegetation or other BMP components). However, large
amounts of sand or salt should be kept out of vegetated
and infiltration BMPs. Sand and salt can smother and/
or kill plants and reduce infiltration/storage capacity.
Sand should also never be used on or adjacent to porous
pavement systems (see detailed BMP section).
In addition, some BMPs, such as bioretention areas
should be installed with a mulch layer that is two to
three inches thick. For maximum insulation effectiveness,
the mulch should be spread evenly and consistently
throughout the BMP (for details on mulch see the individual
BMP sections).
All biological activity is mediated by temperature.
Cold winter temperatures significantly decrease nutrient
uptake and pollutant conversion processes by plants
and microbes; however, soil microbes still live and
consume nutrients even in the dead of winter. Accumulation
of chloride is generally not a problem in shallow
biological systems, as long as very highly concentrated
levels are not directly routed to them.
Infiltration considerations
As water cools its viscosity increases, reducing particlesettling
velocities and infiltration rates into the soil. The
problem with infiltration in cold weather is the ice that
forms both over the tops of infiltration practices and in
the soil pore spaces. To avoid these problems to the extent
possible, the BMP must be actively managed to keep it
dry before it freezes in the fall. This can be done by various
methods including limiting inflow, under-drainage,
and surface disking. Routing the first highly soluble
portions of snowmelt to an infiltration BMP provides the
opportunity for soil infiltration and treatment.
Winter Pollution Prevention Tips
• Choose proper de-icing materials
• Consider pre-wetting brine treatments to salt for
better application
• Load salt trucks on covered, impervious pads
• Calibrate salting vehicles often
• Properly manage salt storage piles
• Identify and avoid salt-sensitive areas prior to
plowing or salting
Snow Storage Tip
Commercial and industrial areas that plow their parking
and paved areas into big piles on top of pavement
could greatly improve runoff management if instead
they dedicated a pervious area within their property for
the snow. Even pushing the plowed snow up and over
a curb onto a pervious grassed area will provide more
treatment than allowing it to melt on a paved surface
and run into a storm sewer.
Vegetation in winter at George George Park,
Clinton Township, MI
LID Manual for Michigan – Chapter 7 Page 127