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

Table 7.12
Stormwater Functions by Infiltration BMP Type
Infiltration
Berms
Infiltration
Basins
Infiltration
Trenches
Volume Peak Rate Water Quality
Can be used to reduce the volume
of runoff and provide infiltration in
accordance with LID stormwater
goals. The volume reduction potential
of berms is a function of the storage
provided (surface and subsurface, if
applicable) and the infiltration that
will occur.
Provides an excellent means of
capturing and infiltrating runoff.
Provides runoff volume storage
during storm events, while the undisturbed
vegetated surface allows
infiltration of runoff into the underlying
soil mantle. Can be sized to meet
the entire channel protection volume
recommended by LID criteria or
sized smaller and used in conjunction
with other LID practices.
Provides an excellent means of
capturing and infiltrating runoff from
small storms. The trench provides
runoff volume storage and infiltration
during small storm events, while
the perforated pipe allows runoff
conveyance during large design
storms or more extreme events.
Dry Wells Dry wells are typically designed to
capture and infiltrate runoff volumes
from small storm events from roof
area.
Subsurface
Infiltration
Provides effective management of
volume. A well-designed system is
capable of infiltrating the majority of
small frequent storms on an annual
basis.
Can be used at mitigating peak
rates for larger storms through two
mechanisms: providing storage for
detention (and on-going infiltration)
behind them and, in some cases,
elongating the flow path through a
site, thereby extending the time of
concentration.
Provides effective management of
peak rates to meet the LID design
criteria. The basin acts as a storage
reservoir during large storm
events, even while runoff infiltrates.
Outlet structures can be designed to
manage peak rates with the use of
weir and orifice controls and systems
can be designed to manage peak
rates for storms up to and including
the 100-year storm.
Provides limited management of
peak rates. The trench may provide
more peak rate benefit for small
frequent storms, rather than large
design storms. Because infiltration
trenches help to provide a decentralized
approach to stormwater
management, they may benefit peak
rate mitigation by contributing to
increased stormwater travel time.
Provides limited management of
peak rates. Provides some peak rate
benefit by reducing direct connections
of impervious area to storm
sewer collection systems, and by
contributing to increased stormwater
travel time.
Can be designed to manage peak
rates by utilizing the stormwater
storage bed, including simple rate
controls such as weirs and orifices
in the overflow control structure.
Capable of infiltrating the majority of
small frequent storms, while managing
peak rates for designs storms up
to the 100-year frequency storm.
Can be expected to achieve pollutant
removals between 30% - 70% and
in the upper ranges especially for
smaller storms.
Effective in reducing total suspended
solids, nutrients, metals, and oil and
grease. Both the vegetative surface
and the underlying soils allow pollutant
filtration. When designed to
capture and infiltrate runoff volumes
from small storm events, they
provide very high pollutant reductions.
Effective in reducing total suspended
solids, metals, and oil and grease.
They provide very high pollutant
reductions when designed to
capture the volume from small
storms because there is little if any
discharge of runoff carrying the
highest pollutant loads. Provide
limited treatment of dissolved pollutants,
such as nitrates.
Effective at capturing and infiltrating
the water quality volume or “first
flush”. Provides very high pollutant
reductions because there is little if
any discharge of “first flush” runoff
which carries the highest pollutant
loads.
Very effective at reducing total
suspended solids, phosphorus,
metals, and oil and grease. Because
many systems are designed to
capture and infiltrate small, frequent
storms, they provide effective water
quality control by reducing pollutants
associated with the “first-flush”.
LID Manual for Michigan – Chapter 7 Page 209