HomeMy Public PortalAboutFinal Draft Detention Basin BrochureRoutine Maintenance
Mow at least two or three times a year, more
frequently if desired. Do not fertilize the grass in
the basin. Consider growing native prairie
plants as a low maintenance alternative to
turfgrass.
Remove debris from all conveyances including
the pilot channel, low flow orifice, and on and
inside the outlet structure. Debris may include
sediment, dead vegetation, trash, etc. These
materials tend to accumulate in the pilot chan-
nel and at the trash rack or low flow orifice.
Repair areas with erosion and replant or sod
patches of bare soil.
Remove problem vegetation such as dense
stands of cattails and trees. Shrubs and trees
growing along berms and embankments must
be removed.
Replace missing or damaged steel grates and
manhole lids on the outlet structure.
Non-Routine Maintenance
Repairing crumbling or cracked pipes and con-
veyances such as the pilot channel and outlet
control structure.
Reconstruction of failed berms, collapsed re-
taining walls, and washed out spillways.
Dredging accumulated sediment that has col-
lected within wet detention basins.
Repairing or replacing safety fences along the
perimeter of steep embankments.
Removing nuisance wildlife such as beavers and
groundhogs.
Grading to restore positive drainage along the
Detention Basins
Post-Construction
Best Management
Practices (BMPs)
Ownership & Maintenance
MSD Project Clear
Division of Environmental Compliance
10 East Grand Avenue
St. Louis, MO 63147-2913
Phone: 314.436.8710
MSDProjectClear.org
Find us @MSDProjectClear
The Takeaway
A detention basins is a private stormwater
management facility and it is the property owner’s
responsibility to maintain it in good working
condition. Maintenance related activities should
never result in a modification to a basin that could
change its approved design or cause it to perform
differently from its approved design. Modifications
to a basin that could result in changes to its
approved design must be approved by MSD
Project Clear’s Development Review Program.
For more
information, scan to
visit our Stormwater
Best Management
Practices (BMP)
Toolbox.
MSD Customer Service: 314.768.6260 Metropolitan St. Louis Sewer District Project Clear MSDProjectClear.org
What is a Detention Basin?
A detention basin is a stormwater management
structure that collects runoff during a rain event and
then releases that water through a control structure
at a reduced flow rate to decrease the risk of
flooding. Detention basins are required on sites
with new development or redevelopment.
Historically, detention basins served as flood control
devices, but modern basins can also be designed to
protect stream channels from excess erosion and in
some cases improve water quality, which benefits
local waterways and adjacent property. Detention
basins may be designed to be dry between rain
events, or remain wet retaining some water
throughout the year.
Who is responsible for maintenance?
Detention basins are private stormwater
management facilities and belong to the property
owner. Therefore, the property owner is responsible
for maintaining the detention basin and ensuring it
is operated in good working condition as agreed
upon. Ordinance No. 15048 provides MSD Project
Clear with the authority to require the property
owner to make repairs when a basin is found to be
in poor condition and not functioning properly.
MSD periodically inspects each basin in its service
area and responds to all related complaints and
concerns.
Inspection & Maintenance
Detention basins require regular inspection and routine
maintenance to insure they work properly when it rains.
If maintenance is ignored, over time the basin will stop
working, which could create a public hazard and/or
cause or contribute to downstream flooding and
property damage. Failing basins could adversely impact
aquatic habitat and create nuisances related to
overgrown plants, unsightly algae, problem wildlife and
insects, and even odors. Basins that are allowed to
decline into a failed state can be expensive to repair!
Inspections
Inspections are integral to maintaining the
performance of a basin and should be performed
regularly or following a major storm event. An
inspection generally includes examining the inlet pipe
(s), forebay (if applicable), interior of the basin
including the pilot channel, the embankments and
berms, the outlet control structure and the outfall. The
purpose of the inspection is to make sure all of these
components are in good working condition and
determine any maintenance activities that may be
necessary to keep the basin working properly.
Inspection findings such as overgrown/invasive
vegetation, accumulated sediment and other debris, a
blocked low flow orifice, and areas with erosion should
be noted and scheduled for maintenance. Corrective
actions should be taken immediately if a serious
condition is discovered.
Maintenance
Basins should be maintained on a regularly basis or as
needed in order to ensure they will operate effectively
during a storm. Regular maintenance will also help to
prevent minor conditions from evolving into major
problems. In general, maintenance should be
performed at a minimum twice each year, in late
winter/early spring and in the fall.
Types of Detention Basins
Wet Detention Basins are basins that contain a
permanent pool of standing water at a designed
elevation. Wet basins function to provide both
stormwater detention for flood control purposes and
improve water quality. Wet basins remove stormwater
pollutants through physical, biological, and chemical
processes within.
Dry Detention Basins are basins that detain water
during and shortly after a rain event, but otherwise
remain dry. Dry basins may be installed above or
below ground. Above ground basins are usually
planted with turfgrass for easy maintenance.
Underground basins contain one or more
interconnected chambers constructed of reinforced
concrete, corrugated metal, high strength plastics.
Dry detention basins are intended for flood control,
but may capture sediment and other debris such as
plant and trash material in the process.