v>EPA
United States
Environmental Protection
Agency
Off ice of Water
Washington, D.C.
EPA832-F-99-014
September 1999
Storm Water
Technology Fact Sheet
Flow Diversion
DESCRIPTION
Flow diversion structures (such as gutters, drains,
sewers, dikes, berms, swales, and graded pavement)
are used to collect and divert runoff to prevent the
contamination of storm water and receiving water.
Flow diversion structures can be used in two ways.
First, flow diversion structures may be used to
channel storm water away from industrial areas so
that it does not mix with on-site pollutants. Second,
flow diversion may be used to carry contaminated
runoff to a treatment facility.
One of the most common methods for diverting
flow is through storm water conveyance systems.
These systems can be constructed from many
different materials, depending on the design criteria
and specifications for the site. Common materials
used for these systems include concrete, clay tiles,
asphalt, plastics, metals, riprap, compacted soils,
and vegetation. These conveyances can be
temporary or permanent.
Flow diversion structures are often modified by
incorporating them into other pollution control
BMPs. For example, diverted flow can be fed into
an infiltration drainfield system, an infiltration
basin, a constructed wetland treatment facility, or
an onsite treatment facility for discharge under the
NPDES program.
Another common modification is to construct a
temporary flow diversion to determine its
effectiveness. If the diversion structure is proven
effective, it may then be made permanent.
APPLICABILITY
Storm water flow diversion systems work well at
most industrial sites. The systems can be used to
direct storm water downslope, away from industrial
areas, and into channels or drain systems. This has
two advantages. First, if storm water is potentially
contaminated, it can be directed to a treatment
facility. Second, if the runoff has not been
contaminated, it can be kept separate from runoff
that has been in contact with contaminated areas.
A good example of the utilization of a diversion
structure is the Isle La Plume Wastewater
Treatment Plant in La Crosse, WI. The area
immediately surrounding the facility has been
regraded in order for the storm water runoff to be
directed into the process tanks. Here, the runoff is
treated along with other wastewater.
ADVANTAGES AND DISADVANTAGES
Some advantages of using storm water conveyance
systems to divert flow include:
Storm water flow is directed around
industrial sites, preventing contamination of
the storm water, and also preventing
flooding of the site.
• System maintenance requirements are low.
• Such conveyances are erosion-resistant.
• System installation may not require
extensive construction.
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Potential disadvantages of flow diversion may
include:
Erosion problems due to concentrated
flows.
• Potential groundwater contamination if
conveyance channels have high infiltration
capacities.
• Inadequately treated discharges to
undersized water treatment facilities.
Space limitations can make diversion
structures impractical.
• Diversion structures my be too expensive
for small facilities or for a site that has
already been constructed.
• Maintenance is required after heavy rains.
DESIGN CRITERIA
Planning for flow diversion structures should
incorporate data from the typical storm water flow.
Also, the patterns of storm water drainage should be
considered so that the channels may be located to
divert and collect the flow efficiently. When
deciding the type of material for the conveyance
structure, planners should consider the material's
resistance to erosion, its durability, and its
compatibility with any pollutants it may carry.
Diversion systems are most easily installed during
facility construction. The diversion system should
be designed to incorporate the site's existing
grades. This will reduce the BMP's design and
construction costs. The site should be graded to
allow for continued movement of runoff through
the conveyance system. (Note: care must be
exercised to limit flow velocities through the
diversion system to reduce the possibility of
erosion.) A typical diversion swale is shown in
Figure 1.
+ I I_L ,
Source: SEWPRC, 1991.
FIGURE 1 TYPICAL DIVERSION SWALE DETAILS
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PERFORMANCE
Properly designed storm water diversion systems
are very effective for preventing storm water from
being contaminated and for routing contaminated
flows to a proper treatment facility. For example,
at Denver International Airport (DIA), flow
diversion techniques intercepts 80 percent of the
glycol used in airplane deicing and prevents it from
entering Barr Lake, the local receiving waterbody.
At the La Crosse, WI, Wastewater Treatment Plant,
approximately one-third of the facility's storm
water runoff is diverted into the plant's treatment
process.
OPERATION AND MAINTENANCE
A maintenance program should be established to
ensure that the system functions properly. Storm
water diversion systems should be inspected to
remove debris within 24 hours after a significant
rainfall event since heavy storms may clog or
damage the system. Flow diversion structures
should also be inspected annually to ensure that
they meet their hydraulic design requirements. This
will ensure peak performance.
DIA has been in operation since 1995 and a
continuous maintenance program is being
implemented. Some techniques include conveying
deicer-contaminated runoff from passenger aircraft
deicing pads to a Pond or the Spent Glycol Storage
Tanks for subsequent recycling and off site reuse, if
the runoff is in sufficient concentration. The
deicer-contaminated storm runoff from other areas
is diverted to storage ponds for pumping to Metro
Wastewater Reclamation District (Metro).
COSTS
Costs vary depending on the type of flow diversion
structure used. For example, the Southeastern
Wisconsin Regional Planning Commission reports
that vegetated swale costs vary between $41.83 and
$246.06 per linear meter ($12.75 and $75 per linear
foot), depending upon swale depth and bottom
width (SEWRPC, costs adjusted from original 1991
document based on 1998 personal communication).
Costs for the Denver International Airport flow
diversion system are in the low millions of dollars
range, however exact capital cost information has
not yet been released.
REFERENCES
1. Denver International Airport, 1999.
Aircraft Deicing Fluid Collection and
Treatment.
2. James M. Montgomery, Consulting
Engineers, Inc., 1992. Site Visit Data.
3. Minnesota Pollution Control Agency, 1989.
Protecting Water Quality in Urban Areas.
4. Southeastern Wisconsin Regional Planning
Commission, 1991. Costs of Urban
Nonpoint Source Water Pollution Control
Measures, Technical Report No. 31.
5. U.S. EPA, 1981. NPDESBMP Guidance
Document.
6. U.S. EPA, Pre-print, 1992. Storm Water
Management for Industrial Activities:
Developing Pollution Prevention Plans and
Best Management Practices. EPA 832-R-
92-006.
7. Washington State Department of Ecology,
1992. Storm Water Management Manual
for Puget Sound.
ADDITIONAL INFORMATION
Center for Watershed Protection
Tom Schueler
8391 Main Street
Ellicott City, MD 21043
Denver International Airport
Bob Nixon, Senior Engineer
8500 Pena Boulevard
Denver, CO 80249
City of La Crosse, Wisconsin
Greg Paul
La Plume Wastewater Treatment Plant
905 Houska Park Drive
La Crosse, WI 54601
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Northern Virginia Planning District Commission
David Bulova
7535 Little River Turnpike
Annandale, VA 22003
Southeastern Wisconsin Regional Planning
Commission
Bob Biebel
916 North East Avenue
P.O. Box 1607
Waukesha, WI 53187-1607
The mention of trade names or commercial
products does not constitute endorsement or
recommendation for the use by the U.S.
Environmental Protection Agency.
For more information contact:
Municipal Technology Branch
U.S. EPA
Mail Code 4204
401 M St., S.W.
1MTB
Excellence in compliance through optimal technical solutions
MUNICIPAL TECHNOLOGY BRANCH
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