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.

-------
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

-------
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

-------
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

-------