United States

Environmental Protection

Agency

Office of Water

Washington, D.C.

EPA 832-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.
Source: SEWPRC, 1991.

FIGURE 1 TYPICAL DIVERSION SWALE DETAILS

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.
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 offsite 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. NPDES BMP 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-R92-006.

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
For more information contact:

Municipal Technology Branch

U.S. EPA

Mail Code 4204

401 M St., S.W.

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.