height and density of growth, and proper selection
and installation of the TRM.

The performance of the TRM-lined conveyance
system depends on the duration of the runoff event
to which it is subjected. For short-term events,
TRMs are typically effective at flow velocities of
up to 50 meters per second (15 feet per second) and
shear stresses of up to 380 Newtons per square
meter (8 pounds per square foot) (Cabalka and
Trotti, 1996). However, specific high-performance
TRMs may be effective under more severe
hydraulic conditions.

TRMs provide long-term water quality benefits by
allowing the growth of vegetation in areas where
impervious conveyance systems would otherwise be
used. While they may reduce flow velocities, hard
armor techniques do not remove pollutants as does
natural vegetation. TRMs can be used in
conjunction with temporary sediment and erosion
control measures to assist communities in
complying with state and local NPDES
requirements. Additionally, TRMs provide a cooler
substrate than traditional hard armor techniques,
reducing water temperature increases that could
otherwise impact aquatic life. Further, the
vegetation itself provides wildlife and aquatic life
habitat. The water quality benefits of TRMs depend
on site conditions and the type and density of
vegetation.

COSTS

In general, the installed cost of TRMs ranges from
$6 to $18 per square meter ($5 to $15 per square
yard). Factors influencing the cost of TRMs

include:

. The type of TRM material required.

. Site conditions, such as the underlying soils,
the steepness of the slope, and other grading
requirements.

. Installation-specific factors such as local

construction costs.

In most cases, TRMs cost considerably less than
concrete and riprap solutions. For example, a

project in Aspen, Colorado, used over 19,000
square meters (23,000 square yards) of TRMs to
line channels for a horse ranch development project
(Theisen, 1996). The TRMs were installed at a cost
of $9.90 per square meter ($8.25 per square yard)
(in 1996 dollars). This was substantially less than
the $24 per square meter ($20 per square yard)
estimate for the rock riprap alternative.

REFERENCES

1. American Association of State Highway
and Transportation Officials, 1992.
Highway Drainage Guidelines, Washington
D.C.

2. Cabalka, D., and J. Trotti, 1996. Beyond
Riprap and Concrete: The Grass Lined
Channel. Erosion Control.

3. Clary, W.P, C.I. Thorton, and S. Abt, 1996.
Riparian Stubble Height and Recovery of
Degraded Streambanks. Rangelands 18(4).

4. Chen, Y.H. and G.K. Cotton,1988. Design
of Roadside Channels with Flexible
Linings. U.S. Department of Transportation,
Federal Highway Administration
Publication No. FHWA-IP-87-7, HEC-15.

5. Lutyens, Don, 1997. The ECTC’s
Installation Guidelines for Rolled Erosion-
Control Products. Geotechnical Fabrics
Report.

6. North American Green, Inc., 1998. Use of
a Composite Turf Reinforcement Mat:
Insurance Against Ohio River 50 Year
Flood. Erosion Discussion 3(1).

7. Synthetic Industries, 1998a. The
Performance Pyramid. Landlok
Applications Manual. Chattanooga,
Tennessee.

8. Synthetic Industries, 1998b. Protective
Channel Linings. Landlok Applications
Manual. Chattanooga, Tennessee


medians, and along streambanks and shorelines.

In addition to their use for new construction
projects, TRMs have been used to retrofit existing
hard armor systems. For example, in 1994, the City
of Chattanooga, Tennessee, began a program to
improve water quality by protecting aquatic habitat
and reducing sediment transport to receiving water
bodies. The City chose to retrofit existing concrete-
lined storm water channels into vegetative swales.
Depending on the hydraulic conditions of the
application, the City chose to use both
biodegradable rolled erosion control products and
turf reinforcement mats. The City has retrofitted
over 32 kilometers (20 miles) of storm water
conveyance systems using this technique.

In addition to improving water quality, TRMs can
provide aesthetic enhancement, especially in areas
lacking vegetative growth. In the city of Louisville,
Kentucky, TRMs are being used to stabilize soil for
vegetation in Waterfront Park, an abandoned
industrial area being converted into a recreational
area (North American Green, 1998). In Waterfront
Park, which is being developed on a hilly site
adjacent to the Ohio River, TRMs not only control
erosion, but they also make it possible for
vegetative growth in the park setting

TRMs will perform well only within their specified
design limitations. Some hydraulic and
environmental conditions dictate that hard armor
techniques are the most appropriate solution. In
general, TRMs should not be used:

. To prevent deep-seated slope failure due to
causes other than surficial erosion.

° When anticipated hydraulic conditions are
beyond the limits of TRMs and natural
vegetation.

. Directly beneath drop outlets to dissipate

impact force (although they may be used
beyond the impact zone).

. Where wave height may exceed 30
centimeters (1 foot) (although they may be
used to protect areas up-slope of the wave
impact zone).

To perform properly, the TRM must be installed
properly and remain in proper contact with the
ground. Critical points in conveyance system
applications where mats can lose support include
points of overlap between mats, projected water
surface boundaries, and channel bottoms. The
Erosion Control Technology Council (ECTC)
publishes installation guidelines for both permanent
and temporary rolled-erosion control products
(Lutyens 1997).

DESIGN CRITERIA

Many state and local erosion and sediment control
manuals, which assist developers in complying with
state and local National Pollutant Discharge
Elimination System (NPDES) programs, specify
guidelines for TRM use and _ applicability.
Additional design procedures for TRM use have
been developed by the U.S. Federal Highway
Administration (Chen and Cotton, 1988) and the
American Association of State Highway and
Transportation Officials (AASHTO, 1992). Most
state transportation departments have a list of
approved products meeting their minimum
performance standards. These standards are
typically based on physical properties of the
product, such as mass per unit area, thickness,
resiliency, porosity, and stiffness.

PERFORMANCE

TRMs provide water quality benefits by allowing
the growth of vegetation in areas where impervious
conveyance systems would otherwise be used. In
general, the performance of TRMs is closely tied to
the vegetative establishment and growth. In a
laboratory study, Clary, et al. (1996) found that the
presence of herbaceous vegetation enhanced
sediment deposition and the channel restoration
process in small-stream systems. Through
experiments in a simulated small stream channel,
Thornton, et al. (1997) found that the ability of
vegetation to entrap and retain sediment increases
with blade length and cross-sectional area of the
vegetation, with retention rates ranging from 30 to
70 percent. The performance of vegetation in
removing sediment and other pollutants depends on
site-specific hydrologic conditions as well as the
underlying soil types, the type of vegetation, the


9. Theisen, Mark, 1996. How to Make
Vegetation Stand Up Under Pressure. Civil
Engineering News.

10. Thorton, C.I., Steven Abt, and W.P. Clary,
1997. Vegetation Influence on Small
Stream Siltation. Journal of the American
Water Resources Association.

11. Trahan, Fred, 1998. Wastewater-treatment
Facility Takes Unique Approach to Erosion
Control. Geotechnical Fabrics Report, 16
(6): 37-39.

12. U.S. EPA, 1992. Storm Water Management
for Construction Activities: Developing
Pollution Prevention Plans And Best
Management Practices. EPA 832 R-92-
005.

ADDITIONAL INFORMATION

City of Chattanooga

Carol Putnam, Stormwater Management Manager
1001 Lindsay St.

Chattanooga, TN 37402

North American Green, Inc.
Tim Lancaster

14649 Highway 41 North
Evansville, IN 47711

Synthetic Industries, Inc.
Deron Austin

4019 Industry Drive
Chattanooga, TN 37416

Washington State Department of Transportation
Dave Rodin, Landscape Architect Office

P.O. Box 1709

Vancouver, WA 98668

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.

fe)
Excelence in complance through optimal technical solutions
MUNICIPAL TECHNOLOGY BRANTHOSS


United States
Environmental Protection
Agency

Office of Water
Washington, D.C.

EPA 832-F-99-002
September 1999

SEPA

Storm Water

Technology Fact Sheet
Turf Reinforcement Mats

DESCRIPTION

This fact sheet describes the use ‘of turf
reinforcement mats (TRMs). TRMs combine
vegetative growth and synthetic materials to form a
high-strength mat that helps to prevent soil erosion
in drainage areas and on steep slopes. TRMs are
classified as a “soft engineering practice,” in
contrast to concrete and riprap, which they may
replace in certain erosion control situations.

High-volume and high-velocity storm water runoff
can erode soil within open channels, drainage
ditches, and swales, and on steep exposed slopes,
increasing the transport of sediments into receiving
waters. Water quality impacts of increased
sediment load include the conveyance of nutrient
and pesticide pollutants, disruption of fish
spawning, and impairment of aquatic habitat.

Traditionally, hard-armor erosion control
techniques such as concrete blocks, rock riprap, and
reinforced paving systems have been employed to
prevent soil erosion in these highly erosive areas.
Although these permanent measures can withstand
great hydraulic forces, they are costly, and they do
not provide the pollutant removal capabilities of
vegetative systems.

TRMs enhance the natural ability of vegetation to
permanently protect soil from erosion. TRMs are
composed of interwoven layers of non-degradable
geosynthetic materials such as polypropylene, nylon
and polyvinyl chloride (PVC) netting, stitched
together to form a three-dimensional matrix. They
are thick and porous enough to allow for soil filling
and retention. In addition to providing scour
protection, the mesh netting of TRMs is designed to

enhance vegetative root and stem development. By
protecting the soil from scouring forces and
enhancing vegetative growth, TRMs can raise the
threshold of natural vegetation to withstand higher
hydraulic forces on stabilization slopes,
streambanks, and channels. In addition to reducing
flow velocities, the use of natural vegetation
provides particulate contaminant removal through
sedimentation and soil infiltration, and improves
the aesthetics of a site.

TRMs offer high shear strength, resistance to
ultraviolet (UV) degradation, and inertness to
chemicals found in soils. Figure 1 illustrates the
applicability of TRMs within the spectrum of
available erosion control techniques. Temporary
erosion control blankets and mats, also shown in
Figure 1, eventually leave vegetation unprotected
and unreinforced, and should only be used to
establish vegetation under mild hydraulic situations.

TRMs, unlike temporary erosion control products,
are designed to stay in place permanently to protect
seeds and soils and to improve germination. TRMs
can incorporate natural fiber materials to assist in
establishing vegetation. However, the permanent
reinforcement structure of TRMs is composed of
entirely non-degradable synthetic materials. The
structure of a typical TRM is illustrated in Figure 2.
A variety of ground-anchoring devices can be used
to secure TRMs, including: u-shaped wire staples,
metal pins, and wood or plastic stakes. Appropriate
ground anchoring devices are chosen based on site-
specific soil and slope conditions.

Vegetative seed selection is based on the
geographic region of the project and site specific
concerns. Sources of information on seed selection


REINFORCED,

CONCRETE
PAVING

CONCRETE PAVING
CONCRETE'BLOCKS!

ROCKIRIPIRAP.

p ES ES EY AE PAE

HIGH PERFORMANCE
TURF REINFORCEMENT MATS

& TURF REINFORCEMENT MATS'

1.5-1.8 m/sec velocity
‘96 N/m’ shear stress
a a ae
5-6 fl/sec velocity
2.0 b/t' shear stress,

TEMPORARY. EROSION
CONTROL BLANKETS:

ISTRAWISIHY DA AUUICIMUUCHES)

DO NOTHING

PERMANENT
NON-DEGRADABLE

MATERIALS

Increasing channel

velocities & shear

stress, longer and
steeper slopes

7.6 m/sec (25 ft/sec) velocity
480 N/m?(10 Ibft) shear stress
LL LE A” Aa” Aa?

43.8 kN/m (3000 Ib/tt )
tensile strength

TEMPORARY
DEGRADABLE
MATERIALS

Decreasing channel

velocities & shear

stress, shorter and
flatter slopes

Source: Synthetic Industries, 1998.

FIGURE 1 EROSION CONTROL TECHNIQUES

include: the U.S. Natural Resource Conservation
Service (NRCS); various university extension
services;and state transportation departments. The
installation area may be seeded before or after the

TRM is installed, depending on the matting
construction and manufacturer's recommendations.


Source: Modified from North American Green, Inc., 1998.

FIGURE 2 THE STRUCTURE OF A
TYPICAL TURF REINFORCEMENT MAT

APPLICABILITY

Turf reinforcement technology may be used in
conjunction with temporary sediment and erosion
control measures to re-establish and protect
vegetation at construction sites. Sediment and
erosion control measures, which are typical
components of storm water pollution prevention
plans, are designed to mitigate construction impacts
on receiving waters. Commonly applied sediment
and erosion control measures include
photodegradable and biodegradable natural fiber
blankets and hydraulic mulches. The use of TRMs
allows vegetative cover to be extended to areas
where site conditions would otherwise limit it. This
helps to establish and maintain a continuous
vegetative cover throughout the applied area. TRMs
can be applied to most sites or structures where
permanent erosion control is required. This
technology has been effectively used in both urban
and rural areas and in a variety of climatic
conditions. Although most effective when used in
fully vegetated areas, TRMs have been used to
prevent erosion even in arid, semi-arid, and high-

altitude regions with limited vegetative growth. In
these areas, vegetation establishment is slow or
difficult, and the TRM matrix is typically filled
with native soils for protection (with the mat acting
to prevent erosion permanently).

Under most climatic or environmental conditions,
reinforced vegetation can protect:

° Surface water conveyance systems (see
channel lining, Figure 3).

° Surficial erosion of slopes.

. Pipe inlets and outlets.

° Shorelines and banks.

ADVANTAGES AND DISADVANTAGES
TRMs are being used to control erosion and
stabilize soil to control runoff from land-disturbing
activities with steep slopes, and to prevent scouring
in storm water detention ponds, water storage

ponds, small open channels, drainage ditches, and
runoff conveyance systems within parking lot

Source: Synthetic Industries, 1998.

FIGURE 3 TRMs AS PROTECTIVE
CHANNEL LININGS