3-EPA
                        United States
                        Environmental Protection
                        Agency
                      Office of Water
                      Washington, D.C.
EPA 832-F-99-002
September 1999
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

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                                                                                       PERMANENT
                                                                                     NON-DEGRADABLE
                                                                                       MATERIALS
                                                                                     Increasing channel
                                                                                     velocities & shear
                                                                                     stress, longer and
                                                                                      steeper slopes
                                                         7.6 m/sec (25 ft/sec) velocity
                                                        480 N/m2 (10 In/ft) shear stress
                                                           43.8 kN/m (3000 Ib/tt)
                                                             tensile strength
      1.5-1.8 m/sec velocity
       96 N/m* shear stress
     5-6 ft/sec velocity
    2.0 ib/ff shear stress
                                                                                     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.

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              --*
                              Permanent Synthetic
                              Ranftxcement
                              Structure

                              Degradade Fiber
                              Matrix (Optional
                              Corrponentthat
                              does not provide
                              Permanent
                              Reinforcement)
Permanent Synthetic
Reinforcement
Structure
Consolidated with
Soil and Vegetation
3em Roots
  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

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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

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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
       DegradedStreambanks. Rangelands 18(4).

4.     Chen, Y.H. and O.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

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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,IN47711

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.
                                                           MTB
 I
 Excellence in compliance through optimal technical
 MUNICIPAL TECHNOLOGY

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