ISO/DTR 18228-8

ISO TR/DTR 18228-8:2024 (E)
ISO /TC 221/SC /WG 6
Secretariat: BSI
Date: 2026-01-14
Design using geosynthetics —
Part 8:
Surface erosion control
Conception utilisant des géosynthétiques — —
Partie 8: Lutte contre l'érosion de surface

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ii
Contents
Foreword . iv
Introduction . v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Types of erosion . 2
4.1 General . 2
4.2 Water erosion . 2
4.3 Wind erosion . 4
5 Design considerations for erosion and sediment control . 5
5.1 General . 5
5.2 Consideration of soil survey information . 5
5.3 Climate and precipitation data . 7
5.4 Topography . 7
5.5 Design approaches . 7
6 Types of geosynthetics for erosion and sediment control . 14
6.1 General . 14
6.2 Light geogrids and geonets . 14
6.3 Geomats . 14
6.4 Reinforced geomats . 15
6.5 Pre-filled geomats . 16
6.6 Geoblankets and natural fibres geotextiles . 16
6.7 Geocells . 17
6.8 Sediment retention systems . 18
6.9 Geotextiles for a silt fence and check dams. 18
6.10 Georolls . 19
6.11 Hard armour systems . 19
6.12 Other products for erosion control . 19
7 Testing of erosion and sediment control products . 21
7.1 General . 21
7.2 Index testing . 21
7.3 Bench-scale testing . 22
7.4 Large-scale performance testing of geosynthetics for erosion control . 23
Annex A (informative) The revised universal soil loss equation (RUSLE) . 25
Annex B (informative) Detailed design for erosion control with geosynthetics on channel banks50
Bibliography . 83

iii
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
bodies (ISO member bodies). The work of preparing International Standards is normally carried out through
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This document was prepared by Technical Committee ISO/TC 221, Geosynthetics.
A list of all parts in the ISO 18228 series can be found on the ISO website.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www.iso.org/members.html.
Field Code Changed
iv
Introduction
The ISO/TR 18228 series provides guidance forinformation regarding designs using geosynthetics for soils
and below ground structures in contact with natural soils, fills and asphalt. The series contains 10ten parts
which cover designs using geosynthetics, including guidance for characterization of the materials to be used
and other factors affecting the design and performance of the systems which are particular to each part, with
ISO/TR 18228--1 providing general guidanceinformation relevant to the subsequent parts of the series.

The series is generally written in a limit state format and guidelines areinformation is provided in terms of
partial
material factors and load factors for various applications and design lives, where appropriate.
This document includes information relating to the erosion control function on slopes and river or channel
banks. Details of design methodology adopted in current practice are provided.

Erosion is a natural process by which soil and rock material is loosened and transported. Natural erosion
occurs primarily on a geologic timescale, but when human activities alter the landscape the process of erosion
can be greatly accelerated. Construction site erosion causes serious and costly problems, both on-site and off-
site. Fluid borne soil erosion process begins by water or wind detaching particles by mechanical forces and
fluid stream over the surface.
When land is disturbed at a construction site, the erosion rate accelerates dramatically. Since ground cover on
an undisturbed site protects the surface, the removal of that cover increases the site’s susceptibility to erosion.
Disturbed land couldcan have an erosion rate 1 000 times greater than the reconstruction rate. Even though
the process of construction necessitates that land be left bare for periods of time, proper planning and use of
erosion prevention measures can reduce the impact of accelerated erosion caused by land development.
Attempting to quantify the costs of soil erosion is challenging at best. The number of variables contributing to
erosion along with the costs for cleaning up the effects are extensive. Soil erosion impairs water resources
used for drinking, navigation, recreation or irrigation.

v
vi
Design using geosynthetics —
Part 8:
Surface erosion control
1 Scope
This document contains general recommendations and guidance forprovides information on the design of
geosynthetics for surface erosion control on slopes and river/ or channel banks.
It does not addressapply to the design of geosynthetics for the stability of slopes and river/ or channel banks
and it. It does not addressapply to coastal protection problemsissues.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content constitutes
requirements of this document. For dated references, only the edition cited applies. For undated references,
the latest edition of the referenced document (including any amendments) applies.
ISO 10318--1, Geosynthetics — Part 1: Terms and definitions
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 10318-1 and the following terms
apply.
ISO and IEC maintain terminologicalterminology databases for use in standardization at the following
addresses:
— ISO Online browsing platform: available at https://www.iso.org/obp
Field Code Changed
— IEC Electropedia: available at https://www.electropedia.org/
3.1 3.1
erosion control revegetation mat
ECRM
geomat placed on a slope without being infilled
3.2 3.2
reinforced geomat
GMA-R
geocomposite composed of an erosion control product and a reinforcing element, e.g.
Note 1 to entry: Examples of reinforced geomats include a geogrid, a steel mesh, yarns or other elements.
3.3 3.3
prefilled geomat
GMA-P
erosion control product prefilled at factory with a bitumen bound mineral filler of stone chippings, or another
filler, affording a sufficiently open structure to allow the vegetation to grow through it
3.4 3.4
georoll
GRO
permeable structure of loose, either natural and/or synthetic, or both, fibres and other elements (natural or
synthetic) formed into tubes inserted inside either natural and/or synthetic, or both, netting. (
Note 1 to entry: A georoll is also known as a.k.a. sediment retention fibre roll, (SRFR)).
3.5 3.5
turf reinforcement mat
TRM
geomat placed on a slope with either topsoil and/or seeds, or both
4 Types of erosion
4.1 General
Erosion is often described as the detachment of soil particles by some force. This force can be due to rainfall,
wind, or other forces. Once detachment occurs, the particles are transported. This is most often caused by
water action, although wind can also be a major contributor. The major types of water erosion are: covered in
4.2.
4.2 Water erosion
4.2.1 General
The main forms of onsite erosion are splash, sheet, rill and gully (see Figure 1Figure 1).). Offsite erosion
includes stream and channel erosion.
4.2.14.2.2 Splash
When vegetative cover is stripped away, the soil surface is directly exposed to impact from rainfall. Splash
erosion results, when the force of raindrops falling on bare or sparsely vegetated soil, detaches soil particles
that can easily be transported by water runoff. This pounding action destroys the soil structure and often a
hard crust forms when the soil dries. This crust inhibits water infiltration and plant establishment, increasing
runoff and future erosion.
4.2.24.2.3 Sheet
The removal of exposed surface soil can be caused by the action of unchanneled surface runoff. Shallow
“sheets” of water flowing over the soil surface cause sheet flow. Sheet flow transports soil particles that have
been detached by splash erosion. The shallow surface flow rarely moves as a uniform sheet for more than a
few metres before absorption into the surface irregularities.
4.2.34.2.4 Rill
As surface flow changes from sheet flow to deeper concentrated flow along the low spots of the soil surface, it
creates rivulets, cutting grooves called rills into the soil surface. The energy of this concentrated flow can both
detach and transport soil particles. The rills are small but well-defined channels that are, at most, only a few
centimetres deep.
4.2.44.2.5 Gully
Some gullies are formed when runoff cuts rills deeper and wider or when the flows from several rills come
together and form a large channel. If the flow of water is enough, large chunks of soil can fall from a gully
headwall in a process called mass wasting. Once a gully is created, it is very difficult to control, and costly to
repair.
4.2.54.2.6 Channel
When stream bank vegetation is disturbed or when the velocity or volume of a stream is increased, channel
erosion can occur. Natural streams have adjusted over time to the quantity and velocity of runoff that normally
occurs within a watershed. The vegetation and rocks lining the banks are enough to prevent erosion under
these steady-state conditions. When a watershed is altered by removing vegetation, by increasing the number
of impervious surfaces, or by paving tributaries, stream flows are changed. Increased volume and velocity of
runoff couldcan cause expansion of gullies into well-defined channels. These changes can disturb the
equilibrium of the stream and cause channel erosion to begin. Channel erosion is commonly found at stream
bends, constrictions where installed structures control the stream flow, or discharge points where storm drain
culverts release storm water into a stream.
Key
1 Raindropraindrop erosion
2 Sheetsheet erosion
3 Rill Erosionrill erosion
4  Gullygully erosion
5 Channelchannel erosion
Figure 1 — Types of soil erosion
4.3 Wind erosion
Wind erosion is a form of erosion occurring in flat, bare areas with dry, sandy soils, or where the soils are
loose, dry, and finely granulated. Wind erosion damages land and natural vegetation by removing soil from
one place and depositing it in another. It causes soil loss, dryness, deterioration and desertification of soil
structure, nutrient and productivity losses, air pollution and sediment transport and deposition. Soil
movement is initiated as a result of wind forces exerted against the surface of the ground. For each specific
soil type and surface condition, there is a minimum velocity to move soil particles. This is called the threshold
velocity. Once this velocity is reached, the quantity of soil moved is dependent upon particle size, the
cloddiness of particles, and wind velocity itself.
4.3.1 Suspension
Suspension occurs when very fine dirt and dust particles are lifted into the wind. They can be thrown into the
air through impact with other particles or by the wind itself. Once in the atmosphere, these particles can be
carried very high and be transported over extremely long distances. Soil moved by suspension is the most
spectacular and easiest to recognize of the three forms of movement.
4.3.2 Saltation
The major fraction of soil moved by wind is through the process of saltation. In saltation, fine soil particles are
lifted into the air by the wind and drift horizontally across the surface, increasing in velocity as they go. Soil
particles moved in the process of saltation cause severe damage to the soil surface and vegetation. They travel
approximately four times longer in distance than in height. When they strike the surface again, they either
rebound back into the air or knock other particles into the air.
4.3.3 Surface creep
The large particles which are too heavy to be lifted into the air are moved through a process called surface
creep. In this process, the particles are rolled across the surface after coming into contact with the soil particles
in saltation.
Wind erosion is not addressed in this document.
5 Design considerations for erosion and sediment control
5.1 General
A designer plans for erosion and sediment control measures based upon information provided from resources
obtained from local and regional agencies, and a detailed field site visit. In addition, the designer can identify
potential erosion and sediment problems, develop design objectives, formulate and evaluate alternatives,
select best erosion prevention measures, and develop a plan. A determination is made about what best
management practices (BMPs) are appropriate. The following stepped process presented belowdescribed in
Clause 5 is advisedan example of best practice.
5.2 Consideration of soil survey information
Soil is a product of its environment. A soil’s erodibility, or the vulnerability of soil to erosion, is a result of a
number of soil characteristics which can be divided into two groups:
— those influencing infiltration, or the movement of water into the ground, and;
— those affecting the resistance to detachment and transported by rainfall and runoff.
Key factors that affect erodibility are soil texture, amount of organic matter, soil structure, and soil
permeability.
Soil texture refers to the size and proportions of the particles making up a particular soil. Sand, silt, and clay
are the three major classes of soil particles. Soils high in sand content are said to be coarse-textured. Because
water readily infiltrates sandy soils, the runoff, and consequently the erosion potential, is relatively low. Soils
high in content of silts and clays are said to be fine-textured or heavy. Clay, because of its stickiness, binds soil
particles together and makes a soil resistant to erosion. However, once heavy rain or fast flowing water erodes
the fine particles, they will travel great distances before settling.
Organic matter consists of plant and animal litter in various stages of decomposition. Organic matter improves
soil structure and increases permeability, water holding capacity, and soil fertility. Organic matter in an
undisturbed soil or a mulch covering over a disturbed soil reduces runoff and erosion potential. Mulch on the
surface also cushions the soil from the erosive impact of rainfall.
Soil structure is the arrangement of soil particles into a larger structural mass. Soil structure affects the soil’s
ability to absorb water. When soil is compacted or crusted, water tends to run off rather than infiltrate. Erosion
hazard increases with increased runoff. A more granular structure is the most effective against slope erosion
since it will more readily absorb and retain water, which reduces runoff and (with sufficient nutrients)
encourages plant growth.
Soil permeability refers to the ability of the soil to allow air and water movement through the soil. Soil texture,
structure, and organic matter all contribute to permeability. As noted above, soils that are least subject to
erosion from rainfall and shallow surface runoff are those with high permeability rates, such as well graded
gravels and gravel-sand mixtures, or those with high cohesion, such as a “fat” clay.
Knowing the type of soil present on the project site will helphelps the designer decide upon the degree of
erosion protection required. The soil type will determine its vulnerability to erosion and its ability to support
vegetation.
Vegetative cover is an extremely important factor in reducing erosion from a site. Vegetation couldcan absorb
energy of rainfall, bind soil particles, slow velocity of runoff water, increase the ability of a soil to absorb water
and remove subsurface water between rainfalls through the process of evapotranspiration. By limiting the
amount of vegetation disturbed and the exposure of soils to erosive elements, soil erosion can be greatly
reduced.
Key
1 – Vegetation absorbs the energy of falling rain
2 – Vegetation helps to maintain absorptive capacity
3 – Vegetation slows the velocity of runoff and acts as a filter to catch sediment
4 – Roots hold soil particles in place

1 vegetation absorbs the energy of falling rain
2 vegetation helps to maintain absorptive capacity
3 vegetation slows the velocity of runoff and acts as a filter to catch sediment
4 roots hold soil particles in place
Figure 2 — Benefits of vegetation
5.3 Climate and precipitation data
The frequency, intensity and duration of rainfall and temperature extremes are principle factors influencing
the volume of runoff from a given area. As the volume and intensity of rainfall increases, the ability of water
to detach and transport soil particles increases. When storms are frequent, intense, and of long duration, the
potential for erosion of bare soils is high. Temperature has a major influence on soil erosion. Frozen soils are
relatively erosion resistant. However, soils with high moisture content are subject to “spew,” or uplift when
frozen and are usually very easily eroded upon thawing.
5.4 Topography
The size, shape and slope characteristics of a watershed influence the amount and duration of water runoff.
The greater the slope length and gradient, the greater the potential for both runoff and erosion. Velocities of
water will increase as the distance from the top of the slope or the gradient of the slope increases. The term
“ground cover” refers principally to vegetation, but it also includes surface treatments such as mulches,
matting, wood chips, and crushed rock. Vegetation is the most effective means of stabilizing soils and
controlling erosion. It shields the surface from the impact of falling rain, reduces flow velocity and disperses
flow.
Vegetation provides a rough surface that slows the runoff velocity and promotes infiltration and deposition of
sediment. Plants remove water from the soil and thus increase the soil’s capacity to absorb water. Plant leaves
and stems protect the soil surface from the impact of rainfall and the roots help maintain the soil structure
while holding the soil in place.
5.5 Design approaches
5.5.1 Slope erosion: Revised universal soil loss equation (RUSLE)
In order to properly design retention and erosion control measures, a designer usually needs tomust calculate
the quantities of water and sediment that will be managed.
Monitoring and modelling of the erosion processes can help to better understand the causes of soil erosion,
make erosion predictions under a range of possible conditions and plan the application of preventive and
restorative strategies for erosion. The current most commonly used model for predicting soil loss from water
erosion on slopes is the Revised Universal Soil Loss Equation revised universal soil loss equation (RUSLE),
developed by the U.S. Department of Agriculture in the 1960s and 1970s.
RUSLE is expressed by the following formula:Formula (1):
A = R ˑ K ˑ L ˑ S ˑ C ˑ P
(1)
where:
A estimated average soil loss (Mg/hectare/year);
R rainfall-runoff erosivity factor (MJˑmm/haˑhrˑyr);
K soil erodibility factor (tonˑhaˑhours/haˑMJˑmm);
L slope length factor;
S slope steepness factor;
C cover-management factor;
P support practice factor.
The RUSLE equation can be used to predict the amount of soil that couldcan be eroded, for example, from
construction sites. Specifically, it enables the most critical source areas to be identified and allows predictions
of the benefits of erosion control measures.
RUSLE is based on a very large number of measurements made on the “standard plot" (see Annex AAnnex A).).
The plot had a constant gradient of 9 %, with a down slope length of 22,13 m (72 feet) and a width of 1,83 m
(6 feet).
Recent research on geosynthetics (GSY) for erosion control on slopes has been carried out with setups of
various lengths and steepness for obtaining values of the cover management factor ( C ) when a slope is
[1]
protected with a specific GSY. The standardized test method in ASTM D6459 is normally a preferred method
for slope erosion performance testing because:
— — at present, it is the only international standard that simulates full-scale conditions of rainfall induced
erosion on a slope;
— — the test procedure has been standardized since 1999 and provides detailed instructions for any labs
use in setting up and performing the tests;
— — it has been used to evaluate a wide variety of erosion control products;
— — test setup allows an actual installation simulation, including anchor pattern, density, depth and joint
overlaps to be examined;
— — test setup is large enough to address all relevant erosion issues, including surface drilling;
— — test results have demonstrated that ASTM D6459 produces performance results that correlate well with
the theoretical results predicted by the Revised Universal Soil Loss Equation (RUSLE),, as reported by
Sprague (2008); andReference [36];
— — thanks to this correlation, the test can provide relevant input to the Revised Universal Soil Loss
Equation RUSLE (see Annex AAnnex A).).
For a given slope (for example, a road cut with a sandy silt surface soil layer) the correct evaluation of the C-
factor for different GSY is fundamental for the design of the erosion control system.
The C-factor for a specific GSY product can be obtained either by a test on a real slope under calibrated rainfall,
and/or laboratory tests with a calibrated rain simulator –, or both, with both working to simulate installation
configuration (pin placement and configuration).
For fallow unprotected ground the C-factor is equal to 1,0; covering the slope with an appropriate GSY for
erosion control can reduce the C-factor down to 0,01 – 0,05, or lower, when still unvegetated, and even lower
when vegetated.
Table A.9Table A.9 in presents a sample of results from publicly posted ASTM D6459 test reports.
These values of the C-factor provide an immediate impression of the efficacy of GSY in protecting slopes
against erosion.
While RUSLE is a tool to estimate the rate of soil loss based on site-specific environmental conditions and a
guide for the selection and design of sediment and erosion control systems for the site, it does not estimate
gully or stream-channel erosion. RUSLE does not determine when soil loss is excessive at a site, when erosion
control systems have failed or sediment yield once it has left the site. The RUSLE user makes such decisions
based upon numerous criteria, of which soil-loss and sediment-yield estimates are an important aspect of
design.
Perhaps theThe most critical parameter in an engineering design is flow resistance before, during and long
after vegetative establishment. Some erosion control materials couldcan be washed away before the
vegetation takes hold while others couldcan temporarily exhibit excellent flow resistance only to lose their
effectiveness as they degrade or decompose over time.
RUSLE and its application to civil engineering problems is presented in detail in Annex AAnnex A.
5.5.2 Channel erosion
Erosion on river and channel banks develop from the shear stresses applied by the stream. If not properly
addressed, riverine erosion couldcan cause significant issues for navigation and human activities. Moreover,
uncontrolled erosion couldcan produce the failure of dikes, with consequent flooding of surrounding areas.
The water flow in rivers and channels produces shear stresses on the bottom and side banks, which are
proportional to water depth and velocity. Such shear stresses can remove soil particles and excavate
progressively deeper into the channel bottom and sides, which couldcan lead to slope failure. Channel bottom
and sides can be protected by lining with different materials (concrete, riprap, GSY, etc.). The calculation
(design or verification) of a bank protection can be made using two different methods based on: Formula (2)
and (3):
— Water velocity: V all
(2)
— Shear stresses applied by the water stream: τ <τ
all
(3)
Vall and τall are the limit values of velocity and shear stresses just before the movement of soil particles start.
The design and selection of GSY for protecting river and channel banks require performance tests, in either
unvegetated and/or vegetated configuration, or both, to assess the limit values of water velocity and shear
stress when the bank is protected with a specific product.
Two basic design concepts are used to evaluate and define a channel configuration that will performperforms
within the accepted limits of stability. These methods are defined as the permissible velocity approach and
the permissible tractive force (shear stress) approach. Under the permissible velocity approach, the channel
is assumed stable if the adopted velocity is lower than the maximum permissible velocity.
The tractive force (boundary shear stress) approach focuses on stresses developed at the interface between
[2 [2] ]
flowing water and the materials forming the channel boundary. . The permissible velocity approach uses
the Gauckler–Manning formula where, with a given depth of flow, D, the mean velocity of water flow (V) can
be calculated as: shown in Formula (4):
2/3 1/2
V = (1 / n) ˑ R ˑ S
h
(4)
where:
V cross-sectional mean velocity (m/s));
1/3
n Gauckler–Manning roughness coefficient (s/m ));
R hydraulic radius (m);
h
S slope of the hydraulic grade line or the linear hydraulic head loss (-), which is equal to the channel
bed slope when the water depth is constant.

The hydraulic radius is defined as the ratio of the channel's cross-sectional area of the flow to its wetted
perimeter (the portion of the cross-section's perimeter that is "wet"):") as shown in Formula (5):
R = A/P
h
(5)
where:
A cross sectional area of flow (m );
P wetted perimeter (m).
The tractive shear stress applied by the water stream is:
τ = γ ˑ D ˑ S
w
(6)
where:
τ tractive shear stress (kPa);
γ unit weight of water (kN/m );
w
D maximum depth of flow (m);
S average bed slope (-).
Design criteria based on flow velocity can be limited because maximum velocities vary widely with channel
length (L), shape (Rh), and roughness coefficients (n). In reality, it is the force developed by the flow, not the
flow velocity itself, that challenges the performance of erosion control systems. Tractive forces caused by
flowing water over the ground surface create shear stresses which can be used as a design parameter
independent of channel shape and roughness. Moreover, the higher stresses developed in channel bends or
other changes in stream channel geometry can be quantified by simplified shear stress calculations, providing
a higher level of design confidence than otherwise possible (Chen & Cotton, 1988).see Reference [37]).
Critical shear stress determinations are meant to be used with velocity calculations for pre-screening of
channel lining designs. Manning's equation remains the primary hydraulic research and design tool. However,
as everyday practice has determined, a simplified screening criterion such as maximum shear stress is
necessary to ensure properly engineered design of channel lining erosion control systems.
The duration of flow is of some importance. In general, the design of erosion control materials is based on
relatively short flow durations during testing, e.g. 30 minutes for unvegetated and 60 minutes for vegetated
conditions. Though flow velocities decrease over time, it has been assumed in standard testing protocols that
soil loss does not continue to increase with flow duration. Thus, manufacturers of geosynthetics for erosion
control often express the erosion resistance of their materials in terms of maximum allowable flow velocity
that has been determined by relatively short-term testing. This erosion resistance does not reflect any
additional erosion damage resulting from flows continuing over a period of several hours. It can be important
for a designer to consider flow duration in appropriate design. Figure 2Figure 2 provides preliminary
indications.
Design examples for erosion control with geosynthetics in channel applications is presented in Annex BAnnex
B.
Figure 3
KEY
1 – Fully vegetated TRM
2 – Non-vegetated TRM or ECRM
3 – 100% cover
4 – Poor cover
A – Hard armor systems
B – Soft armor zone
C – Limits of natural vegetation
D – Bare soil erosion
[SOURCE: Reference [3], reproduced with shows the permission of the authors.]

Figure 3 — Allowableallowable design water velocity, V , for various classes of erosion control materials.
allow
Key
1 fully vegetated TRM
2 non-vegetated TRM or ECRM
3 100 % cover
4 poor cover
A hard armor systems
B soft armor zone
C limits of natural vegetation
D bare soil erosion
[SOURCE: Reference [3], reproduced with the permission of the authors.]
Figure 3 — Allowable design water velocity V
allow
5.5.3 Sediment control
Going hand in hand with aggressive erosion control measures would normally beis typically a well-conceived
sediment control plan. Vegetation is clearly the finest sediment control product on the planet, but in lieu of
vegetation, sediment retention devices (SRDs) are usually needed.
Geosynthetic silt fences have become a standard construction practice over much of the world, replacing straw
and hay bales, brush layers and rock check dams. Silt fences are generally installed at the beginning of the
construction project and usually consist of woven slit tape geotextiles mounted on a prefabricated fence. A
well-designed silt fence will initially screen silt and sand particles from runoff. A soil filter is formed adjacent
to the silt fence and reduces the ability of water to flow through the fence. This leads to the creation of a pond
behind the fence which serves as a sedimentation basin to collect suspended soils from runoff water. To meet
such needs, the geotextile would normally havetypically has properly sized openings to form the soil filter,
and the storage capacity of the fence wouldis usually be adequate to contain the volume of water and sediment
anticipated during a major storm.
Porous sediment control structures are an additional geosynthetic approach to sediment control. A three-
dimensional mouldable mass of crimped synthetic fibres couldcan be placed in fills or gullies to provide
passive sediment control. Placed by hand with its size and shape determined by the installer, applications
include fill and gully repair, ditch checks, sediment traps, and perimeter berming.
Design for sediment control is typically event based and is not considered in this document.
6 Types of geosynthetics for erosion and sediment control
6.1 General
Various GSY are widely used for erosion control applications. GSY can be in the form of a mat, sheet, grid or
web of either natural fibre, such as jute, coir or wood wool, or artificial fibre, such as polyethylene, nylon or
polypropylene. Several products are commercially available for use in erosion control, where they interact as
a composite with the soil and vegetation. The general goal of erosion control GSY is to protect the soil from
erosion, either indefinitely or until vegetation can establish itself.
Geosynthetics can serve as the complete erosion and sediment control product, or a part of a composite
structure serving the designed product function. The followingClause 6 presents some of the geosynthetic and
geosynthetic-related products used for erosion and sediment control.
6.2 Light geogrids and geonets
Biaxially oriented light geogrids and geonets are two-dimensional products typically manufactured from
polypropylene or polyethylene resins (see Figure 4Figure 4).). They vary in composition, strength, elongation,
aperture size and shape. Colour and ultraviolet stability can be designed into the product for specific site
requirements and service life durations. They can be placed on a slope to assist vegetation in resisting erosion
forces and, since they do not absorb moisture, they do not shrink and swell. Biaxially oriented light geogrids
and geonets are often used to create more complex products and are even used alone to anchor loose fibre
mulches such as straw, hay and wood chips.

Figure 4 — Examples of biaxially oriented light geogrids and geonets
6.3 Geomats
Geomats (see Figure 5Figure 5)) are generally made of synthetic material filaments or nets, tangled together
to form a highly deformable layer 10 mm to 20 mm thick, featuring very high porosity (greater than 90 % on
average).
Geomats can protect the soil against rainfall splash and runoff by keeping in place soil particles; moreover,
Geomatsgeomats can increase the shear resistance of the roots system several times over.
They can be used on slopes and along the banks of canals and river courses for the following applications:
— erosion protection on slopes caused by the impact of rain drops and runoff; and
— lining of river/ or channel banks with low water velocities.

Figure 5 — Examples of geomats
6.4 Reinforced geomats
Reinforced geomats (see Figure 6Figure 6)) are geocomposites manufactured by joining a geomat and a
geogrid or metallic mesh, having a tensile strength in the range 50 kN/m –to 300 kN/m.
Reinforced geomats afford all the characteristics of geomats, plus they afford high tensile strength.
They can be used on long and steep slopes, along the banks of canals and river courses with relatively high-
water velocities, or where high tensile strength is needed.

Figure 6 — Examples of reinforced geomats
6.5 Pre-filled geomats
Geomats can be prefilled, when manufactured, with a bitumen bound mineral filler of stone chippings or
another filler to provide erosion protection in case of high-water velocities and small wave attack for surfaces
permanently subjected to water impact (see Figure 7Figure 7).).
These prefilled geomats usually afford a sufficiently open structure to allow the vegetation to grow through it.

Figure 7 — Example of geomat prefilled with bitumen and gravel
6.6 Geoblankets and natural fibres geotextiles
Geoblankets are a particular class of geosynthetics made up of natural or synthetic fibres (see Figure 8Figure
8),), in the form of a mat of fibres held together with natural or synthetic light weight meshes. Natural fibres
couldcan be used to form woven geotextiles.
Geoblankets can protect a slope against rain splash, but the protection against runoff is very limited.
Geoblankets made of natural fibres can absorb high amounts of water. During their natural degradation, they
can produce nutrients for the vegetation. These materials can be used for temporary erosion control on slopes
and along the banks of canals and river courses with low water velocities.

Figure 8 — Examples of geoblankets and natural fibres geotextiles
6.7 Geocells
Geocells are honeycomb products manufactured by joining polymeric strips or geotextile strips through
welding, gluing or stitching (Figure 9(Figure 9).).
The only function afforded by geocells is lateral confinement: the lateral movements of the soil infilled in the
cells is prevented or limited by the cell walls and by the other surrounding cells. Hence, geocells by themselves
...