Chapter 3
Erosion and Sediment Control Practices
Environmental Protection Handbook
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CHAPTER 3: EROSION AND SEDIMENTATION CONTROL PRACTICES
TABLE OF CONTENTS
3.1 INTRODUCTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-1
3.2 STABILIZATION PRACTICES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-2
Preservation and Protection of Natural Vegetation . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-3
Filter Strips . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-5
Land Grading . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-6
Surface Roughening . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-7
Temporary Seeding . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-8
Permanent Seeding and Planting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-10
Mulches, Mats and Geotextiles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-11
Soil Binders/Tackifiers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-14
Soil Retaining Walls . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-15
Soil Bioengineering . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-16
3.3 STRUCTURAL PRACTICES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-19
Perimeter Dikes and Swales . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-19
Drainage Swales . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-20
Temporary Storm Drain Diversion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-21
Silt Fence . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-22
Gravel/Stone Filter Berm . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-24
Stabilized Construction Entrance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-24
Check Dams/Triangular Dikes/Berms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-25
Sediment Traps . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-27
Temporary Sediment Basin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-30
Storm Drain Inlet Protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-31
Outlet Protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-33
Gabion Inflow Protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-34
3.4 REFERENCES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-35
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EROSION CONTROL KEYS
The keys to controlling erosion and
soil loss on construction sites are to:
C Protect the soil surface from rain
drop impact,
C Maintain 
soil’s 
water 
holding
capacity,
C Slow storm water runoff speed,
C Minimize slope lengths,
C Plan to control storm water runoff,
C Match practices to individual site
conditions, and
C Maintain erosion, sediment and
stormwater control practices.
CHAPTER 3: EROSION AND SEDIMENTATION CONTROL PRACTICES
3.1
INTRODUCTION
Erosion from construction sites, dirt roads and other disturbed lands are a source of sediment, toxic chemicals,
and excess nutrients that can pollute coastal waters. Runoff from construction sites is by far the largest source
of sediment in urbanizing areas (U.S. EPA, 1993; U.S. EPA, 1992). Sediment eroded from dirt roads,
construction sites and other cleared areas is the primary pollutant impairing V.I. water quality (DPNR-DEP and
USDA-NRCS, 1998). A 1986 study of erosion rates on St. Thomas and St. Croix estimated erosion from a
disturbed dirt road site to be 591 tons/acre/year (Wernicke, Seymour and Mangold, 1986). Studies of erosion
rates in the Fish Bay watershed on St. John have soil loss from dirt roads of between 100 to 600 tons per year
(MacDonald, et. al., 1997; Sampson, 1997). 
Erosion control practices reduce the amount of soil that erodes from construction sites. Sediment control
practices remove eroded soil from stormwater before it leaves the construction site and is deposited onto
roadways and down-slope properties and into guts, ponds and coastal waters. Using erosion and sediment
control practices is an important part of stormwater pollution prevention. These practices have been developed
by the USDA Soil Conservation Service/Natural Resources Conservation Service, various local and state
government agencies, and erosion control professionals and product manufacturers.
The selection of the best soil erosion and sediment control practices for construction sites should be based upon
the nature of the construction activity and the conditions that exist at the construction site.  A properly designed
erosion and sediment control plan should:
•
Minimize the amount of disturbed soil on the
construction site. This will decrease the potential amount
of soil that erodes from the site, reducing the number and
complexity of practices needed to remove sediment from
site runoff.
•
Prevent runoff from off-site areas from flowing
across disturbed areas. This will reduce the amount of
stormwater that comes into contact with bare soils.
Reducing runoff flow over bare soils decreases soil erosion
and reduces the volume of stormwater needing treatment
to remove sediment.
•
Slow the runoff flowing across the site. High runoff
velocities reduce water seepage into the soil, increase runoff volume, and cause soil particles to detach
from the soil surface. High runoff velocities can cause severe gully erosion, especially on steep slopes.
Make grades as gradual as possible without excessively modifying existing site conditions.
•
Remove sediment from on-site runoff before it leaves the site. Because vegetation used for soil
stabilization may not establish itself before a severe storm occurs, on most construction sites it will be
necessary to install practices that can remove sediment from runoff before it leaves the site. 
•
Plan soil disturbance activities for the dry season. This will help to minimize erosion by
scheduling site disturbance activities to occur during times of little or no rainfall.
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How these objectives are met depend upon site characteristics and the type of construction activity. The
following sections describe stabilization and structural practices for erosion and sediment control. Construction
specifications and design procedures for each practice are provided in Appendix B.
3.2
STABILIZATION PRACTICES
Preserving existing vegetation and re-planting cleared/bare soils as soon as possible after earth
change is the most effective way to control erosion. Plant cover reduces erosion potential by:
•
Protecting the soil surface from the impact of falling rain drops (reducing erosion);
•
Slowing runoff velocity (or speed) and allowing sediment to settle out (reducing off-site sediment loss);
•
Physically holding the soil in place with plant roots (erosion control); and
•
Increasing infiltration (or seepage) rates by improving the soil’s structure and porosity. 
Vegetative cover can be grass, trees, shrubs, ground covers, other types of plants, or any combination of these.
Grasses are used most commonly because they grow quickly and have fibrous root systems that can rapidly
stabilize soils. Other soil stabilization practices such as mulching or matting may be used during the dry season
when seeds have difficulty establishing themselves. Newly planted shrubs and trees establish root systems more
slowly, so keeping existing ones is a more effective practice. Existing vegetation is adapted to the area, whereas
many exotic plant species that are planted after construction may prove to be less successful.
Vegetative and other stabilization practices can be either temporary or permanent. Temporary practices provide
cover for exposed or disturbed areas for short time periods or until permanent erosion controls are in place.
Permanent vegetative practices are used when soil-disturbing activities are completed or when erosion is
occurring on a site that is otherwise stabilized. It is generally preferable to permanently stabilize disturbed soils
as soon as possible. The stabilization practices presented in this chapter include:
•
Preservation and Protection of Natural Vegetation
•
Filter Strips
•
Land Grading
•
Surface Roughening
•
Temporary Seeding 
•
Permanent Seeding and Planting
•
Mulch, Mats and Geotextiles
•
Soil Binders/Tackifiers
•
Soil Retaining Walls
•
Soil Bioengineering
Stabilization practices should be initiated as soon as practicable in sections of the site where
construction activities have temporarily or permanently ceased, but in no case more than 14 days
after the construction activity in that part of the site has temporarily or permanently stopped.
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Preservation and Protection of Natural Vegetation
When and Where to Use Natural Vegetation Preservation
Figure 3.1. Diagram showing site where natural
vegetation is preserved around the perimeter (Toni
Thomas, UVI-CES).
What to Consider
The preservation of natural vegetation (existing trees, vines, bushes, and grasses) provides natural buffer zones
to slow runoff and filter sediment. Often areas of a construction site are unnecessarily cleared. Only those areas
essential for construction activities should be cleared (building footprints, road/drive ways, cistern and septic
system areas). Other areas should remain undisturbed, particularly critical areas such as those with steep slopes
and/or highly erodible soils, or areas around guts, ponds or coastal waters.
Preserving natural vegetation on the site by clearing only the area where structures will be built minimizes erosion
potential, protects water quality, provides aesthetic benefits, and is cost-effective in the long term. This practice
is a permanent control practice.
This practice applies to all construction sites. Natural vegetation preservation is particularly beneficial in or near
floodplains, wetlands, guts, steep slopes, and other areas where erosion controls would be difficult to establish, install,
and/or maintain. Virgin Islands Law (V.I. Code Annot. Title 12, sections 121 to 125) prohibits “...the cutting or
injury of any tree or vegetation within 30 feet of the center of any natural watercourse, or within 25 feet of the edge
of such watercourse, whichever is greater.” This chapter goes further to define a natural watercourse as “...any stream
with a reasonably well-defined channel, and includes streams which have a permanent flow, as well as those which
result from the accumulation of water after rainfalls and which regularly flow through channels formed by the force
of the waters,” i.e., guts. In many instances, guts may flow for only a few days or weeks during the year. However,
the vegetation within or bordering these guts is very important for maintaining water quality and may contain rare,
endangered or threatened plant and animal species.
On-site vegetation preservation should be planned before any
site disturbance begins (Figure 3.1). Preservation requires good
site management to minimize the impact of construction
activities on existing vegetation. Heavy equipment can ruin the
topsoil through compaction and kill desirable plants. The
proposed limits of land disturbance should be
physically marked off to ensure that only the required
land area is cleared. Clearing promotes unwanted weed
growth because of increased exposure to sunlight. Hard-to-
control plants like guinea grass, vines, tan-tan and casha can
rapidly take over cleared areas. Hand-clearing preserves existing
vegetation while removing unwanted plants.
Trees to be preserved should be clearly marked and protected from ground disturbances around
the base of the tree. Trees should be protected with tree armoring, fencing, or a tree well (Figure 3.2). Limit
soil placement over existing tree and shrub roots to a maximum of 3 inches. Retaining walls or terraces should
be used to protect roots of trees and shrubs when grades are lowered. Lowered grades should start no closer than
the tree’s dripline. Care should be taken to minimize damage to tree limbs and root systems. Contact the
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Figure 3.2. Tree protection practices (Maryland Department of the Environment, 1994).
How Effective is Natural
Vegetation Preservation?
Department of Planning and Natural
Resources (DPNR), the DPNR
Division of Fish & Wildlife, the UVI
Cooperative Extension Service (CES),
or the V.I. National Park for
information on rare or endangered
species before removing trees or other
vegetation. 
Since soils are so shallow in the Virgin
Islands, topsoil is a rare commodity
and should be conserved. As little
existing topsoil should be removed as
possible. Where topsoil has been
removed, soil should be stockpiled on
the site so that it can be re-applied.
Soil 
stockpiles 
must 
be
temporarily seeded or covered
with a tarp, mat or geotextile to
prevent erosion. Compatibility of
existing and imported topsoils should
be checked to ensure maximum
growth potential for the desired
vegetation.
Preservation and enhancement of natural vegetation is the most effective erosion and sediment control practice.
Any ground disturbance on a site results in increased erosion from that site. By minimizing land clearing to the
areas where final structures will be located (building footprints, driveways, septic systems, etc.), overall site
erosion is minimized. The vegetation remaining on the site also works as a filter to trap sediments and other
pollutants (see Filter Strips). A natural vegetation zone around the building area will also provide a windbreak,
shade, privacy barrier, noise buffer, dust filter, and wildlife habitat. However, other practices may also be needed
to control erosion and sediment loss, especially from roadways or driveways.
ADVANTAGES OF NATURAL VEGETATION PRESERVATION/PROTECTION
•
Is inexpensive and already established.
•
Can handle higher quantities of stormwater runoff than newly seeded areas.
•
Is already established, therefore is immediately effective.
•
Has good pollutant filtering capacity since preserved natural vegetation and root structure are usually denser
than in newly seeded areas.
•
Provides areas for infiltration, reducing stormwater runoff volume and velocity.
•
Requires less maintenance than planting new vegetation and is more likely to successfully control erosion and
sedimentation.
•
Holds existing topsoil on ground so that new soil does not have to be brought in.
•
Provides noise buffers and screens for onsite operations.
•
Provides a windbreak, shade, privacy barrier, dust filter, and wildlife habitat.
•
Enhances aesthetics and property values.
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Filter Strips
When and Where to Use Filter Strips
Figure 3.3. Vegetated buffer strip design (Schueler, 1987).
What to Consider
Filter strips are vegetated strips of land used to remove sediment and other pollutants from stormwater runoff
by slowing runoff speeds, filtering out sediment and other pollutants, and providing some infiltration. Filter strips
are different from buffer strips (as described in Chapter 4) because their effectiveness is not measured by their
ability to improve stormwater infiltration. A filter strip can be an area of vegetation that is left undisturbed during
construction, or it can be newly planted. Filter strips can be either temporary or permanent practices.
Filter strips can be used at any site that can support vegetation. Filter strips are best suited for treating runoff
from roads and highways, small parking lots, construction sites and pervious surfaces (CWP, 2000a). Filter strips
are used at the lower edge of cleared or disturbed areas, small parking lots or home sites, or above structural
practices such as swales or diversions. They are particularly effective on flood plains, next to wetlands, ponds and
guts, and on steep unstable slopes. Filter strips should always be used around guts and other drainage
ways, ponds, and coastal waters, and are most effective if they are buffers (see Chapter 4)
consisting of native vegetation left undisturbed during construction. If native vegetation does not
provide enough ground cover, it can be supplemented with native grass seed, such as bahia or hurricane grass.
The type and quantity of pollution that
filter strips will be treating must be
determined. Slopes, soils, plant species,
construction timing, watering needs, and
operation and maintenance methods
should be considered in designing a filter
strip. If the filter has outlet flow, it must
be non-erosive.
Filter strips are typically used to treat very
small drainage areas. The limiting design factor is the length of flow contributing to the filter strip. The slope
length contributing runoff to a filter strip should not exceed 75 feet for impervious areas (including compacted
soil) or 150 feet for pervious areas (CWP, 2000a). Filter strips are most effective on slopes of 5% or less, and
grassed filter strips should be at least 15 feet wide, forested filter strips should be at least 50 feet wide. Steeper
slopes require wider widths (for example, a 20 - 30% slope requires a grassed strip at least 25 feet wide, (USDA-
SCS, 1993a).
If filter strips are composed of preserved existing vegetation, good planning and site management are needed to
protect them against disturbances such as grade changes, excavation, equipment damage, and other activities.
Establishing new filter strips requires the establishment of good grass cover, trees and shrubs (see Preservation
and Protection of Natural Vegetation (page 3-3) or Permanent Seeding and Planting (page 3-10)). Careful
maintenance is important to ensure healthy vegetation. The need for routine maintenance like mowing, pruning,
irrigation, and weed and pest control will depend on the species of plants and trees used. Native plant species
will require minimum maintenance while exotic species may require significant inputs (irrigation, pesticides,
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How Effective Are Filter Strips?
Land Grading
Figure 3.4. Land grading details (Empire State Chapter, Soil and Water
Conservation Society, 1991).
When and Where to Use Land Grading
nutrients). Maintaining planted areas may require debris removal and protection against unintended uses or
traffic.
Filter strips can be very effective in removing sediment from stormwater if dense plant growth is present (i.e.,
if existing vegetation is preserved or newly planted vegetation grows quickly and thickly). Filter strips can also
slow and reduce stormwater flow through infiltration of excess water so that downstream erosion is greatly
reduced.
ADVANTAGES OF FILTER STRIPS
•
Filter sediment and other pollutants from stormwater runoff before it reaches drainage channels, guts,
ponds, and/or coastal waters.
•
Prevent erosion on the vegetated area of the site.
•
Provide areas for infiltration, reducing the volume and speed of stormwater runoff.
•
Native (or existing growth) filter strips have lower maintenance requirements.
•
Are very low cost if using existing vegetation.
•
Provide screens and buffers for noise and privacy, provide areas for wildlife habitat and improve site
appearance. 
DISADVANTAGES OF FILTER STRIPS
•
Limit the amount of land area to be used for construction and other activities.
•
Require plant growth before they are effective (for newly planted filter strips).
•
May not be feasible for small lots.
Land grading is the reshaping or alteration of the
existing land surface to provide for better utilization,
improvement of drainage, and erosion control
(Figure 3.4). Land grading requires a well-developed
plan using an engineering survey and layout. The
land grading specification is used to provide for
erosion control and vegetation establishment on
those areas of the construction site where the
existing land surface will be disturbed by grading
activities.
Proper land grading practices should be used in all land disturbing activities, and particularly on sites where
surface irregularities, slopes, soil type, obstructions, or wetness interfere with planned uses; or where the desired
land use requires designed land surfaces. Serrated cut slopes (Figure 3.5) should be used for steep cuts
behind buildings or adjacent to driveways or roads to prevent landslides. These slopes can then be
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Figure 3.5. Typical section of serrated cut slope (Empire State Chapter
Soil and Water Conservation Society, 1991).
What to Consider
Surface Roughening
Figure 3.6. Surface roughening details - stair-stepping (Empire State
Chapter Soil & Water Conservation Society, 1991).
When and Where to Use Surface
Roughening
planted with temporary or permanent vegetation (see Seeding & Planting section). Special attention should be
given to maintaining or improving habitat for rare, threatened or endangered species, where applicable (contact
the DPNR Division of Fish and Wildlife for information on Virgin Islands habitat requirements).
The grading plan should incorporate building
designs and street layouts that fit into and utilize
the existing topography, vegetation and other
desirable natural features to avoid extreme grade
modifications. The effect of grading on runoff
quantity and surface storage should be considered.
Stormwater runoff will be increased by removal of
vegetation and surface storage areas (depressions).
Water quality will be affected by an increased rate of erosion during construction. Sediment loss will vary with
changes in runoff. Factors determining potential sediment loss (and appropriate control practices) include slope
before and after grading, results of the construction process, and the amount of vegetation re-established on the
graded or shaped site. All disturbed areas MUST be stabilized structurally or vegetatively upon
completion of construction activities.
ADVANTAGES OF LAND GRADING
•
Minimizes the amount of erosion from graded areas and cut and/or fill slopes.
•
Prepares land for construction purposes.
DISADVANTAGES OF LAND GRADING
•
May be difficult on small lots and/or lots with steep slopes.
Surface roughening roughens a bare soil surface
with horizontal grooves running across the slope,
stair-stepping, or tracking with construction
equipment (Figure 3.6). This practice is used to
ease establishment of vegetation by seed, to reduce
stormwater runoff velocity, increase infiltration,
reduce erosion, and trap sediment.
All slopes, especially those steeper than 3:1 (33%),
require surface roughening to facilitate vegetative
stabilization.
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What to Consider
Figure 3.7. Surface roughening details - grooving (Empire State Chapter
Soil & Water Conservation Society, 1991).
Temporary Seeding
When and Where to Use Temporary Seeding
What to Consider
There are many different ways to roughen soil
surfaces. Selecting the best method depends on
the type of slope. Steepness, mowing requirements
(if any), and a cut or fill slope operation are all
factors that need to be considered in selecting a
roughening method. A common roughening
method on moderate slopes is to run the
bulldozer/backhoe up and down the slope so that the treads create horizontal indentations (grooving, Figure 3.7).
ADVANTAGES OF SURFACE ROUGHENING
•
Reduce runoff speed and decrease the distance of overland runoff flow.
•
Hold moisture better than do smooth slopes and minimize sheet and rill erosion.
DISADVANTAGES OF SURFACE ROUGHENING
•
May increase cut and fill costs and cause sloughing if excessive water infiltrates the soil.
Temporary seeding is used to reduce erosion and sedimentation on areas that will not be stabilized for a long
time or where permanent plant growth is not necessary or appropriate. A short-term cover of fast-growing
grasses is seeded on a cleared or disturbed site to keep soils from being carried offsite by stormwater runoff or
wind. Seeding can be performed by hydroseeding, hand broadcasting, or installing seeded erosion control mats.
Seeded areas can also be covered with erosion control mats to conserve moisture, prevent wash out, and protect
seeds from birds and insects (see Mulch, Mats & Geotextiles, page 3-11).
Temporary seeding should be performed no later than 14 days after the halt of construction activities on all
disturbed areas that are likely to be re-disturbed, but not for several weeks or more. This includes denuded areas,
cuts, fills, soil stockpiles, sides of sediment basins, and temporary roadbanks. Temporary seeding should take
place as soon as possible after the last land disturbing activity in an area. It is especially important on
critical areas such as dams, dikes, levees, cuts, fills, and denuded or gullied areas.  
Proper seed bed preparation and the use of high-quality seed are needed to grow grass for effective erosion
control. Soil that has been compacted by heavy equipment may need to be loosened with a rake or tiller. Top-
soiling is not necessary for temporary seeding, but it may improve chances for vegetation establishment. Seed
bed preparation may also require fertilizer application to make conditions more favorable to plant growth. Proper
fertilizer application, seeding mixtures and seeding rates vary depending on site location, soil type, slope, and
weather.  
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Figure 3.8. Hydroseeding side slopes and outside rim of a
sediment basin (Estate New Hernhut, St. Thomas, 1998).
How Effective is Temporary Seeding?
It is very important to select appropriate grass species and to time seeding. Seeding native or naturalized grass
species will increase the odds for success in establishing vegetation. Native species also tend to have lower
maintenance needs because they are adapted to the environmental conditions in the area. The UVI Cooperative
Extension Service or USDA Natural Resources Conservation Service (NRCS, formerly the Soil Conservation
Service) can supply information on suitable native grasses. Local suppliers, the Cooperative Extension Service,
or USDA-NRCS can supply information on best seed mixes and fertilizer and irrigation needs.
Seeded areas on slopes steeper than 4:1 or in sandy, clayey or caliche soils should be covered with mulch or
erosion control mats (see Mulch, Mats & Geotextiles, page 3-11) to provide protection from rainfall and to
prevent birds from eating the seed. Seeded areas should also be mulched and matted if the weather is excessively
dry or if heavy rain is expected before the seed sprouts. Frequent inspections are necessary to ensure that the
grass is growing properly and to determine if irrigation is needed. If grass does not grow quickly or thick enough
to prevent erosion, the area should be reseeded as soon as possible. 
Hydroseeding is an erosion control practice used to rapidly
stabilize disturbed soils with grasses (Figure 3.8).
Hydroseeding equipment is used to uniformly apply a
combination of grass seed, water, fertilizer, mulch and
tackifier to an area to be seeded. Grass seed, paper fiber
mulch, water, and even fertilizer are mixed together in the
hydroseeder tank and then sprayed out over the disturbed
soil area. This equipment allows rapid stabilization of a site
with a minimum amount of labor. DPNR-CZM owns two
hydroseeders maintained by the UVI Cooperative
Extension Service (CES) that are leased to government
agencies and the general public upon completion of an
equipment certification workshop. For more information
on the DPNR/UVI-CES hydroseeding program, contact CES at (340) 693-1080.
This practice, along with Preservation and Protection of Natural Vegetation (page 3-3) and Permanent Seeding
and Planting (page 3-10), is most effective in reducing erosion and sedimentation from a construction site,
especially in areas where soils are unstable because of their slope, texture, structure, a high water table, or high
winds. However, seeding with non-native grasses not adapted to the Virgin Islands climate and soil conditions
may not be as effective due to low survival rate and higher maintenance requirements.
Once vegetation is established, its roots hold the soil in place and the vegetation also slows down runoff, increases
infiltration, and filters sediments from runoff. However, temporary seeding may not be effective in arid and semi-
arid regions (eastern portions of the islands) or during dry seasons (where/when climate prevents fast plant
growth). In those areas, mulch, erosion control mats or geotextiles may be more appropriate for the short term.
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Permanent Seeding and Planting
When and Where to Use Permanent Seeding & Planting
Figure 3.9. A low-maintenance, natural landscape in
a dry area (Estate Nazareth, St. Thomas, 1995).
What to Consider
ADVANTAGES OF TEMPORARY SEEDING
•
Is generally inexpensive and easy to do.
•
Quickly establishes grass cover when conditions are adequate.
•
Provides excellent soil stabilization, provides sediment filtering capability, and is visually pleasing.
•
May help reduce costs of maintenance of other erosion controls (i.e., silt fences, sediment traps/basins may
need to be cleaned out less often).
•
Reduces stormwater runoff rates and volume.
•
Hydroseeding has lower labor costs than hand application methods – one person can operate a hydroseeder
to apply seed, mulch and fertilizer simultaneously.  
•
Hydroseeding also applies grass seed more evenly, results in faster germination, produces better grass
stands, and provides for easier transportation and storage.
•
Improves the appearance of the site.
DISADVANTAGES OF TEMPORARY SEEDING
•
Depends on adequate rainfall or irrigation for success, especially prior to establishment.
•
May require fertilizing of plants grown on some soils (particularly caliche), which can be more expensive and
cause downstream water quality problems.
•
Temporary vegetation requires protection from equipment and heavy use once seeded.
Permanent seeding and planting is the planting of permanent plant cover such as trees, shrubs, vines, grasses or
legumes on highly erodible or critically eroding areas, or on disturbed soils at the completion of earth change
activities. This practice provides soil stabilization and reduces stormwater runoff and sediment loads to guts and
coastal waters by slowing runoff velocity and increasing runoff infiltration. Vegetation also filters sediment and
other pollutants, improves wildlife habitat, and enhances the appearance of a site and its property value.
Permanent seeding and planting should be used to stabilize all disturbed areas once construction
has been completed in that area. Permanent vegetation
establishment is especially important on steep slopes and grades, in
filter strips, buffer areas, and vegetated swales, and along guts,
ponds and coastal areas.  
It is very important to select appropriate plant species and to
carefully time planting. Planting native or naturalized species will
increase the odds for success in establishing vegetation. Native
species also tend to have lower maintenance needs because they are
adapted to local environmental conditions. Many low-maintenance,
native plants can be added to the site’s landscaping (Figure 3.9).
Some good native plants available in local nurseries include wild
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3-11
Figure 3.10. Newly planted vetiver hedge (UVI St.
Thomas, 1999).
Mulch, Mats and Geotextiles
frangipani, orange man jack, pink cedar, sea grape, lignum vitae, turpentine tree, teyer palm, sabal palm, wild
ferns, wild anthurium, and spider lily. 
Some exotic plants can also be incorporated into the landscape. Be
careful to choose species that won’t escape into natural areas and
crowd out native plants. Vetiver grass (Vetiveria zizanioides) hedges
can be planted across slopes (along the contour) to form a living
terrace (Figure 3.10). Vetiver is a non-native, non-invasive,
clumping grass species. It is used in Africa, India and Southeast Asia
to stabilize slopes and channels by trapping sediment behind the
grass. Some exotic ornamental plant species that can be used around
the home include hibiscus, bougainvillea, oleander, croton,
heliconia, ginger, isora, aralia, agave, and non-native palms. Fruit
trees and vegetable gardens can also be planted once construction is completed. The UVI Cooperative Extension
Service (CES) or USDA Natural Resources Conservation Service (NRCS, formerly the Soil Conservation Service,
SCS) can supply information on suitable native and exotic plant species. Local suppliers, CES or USDA-NRCS
can supply information on best seed mixes and fertilizer and irrigation needs.
ADVANTAGES OF PERMANENT SEEDING & PLANTING
•
Quickly establishes vegetative cover when conditions are adequate.
•
Provides excellent soil stabilization and sediment filtering capability.
•
Improves stormwater infiltration, reducing stormwater runoff speed and volume.
•
Provides a windbreak, shade, privacy barrier, dust filter, and wildlife habitat.
•
Improves site appearance and property values.
DISADVANTAGES OF PERMANENT SEEDING & PLANTING
•
Depends on adequate rainfall or irrigation for success.
•
May require fertilizing of plants grown on some soils (particularly caliche), which can be more expensive and
cause downstream water quality problems.
•
Permanent vegetation requires protection from equipment and heavy use once seeded.
Mulching is a temporary soil stabilization or erosion control practice. Mulching uses materials such as cut grass,
woodchips, wood fibers, straw, or gravel to cover the soil surface to temporarily stabilize disturbed areas until
vegetation is established or construction is completed. Mulching also reduces the speed of stormwater runoff over
bare soils. When used together with seeding and planting, mulching can aid in plant establishment by holding
seed, fertilizer, and topsoil in place; by helping to retain moisture; by insulating against high temperature, and
by protecting seed from birds.
Erosion control mats are materials (straw, coconut, wood, or synthetic fiber) that have been woven into a mat
or blanket and are backed with plastic or jute netting. Erosion control mats offer the same benefits as mulch but
are more stable and can withstand much higher stormwater velocities than loose mulch. They are used to
temporarily stabilize bare soils or slopes during construction when it is difficult to establish temporary vegetation
(due to dry, stony, or steep soil conditions). Mats are also used with permanent seeding and planting to help hold
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Environmental Protection Handbook
When and Where to Use Mulch, Mats and Geotextiles
Figure 3.11. Straw mat used to stabilize
seeded slope (UVI St. Thomas, 1999).
What to Consider
soils in place until grass or other plants can become established. Figure 3.10 shows how erosion control mats
are used for erosion control in a drainage swale.
Netting is typically made from jute, coconut or other wood fiber, plastic, paper or cotton and can be used to hold
mulch onto the ground. Netting can also be used alone to stabilize soils while plants, such as ground covers,
become established. However, it does not retain moisture or temperature well.
Other materials, called filter fabrics or geotextiles, are also used for erosion control. These materials are made
by weaving or bonding fibers made from synthetic materials such as polyester, nylon, polyvinyl chloride (PVC),
or other material. Mats, netting and other filter fabrics are used in areas with steep slopes where loose mulch
and seed are vulnerable to being washed away, or where vegetation is difficult to establish.
Loose mulch should only be used on fairly level slopes, or in areas that
only need short-term stabilization. Erosion control mats or geotextiles
are often used alone in areas where temporary seeding cannot be used
because of season or soil/slope conditions. Mats can provide immediate,
effective erosion control. In critical areas such as drainage swales ,
channels, or along shorelines, mats or geotextiles can be used to provide
channel stabilization. There are many different types of erosion control
mats. Erosion control mats can be used for a wide range of slopes and
stormwater flow rates. For example, 100% straw mats can be used on
slopes up to 3:1 in steepness and 75 feet in length or in low-flow swales
(Figure 3.11). Straw/coconut mats can be used on steeper slopes (2:1 -
1:1, depending on length) and medium flow discharge channels.
Coconut fiber or synthetic mats provide long term protection on steeper
slopes or in high discharge channels. Check the manufacturer’s
specifications to determine which material is appropriate for a given
application. 
Geotextiles can be used alone as matting to stabilize flow in channels and swales, to protect seedlings on recently
planted slopes, or to protect tidal or drainage banks where moving water may wash out new plantings. When
properly anchored, geotextiles can provide stabilization on slopes up to 30-40% (depending upon material type).
Geotextiles are also used as separators. For example, filter fabric can be placed between gravel or rip-rap and
soil. This “sandwiching” prevents the gravel from being compacted into the underlying soil and prevents the soil
underneath the rip-rap from being eroded.
Mulch should be applied to moderate slopes (< 10%) and soils that are not highly erodible. On steep slopes,
highly erodible soils, or in swales (see sections on Drainage Swales and Grassed Swales) erosion control mats
or geotextiles should be used and anchored into place with staples (anchoring patterns depend on slope steepness
and length and flow rate, see Figure 3.12). On extremely arid sites where grasses cannot survive, native ground
covers or shrubs can be planted in jute or coir (coconut fiber) netting. Filter fabric or erosion control mats can
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3-13
Figure 3.12. An example of erosion control matting of a drainage swale
(Maryland Department of the Environment, 1994).
How Effective are Mulch, Mats, and Geotextiles?
also be used for this purpose. Before stabilizing an
area, it is important to have all sediment controls
installed and for runoff to be diverted away from
the area to be planted.
Final grading is not necessary before mulching.
Mulched areas should be inspected often to find
where mulch has been loosened or removed.
These areas should be reseeded, if necessary, and
the mulch cover replaced immediately. 
When selecting erosion control mats or
geotextiles, choose an appropriate type for the
intended use. Follow manufacturer
recommendations or seek advice from the USDA
Natural Resources Conservation Service or the
UVI Cooperative Extension Service. Areas covered
with mats or geotextiles should be inspected
regularly to determine if cracks, tears, or breaches have occurred. If so, repairs should be made immediately.
Effective netting and matting requires firm and continuous contact between the fabric and the soil. If there is
no contact, the material will not hold the soil in place and erosion will occur underneath it. Matting should be
able to withstand stormwater runoff speeds of up to 5 feet per second.  
Mulch, mats and geotextiles are very effective in reducing erosion and are very cost-effective, as compared to
retaining walls or purchasing new top soil. Mulch alone should only be used for temporary protection of the soil
surface on fairly level slopes. The useful life of mulch, mats and geotextiles varies according to the material and
amount of rainfall, from a minimum of 1 month for mulch to 3 years for geotextiles.  
ADVANTAGES OF MULCH, MATS AND GEOTEXTILES
C
Provide immediate, effective protection of exposed and/or eroding soils. 
C
Mulch, mats and geotextiles retain moisture, minimizing the need for watering.
C
Organic mulch, mats and netting do not need to be removed because they are biodegradable.
C
Mats protect seeds from birds and other animals.
C
Mats and geotextiles are less expensive than structural practices and a wide variety are available to match
specific needs.
C
Are convenient to install.
DISADVANTAGES OF MULCH, MATS AND GEOTEXTILES
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Environmental Protection Handbook
Soil Binders/Tackifiers
When and Where to Use Soil Binders/Tackifiers
What to Consider
C
Mulch and/or mats may delay seed germination in some species.
C
Mulch can be easily blown or washed away by runoff if not secured.
C
Mats are difficult to anchor into stony or compacted clay soils.
C
Mats may inadvertently contribute to weed growth, since they hold in moisture.
C
Geotextile effectiveness may be reduced significantly if the fabric is not properly selected or installed.
C
Many geotextiles are photodegradable and must be protected prior to installation.
Soil binders or tackifiers are chemical polymers or emulsions sprayed onto the soil surface to provide soil
stabilization. There are many different types of chemical polymers on the market that provide varying degrees
of stabilization. Soil polymers are used for temporary erosion control, and are typically applied using
hydroseeding equipment, with or with out seed and/or mulch. 
Soil binders are often used on extreme slopes and droughty (very dry) soils where it is difficult to establish
vegetation. Tackifiers are typically used in conjunction with hydroseeding (see Temporary Seeding page 3-8) to
stabilize soils and hold grass seed and mulch in place until germination and root establishment occurs. Binders
and/or tackifiers can also be used to hold loose mulch in place on soils. Some tackifiers and binders can also help
to conserve moisture in soils. These chemicals are also effectively used on construction sites for dust suppression.
There are many different types of soil binders and tackifiers available. Some materials are more toxic than others,
and some may or may not be biodegradable. The type of material chosen depends on the site’s slope and soils,
the season and geographic area of the site (for example, whether the site is on the dry east end or wetter north
side of an island), the longevity of the material, whether or not seed and/or mulch will be applied with the
material, and whether or not it is an acceptable material to be used in the hydroseeding equipment. Products
should be carefully investigated. Practice application/installation varies by manufacturer; see manufacturer
guidelines for specific installation specifications. The International Erosion Control Association (IECA) website
provides a partial list of erosion control product vendors at: www.ieca.org.
ADVANTAGES OF SOIL BINDERS/TACKIFIERS
C
Provide short-term stabilization of severe, dry and/or stony slopes that are difficult to vegetate.
C
Can provide stabilization for 2 to 18 months, depending on the material and site conditions.
C
Are useful for holding seed, mulch and fertilizer in place on steep slopes.
C
Aid in conserving soil moisture.
C
Provide excellent dust control.
C
Some are non-toxic and/or biodegradable.
DISADVANTAGES OF SOIL BINDERS/TACKIFIERS
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3-15
Soil Retaining Walls
Figure 3.13. Rock retaining walls installed to stabilize base of steep
slope above a sediment basin (Estate New Hernhut, St. Thomas,
2000).
When and Where to Use Retaining Walls
What to Consider
C
Many are not suitable for long term stabilization (over 6 months).
C
Some may be toxic or persist in the environment.
C
Some forms may clog hydroseeding equipment used to apply material.
C
Do not prevent mass-wasting (landslides).
Soil retaining walls are structures used to hold loose or unstable soil firmly in place. For example, soil tie backs
and retaining walls can be used during excavation to prevent cave-ins and accidents, but they also are excellent
permanent erosion control practices that retain soils and slopes to prevent them from moving. There are many
different types of soil retaining structures that can be used. Some basic ones include:
•
Skeleton Sheeting: Skeleton sheeting is the least expensive soil retaining system. It requires the soil
to be cohesive (like clay). Construction grade lumber is used to brace the excavated face of the slope.
This is a temporary practice.
•
Continuous Sheeting: Continuous sheeting uses a material such as steel, concrete or wood to cover
the face of the slope in a continuous manner. Struts and boards are placed along the slope to provide
continuous support to the slope face.
•
Permanent Retaining Walls: Permanent retaining walls may be necessary to provide support to the
slope after construction is completed. Concrete, stone, or wood (horizontal telephone poles, etc.)
retaining walls can be built and left in place.
Soil retaining walls should be used where other
methods of soil retention are not practical. They are
especially applicable in the Virgin Islands to retain cut
slopes along road and drive ways, parking lots, building
sites, and other cut and fill areas where slopes or soils
are not suitable for vegetative stabilization (Figure
3.13).
Soil retaining walls are used for both erosion control and safety purposes. Retaining wall design must address
foundation bearing capacity, sliding, overturning, drainage, and loading systems. These are complex systems and
all but the smallest retaining walls should be designed by a licensed engineer.
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Environmental Protection Handbook
Soil Bioengineering
When and Where to Use Soil Bioengineering
What to Consider
ADVANTAGES OF RETAINING WALLS
•
Provide safety to workers.
•
Can be used as either temporary or permanent structures (depending upon design).
•
Are exceptionally effective in preventing erosion and landsliding from unstable slopes and soils that cannot
be stabilized using conventional methods.
DISADVANTAGES OF RETAINING WALLS
•
Require the expertise of a professional engineer for all but the smallest retaining walls.
•
May be expensive to design and install, depending upon site constraints, size and material used.
Soil bioengineering combines mechanical, biological and ecological concepts to stop and prevent shallow slope
failures (or landslides) and erosion. The soil bioengineering practices discussed in this section can be divided into
two general categories: living and non-living.  
The living approach uses live plants to provide soil reinforcement and prevent surface erosion. Vegetated rock
gabions and vegetated rock walls use porous structures with openings that plant cuttings are inserted into. The
rock provides immediate resistance to sliding, erosion and washout. As the vegetation becomes established, roots
bind the slope together into a unified mass.
Non-living approaches use rigid structures, like gravity retaining walls and rock buttresses to retain soil. Plants can
be used in conjunction with these structures to create vegetated structures. The plants enhance the structures
and help to reduce surface erosion.
Soil bioengineering techniques are generally appropriate for immediate protection of slopes against surface
erosion and shallow mass wasting (landslides), and provide cut and fill slope stabilization, earth embankment
protection, and small gully repair treatment. These techniques are used when vegetative stabilization alone is not
feasible. The use of soil bioengineering practices is limited on rocky or gravelly slopes that lack sufficient soil or
moisture to support plant growth. Soil-restrictive layers, such as hardpans, may also prevent root growth.
Soil bioengineering is often a useful alternative for small, highly sensitive, or steep sites where the use of
machinery is not feasible and hand labor is a necessity. However, rapid vegetative establishment may be difficult
on extremely steep slopes.  The soil bioengineering system selected should fit the site. The slope, soils, geology,
hydrology and existing vegetation should be taken into account when designing the system. Existing vegetation
should be retained whenever possible to provide protection against surface erosion and shallow slope failures.
This vegetation can also be a source of cuttings to use in the practice. Native plant species that root easily should
be used (turpentine tree (Bursera simaruva), white manjack (Cordia sulcata), hog plum (Spondias mombin), orchids,
bromeliads, anthuriums – see USDA-NRCS Common Planting Table) or contact the USDA Natural Resources
Conservation Service, UVI Cooperative Extension Service, or the V.I. Department of Agriculture for information
on appropriate plants. The following soil bioengineering practices are most appropriate for conditions in the
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3-17
Figure 3.14. Vegetated rock gabion details (USDA-SCS, 1992). (Note:
rooted/leafed condition of the living plant material is not representative of
the time of installation).
Figure 3.15. Vegetated rock wall details (USDA-SCS, 1992). (Note:
Rooted/leafed condition of the living plant material is not representative
of the time of installation).
Figure 3.16. A low wall with plantings established on the slope above
(USDA-SCS, 1992).
Virgin Islands, although other practices may be applicable (consult the USDA-NRCS for further information on
soil bioengineering practices).
Vegetated Rock Gabions: Rock gabions are
rectangular baskets made from triple-twisted,
hexagonal mesh of heavily galvanized steel wire
placed in position, wired to adjoining gabion
baskets, filled with large stone, and then folded
shut and wired at the ends and sides. Live
branches (or seeds) are then placed on each
consecutive layer between the rock-filled baskets.
These branches will take root inside the gabion
basket and in the soil behind the baskets, binding
the gabions to the slope (Figure 3.14).
This practice is used at the base of a slope where
a low wall may be needed to stabilize the toe of
the slope and reduce its steepness. It is not
designed to resist large, lateral earth stresses.
Vegetated rock gabions should be built a
maximum of 5 feet in height, overall, including
the excavation needed for a stable foundation.
This practice is useful where space is limited and
a more vertical structure is needed.
Vegetated Rock Wall: A vegetated rock wall is a
combination of rock and live branch cuttings used
to stabilize and protect the toe of steep slopes.
Vegetated rock walls are different from retaining
walls because they are placed against relatively
undisturbed earth and are not intended to resist
large lateral earth pressures (Figure 3.15).
Vegetated rock walls are used where a low wall
may be needed to stabilize the toe of the slope and
reduce its steepness. This practice is especially
useful where space is limited and natural rock is
available.
Low wall/slope face plantings: This practice
consists of a low retaining wall placed at the foot
of a slope so that the slope can be flattened for
planting. Vegetation established on the face of the
slope protects against both surface erosion and
shallow land slides (Figure 3.16). Different types
of retaining walls can be used as low walls, the
simplest being a gravity wall that resists lateral
earth movement with its weight or mass. This
includes masonry and concrete walls as well as
reinforced earth or geogrid walls.  
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Environmental Protection Handbook
Tiered wall/bench plantings: An alternative to a low wall with a face planting is a tiered retaining wall, or terrace,
system. This alternative effectively allows vegetation to be planted on slopes that would otherwise be too steep.
Shrubs and trees planted on the benches screen the structure behind them and lend a more natural appearance
while their roots protect the benches. Virtually any type of retaining structure can be used in a tiered wall system.
A tiered wall system allows plant propagation on steep slopes and embankments.
ADVANTAGES OF SOIL BIOENGINEERING
•
Soil bioengineering systems generally require minimal access for equipment and workers and cause
relatively minor site disturbance during installation.  
•
Combined slope protection systems can be more cost-effective than the use of either vegetative treatments
or structural practices alone, especially when using indigenous plant material.  
•
Are exceptionally effective in preventing erosion and landsliding from unstable slopes and soils that cannot
be stabilized using vegetative methods alone.
•
Can withstand heavy rainfalls immediately after installation.
•
Is self-repairing by regeneration and growth once vegetation is established.
•
Requires little maintenance.
DISADVANTAGES OF SOIL BIOENGINEERING
C
May be expensive to design and install, depending upon site constraints, size and materials used.
C
Depending on the species of plant material used, may be difficult to get adequate vegetation establishment.
C
Requires periodic inspections until vegetation is established.
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3-19
Perimeter Dike/Swale
When and Where to Use Perimeter Dikes/Swales
3.3
STRUCTURAL PRACTICES
Structural practices are used in sediment and erosion control to divert stormwater runoff away from exposed
areas, to convey runoff, to prevent sediment from moving offsite, and to reduce the erosive forces of runoff
waters. These controls can be either permanent or temporary practices, depending on how they are used. The
structural practices described in this chapter include:
•
Perimeter Dike/Swale
•
Drainage Swale
•
Temporary Storm Drain Diversion
•
Silt Fence
•
Gravel/Stone Filter Berm
•
Stabilized Construction Entrance
•
Check Dams/Triangular Dikes/Berms
•
Sediment Traps
•
Temporary Sediment Basin
•
Storm Drain Inlet Protection
•
Outlet Protection
•
Gabion Inflow Protection
Temporary structural practices are used during construction to prevent sediment from moving offsite. The length
of time that temporary practices are functioning varies since the sediment control strategy may change as
construction activities progress. Permanent structural practices are used to convey stormwater runoff to a safe
outlet away from erodible areas and/or to treat stormwater runoff to remove sediment. Permanent structural
practices remain in place and continue to be used after construction is completed.
In general, structural sediment control practices are less effective that erosion control – i.e., it is much easier and
more cost effective to keep the soil in place than it is to attempt to remove soil from stormwater. This is
particularly true in the Virgin Islands since predominant soil types have high clay content. Clays are particularly
difficult to remove from stormwater because of their very small particle size and propensity to stay suspended
in stormwater for long time periods. Most practices, such as silt fences, sediment traps, and
gravel/stone filter berms, are not effective in removing clays from stormwater runoff.
A perimeter dike is a ridge of compacted soil. A swale is an excavated trench or channel. These two practices are
used together to prevent stormwater runoff generated outside a construction site from entering and crossing the
site and eroding bare soils or disturbed areas. Perimeter dikes and swales reduce the volume and speed of runoff
on a site  and channel stormwater to a stabilized discharge area or sediment trap (see sections on Sediment Traps
and Temporary Sediment Basins). The dike is built using the soil dug from the adjoining swale placed along the
perimeter of the construction site or disturbed area. Dikes and swales can be either temporary or permanent
stormwater control structures.
Perimeter dikes/swales are generally built around the edge of the site before any earth change activity takes place.
They may also be used to protect existing buildings, topsoil stockpiles, or other small areas that have not yet been
fully stabilized. They are appropriate for sites less than or equal to two (2) acres in size. 
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Figure 3.17. Examples of perimeter dikes/swales (U.S. EPA, 1992).
What to Consider
Drainage Swale
When and Where to Use Drainage Swales
If temporary dikes and swales are to remain
in place longer than 10 days they must be
stabilized using either vegetation, erosion
control matting, geotextile, rip-rap, or some
other material. The distance from the bottom of
the swale to the top of the dike should not be less
than 18 inches.  The bottom width of the dike and
width of the swale should be a minimum of three
(3) feet. The maximum allowable grade should NOT exceed 20 percent. Figure 3.17 shows two different types
of perimeter dike/swale.
Stormwater runoff diverted by a perimeter dike/swale should be directed to an appropriate area for sediment
removal (a sediment trap, basin, or filter area: see sections on Sediment Traps, Sediment Basins, and Filter
Strips). Temporary perimeter dikes/swales may stay in place as long as 12 to 18 months, provided they are
properly stabilized and inspected and maintained on a regular basis. They should remain in place until the area
they were built to protect is permanently stabilized. Temporary and permanent control practices should be
inspected once a week on a regular schedule and after every large or intense rain storm. Repairs should be made
promptly.
ADVANTAGES OF PERIMETER DIKES/SWALES
•
Are easy to install and are effective for channeling stormwater runoff away from areas subject to erosion.
•
Can handle flows from large drainage areas.
•
Are inexpensive because they use materials and equipment normally found onsite.
DISADVANTAGES OF PERIMETER DIKES/SWALES
•
Can cause erosion and sediment transport downstream if they are not properly designed, built or stabilized.
•
If water flows too fast, vegetation may be difficult to establish – slopes less than 20% are recommended.
•
Require frequent maintenance, inspections and repairs.
A drainage swale is a channel excavated and located to convey runoff to a desired location. It typically has a lining
of vegetation, erosion control matting, geotextile, rip-rap, concrete, or some other material.  
A drainage swale is used to route stormwater around or through an area without causing erosion. A swale can
convey runoff from an undisturbed area surrounding the construction site to a stabilized outlet, where runoff
is discharged at non-erosive rates. It can also be used to divert sediment-laden runoff away from a disturbed area,
across disturbed areas to shorten overland flow distances, or from the base of a slope to a sediment trapping
device.
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What to Consider
Figure 3.18. Temporary swale design example (Empire State Chapter,
Soil and Water Conservation Society, 1997).
Swale A
Swale B
Maximum Drainage Area Contributing Runoff
< 5 Acres
5 - 10 Acres
Bottom Width of Flow Channel
4 feet
6 feet
Depth of Flow Channel
1 foot
1 foot
Side Slopes
2:1 (50% or 26°)or flatter
2:1 or flatter
Grade
0.5% minimum
20% maximum
0.5% minimum
20% maximum
Table 3.1. Example drainage swale designs (Empire State Chapter, Soil and Water Conservation Society, 1997).
Temporary Storm Drain Diversion
When and Where to Use Temporary Storm Drain Diversions
Swales should be lined with grass, sod, erosion
control mats, geotextiles, rip-rap, or concrete. The
type of liner used is dependent on the volume and
velocity of the stormwater runoff to be conveyed.
The swale should have a positive grade and should
have no dips or low points where stormwater can
collect. Figure 3.18 shows an example of swale
design and Table 3.1 provides an example of how to design two different sized drainage swales.
ADVANTAGES OF DRAINAGE SWALES
•
Swale excavation can be easily performed with earth moving equipment.
•
Can transport large volumes of runoff.
DISADVANTAGES OF DRAINAGE SWALES
•
Stabilization and design costs can make construction expensive.
•
Effective use is restricted to areas with relatively flat slopes (< 8% for most designs).
A temporary storm drain diversion is a pipe that redirects an existing storm drain system or outfall channel so
that it discharges into a sediment trap or basin.
Storm drain diversions should be used to temporarily divert stormwater runoff flow going to a permanent outfall.
This diverted flow should be directed to a sediment trapping device (see Sediment Traps or Temporary Sediment
Basins section). A temporary storm drain diversion should be used for as long as the area draining to the storm
drain remains disturbed.
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Environmental Protection Handbook
What to Consider
Silt Fence
Figure 3.19. Poor silt fence placement (left) vs. proper silt
fence placement (right) (Fifield, 1996).
When and Where to Use Silt Fences
Figure 3.20. Properly installed reinforced silt
fence - note trenching, wire mesh and steel
bars (Estate Caret Bay, St. Thomas, 1999).
Since the existing storm drain system will be modified, careful consideration needs to be given to the pipe
configuration and the resulting impact of installation. The temporary diversions will need to be removed once
construction is completed and the original storm drain system is restored. Therefore, appropriate restoration
measures should be taken, such as flushing the storm drain before removing the sediment trapping device, and
stabilizing the outfall and restoring grades.
ADVANTAGES OF TEMPORARY STORM DRAIN DIVERSIONS
•
Requires little maintenance once installed.
DISADVANTAGES OF TEMPORARY STORM DRAIN DIVERSIONS
•
Disturbs existing storm drain patterns.
A silt fence, or filter fabric fence, is a temporary practice for sediment control. A silt fence is made of geotextile
or filter fabric stretched across wood posts, rebar or a wire support fence. The lower edge of the material is
vertically trenched into the ground and covered by backfill. Silt
fences are most effective for removing sediment from overland
flow. They reduce sediment loads entering receiving waters.
They are also used to catch wind blown sand and to create an
anchor for sand dune creation. Along with the typical wooden
post and filter fabric method, there are several variations of
filter fabric fence installation including fencing that can be
purchased with pre-sewn pockets for use with steel rebar fence
posts. (Use of steel rebar for fence posts is recommended in the
Virgin Islands, especially on slopes greater than 20% or in
stony or clayey soils).
Silt fences are the most widely and most incorrectly used
sediment control practice in the Virgin Islands. 
Silt fences should only be used to detain sediment on  small construction
sites, such as individual home sites. Silt fences should be installed prior
to earth change activities. The fence should be placed away from the
bottom of the slope (to increase holding capacity), along a line of
uniform elevation perpendicular to the direction of flow (Figure 3.19).
Silt fence material MUST be trenched into the ground to work properly
(Figure 3.20). Fencing can also be placed across the direction of
stormwater flow at the outer boundary of the work area. Silt fences
should NEVER be installed in guts or swales.
Chapter 3
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3-23
Figure 3.21. Properly installed silt
fence (Estate St. George’s Hill, St.
Croix, 1998).
What to Consider
Slope Steepness
Maximum Slope Length
(feet)
2:1 (50% or ~26°)
50
3:1 (33% or ~19°)
75
4:1 (25% or ~14°)
125
5:1 (20% or ~11°)
175
Flatter than 5:1
200
Table 
3.2. 
Maximum 
allowable 
slope 
lengths
contributing runoff to a silt fence (Empire State Chapter,
Soil and Water Conservation Society, 1997).
Silt fences used on slopes greater than 20% (5:1 or , or installed in rocky or clayey soils, should use 3/8" - ½" steel
rebar  stakes instead of wooden posts (Figure 3.21). Silt fences installed on slopes greater than 40% should use
3/8" - ½" steel rebar and wire mesh backing to prevent the fence from being knocked down by heavy stormwater
flows. Double the height of the silt fence on slopes steeper than 1:1 or with a
greater than recommended slope length (see Table 3.2). Attach the top and
bottom of the second layer of geotextile to the rebar and wire mesh so that it
overlaps the first layer by 6 inches. Staple the two layers together.
A silt fence is NOT appropriate for controlling runoff from a large area (greater
than 5 acres). However, this type of fence is much more effective than a straw
bale barrier if properly installed and maintained. (Straw bale barriers are NOT
recommended for use in the Virgin Islands). Silt fences MUST be anchored and
trenched into the ground or else they will fail. They should always be used in
combination with other erosion and sediment control practices, such as
temporary seeding, perimeter dikes and swales, drainage swales, sediment traps,
etc. The area below a silt fence should be undisturbed ground.
The effective life span for a silt fence depends on the material and
maintenance. Silt fences require frequent inspection and prompt
maintenance to maintain effectiveness. The fence should be
inspected after each rainfall. Check for areas where runoff has
eroded a channel beneath the fence, or where the fence has
sagged or collapsed from runoff flowing over the top. Remove
sediment when it is one-third to one-half the height of the fence,
or after each storm. (Accumulated sediment can be used for
landscaping purposes once construction is completed.) Table 3.2
lists maximum slope lengths (distance down-slope between silt
fences) for a silt fence depending upon steepness. 
Maximum drainage area for overland flow to a silt fence should not exceed ½ acre per 100 feet of fence. Also, do
not use silt fences to retain sediment from concentrated stormwater flow (such as in a channel, gully, gut or other
drainage way), the material is not designed and manufactured to withstand the force of concentrated flows.
ADVANTAGES OF SILT FENCING
•
Reduces the speed of stormwater runoff and removes some sediment from runoff, protecting downstream
areas from sedimentation.
•
Is inexpensive and easy to install.
•
Is suitable for smaller developments (such as individual home sites or those less than 5 acres).
•
Requires minimal clearing and grubbing for installation.
DISADVANTAGES OF SILT FENCING
C
Is not suitable for larger developments (greater than 5 acres).
C
Un-reinforced (no steel rebar, wire netting) silt fences are not suitable for slopes greater than 20%.
C
Fences with wood stakes are difficult to install in stony or clayey soils - use steel rebar stakes instead.
C
WILL FAIL IF IT IS NOT PROPERLY ANCHORED AND TRENCHED INTO THE GROUND!
C
Requires frequent inspection and maintenance to ensure effectiveness.
Chapter 3
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3-24
Environmental Protection Handbook
Gravel/Stone Filter Berm
When and Where to Use Filter Berms
What to Consider
Figure 3.22. Example of a gravel filter berm (U.S. EPA, 1992).
Stabilized Construction Entrance
A gravel, stone or rock berm is a temporary barrier of loose gravel, stone, or rock built across the bottom of a
slope to slow runoff from leaving a site. They can also be used to divert flow from an exposed traffic area. These
berms can also be used for directing runoff from a right-of-way to a stabilized outlet.
Gravel or stone filter berms are used where roads and other rights-of-way under construction accommodate
vehicular traffic. They are meant for use in areas with gentle slopes. They also may be used at traffic areas within
a construction site. Berms should be used in conjunction with other temporary sediment control
practices, such as diversion dikes and swales, drainage swales, silt fences, temporary seeding,
and/or sediment traps.
Berm spacing depends on the steepness of the
slope – berms should be placed closer
together as the slope increases. The berm
should be inspected regularly after each
rainfall, or if breached by construction or
other vehicles. All needed repairs should be performed immediately. Accumulated sediment should be removed
and properly disposed of and the geotextile or filter material replaced, as necessary (Figure 3.22).
ADVANTAGES OF FILTER BERMS
•
Reduce the speed of stormwater runoff.
•
Berms are fairly inexpensive and easy to install, and work well on slopes up to 40%.
DISADVANTAGES OF FILTER BERMS
•
Have a limited life span.
•
Can be difficult to maintain due to clogging with mud.
•
Frequent inspection and maintenance is necessary to ensure effectiveness.
A stabilized construction entrance is a section of the construction road adjacent to a paved road that is stabilized
with geotextile and large stone or gravel. A stabilized construction entrance is designed to reduce the amount
of soil tracked off of the construction site by vehicles leaving the site. The rough surface of the stone or gravel
shakes and pulls the soil off of vehicle tires as they drive over the entrance. The stone also reduces erosion and
rutting on the portion of the road that it is installed on by protecting the soil below. Filter fabric or geotextile
separates the stone from the underlying soil, preventing the stone from being ground into the soil. The fabric
also reduces rutting caused by vehicle tires by spreading the weight of the vehicles over a larger soil area than the
tire width.
Chapter 3
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3-25
When and Where to Use Stabilized Construction Entrances
Figure 3.23. Stabilized construction entrance design (Empire State Chapter, Soil and Water
Conservation Society, 1997).
What to Consider
Check Dams/Triangular Dikes/Berms
When and Where to Use Check Dams
A stabilized construction entrance should be installed at every point where traffic enters or leaves a construction
site before construction begins on the site. For individual home sites, the construction entrance should be
located where the permanent driveway will be sited. Stabilized construction entrances should not be used on
existing pavement.
Stabilized construction entrances
should be wide and long enough
so that the largest construction
vehicle will fit in the entrance
with overlap available. A good
rule of thumb is for the entrance
to be a minimum of 50 feet long
(30 feet for an individual home
site) and 10 feet wide with a flare
at the existing road to provide
turning radius. Stone, rock or gravel (2" - 3") should be placed at least 6 inches deep on top of geotextile over
the length and width of the entrance (Figure 3.23).
ADVANTAGES OF STABILIZED CONSTRUCTION ENTRANCES
•
Are very effective in reducing the amount of soil tracked off of a construction site.
•
Can improve the appearance of the construction site from the public’s point of view.
DISADVANTAGES OF STABILIZED CONSTRUCTION ENTRANCES
•
Only work if they are installed at every location where traffic leaves and enters the site.
•
Cannot always remove all of the soil tracked off of disturbed areas by vehicles.
•
Stone may have to be added to maintain effectiveness.
A check dam is a small, temporary or permanent dam constructed across a drainage ditch, swale, or channel to
reduce the speed of concentrated flows. Reduced runoff speed reduces erosion and gullying in the channel and
allows sediments to settle out.
A check dam should be installed in steeply sloped swales or channels, or in swales where adequate vegetation
cannot be established. Check dams limit erosion by reducing flow in small open channels that are degrading or
subject to erosion. A check dam may be built from stone, rip-rap, pea gravel-filled sand bags, or manufactured
pervious berms or barriers such as a Triangular Silt Dike™ (Figure 3.24), EnviroBerm®, Geo-Ridge® berm,
Chapter 3
Erosion and Sediment Control Practices
3-26
Environmental Protection Handbook
Figure 3.24. Installation of a triangular dike as a check
dam in a drainage swale (Estate St. George’s Hill, St.
Croix, 1998).
What to Consider
Figure 3.25. Check dam design example (Empire State Chapter, Soil and
Water Conservation Society, 1997).
coir (coconut fiber) rolls or “logs,” or other similar product..
Check dams should NOT be built in streams or guts.
They block normal streamflow, altering drainage patterns, and
can lead to channel bypass and dramatically increased erosion.
Check dams should be used only in small open channels that
will not be overtopped by flow once the dams are built. The
maximum drainage area above the check dam should not be
larger than two (2) acres. The center section of the
check dam should be lower than the edges, and
should not be higher than two (2) feet. Check dam
side slopes should be 2:1 or flatter. Dams should
be spaced so that the toe of the upstream dam is at
the same elevation as the top of the downstream
dam (Figure 3.24).
After each significant rainfall, check dams should
be inspected for sediment and debris
accumulation. Sediment should be removed when
it reaches one half the original dam height. Check
for erosion at edges and repair promptly. After
construction is complete, all stone and rip-rap
should be removed if vegetative erosion controls
will be used for permanent stabilization. It is
important to know expected erosion rates and
runoff flow rate for the swale or channel in which
this practice is to be installed. Contact DPNR’s Division of Environmental Protection, USDA Natural Resources
Conservation Service, the UVI Cooperative Extension Service, or a licensed engineer for assistance in designing
this practice.
ADVANTAGES OF CHECK DAMS
•
Are inexpensive and easy to install.
•
May be used permanently if designed properly.
•
Allow a high proportion of sediment in stormwater runoff to settle out.
•
Reduce velocity and may provide water aeration.
•
May be used where it is not possible to divert runoff flow or otherwise stabilize the channel.
DISADVANTAGES OF CHECK DAMS
•
May kill grass linings in channels if the water level remains high after it rains or if there is significant
sedimentation.
•
Can reduce the hydraulic capacity of the channel.
•
May create turbulence that can erode channel banks.
Chapter 3
Erosion and Sediment Control Practices
Environmental Protection Handbook
3-27
Sediment Traps
Figure 3.26. Storm inlet sediment trap design (Empire
State Soil and Water Conservation Society, 1991).
When and Where to Use Sediment Traps
Figure 3.27. Rip-rap outlet sediment trap example (Maryland Department of the
Environment, 1994).
What to Consider
A sediment trap is built by excavating a pond or by installing an
earthen embankment across a low area or drainage swale. An
outlet or spillway from the trap is built using large stones or
aggregate to slow the release of stormwater runoff. Sediment
traps are designed to retain runoff long enough to allow most
of the sediment to settle out. There are six basic types of
sediment traps: pipe outlet traps, grass outlet traps, storm inlet
traps, swale traps, stone outlet traps, and rip-rap outlet traps.
A temporary sediment trap should be used in conjunction with
other temporary practices, such as gravel construction
entrances, temporary seeding, silt fences, and diversion dikes,
swales, or channels. Sediment traps are suitable for small
drainage areas and should be installed at
stormwater discharge points from a
disturbed area. Pipe, stone and grass
outlet sediment traps can handle
maximum drainage areas of 5 acres or
less; storm inlet traps can handle 3 acres
or less; swale traps can handle 2 acres or
less; and rip-rap outlet traps can handle
10-15 acres. Sediment traps should NOT
be installed in guts or used to artificially
break up a natural drainage area into
smaller sections where a larger device
(sediment basin) would be more
appropriate. Figures 3.26 to 3.29 show
the different types of outlets that can be
used with sediment traps. Larger drainage
areas require larger sediment traps, and
larger traps require more detailed
engineering design.
The sediment trap should be large enough to allow soil particles to settle out of stormwater and should have
enough capacity to store collected sediment until it is removed. The volume of sediment storage that the
sediment trap provides depends upon the amount and intensity of expected rainfall and on estimated quantities
of sediment in stormwater runoff. However, storage capacity should allow for an average of 3600 cubic feet per
acre of drainage area contributing stormwater to the trap. This sizing is used in areas where the soils have high
clay contents in order to allow for greater settling of fine particles. Due to the predominance of clayey soils in
Chapter 3
Erosion and Sediment Control Practices
3-28
Environmental Protection Handbook
Figure 3.28. Grass outlet and swale outlet sediment trap designs (Empire
State Chapter, Soil and Water Conservation Society, 1997).
the Virgin Islands, sizing basins to 3600 ft3 per
acre of drainage area will allow for greater
sediment removal through longer retention of
sediment-laden stormwater. However, larger
sediment traps need more detailed engineering
design and may not be practical for small sites.
Sediment traps should be installed prior to
grading or filling, and they must be located at least
20 feet away from an existing building foundation.
Sediment trap embankment height should not
exceed 5 feet and should have a minimum 4 foot
wide top and side slopes of 2:1 or flatter. The trap
embankment should be compacted during
construction. The sediment trap outlet should be
designed so that sediment does not leave the trap
and so that erosion at or below the outlet does not
occur. Sediment traps must outlet water onto
stabilized (preferably undisturbed) ground, or into
a stabilized channel, drainage, or storm drain
system (Maryland Department of the
Environment, 1994). Contact DPNR’s Division of
Environmental Protection, USDA Natural
Resources Conservation Service, the UVI
Cooperative Extension Service, or a licensed
engineer for assistance in designing this practice.
The effective life of a sediment trap depends on proper maintenance. The trap should be easily
accessible for regular maintenance and sediment removal. Traps should be inspected after each rainfall and
cleaned when one-third (a) to one-half (½) the design volume has been filled with sediment. The trap should
continue to be used and maintained until the site is permanently stabilized by vegetation and other permanent
practices. After completion of construction and site stabilization, all sediment traps should be removed and the
trap areas should be graded and vegetatively stabilized.
ADVANTAGES OF SEDIMENT TRAPS
•
Protect downstream areas from sedimentation.
•
Are relatively inexpensive and easy to install.
•
Are suitable for individual home sites or smaller developments (up to 10 acres, depending upon the type of
sediment trap (see Appendix B).
DISADVANTAGES OF SEDIMENT TRAPS
C
Are not suitable for large developments or steep slopes.
C
Are only effective if properly maintained.
C
Will not remove very fine silts and clays from stormwater runoff.
C
Must be removed after construction and stabilization are completed, unless converted to a permanent
retention basin (see Chapter 4).
Chapter 3
Erosion and Sediment Control Practices
Environmental Protection Handbook
3-29
Figure 3.29. Examples of pipe and stone outlet sediment traps (Maryland Department of the Environment, 1994).
Chapter 3
Erosion and Sediment Control Practices
3-30
Environmental Protection Handbook
Temporary Sediment Basin
When and Where to Use Temporary Sediment Basins
What to Consider
Figure 3.30. Temporary sediment basin design (U.S. EPA, 1992).
A temporary sediment basin is a settling pond with a controlled stormwater release structure used to collect and
store sediment produced by construction activities. A sediment basin can be constructed by excavation and/or
by placing an earthen embankment across a low area or drainage swale or channel. Sediment basins can be
designed to maintain a permanent pool or to drain completely dry. The basin detains sediment-laden runoff from
larger drainage areas long enough to allow most of the sediment to settle out.
The pond has a riser and pipe outlet with a gravel outlet or spillway to slow the release of runoff and provide
some sediment filtration. By removing sediment, the basin helps prevent clogging of offsite conveyance systems
and sediment-loading of receiving waters.  
Temporary sediment basins are usually designed for disturbed areas larger than 5 acres. A sediment basin should
be installed before clearing and grading is undertaken. It should NOT be built in a stream or gut. The creation
of a dam at these sites may result in destruction of aquatic and moist forest habitats and flooding may result from
dam failure. A temporary sediment basin should only be used at sites where there is sufficient space and
appropriate topography. A temporary sediment basin used in combination with other control practices such as
temporary seeding, diversion dikes and swales, drainage swales, and/or mulching and matting is especially
effective in removing sediment.
The pond area in a temporary sediment basin should be large enough to hold runoff long enough for sediment
to settle out. Sufficient space should be allowed for collected sediments. Sediment trapping efficiency is improved
by providing the maximum surface area
possible. Because finer silts and clays may not
settle out completely, additional erosion
control measures should be used to minimize
release of fine silt. Runoff should enter the
basin as far from the outlet as possible to
provide maximum retention time (i.e., the
flow path, or length of flow in the sediment
basin should be maximized. Appendix B has
detailed specifications and criteria to follow in
designing a sediment basin to fit each specific
site. Figure 3.30 depicts a sample sediment
basin design.
The useful life of a sediment basin
depends on regular maintenance.
Sediment basins should be readily accessible
for maintenance and sediment removal. They
should be inspected after each rainfall event
and be cleaned out when about half the
Chapter 3
Erosion and Sediment Control Practices
Environmental Protection Handbook
3-31
Storm Drain Inlet Protection
Figure 3.31. Example installation and diagram for
Beaver Dam™ storm drain inlet protection (Dandy
Products, Inc., 2001).
When and Where to Use Inlet Protection
volume has been filled with sediment. The basin should remain in operation and be properly maintained until
the construction site is permanently stabilized by vegetation. If the basin is located near a residential area, it is
recommended for safety reasons that a sign be posted (child hazard, no playing) and that the area be secured by
a fence. A well-built temporary sediment basin that is large enough to handle post-construction runoff volume
may later be converted to use as a permanent stormwater management structure (see Chapter 4).
The outlet pipe and spillway of the sediment basin should be designed by an engineer based upon an analysis of
the expected runoff flow rates from the site. Contact DPNR’s Division of Environmental Protection, USDA
Natural Resources Conservation Service, the UVI Cooperative Extension Service, or a licensed engineer for
assistance in designing this practice.
ADVANTAGES OF TEMPORARY SEDIMENT BASINS
•
Protects downstream areas from clogging or damage due to sediment deposits generated during
construction activities.
•
Can trap smaller sediment particles than sediment traps due to longer detention time.
•
Can be converted to a permanent stormwater detention structure, once construction is complete.
DISADVANTAGES OF TEMPORARY SEDIMENT BASINS
•
Requires regular maintenance and removal of accumulated sediment and debris.
•
Will not remove very fine silts and clays unless used in conjunction with other sediment and erosion control
practices.
•
Is more expensive than other methods of sediment removal and requires larger area for installation.
•
Requires careful adherence to safety practices since ponds may attract children.
Storm drain inlet protection consists of a permeable barrier placed
around any inlet or drain to filter sediment out of stormwater. This
practice prevents sediment from entering the storm drain inlet
structures and getting into the storm drain system. It also prevents
the silting-in of inlets, storm drainage systems, or receiving
channels.  Inlet protection may be composed of gravel and stone
with a wire mesh filter, block and gravel, or geotextile (filter fabric).
There are four basic types of inlet protection recommended in the
V.I.: stone and block drop inlet protection, excavated drop inlet
protection, curb drop inlet protection, and geotextile drop inlet
protection (see Figures 3.32 and 3.33). Commercially manufactured
inlet inserts (Beaver Dam™, Silt Sack™, etc., see Figure 3.31) that
remove sediment and other pollutants from are also available, but
have not been tested in the V.I.
This practice should be used where the drainage area to an inlet is
disturbed, it is not possible to temporarily divert the storm drain
outfall into a trapping device, for small drainage areas where storm
drain inlets will be ready for use before final stabilization, where a
Chapter 3
Erosion and Sediment Control Practices
3-32
Environmental Protection Handbook
Figure 3.32. Examples of filter fabric drop inlet and curb drop
inlet storm drain protection (Empire State Chapter, Soil and
Water Conservation Society, 1997).
Figure 3.33. Examples of stone and block inlet and excavated drop
inlet storm drain protection (Empire State Chapter, Soil and Water
Conservation Society, 1997).
What to Consider
permanent storm drain structure is being constructed
onsite, or where watertight blocking of inlets is not
advisable. Straw bales are NOT recommended for this practice. It should NOT be used in place of sediment
trapping devices. 
Geotextiles are used for inlet protection when stormwater flows are relatively small with low velocities (Figure
3.32). This practice cannot be used where inlets are paved because the filter fabric must be staked into the
ground. However, commercially manufactured inlet inserts (Beaver Dam™, Silt Sack™, etc., see Figure 3.31)
can be used over flat grates, for curb and gutter inlets, or median barrier inlets. Block and gravel filters can be
used where velocities are higher. Gravel and mesh filters can be used where flows are higher and subject to
disturbance by site traffic (Figure 3.33). 
Storm drain inlet protection is not meant for use in drainage areas that are larger than one acre or for large,
concentrated stormwater flows. This practice should be installed before any soil disturbance takes place in the
drainage area. The type of material used will depend on site conditions and the size of the drainage area.
Chapter 3
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Environmental Protection Handbook
3-33
Outlet Protection
Figure 3.34. Examples of rock outlet protection
designs (U.S. EPA, 1992).
When and Where to Use Outlet Protection
What to Consider
Inlet protection should be used in combination with other practices, such as small sediment traps, to provide
more effective sediment removal. Inlet protection structures should be inspected regularly, especially after a
rainstorm. Repairs and sediment removal should be performed as necessary. This practice should be removed
only after the disturbed areas are completely stabilized.
ADVANTAGES OF STORM DRAIN INLET PROTECTION
•
Effective in preventing clogging of existing storm drainage systems and reduces receiving water siltation.
•
Reduces the amount of sediment leaving the site.
DISADVANTAGES OF STORM DRAIN INLET PROTECTION
•
May be difficult to remove collected sediment.
•
Requires regular maintenance and cleaning.
•
May cause erosion elsewhere if clogging occurs.
•
Is practical only for low sediment, low volume flows (disturbed areas 1 acre or less).
Outlet protection reduces the depth, speed and energy of
concentrated stormwater flows, reducing erosion and scouring at
stormwater outlets of culverts, swale and drainage channels. Outlet
protection also reduces the potential for downstream erosion. This
protection can be achieved through a number of methods including
stone or rip-rap, concrete aprons, paved sections, and settling basins
installed below the storm drain outlet.
Outlet protection should be installed at all pipe, interceptor
dike, swale, culvert or channel section outlets where the
velocity of flow may cause erosion at the pipe outlet and in
the receiving channel. This practice applies to culvert outlets of
all types; pipe conduits from all sediment basins, dry stormwater
ponds, and permanent ponds; and new channels built as outlets for
culverts or other drainage ways. Outlet protection should also be
used at outlets where the velocity of flow at the design capacity may
result in plunge pools (small permanent pools located at the inlet to
or the outfall from control practices). Outlet protection should be
installed early during construction activities, but may be added at
any time, as necessary.
The exit speed of runoff as it leaves the outlet protection structure
should be reduced to levels that minimize erosion. The design of
outlet protection depends on the location. Pipe outlets at the top of
Chapter 3
Erosion and Sediment Control Practices
3-34
Environmental Protection Handbook
Gabion Inflow Protection
When and Where to Use Gabion Mattresses
Figure 3.35. Gabion mattress inflow protection (Maryland Department of
the Environment, 1994).
What to Consider
cuts or on slopes steeper than 10 percent cannot be protected by rock aprons or rip-rap sections because re-
concentration of runoff flows and high velocities may occur after the flow leaves the apron. Contact DPNR’s
Division of Environmental Protection, USDA Natural Resources Conservation Service, the UVI Cooperative
Extension Service, or a licensed engineer for assistance in designing for tailwater depth, apron size, bottom grade,
alignment, materials, thickness, stone quality, and filter for this practice. Appendix B contains design
specifications and example design procedure calculations (see example in Figure 3.34).
Once a rip-rap outlet has been installed, maintenance needs are usually low. Outlet protection should be
inspected on a regular schedule to look for erosion and scouring and to check if any stones have been dislodged.
Outlets must be kept clean of clogging debris. Repairs should be made promptly.  
ADVANTAGES OF OUTLET PROTECTION
•
Provides, with riprap-lined apron (the most common outlet protection), a relatively low-cost method that can
be installed easily on most sites.
•
Removes sediment in addition to reducing runoff speed.
•
Can be used at most outlets where flow speed is high.
•
Is an inexpensive but effective practice.
•
Requires less maintenance than many other practices.
DISADVANTAGES OF OUTLET PROTECTION
•
May cause problems in removing collected sediment (without removing and replacing the outlet protection
structure itself).
•
May require frequent maintenance for rock outlets with high velocity flows.
•
May be unsightly.
Gabion inflow protection uses a temporary, lined drainage way installed to convey concentrated stormwater
runoff into sediment traps and basins in order to prevent erosion of the flow channel. Gabions are constructed
of rock or concrete within a flow channel to stabilize the channel. It should be used in conjunction with dikes,
swales or other water control devices as warranted by site conditions.
Gabion inflow protection should be used where
stormwater runoff entering sediment basins or
traps will cause erosion of the embankments or
channels leading to them. Runoff can be directed
to the entrance of the gabion using dikes or swales.
A gabion mattress should be constructed of
9'x3'x9' gabion baskets to form a cross-section one
foot deep with 3:1 side slopes and a 3 foot bottom
width (see Figure 3.35). The top mattress should
Chapter 3
Erosion and Sediment Control Practices
Environmental Protection Handbook
3-35
be anchored into the ground at least one foot. Geotextile (or filter) fabric should be installed under all gabion
baskets. The fabric used should be the same as that used for swale channel stabilization (see Drainage Swale and
Silt Fence sections).  
ADVANTAGES OF GABION INFLOW PROTECTION
•
Removes sediment in addition to reducing runoff speed.
•
Can be used at most inlets where flow speed is high.
•
Requires less maintenance than many other practices.
DISADVANTAGES OF GABION INFLOW PROTECTION
•
May cause problems in removing collected sediment (without removing and replacing the inlet protection
structure itself).
•
May require frequent maintenance for gabion inlets with high velocity flows.
•
May be expensive.
3.4
REFERENCES
CWP. 2000a. Stormwater Management Factsheet: Grassed Filter Strip, Center for Watershed Protection, Stormwater
Manager’s Resource Center website  www.stormwatercenter.net, Ellicott City, Maryland.
Dandy Products, Inc. 2001. Sediment Control Solutions for All Stormwater Systems and Dewatering Projects, Dandy
Products, Inc., Grove City, Ohio, website: www.dandyproducts.com.
DPNR-DEP and USDA-NRCS. 1998. Unified Watershed Assessment Report - United States Virgin Islands, Virgin
Islands Department of Planning and Natural Resources in cooperation with USDA Natural Resources
Conservation Service, Caribbean Area, St. Croix, USVI.
Empire State Chapter, Soil and Water Conservation Society. 1997. New York Guidelines for Urban Erosion and
Sediment Control Update, Syracuse, New York.
Empire State Chapter, Soil and Water Conservation Society. 1991. New York Guidelines for Urban Erosion and
Sediment Control, Syracuse, New York.
Fifield, J.S. 1996. Field Manual for Effective Sediment and Erosion Control Methods, HydroDynamics, Inc., Parker, CO.
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