3 slope protection

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Kentucky Construction Site BMP Planning and Technical Specifcations Manual

4.5 Slope Protection

General Inormation

Relatively at areas—those with slopes o 2 percent or less—can be treated to a largeextent through controlled clearing and grading, mulch, and temporary or permanent seed.Slopes greater than that, however, require more attention to sheet runo volume and the

management o areas where ows converge and are transported to downstream receivingwaters. Sediment barriers, rolled erosion control products, and greater attention to downslopedrainage are usually needed on slopes, especially those that are steep and long.

This section addresses erosion protection and sediment control approaches specifcally orslopes. In general slopes that are long (50 eet or more), steep (5 percent plus), and composedo highly erodible (silty) soils require more protection that shorter, atter slopes o lesserodible soil. Slope protection approaches discussed below include erosion control blanketsand tur reinorcement mats, which can also be used or ditch protection, surace roughening,slope drains, gabion structures, and cellular mats.

Approximate Slope Conversions

Approximate slope conversions (horizontal:vertical)

Percent Slope Ratio Degrees

100% 1:1 45º

50% 2:1 27º

33% 3:1 18º

25% 4:1 14º

10% 10:1 6º

Slope Protection Basics

Protecting slopes rom erosion requires several actions that must be taken together. No singleapproach will be successul, especially i the slope is steep or has highly erodible soils (see

table). Use one or more o the ollowing actions to reduce erosion on slopes: Divert upland runo —Install a berm or channel above the slope to divert upland rain runo around the bare soil area or a stable ditch to move upland ows through the site withoutpicking up additional sediment.

Control slope runo— I slopes are broken up into benches or steps, runo can be collectedand diverted along berms or in channels to pipe or channel slope drains.

Till seedbed or condition the soil —Dozer tracks up and down slopes help hold soil in place.See the table below or inormation on how the condition o the soil surace (e.g., compacted,tracked) can increase or decrease erosion.

Seed and mulch— This is the best and cheapest protection by ar. See temporary andpermanent seeding Fact Sheets or details on seed types, application rates, and mulch,

blanket, and mat products.Silt ence or brush barrier— These should be installed at the toe o the slope, and every 75 to125 eet apart on long slopes.

Retaining wall— Extremely steep slopes can be leveled out and shortened into two or moresteps or benches by installing retaining walls o rock, brick, block, wood, logs, or othermaterial. I rock layers are present along the slope, use these to establish frm benches in astair-step pattern.

Blankets or armoring— Long slopes (greater than 100 eet) exceeding 3H:1V with highlyerodible soils need to be protected with erosion control blankets or tur reinorcement mats.Rock mulch and lined downdrain channels might be needed on steep slopes to control gullying.



6 Technical Specifcations or BMPs

Soil Conditions vs. Erosion

Soil Conditions vs. Erosion

If soil is: Erosion will be:

Compacted and smooth 30 percent more

Tracks across slopes 20 percent more

Tracks up & down slopes 10 percent less

Rough and irregular 10 percent less

Rough & loose to 12" deep 20 percent less

Slope Angle and Soil Type vs. Erodibility

Slope angle Erodibility Soil type

50%

40%

30%

20%

15%

10%

5%

< 5%

Very high

Very Low

Silt

Silty sand

Clayey sand

Organic soil

Clays

Silty gravel

Sand

Gravel

The value o seed on a slope: the let (seeded) section shows almost no erosion; right side rills are quickly becoming gullies. Seed and mulch slopes as soon as nal grade is established or best results. Bare areas must be seeded or mulched within 14 days i no work is planned during the next week.





4.5.1 Silt Fence

Defnition

A silt ence is a temporary sediment barrier consisting o flter abric entrenched into thesoil and attached to supporting posts. Silt ences are downhill rom bare soil areas and

are installed with a trencher or by a slicing machine to prevent against common silt enceailures.

Purpose

Silt ences are common sediment control devices. Silt encing should be installed wheresediment-laden water can pond, thus allowing the sediment to all out o suspension andseparate rom the runo. Runo will also bleed through the silt ence abric, providingphysical fltering or larger sediment particles. Reasons or the high ailure rate o improperly designed (located) and installed silt ence include

• Improper placement on the site

• Allowing excessive drainage area to the silt ence structure

• Shallow trenches with little or no soil compaction

• Inadequate attachment to posts

• Failure to maintain the silt ence ater installation

• Installing silt ence along property boundaries, producing concentrated runo

Design Criteria

Silt encing must be installed only where water can pond. Speciy silt encing downgradientrom bare soil areas, installed on the contour i possible, with the ends turned up to preventbypassing. Provide adequate setbacks rom slope toe or routine maintenance and access.

Silt encing can be used where• Non-concentrated sheet ow will occur

• Protection o adjacent property or nearby surace waters is required

• The size o the drainage area is no more than 1/4 acre per 100 linear eet o silt ence

• The maximum ow path length above the barrier is 100 eet or slopes less than 2percent, and 50 eet or slopes up to 10 percent

Silt encing is commonly used to pond, settle, and lter sediment rom sheet runo. Install at proper spacing on

slopes; set back rom slope toe to allow or maintenance. Make sure encing is

trenched in properly and stakes are onthe downhill side. Inspect requently to detect and address bypasses,undercutting, and overtopping.




• The maximum slope gradient above the barrier is 2H:1V

• Silt encing can be used in at, short swales (i.e., slope is less than 2 percent; lengthis less than 200 eet) that drain less than 2 acres, i silt encing is spaced every 50 eet.

• Reinorced silt ence must be required when the contributing slope is longer than 100eet and greater than 3 percent and the design lie o the silt ence is greater than 6months.

Silt Fence Spacing on Long Slopes

Land Slope Max. Slope Distance

3% – 5% 100 ft.

5% – 10% 75 ft.

10% – 20% 50 ft.

20% – 50% 25 ft.

Silt encing should not be used

• Around the perimeter o the construction site, unless J-hooks are used. Longcontinuous runs o silt ence will divert and concentrate sediment-laden runo andalmost certainly result in ailure. A good general rule is to drain no more than 1/3

acre o disturbed area into each discrete J-hook;

• In ditches, channels, or streams. Silt ences cannot handle the volumes generatedby concentrated channel ows. When installed across a concentrated ow path,undercutting or end cutting o the ence oten occurs, or the ence is pushed over bythe orce o the ow.

Construction Specifcations

Silt ences have a useul lie o one season. Their principal mode o action is to slow andpond the water and allow soil particles to settle with some minor fltration through theabric. Silt ences are not designed to withstand high heads o water, and thereore shouldbe located where only shallow pools (i.e., 1.5 eet or less) can orm. Their use is limited tosituations in which sheet or overland ows are expected.

• Dig a trench on the contour at least 6 inches wide and 6 inches deep below the areato be treated, taking care to install J-hooks where ows will travel along the silt ence.Turn ence ends uphill to trap potential bypasses as needed.

• I posts are already attached to abric, position the encing so the posts are installedon the downhill side o the abric. Drive posts to a depth o 1 oot below the bottom o the trench, against downslope trench wall or extra support. Posts or all silt encingare spaced 6 eet apart.

• Push abric into the trench, and spread abric along trench bottom and sides; backfllthe trench and compact the soil. A preerred installation technique in deep, easily-worked soils with minimal rock content involves static slicing o the ence into theground with a chisel-plow implement such as the Tommy Silt Fence Machine orequivalent. The flter abric is wire-tied directly to the posts with three diagonal ties.

• The height o a silt ence must be 18 inches minimum and 30 inches maximum.Sediment storage height and ponding height must not exceed 18 inches.

• Silt ences placed at the toe o a slope must be set at least 6 eet back rom the toe toincrease ponding volume and provide room or maintenance.




Inspection and Maintenance

All sediment barriers should be placed downgradient rom bare areas to be treated. Theends o the barrier should be turned uphill or otherwise confgured to prevent end-aroundbypasses.

• Inspect ence or proper installation and compaction by pulling up on the ence whilekicking the toe o the abric. I the ence comes out o the ground, do not accept theinstallation.

• I there are long, linear runs o silt ence without J-hooks, do not accept the

installation.

• Silt ences and flter barriers must be inspected weekly and ater each storm o greaterthan one-hal inch. Any required repairs must be made immediately.

• Sediment should be removed when it reaches 1/3 height o the ence or 18 inchesmaximum.

• The removed sediment must be spread and vegetated or otherwise stabilized so that itdoes not result in muddy runo to nearby ditches or surace waters.

• Silt ences must be removed when they have served their useul purpose, but notbeore the upslope area has been permanently stabilized (e.g., vegetated) and any

sediment stored behind the silt ence has been removed. Silt ences and othertemporary controls must be removed beore project close-out.

Make sure silt ence abric istrenched in and is upslope o

stakes. Leave room between theencing and the upgradient slope or removing accumulated sediment.

Install silt encing on the contour, with the endsturned uphill to trap muddy runo and prevent bypasses. Remove silt ences when grass isestablished.

Do not use silt encing inareas o concentrated fows.

For best results, triple-seed ditches and line with erosion

control blankets.




Silt ence is unctioning well, but needsmaintenance. Set ences back rom the toeo the slope, to allow room or sediment to accumulate and maintenance.

Use several short lengths o silt ence and J-hooks to intercept converging runo in critical areas, such as property corners.This can help relieve stress and prevent ailure at the corners.

Silt ence installed backwards—note that stakes are on the uphill,rather than downhill, side o the abric. Ponding fows against this ence will push the abric away rom the stakes, causingailure and releasing sediment to the small stream on the right.

Use multiple silt encesat proper spacing (seetable) to protect long,unvegetated slopes. Fences

provide only temporary protection and can beremoved when the area is

seeded and mulched.

Good installation o “super” (i.e.,wire reinorced) silt ence. Notethat wire is installed betweenthe abric and stakes, and

provides a web o support as the ponded fow pushes against theabric. Also, note the grass stripbetween the bare area and theence, which helps to slow and lter fows beore ponding alongthe ence line.





4.5.2 Brush, Rock, and OtherSediment Barriers

Defnition

Brush, rock, and other commercial barriers can be used as a temporary sediment barrierinstead o a silt ence.

Purpose

The purpose o any sediment barrier is to provide a place where sediment-laden water canpond, thus allowing the sediment to all out o suspension and separate rom the runo.

Design Criteria

Sediment barriers should be installed where non-concentrated sheet ow will occur. Theyshould not be used in ditches, channels, or streams. Sediment barriers are usually placed aew eet beyond the toe o a slope, or across long slopes at specifc intervals. When placingsediment barriers, consider materials on hand that might be used (e.g., brush cleared rom

the site, shot rock) during initial clearing and grading work. Silt ences or commercialsediment barrier products should be sited ar enough away rom the toe o the slope toallow or maintenance (i.e., access by a small loader, truck). There are several other actorsto consider in placing silt ences, rock sediment flters, or other commercial sedimentbarriers:

• Place flters on downhill edge o bare soil areas.

• Make sure the flter catches all the muddy runo.

• Turn the ends o the barrier uphill to prevent bypasses

• The goal is to pond runo, to flter and settle it out.

• Install multiple sediment flters on long slopes.

• Spacing on long slopes is every 60 to 110 eet.

• Put flters across slopes, on the contour (level).

Placement criteria are similar to those specifed or silt ences (see the preceding section).

I rock will be used at the site eventually,it could be benecial to have it delivered

early or use as a sediment barrier in thevicinity o its nal use. Other sediment barriers include brush cleared romthe site, ber (log) rolls, and other commercial products.





Brush cleared rom the site can make an excellent sediment flter i it is properly placed andbuilt up well. Brush barriers are installed on the contour and are 2–5 eet high and 4–10eet wide at the base. They should be walked down with a loader or dozer to compress thematerial.

A rock berm can also provide an eective and low-maintenance sediment barrier. Rockberms placed in concentrated ow areas unction as sediment traps (or more inormationon that type o application, see Section 4.7.1). Longer rock berms constructed as sheet

runo sediment barriers should be 18" to 30" in height and consist o stone 2–6 inches indiameter.

Fiber rolls and other commercial products made rom coconut fber, plastic, wood shavings,compost, or other material can also be used as sediment barriers on slopes atter than 10:1.Follow manuacturers’ installation instructions and ensure that sediment flter spacing onslopes is correct.

For inormation on locating and installing rock or commercial barriers, see constructionspecifcations or silt ences in the preceding section.


Sediment barriers should be inspected weekly and ater each rainall o greater than one-hal inch. Look or signs o bypassing along the sides, undercutting below the barrier,

overtopping, or blowout. Make required repairs immediately. For recurring blowouts,consider pulling some upland muddy ow away and trapping it beore it can reach theblowout area. Use a J-hook or other strategically placed barrier.

Remove sediment when it reaches 1/3 height o the ence or 9 inches maximum. Spread theremoved sediment and vegetate or otherwise stabilize it.

Remove sediment barriers when they have served their useul purpose but not beore theupslope area has been permanently stabilized (i.e., vegetated or otherwise covered) and anysediment stored behind the barrier has been removed.

Fiber rolls provide excellent protection or residential lots. They can be stepped over and driven over, and are preerable to silt encing in tight areas.

Brush cleared rom the site used as a temporary downslope sediment barrier. Make sure barrier intercepts and ponds up muddy runo. Removewhen grass is established.

Super (wirereinorced) silt encein the oreground,

supplemented by rock sediment barrier (background).Use rock or other

sediment barrierswhen appropriate.





4.5.3 Erosion Control Blankets andTur Reinorcement Mats

Defnition

Temporary erosion control blankets (ECBs) and permanent tur reinorcement mats (TRMs),known generally as rolled erosion control products, are single or multiple layer sheetscomposed o natural or synthetic material that is woven, sewn, bonded, or otherwisemanuactured or placement on bare soil slopes or ow channels. They have beendescribed as a temporary, degradable products composed o processed natural or polymerfbers mechanically, structurally, or chemically bound together to orm a continuous matrixto provide erosion control and acilitate vegetation establishment.

Purpose

ECBs are used to temporarily stabilize and protect disturbed soil rom raindrop impactand surace erosion, to increase infltration, decrease compaction and soil crusting, andto conserve soil moisture. Mulching with ECBs will increase the germination rates or

grasses and legumes and promote vegetation establishment. ECBs also protect seeds rompredators, reduce desiccation and evaporation by insulating the soil and seed environment.

Some types o ECBs and tur reinorcement mats are specifcally designed to stabilizechannelized ow areas. These blankets and mats can aid the establishment o vegetationin waterways and increase the maximum permissible velocity o the given channel byreinorcing the soil and vegetation to resist the orces o erosion during runo events.Stems, roots and rhizomes o the vegetation become intertwined with the mat, reinorcingthe vegetation and anchoring the mat.

Design Criteria

All fnal slopes 2H:1V or steeper should be protected with an ECB. ECBs are constructedo various degradable organic / synthetic fbers that are woven, glued or structurally bound

with nettings or meshes. The most widely used ECBs are made rom straw, wood excelsior,coconut, polypropylene or a combination thereo stitched or glued together or into orbetween biaxially oriented process nettings or woven natural fber nettings. They are useulon sites requiring greater, more durable or longer-lasting erosion protection. Applicationsinclude gradual to steep slopes, low to moderate ow channels and low-impact shorelinings. Because these degradable materials are designed to provide temporary erosionprotection, they generally are limited to areas where natural, unreinorced vegetation alonewill provide long-term soil stabilization.

Erosion control blankets provide excellent protection or seedbeds, especially

on slopes and in areas o high winds.Blankets can be used to stabilize ditcheswith fatter slopes. For steeper ditches,use tur reinorcement mats.




The unctional longevity o ECBs can be varied to accommodate the site-specifcrequirements. Some ECBs are designed to last or less than 3 months or use in high-maintenance areas that will be mowed soon ater tur establishment, while others are madeto provide longer-lasting protection in applications requiring erosion control/mulch or upto 3 years.

TRMs consist o various UV-stabilized, synthetics fbers and flaments processed intopermanent, high-strength, 3-D matrices. Common examples include cuspated polyethylenemeshes heat-bonded together, extruded monoflaments o nylon or PVC heat-bonded attheir intersections, and crimped polyolefn fbers and other materials mechanically stitched

between high-strength nettings. TRMs are designed or permanent and critical hydraulicapplications such as drainage channels, where design discharges exert velocities and shearstresses that exceed the limits o mature, natural vegetation. Though some TRMs alsocontain degradable components to supplement their permanent structures, all TRMs bydefnition have a permanent three dimensional structure with high-tensile strength thatunctions as a matrix or entangling plant roots, stems and soils.

Together, the TRM and vegetation orm a continuous composite—a unifed, living mat.This synergism increases root systems’ lateral strength, reducing plant dislodgement underhigh-velocity, high-shear stress ows. The TRM’s permanent structure also unctions toconsolidate and protect the soils in which the plants are anchored, preventing soil rombeing stripped out o the vegetative cover and the resulting weakening o the root support.TRMs are oten used in situations where the green alternative is preerred to hard armor.

Select the ECB or TRM according to slope steepness and length and expected sheer stress i application is to a ow channel or ditch. I the area will be mowed eventually, consider thespecifed breakdown time or ECB plastic netting. TRM areas should not be mowed untilvegetation is well established, and then as little (or as high) as possible. The table at the endo this section provides guidance on the application o various blankets and mats. An ECBor mat should be used in all drainage channels with slopes o 2 percent or more, and in theollowing conditions:

• Slopes and disturbed soils where mulch must be anchored and other methods suchas crimping or tackiying are not easible nor adequate

• Steep, long slopes, generally steeper than 3H:1V and longer than 50 eet

• Slopes where erosion hazards are high

• Critical slopes adjacent to sensitive areas such as streams and wetlands

• Disturbed soil areas where planting is likely to be slow in providing adequateprotective cover

Take care to choose the type o blanket or matting that is appropriate or the specifcneeds o a project. There are many soil stabilization products available today, and itis very difcult to cover all the advantages, disadvantages and specifcations o all themanuactured blankets and mats. Thereore, as with many erosion control type products,there is no substitute or a thorough understanding o manuacturer’s instructions andrecommendations and a site visit by a designer or plan reviewer to veriy a product’sappropriateness.


ECBs and TRMs are designed to cover germinating seed and provide a protective matrixthat helps anchor seed to the underlying soil. (Note: a ew TRMs have seed embeddedin the mat.) This requires complete, uniorm contact with the soil, solid stapling, andattention to topslope anchoring, overlaps, and other installation details, as noted below.




Site Preparation

Proper site preparation is essential to ensure complete contact o the protection matting withthe soil.

• Grade and shape area o installation

• Remove all rocks, roots, clods, vegetative, or other obstructions so that the installedblankets or mats will have direct contact with the soil

• Prepare seedbed by loosening 2–3 inches o topsoil above fnal grade

• Incorporate amendments, such as lime and ertilizer, into soil according to soil testand the seeding plan

Seeding

Seed the area beore installing blanket or erosion control and revegetation. Seeding atermat installation is sometimes specifed or tur reinorcement application—check themanuacturer’s instructions. When seeding beore blanket installation, reseed all check slotsand other areas disturbed during installation.

Where soil flling is specifed or certain TRMs, seed the matting and the entire disturbedarea ater installation and beore flling the mat with soil. Follow the manuacturer’sinstructions to ensure proper installation.

Anchoring

U-shaped wire staples, metal geotextile stake pins, or triangular wooden stakes can be usedto anchor ECBs and TRMs to the ground surace. Wire staples should be a minimum o 11gauge. Metal stake pins should be 3/16 inch diameter steel with a 1.5 inch steel washer atthe head o the pin. Wire staples and metal stakes should be driven ush to the soil surace.All anchors should be 6–8 inches long and have sufcient ground penetration to resistpullout. Longer anchors might be required or loose soils. Use biodegradable composite orwooden stakes where dislodged metal staples or stakes might cause extreme hazards, suchas near airport runways or areas where uture mowing might cause risk.

Installation on Slopes

Begin at the top o the slope and anchorthe blanket in a 6 inch deep by 6 inch widetrench. Backfll trench and tamp earth frmly.

• Unroll blanket downslope in thedirection o the water ow.

• The edges o adjacent parallel rollsmust be overlapped at least 3 inchesand be stapled through the overlappedarea at least every 3 eet on slopes lessthan 4H:1V and every 2 eet on steeperslopes.

• When blankets must be spliced, placeuphill blanket end over downhill

blanket (shingle style) with 6-inchoverlap. Staple through overlappedarea, approximately 12 inches apart.

• Lay blankets and mats loosely and maintain direct contact with the soil—do notstretch. Ensure good, consistent, direct soil contact.

• ECBs and TRMs must be stapled sufciently to anchor the blanket and maintain contactwith the soil. Staples must be placed down the center and staggered with the staplesplaced along the edges. Steep slopes (1H:1V to 2H:1V) require at least two staples persquare yard. Moderate slopes (2H:1V to 3H:1H) require 1-2 staples per square yard (1staple 3 every eet on center). Gentle slopes require one staple per square yard.

Install blankets and mats vertically on long slopes. Trenchand staple top section, overlap sides 3 to 6 inches.Follow manuacturer’s directions regarding stapling and

slope limitations. For areas that will be mowed, speciy blankets without plastic netting or material designed todecompose within 6 months.




Installation in ditches and channels

Dig initial anchor trench 12 inches deepand 6 inches wide across the channel (i.e.,parallel to the ow direction) at the lowerend o the project area.

• Excavate intermittent check slots, 6inches deep and 6 inches wide acrossthe channel at 25–30 oot intervalsalong the channel.

• Cut longitudinal channel anchorslots 4 inches deep and 4 inches widealong each side o the installation tobury edges o matting. These anchorslots will mark the upper elevationo the ECB or TRM along the channelside slopes, and should be above the 10 year, 24-hour peak ow line. Wheneverpossible extend the ECB or TRM 1 oot or more above the crest o channel side slopes.

• Beginning at the downstream end and in the center o the channel, place the initialend o the frst roll in the anchor trench and secure with astening devices at 1-ootintervals. Note: Matting will initially be upside down in anchor trench.

• In the same manner, position adjacent rolls in the anchor trench, overlapping thepreceding roll a minimum o 6–8 inches.

• Secure these initial ends o mats with anchors at 1-oot intervals, backfll andcompact soil.

• Unroll the center strip o matting upstream. Stop at the next check slot or terminalanchor trench.

• Unroll adjacent mats upstream in similar ashion, maintaining a 3-inch overlap.

• Fold and secure all rolls o matting snugly into all transverse check slots. Lay the matin the bottom o the slot then old back against itsel. Anchor through both layers o

mat at 1-oot intervals, then backfll and compact the soil. Continue rolling all matwidths upstream to the next check slot or terminal anchor trench.

• Alternate method or noncritical installations: place two rows o anchors on 6-inchcenters at 25–30 eet intervals in lieu o excavated check slots. Shingle-lap the splicedends by a minimum o 1 oot with the upstream mat on top (to prevent upliting bywater) or begin new rolls in a check slot. Anchor the overlapped area by placing tworows o anchors, 1 oot apart on 1-oot intervals.

• Place the edges o outside mats in previously excavated longitudinal slots, anchorthem using the prescribed staple pattern, then backfll and compact the soil.

• Anchor, fll, and compact the upstream end o the mat in a 12-inch by 6-inch terminaltrench.

• Secure the mat to the ground using U-shaped wire staples, geotextile pins, or woodenstakes.

• Seed and fll the TRM with soil, i specifed.

• Soil flling (i specifed or TRM)

• Ater seeding, spread and lightly rake one-hal to three-quarter inch o fne topsoilinto the mat apertures to completely fll the mat thickness. Use the backside o a rakeor other at implement. Spread topsoil using lightweight loader, backhoe, or otherpower equipment. Avoid making sharp turns with the equipment.

Ditch installation or blanket or mat. Triple-seed ditch, trenchin upslope blanket sides, and staple down securely. Lay ditch

sections horizontally, lapping upslope sections over downslope sections. Use plenty o staples below the water line.




ErosionControlTechnologyCouncilStandardSpecifcationorTemporaryRolled

ErosionControlProducts

Forusewherenaturalvegetational onewillprovidepermanen

terosionprotection

ULTRASHORTTERM:Typical3-MonthFunctionalLongevity

Type

Product

Descr iption

MaterialComposition

SlopeApplicatio

ns*

ChannelApplications*

Minimum

TensileStrength1

Maximum

Gradient

C

Factor2,5

PermissibleShear

Stress3,4,6

1.A

MulchControl

Nets

Aphotodegradablesyntheticmeshorw

ovenbiodegradable

naturalbernetting.

5:1(H:V)

<

0.10@5:1

=0.25lbs/t2

5lbs/t

1.B

NetlessRolled

ECBs

Naturaland/orpolymerbersmechanic

allyinterlockedand/

orchemicallyadheredtogethertoorm

aRECP.

4:1(H:V)

<

0.10@4:1

=0.5lbs/t2

5lbs/t

1.C

Single-netECBs

&OpenWeave

Textiles

Proces seddegradablenaturaland/orpo

lymerbers

mechanicallyboundtogetherbyasinglerapidlydegrading,

syntheticornaturalbernettingorano

penweavetextile

opr ocessedrapidlydegradingnaturalorpolymeryarnsor

twineswovenintoacontinuousmatrix.

3:1(H:V)

<

0.15@3:1

=1.5lbs/t2

50lbs/t

1.D

Double-netECBs

Processeddegradablenaturaland/orpo

lymerbers

mechanicallyboundtogetherbetweentworapidly

degrading,syntheticornaturalbernettings.

2:1(H:V)

<

0.20@2:1

=1.75lbs/t2

75lbs/t

SHORT-TERM:Typical12-M

onthFunctionalLongevity

Type

Product

Description

MaterialComposition

SlopeApplicatio

ns*

ChannelApplications*

Minimum

TensileStrength1

Maximum

Gradient

C

Factor2,5

PermissibleShear

Stress3,4,6

2.A

MulchControl

Net s

Aphotodegradablesyntheticmeshorw

ovenbiodegradable

naturalbernetting.

5:1(H:V)

<

0.10@5:1

=0.25lbs/t2

5lbs/t

2.B

NetlessRolled

ECBs

Naturaland/orpolymerbersmechanic

allyinterlockedand/

orchemi callyadheredtogethertoorm

aRECP.

4:1(H:V)

<

0.10@4:1

=0.5lbs/t2

5lbs/t

2.C

Single-netECBs

&OpenWeave

Textiles

Anerosioncontrolblanketc omposedoprocessed

degradablenaturalorpolymerbersmechanicallybound

togetherbyasingledegradablesynthet

icornaturalber

nettingtoormacontinuousmatrixoranopenweavetextile

composedoprocesseddegradablenaturalorpolymeryarns

ortwineswovenintoac ontinuousmatrix.

3:1(H:V)

<

0.15@3:1

=1.5lbs/t2

50lbs/t

2.D

Double-netECBs

Processeddegradablenaturaland/orpo

lymerbers

mechanicallyboundtogetherbetweentwodegradable,

syntheticornaturalbernettings.

2:1(H:V)

<

0.20@2:1

=1.75l bs/t2

75lbs/t




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F o r a p p l i c a t i o n s i n d i t c h e s

a n d c h a n n e l s , a n d o n s l o p e s n o t e x c e e d i n g 0 . 5

H : 1 V w h e r e v e g e t a t i o n a l o n e w i l l n o t s u s t a i n e x p e c t e d o w c o n d i t i o n s a n d / o r p r o v i d e

s u f c i e n t l o n g - t e r m e r o s i o n p r o t e c t i o n

T y p e 1

P r o d u c t

D e s c r i p t i o n

M a t e r i a l C o m p o s i t i o n

M i n i m u m

T e n s i l e S t r e n g t h 2 ,

3

M i n i m u m T

h i c k n e s s

( A S T M

D 6 5 2 5 )

U V S t a b i l i t y

( A S T M

D 4 3 5 5

@

5 0 0 H o u r s )

C h a n n e l

A p p l i c a t i o n s

P e r m i s s i b l e S h e a r

S t r e s s 4 ,

5

5 . A

T R M

L o n g t e r m , n o n - d e g r a d a b l e r o l l e d e r o s i o n

c o n t r o l p r o d u c t c o m p o s e d o U V s t a b i l i z e d ,

n o n d e g r a d a b l e , s y n t h e t i c b e r s , l a m e n t s ,

n e t t i n g s a n d / o r w i r e m e s h p r o c e s s e d

i n t o t h r e e d i m e n s i o n a l r e i n o r c e m e

n t

m a t r i c e s d e s i g n e d o r p e r m a n e n t a

n d

c r i t i c a l h y d r a u l i c a p p l i c a t i o n s w h e r e d e s i g n

d i s c h a r g e s e x e r t v e l o c i t i e s a n d s h e a r s t r e s s e s

t h a t e x c e e d t h e l i m i t s o m a t u r e , n a t u r a l

v e g e t a t i o n .

T R M s p r o v i d e s u c i e n t t h i c k n e s s , s t r e n g t h

a n d v o i d s p a c e t o p e r m i t s o i l l l i n g

a n d /

o r r e t e n t i o n a n d t h e d e v e l o p m e n t o

v e g e t a t i o n w i t h i n t h e m a t r i x .

1 2 5 l b s / t

0 . 2 5

i n c h e s

8 0 %

= 6 . 0

l b s / t 2

5 . B

T R M

1 5 0 l b s / t

0 . 2 5

i n c h e s

8 0 %

= 8 . 0

l b s / t 2

5 . C

T R M

1 7 5 l b s / t

0 . 2 5

i n c h e s

8 0 %

= 1 0 . 0

l b s / t 2

N O T E S :

1

F o r T R M s c o n t a i n i n g d e g r a d

a b l e c o m p o n e n t s , a l l p r o p e r t y v a l u e s m u s t b e o b t a i n e d o n t h e n o n - d e g r a d a b l e p o r t i o n o

t h e m a t t i n g a l o n e .

2

M i n i m u m A v e r a g e R o l l V a l u e s , m a c h i n e d i r e c t i o n o n l y o r t e n s i l e s t r e n g t h

d e t e r m i n a t i o n u s i n g A S T M

D 6 8 1 8 ( S u p e r s e d e s M o d .

A S T M

D 5 0 3 5 o r R E C P s )

3

F i e l d c o n d i t i o n s w i t h h i g h - l o

a d i n g a n d / o r h i g h s u r v i v a b i l i t y r e q u i r e m e n t s m a y w a r r a n t t h e u s e o a T R M

w i t h a t e n s i l e s t r e n g t h o 3 , 0

0 0 l b / t o r g r e a t e r .

4

S h e a r s t r e s s t h a t u l l y v e g e t a

t e d T R M c a n s u s t a i n w i t h o u t p h y s i c a l d a m a g

e o r e x c e s s e r o s i o n ( 0 . 5

i n ) s o i l l o s s ) d u r i n g a

3 0 - m i n u t e f o w i n l a r g e - s c a l e t e s t i n g .

5

A c c e p t a b l e l a r g e - s c a l e t e s t i n

g p r o t o c o l m a y i n c l u d e A S T M

D 6 4 6 0 o r o t h e

r i n d e p e n d e n t t e s t i n g d e e m e d a c c e p t a b l e b y

t h e e n g i n e e r .




• Do not drive tracked or heavy equipment over the mat. Avoid any trafc over thematting i loose or wet soil conditions exist.

• Use shovels, rakes or brooms or fne grading and touch up. Smooth out soil flling,just exposing the top netting o matrix.


All blankets and mats should be inspected periodically ollowing installation.

• Inspect installation ater signifcant rainstorms to check or erosion and undermining.Any ailure should be repaired immediately.

• I washout or breakage occurs, reinstall the material ater repairing the damage to theslope or drainageway.

Erosion control blankets (top right) are thinner and degrade quicker than tur reinorcement mats(lower let). Blankets are used on shorter, fatter

slopes and low-fow ditches. Mats can be used on steep slopes and high-velocity ditches.

Blankets are highly recommended or long, steep slopes(i.e., longer than 75 eet and steeper than

3H:1V). Trench in topo blankets, overlap

sides, and use plenty o staples. Blankets

can become saturated and heavy ater a rainand begin to slip downthe slope i not staked

securely.

Very good installation o tur mat inlong, steep, high-fow ditch below long slope.

Good use o straw and excelsior blankets on streambank stabilization project. Note that the bottom o stream isnot disturbed to preserve habitat. This site is ready or live

stakes, tree plantings, or other vegetation (see Section4.7, Stream and Wetland Protection).

Seeding on long, steep slope protected by straw erosion control blanket. Make sure blankets are stapled down securely or these

applications to prevent blankets rom sliding downhill whenweighted down with rain and ugitive sediment.





4.5.4 Temporary Slope Drains

Defnition

A temporary slope drain is a pipe or lined (TRM, rock, or concrete) ditch or channelextending rom the top to the bottom o a cut or fll slope during the construction period.

Purpose

Temporary slope drains serve to convey concentrated runo down the ace o a cut or fllslope without causing erosion. They are generally used in conjunction with diversions toconvey runo down a slope until permanent water management measures can be installed.

Design Criteria

Use the design criteria below or both pipe and channel slope drains. For channels, see thesection on Channels and Ditches or inormation on lining temporary and permanent slopedrains constructed as open conveyances.

General— It is very important that these temporary structures be sized, installed, andmaintained properly, because their ailure will usually result in severe erosion o the slope.

The entrance section to the drain should be well entrenched, staked down, and stable sothat surace water can enter reely. The drain should extend downslope beyond the toe o the slope to a stable area or appropriately stabilized outlet.

Pipe capacity— The pipe should be able to handle peak ow rom the 10-year, 24-hourstorm. Use 10-inch diameter or larger pipe to convey runo rom areas up to one-third acre;12-inch or larger pipe or up to hal-acre drainage areas, and 18-inch pipe or areas up toone acre. Multiple pipes or channels are oten required or large areas, spaced as needed.

Conduit— Construct the slope drain pipes rom heavy-duty, exible materials such asnon-perorated, corrugated plastic pipe, or open top overside drains with tapered inlets, orcorrugated metal pipe (CMP). Install reinorced, hold-down grommets or stakes to anchorthe conduit at intervals not to exceed 10 eet with the outlet end securely astened in place.CMP or corrugated plastic pipe must have one anchor assembly or every 20 eet o slope

drain. The conduit must extend beyond the toe o the slope.

Entrance— Construct the entrance to the slope drain o a standard ared-inlet section o pipe with a minimum 6-inch metal toe plate. Make all fttings watertight. A standard T-section ftting can also be used at the inlet. An open top ared inlet or overside drain canalso be used.

Temporary diversion— Generally, use an earthen diversion with a dike ridge or berm todirect surace runo into the temporary slope drain. Make the height o the ridge over thedrain conduit a minimum o 1.5 eet and at least 6 inches higher than the adjoining ridge

Securely installed plastic pipe unctionsvery well as a temporary slope drain.Inspect ater rainall to make sure fowsare routed into drain pipe, and outlet areas are stable and not eroding.




on either side. The lowest point o the diversion ridge should be a minimum o 1 oot abovethe top o the drain so that design ow can reely enter the pipe.

Outlet protection— Protect the outlet o the slope drain rom erosion with an energydissipator. (i.e., rock apron or other armoring).


A common ailure o slope drains is caused by water saturating the soil and seeping alongthe pipe. Proper backflling around and under the pipe haunches with stable soil materialand hand-compacting in 6 inch lits to achieve frm contact between the pipe and the soil atall points will reduce this type o ailure.

• Place slope drains on undisturbed soil or well-compacted fll at locations andelevations shown on the plans.

• Slightly slope the section o pipe under the dike toward its outlet.

• Compact the soil under and around the entrance section in lits not to exceed 6inches.

• Ensure that fll over the drain at the top o the slope has a minimum depth o 1.5 eetand a minimum top width o 4 eet. The sides should have a 3H:1V slope.

• Ensure that all slope drain connections are watertight.

• Ensure that all fll material is well compacted. Securely asten the exposed section o the drain with grommets or stakes spaced no more than 10 eet apart.

• Extend the drain beyond the toe o the slope and adequately protect the outlet romerosion.

• Make the settled, compacted dike ridge no less than 1 oot higher than the top o thepipe inlet.

Immediately stabilize all disturbed areas ollowing construction.


Inspect slope drains and supporting diversions weeklyand ater every signifcant rainall and promptly makenecessary repairs. When the protected area has beenpermanently stabilized, temporary measures canbe removed, materials disposed o properly, and alldisturbed areas stabilized appropriately.

Rock-lined slope drains (let) should have a non-woven geotextileunderliner, to prevent erosion and undermining. Use rock or sandbagberms to route runo into slope drains (right). Stake down plastic pipe

securely. Control outlet erosion with a fow dissipator (see Section 4.5).

This is a very good installation o a rock-lined slope drain. Inspect weekly until site is

stabilized.





4.5.5 Gabion Baskets and Mattresses

Defnition

Gabions are rectangular galvanized wire baskets flled with stones used as pervious, semi-exible building blocks or slope and channel stabilization. Live rooting branches can be

placed between the rock-flled baskets.

Purpose

Gabions protect slopes and streambanks rom the erosive orces o moving water. Rock-flled gabion baskets or mattresses can be used as retaining walls or slopes, to armor thebed or banks o channels, or to divert ow away rom eroding channel sections. Rock-flledor vegetated rock gabions are used on streambank sections subject to excessive erosionbecause o increased ows or disturbance during construction. Gabions can be specifedwhere ow velocities exceed 6 eet per second and where vegetative streambank protectionalone is not sufcient. Gabions can be used to construct deectors or groins intended todivert ow away rom eroding streambank sections. Gabions are also used to constructretaining walls and grade control structures. Gabion walls are appropriate where

• An excessively steep stream bank must be stabilized and vegetative or extrememechanical means o stabilization (i.e., pulling back bank) are not easible because o site conditions.

• The vertical integrity o a soil bank needs a higher tensile strength to reducesloughing o the streambank.

• There is moderate to excessive subsurace water movements that could be creatingerosion and damaging other types o nonpermeable structures.

• The slope must be modifed while heavy machinery is unavailable to the site.

• Fill must be disposed o along an eroding streambank (fll can be placed behindgabion to modiy slope).

• A retaining or toe wall is needed to stabilize the slope.

• Rock riprap is an appropriate practice, but the available or desired rock size (smaller)is not sufcient alone to resist the expected shear stress exerted on the revetment.Gabions allow the use o a smaller size rock than would be possible without the wirebaskets because the rock is bound by the wire mesh, creating a more monolithicstructure.

Galvanized wire can be abricated into box-like gabion baskets(let) or fatter mattresses. Mixingmulch and soil into gabion

structures—or applying it to the

surace ater construction—canhelp establish vegetation that provides a soter look.




Design Criteria

There are several types o gabion structures andapplications useul on construction sites, as summarizedbelow. Gabion structures are not recommended or steeplysloping channels where rock or high volumes o gravelsediment move at high velocity in the channel bed becauseo the possibility o damage to the wire mesh and ailure o the basket or mattress structure.

Gabion wall— Basically a gravity wall that relies on itsown weight and rictional resistance to resist sliding andoverturning rom lateral earth pressure.

Vegetated rock gabion— A rock-flled gabion earth-retaining structure that has live branches placed betweeneach consecutive layer o rock-flled baskets. The live branches will take root inside thegabion and into the soil behind the structure. The vegetation will consolidate the structuresand bind it to the slope.

Gabion defector— Deector or groins project into the streams and divert ows away romeroding streambank sections.

Gabion aprons— Rock-flled gabions or gabion mattress used as outlet protection, energydissipators, or spillways. These semiexible gabions are designed to settle without

racturing and adhere to the ground i scour occurs.Grade control— Drop structures or weirs. Gabion baskets and mattresses can be combinedto construct check dams or weirs.

Channel lining— Gabion mattresses can be used to line channels. The lining thicknessdepends on many actors such as the type o rock, design ow velocity, sediment andbedload, and channel gradient.

Gabion mattresses— Also reerred to as Reno mattresses or revet mattresses, gabionmattresses are not as thick as gabions, usually one-hal, three-quarters, or 1 oot thick.Gabion mattresses are used to line channels, armor streambanks and slopes, and used withgabions or grade-control structures (spillways or aprons).

Gabions and gabion mattresses are oten preerable to rock riprap alone. For any given

hydraulic condition, the gabion or gabion mattress revetment thickness is one-third o anequivalent riprap design. Gabions and gabion mattresses are exible and ree draining, thusallowing some soil settling. They can be used in unstable streambeds and streambanks.Gabions can provide an important component to a bioengineering solution or streambankor slope erosion because they allow the growth and establishment o natural vegetation.

Gabion containers are generally abricated rom a double-twist, hexagonal mesh o heavilyzinc-coated wire. Some gabions use welded wire. As an option, the wire can be coated withPVC. Wire diameter is 0.086 inches or the double-twisted gabion mattress and 0.106–0.120inches or the double-twisted gabion. The welded wire gabion uses wire diameters o 0.120inches or greater. The rectangular gabions are divided into cells with diaphragms o equalcapacity. The compartments add strength and assure that the ull material remains evenlydistributed. Gabions and gabion mattresses come in various sizes.

Choose the dimensions o the gabions or combination o gabions to meet the designrequirement site conditions. The mesh opening or gabions is typically or nominally 3.25x 4.5 inches. Some gabion mattresses have mesh openings o approximately 2.5 x 3.25inches. Both styles perorm hydraulically equivalent.

The use of gabion structures in urban areas isnot recommended, becauseof the possibility that they will harbor rodents and other pests. Some countiesand cities in Kentucky havebanned gabion structures

except in extremeconditions, where no other material is appropriate.




Typical Gabion Basket Sizes

Letter Code Length(ft)

Width(ft)

Depth(ft)

Number ofCells

Capacity(cubic yards)

A 6 3 3 1 2

B 9 3 3 2 3

C 12 3 3 3 4

D 6 3 1.5 1 1

E 9 3 1.5 2 1.5

F 12 3 1.5 3 2

G 6 3 1 1 0.666

H 9 3 1 2 1

I 12 3 1 3 1.333

T 9 6 .75 3 2.0

U 12 6 .75 4 1.33

Q 9 6 .5 3 1.33

S 9 6 .5 2 1.0

Construction SpecifcationsInstall gabions in accordance with manuacturer’s standards and specifcations.

• Gabions must be abricated so that the sides, ends, lid and diaphragms can beassembled at the construction site into rectangular baskets o the sizes specifed andshown on the construction drawings.

• Gabions must be o single-unit construction; the base, lid, ends and sides must beeither woven into a single unit or one edge o these members connected to the basesection o the gabion so that the strength and exibility at the connecting point is atleast equal to that o the mesh.

• Where the length o the gabion exceeds 1.5 times its horizontal width, the gabionmust be divided by diaphragms o the same mesh and gauge as the body o the

gabion, into cells whose length does not exceed the horizontal width.

• Gabions and mattresses are unolded and assembled at the job site. Corners are frstjoined together and then the diaphragms are attached to the side panels.

• Each gabion must be assembled by tying all untied edges with lacing wire orapproved asteners. The lacing wire must be tightly looped around every other meshopening along the seams so that single and double loops are alternated.

• The gabion or gabion mattress must be securely keyed into the streambank orstreambed to assure that ows do not erode the soils beneath or around it.

• Starting at the lowest point o the slope, excavate the loose material 2–3 eet belowthe ground elevation until a stable oundation is reached.

• Excavate the back o the stable oundation slightly deeper than the ront so theoundation tilts back into the slope.

• A line o empty gabion units must be placed in the bottom o its excavation andthe baskets are to be joined together along adjacent edges, both horizontally andvertically. The base o the empty gabions placed on top o a flled line o gabions mustbe tightly wired to the latter at ront and back.




• To achieve better alignment and fnish in gabion walls, stretching o the gabions isrecommended.

• For gabions greater than 18 inches, connecting wires (wires tied to opposite aces o each gabion cell) must be installed during flling operations.

• Hand-packing the gabion baskets or mattresses is preerred, but mechanical fllingis acceptable i care is taken to avoid bending, distorting, or damaging the wirestructures. Gabions must be flled to a depth o 12 inches and then two connectingwires must be tightly tied to opposite aces o each gabion cell at a height o 12 inches

above the base. Gabions must then be flled with a urther depth o 12 inches and twoconnecting wires must be similarly tied at this level. Then gabions must be flled tothe top.

• Fill gabions with appropriately sized river rock or quarry stone or other approvedinfll material. Use o hard material with high specifc gravity is recommended. Thetops o the gabions are then closed along edges and diaphragms using lacing wire orapproved asteners. Keep voids and bulges in the gabions to a minimum to ensureproper alignment and a neat, compact, square appearance.

• The stone size to fll gabions must be 3–5 inches or gabion mattresses and 4–8 inchesor gabion baskets.

Inspection and MaintenanceInspection o construction methods during the gabion assembly, placement, and fllprocess will help ensure that the structure perorms as intended. All structures should bemaintained in an as built condition. Structural damage caused by storm events should berepaired as soon as possible to prevent urther damage to the structure or erosion o thestreambank.

During inspection, look or undercutting,bypassing, or other ow-related erosionproblems. Check to ensure that basket wiring isadequate, and components are not separating(i.e., sidewalls becoming detached). Repairbaskets that appear to be splitting; use rock or

other armoring to repair eroded areas.

Gabions can protect banks in areas o high velocity fows. Some designers preer TRMs in these situations,i space is available to slope banks back appropriately.

Gabion mattresses can replace tur

mats in high-fow, high-velocity channels. Mixing mulch and soil intothe rock can help support vegetationor a “greener” look.





4.5.6 Cellular Confnement Systems

Defnition

A cellular confnement system (CCS) is a three-dimensional, honeycombed, sheet, mat,or interlocking structure flled with soil and planted with vegetation used to stabilize the

surace o earthen cut and fll slopes.

Purpose

CCSs are permanent erosion control practices intended to stabilize infll materials or slopeand channel protection, load support, and earth retention applications. The expandablepanels create a cellular system that confnes topsoil infll, protects and reinorces the plant’sroot zone, and permits infltration and natural subsurace drainage. The honeycomb shapedcells encapsulate and prevent erosion o the infll material. The cellular confnementsystems are used or

• Revetments— Filling the cells with topsoil or rock and vegetation can provide analternative to hard armor revetment systems

• Erosion control on steep slopes— Cells can be flled with soil and vegetated orflled with granular materials. Slopes as steep as 1H:1V can be treated with cellularconfnement systems. Application on steep slopes may require tendons or systemstability and security against sliding.

• Flexible channel lining systems—either vegetated or rock flled.

• Road stabilization—cells confne and reinorce select fll materials, therebyincreasing load-bearing capacities. Creates a porous pavement system with aggregateor topsoil/vegetation infll.

• Temporary low-water stream crossings.


Site PreparationThe surace o the slope should be leveled, with stones and debris removed. Gullies shouldbe flled and well compacted. Major obstacles such as boulders can be let in place. Simplycut out panels around them.

Following excavation and fll placement operations, shape and compact the subgradesuraces to the designed elevations and grades.

Excavate the area so that when cellular confnement systems are installed, the top o thesection is ush with or slightly lower than the adjacent terrain or fnal grade.

Remove unstable subgrade soils when required and install geotextile underliner i specifed.

Concrete and plastic cellular blankets, likethis open-celled concrete block product,

provide heavy armoring while supportingvegetation that sotens the nal look.



Installation

Follow manuacturer’s instructions regarding application type, slope limits, installationprocedure, appropriate fll material, and so on.

• Anchor the cellular confnement system sections at the top o the slope across a 2–4oot ledge. Expand and stretch the cellular confnement system down the slopes.

• The type o anchors and requency o anchoring will depend on site conditions.Typically, every other cell across the top section is anchored with J-pins or othersuitable anchor devices. This anchoring pattern is repeated every 6 eet down the

slope.

• The cells should be anchored securely to prevent deormation o the panel whilebackflling. Depending on the slope angle and fll soils involved, intermediateanchorage will be necessary on some interior cells to limit sideways deormation,ensure stability and avoid overloading the upper sections.

• Additional panels are abutted together and joined with staples, hog rings or othersuitable asteners.

Infll Placement

Place the fll material in the expanded cells with suitable equipment such as a backhoe,

ront-end loader or conveyer.• Limit drop height to 3 eet to reduce crushing orce on cell material.

• On steep slopes, infll rom the crest to the toe to prevent displacement anddeormation o the cellular confnement system.

• Overflling and compacting o infll depend on the type and consistency o materialand the depth o the cells.


Inspect slope periodically and ater signifcant rainstorms to check or erosion. Any ailureshould be repaired immediately.

I vegetation has not been established, ertilize andreseed damaged and sparse areas immediately.

Cellular concrete mat used to stabilize banks in a highly erodible silty loam soil. Double- or triple-seed these applications immediately ater installation. Mulch might be needed to support seeded areas until

i bli h d

Plastic cellular blanket installed on a steep,long slope. Work closely with manuacturerson these applications to ensure proper design,installation, and initial maintenance.

Cellular blankets provide an aesthetic alternative to poured concrete walls and th d i t ll ti

3 slope protection

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