erosion and sediment control specifications...effective erosion and sedimentation control requires...

EROSION

AND

SEDIMENT CONTROL

SPECIFICATIONS

Approved byMissouri Department Of Natural Resources

November 23, 1992

City of Kansas City, Missouri

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PURPOSE:

The purpose of these specifications is to prevent soil erosion and sedimentation from leaving constructionsites that occur from non-agricultural development and construction activities within the City by requiringproper provisions for water disposal and the protection of soil surfaces during and after construction, in orderto promote the safety, public health, convenience and general welfare of the community.

SCOPE:

The requirements set forth in these specifications apply to any project that disturbs 5 acres of total land areaor more or is part of a common plan or sale of projects of 5 acres or more.

RESPONSIBILITIES:

It shall be the responsibility of the design engineer to prepare an erosion and sedimentation control plan. Thefollowing note shall be added to the erosion control plan for privately financed projects:

“This Erosion Control Plan has been placed in the City’s file for this project. The plan appears tofulfill the Missouri Department of Natural Resources’ technical criteria and the criteria for erosioncontrol and requirements of the City. I understand that additional erosion control measures may beneeded if unforeseen erosion problems arise or if the submitted plan does not function as intended.The requirements of this plan shall run with the land and be the obligation of the land owner untilsuch time as the plan is properly completed, modified or voided.”

___________________ ____________Property owner’s name Dateand signature

For publicly financed projects, the design engineer shall add to the contract documents language thatobligates the prime contractor who is awarded the contract the responsibility of adding additional erosioncontrol measures as needed if unforeseen erosion problems arise or if the submitted plan does not function asintended. The requirements of the plan shall be the prime contractor’s responsibility until the plan is properlycompleted, modified or voided.

Approved and adopted as Official Document No. 940108

this 18th day of March, 1994.

George E. Wolf, Jr., P.E.Acting Director of Public WorksKansas City, Missouri

SECTION 10 EROSION AND SEDIMENT CONTROL

10.01 GENERAL

Erosion is a natural process where soil and rock are loosened and removed. Natural erosionoccurs at a very slow pace, but when land is disturbed on a construction site, the erosionrate increases dramatically. The major problem associated with erosion on a constructionsite is the movement of soil off the site and its impact on water quality and drainagesystems.

Sedimentation is the deposition of soil particles that have been transported by water andwind. The quantity and size of the material transported increases with the velocity of therunoff. Sedimentation occurs when the water in which the soil particles are carried issufficiently slowed for a long enough period of time to allow particles to settle out.

Some of the negative impacts of erosion and sedimentation would include: the degradationof a streams ecology, a reduction in the storage volume of reservoirs, the clogging ofstreams and drainage systems, and damage to adjacent property due to siltation.

Identifying erosion problems at the planning stage and noting highly erodible areas helps inselecting effective erosion control practices and estimating storage volumes for sedimenttraps and basins. This section focuses on the prevention of sedimentation and water-generated soil erosion.

10.02 PRINCIPLES OF EROSION AND SEDIMENTATION CONTROL

Effective erosion and sedimentation control requires that the soil surface be protected fromthe erosive forces of wind, rain and runoff and that the eroded soil be captured and retainedon-site. The following principles are effective when they are integrated into a system ofcontrol practices and management techniques to control erosion and prevent sedimentationoff-site.

A. Fit the Development to Existing Site Conditions

Review and consider all existing conditions in the initial site selection for theproject. Select a site that is suitable rather than force the terrain to conform todevelopment needs. Ensure that development features follow natural contours.Steep slopes, areas subject to flooding, and highly erodible soils severely limit asite’s use, while level, well-drained areas offer few restrictions. Any modificationof a site’s drainage features or topography requires protection from erosion

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and sedimentation.

B. Minimize the Extent and Duration of Exposure.

Scheduling can be a very effective means of reducing the hazards of erosion.Schedule construction activities to minimize the exposed area and the duration ofexposure. In scheduling, take into account the season and the weather forecast.Stabilize disturbed areas as quickly as possible.

C. Protect Areas to be Disturbed from Stormwater Runoff

Use dikes, diversions, and waterways to intercept runoff and divert it away fromcut-and-fill slopes or other disturbed areas. To reduce on-site erosion, install thesemeasures before clearing and grading.

D. Stabilize Disturbed Areas

Removing the vegetative cover and altering the soil structure by clearing, grading,and compacting the surface increases an area’s susceptibility to erosion. Applystabilizing measures as soon as possible after the land is disturbed. Plan andimplement temporary or permanent vegetation, mulches, or other protectivepractices to correspond with construction activities. Protect channels from erosiveforces by using protective linings and the appropriate channel design. Considerpossible future repairs and maintenance of these practices in the design.

E. Keep Runoff Velocities Low

Clearing existing vegetation reduces the surface roughness and infiltration rate andthereby increases runoff velocities and volumes. Use measures that break the slopesto reduce the problems associated with concentrated flow volumes and runoffvelocities. Practical ways to reduce velocities include conveying stormwater runoffaway from steep slopes to stabilized outlets, preserving natural vegetation wherepossible, and mulching and vegetating exposed areas immediately afterconstruction.

F. Retain Sediment on the Site

Even with careful planning some erosion is unavoidable. The resulting sedimentmust be trapped on the site. Plan the location where sediment deposition will occurand maintain access for cleanout. Protect low points below disturbed areas bybuilding barriers to reduce sediment

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loss. Whenever possible, plan and construct sediment traps and basins before otherland-disturbing activities.

G. Inspect and Maintain Control Measures

Inspection and maintenance is vital to the performance of erosion andsedimentation control measures. If not properly maintained, some practices maycause more damage than they prevent. Always evaluate the consequences of ameasure failing when considering which control measure to use, since failure of apractice may be hazardous or damaging to both people and property. For example,a large sediment basin failure can have disastrous results, low points in dikes cancause major gullies to form on a fill slope. It is essential to inspect all practices todetermine that they are working properly and to ensure that problems are correctedas soon as they develop.

10.03 Practice Standards and Specifications

This section contains standards and specifications on a variety of erosion and sedimentcontrol practices for use on construction sites and similarly disturbed areas. These practicestandards are designed to establish uniformity in the selection, design, review, approval,installation and maintenance of practices contained in erosion and sediment control plans.They establish the minimum degree of technical adequacy in planning, designing andapplying erosion and sediment control practices on disturbed areas. Alternate practicesmay be approved for individual erosion and sediment control plans. Such approval shouldbe based on specific site conditions and where approval will not contravene the intent andpurposes of the following practice standards.

WHEREVER CONFLICTING PROVISIONS OR REQUIREMENTSOCCUR BETWEEN THESE SPECIFICATIONS AND ANY OTHERSPECIFICATIONS, CODES OR LAWS, THE MOST RESTRICTIVESHALL GOVERN.

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TABLE OF CONTENTS

Page

10.03.1Site Preparation.1 Land Grading...................................................................................................................2.2 Surface Roughening ........................................................................................................5.3 Topsoiling........................................................................................................................7.4 Tree Preservation and Protection ..................................................................................10.5 Temporary Construction Entrance ................................................................................14

10.03.2Surface Stabilization.1 Temporary Seeding .......................................................................................................17.2 Permanent Seeding........................................................................................................20.3 Mulching .......................................................................................................................26.4 Sodding .........................................................................................................................31.5 Trees, Shrubs, Vines and Ground Cover.......................................................................35.6 Riprap............................................................................................................................41

10.03.3Runoff Control Measures.1 Temporary Diversion Dike............................................................................................46.2 Permanent Diversion Dike ............................................................................................49.3 Right-of-Way Diversion................................................................................................52.4 Temporary Perimeter Dike............................................................................................54

10.03.4Runoff Conveyance Measures.1 Grass Lined Channels....................................................................................................58.2 Riprap and Paved Channel ............................................................................................62.3 Temporary Slope Drains ...............................................................................................66.4 Paved Flume or Chutes .................................................................................................70

10.03.5Outlet Protection.1 Level Spreader...............................................................................................................75.2 Outlet Stabilization Structures ......................................................................................78

10.03.6Inlet Protection.1 Excavated Inlet Protection (Temporary) .......................................................................82.2 Fabric Drop Inlet Protection (Temporary) ....................................................................84.3 Block and Gravel Inlet Protection

(Temporary) ..................................................................................................................87

10.03.7Sediment Traps and Barriers.1 Temporary Sediment Trap. . ........................................................................................92.2 Sediment Basin..............................................................................................................97.3 Sediment (Silt) Fence ..................................................................................................104.4 Temporary Straw Bale Barrier ....................................................................................107

10.03.8Streambank Protection.1 Vegetative Streambank Protection ..............................................................................110.2 Structural Streambank Protection................................................................................113

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10.03.1 SITE PREPARATION

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10.03.1.1 — LAND GRADING

Definition

Reshaping the ground surface by grading to plan as determined by engineering survey and layout.

Purpose

The practice is for one or more of the following purposes: (1) provide sites more suitable forbuildings, facilities, and other land uses; (2) improve surface drainage; and (3) control erosion andreduce sediment.

Conditions Where Practice Applies

This practice is applicable where grading to planned elevation is practical for the purposesenumerated above.

Design Criteria

The grading plan shall be based upon adequate surveys and investigations. The plan must show thelocations, slopes, cuts, fills, and finish elevations of the surfaces to be graded together withauxiliary practices for erosion control, slope stabilization, safe disposal of runoff water, anddrainage facilities such as waterways, lined ditches, diversions, grade stabilization structures, andsurface and subsurface drains. The following requirements shall be incorporated into the plan:

1. Where feasible, cut and fill slopes shall not be steeper than 2:1.

2. Where feasible, benches or diversions shall be provided on slopes steeper than 3:1 whenvertical height of slope exceeds 15 feet.

3. Provisions must be made to safely conduct surface runoff to storm drains or to stable watercourses to insure that surface runoff will not damage slopes or other graded areas.

4. Subsurface drainage must be provided where necessary to intercept seepage that wouldadversely affect slope stability or create excessively wet site conditions.

5. Slopes shall not be created so close to property lines as to endanger adjoining propertieswithout adequately protecting such properties against erosion, slippage, settlement,subsidence, or other related damages.

6. Fills must consist of approved clean material from cut areas, borrow pits, or otheracceptable sources. Fill shall be

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placed in lifts not to exceed 1 foot and compacted at density shown on plan.

Construction Specifications

1. Construct and maintain all erosion and sedimentation control practices and measures inaccordance with the approved sedimentation control plan and construction schedule.

2. Remove good topsoil from areas to be graded and filled, and preserve it for use in finishingthe grading of all critical areas.

3. Scarify areas to be topsoiled to a minimum depth of 2 inches before placing topsoil.

4. Clear and grub areas to be filled to remove trees, vegetation, roots, or other objectionablematerial that would affect the planned stability of the fill.

5. Ensure that fill material is free of brush, rubbish, rocks, logs, stumps, building debris, andother materials inappropriate for constructing stable fills.

6. Place all fill in layers not to exceed 9 inches in thickness, and compact the layers asrequired to reduce erosion, slippage, settlement, or other related problems.

7. Do not incorporate frozen material or soft, mucky, or highly compressible materials intofill slopes.

8. Do not place fill on a frozen foundation, due to possible subsidence and slippage.

9. Keep diversions and other water conveyance measures free of sediment during all phasesof development.

10. Handle seeps or springs encountered during construction in accordance with approvedmethods.

11. Permanently stabilize all graded areas immediately after final grading is completed on eacharea in the grading plan. Apply temporary stabilization measures on all graded areas whenwork is to be interrupted or delayed for 30 working days or longer.

12. Show topsoil stockpiles, borrow areas, and spoil areas on the plans, and make sure they areadequately protected from erosion. Include final stabilization of these areas in the plan.

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Maintenance

Periodically check all graded areas and the supporting erosion and sedimentation control practices,especially after heavy rainfalls. Promptly remove all sediment from diversions and other water -disposal practices. If washouts or breaks occur, repair them immediately. Prompt maintenance ofsmall eroded areas before they become significant gullies is an essential part of an effectiveerosion and sedimentation control plan.

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10.03.1.2 - SURFACE ROUGHENING

Definition

Roughening a bare soil surface with horizontal grooves running across the slope, stair stepping, ortracking with construction equipment.

Purpose

To aid the establishment of vegetative cover from seed, to reduce runoff velocity and increaseinfiltration, and to reduce erosion and provide for sediment trapping.


All construction slopes require surface roughening to facilitate stabilization with vegetation, withparticular attention given to those areas where the slopes exceed 3:1.

Planning Considerations

Rough slope surfaces are preferred because they aid the establishment of vegetation, improvewater infiltration, and decrease runoff velocity. Graded areas with smooth, hard surfaces may beinitially attractive, but such surfaces increase the potential for erosion. A rough, loose soil surfacegives a mulching effect that protects lime, fertilizer, and seed. Nicks in the surface are cooler andprovide more favorable moisture conditions than hard, smooth surfaces; this aids seedgermination.

There are different methods for achieving a roughened soil surface on a slope, and the selection ofan appropriate method depends upon the type of slope. Roughening methods include stair-stepgrading, grooving, and tracking. Factors to be considered in choosing a method are slopesteepness, mowing requirements, and whether the slope is formed by cutting or filling.


1. CUT SLOPE ROUGHENING FOR AREAS NOT TO BE MOWEDStair— step grade or groove cut slopes with a gradient steeper than 3:1.

Use stair— step grading on any erodible material soft enough to be ripped with a bulldozer.Slopes consisting of soft rock with some subsoil are particularly suited to stair-stepgrading.

Make the vertical cut distance less than the horizontal distance, and slightly slope thehorizontal position of the “step” in toward the vertical wall.

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Do not make individual vertical cuts more than 2 feet in soft materials or more than 3 feetin rocky materials.

Grooving uses machinery to create a series of ridges and depressions that run across theslope (on the contour).

Groove using any appropriate implement that can be safely operated on the slope, such asdiscs, tillers, spring harrows, or the teeth on a front— end loader bucket. Do not make suchgrooves less than 3 inches deep nor more than 15 inches apart.

2. FILL SLOPE ROUGHENING FOR AREAS NOT TO BE MOWEDPlace fill slopes with a gradient steeper than 3:1 in lifts not to exceed 9 inches, and makesure each lift is properly compacted. Ensure that the face of the slope consists of loose,uncompacted fill 4 to 6 inches deep. Use grooving, as described above, to roughen the faceof the slopes, if necessary.

Do not blade or scrape the final slope face.

3. CUTS, FILLS, AND GRADED AREAS THAT WILL BE MOWEDMake mowed slopes no steeper than 3:1.

Roughen these areas to shallow grooves by normal tilling, discing, harrowing, or use ofcultipacker— seeder. Make the final pass of any such tillage implement on the contour.

Make grooves formed by such implements close together (less than 10 inches) and not lessthan 1 inch deep.

Excessive roughness is undesirable where mowing is planned.

4. ROUGHENING WITH TRACKED MACHINERYLimit roughening with tracked machinery to sandy soils to avoid undue compaction of thesoil surface. Tracking is generally not as effective as the other roughening methodsdescribed.

Operate tracked machinery up and down the slope to leave horizontal depressions in thesoil. Do not back-blade during the final grading operation.

5. SEEDINGImmediately seed and mulch roughened areas to obtain optimum seed germination andgrowth.

Maintenance

Periodically check the seeded slopes for rills and washes. Fill these areas slightly above theoriginal grade, then reseed and mulch as soon as possible.

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10.03.1.3 - TOPSOILING

Definition

Obtaining topsoil from other places and spreading it over the areas to be stabilized.

Purpose

To provide a suitable soil medium for vegetative growth on areas where other measures will notproduce or maintain a stand of desirable vegetation.


This practice is recommended for sites of 2:1 or flatter slopes where:

a) The texture of the exposed subsoil or parent material is not suitable to produceadequate vegetative growth.

b) The soil material is so shallow that the rooting zone is not deep enough to supportplants and furnish continuing supplies of moisture and plant food.

c) The soil to be vegetated contains material toxic to plant growth.


1. MATERIALSTopsoil may be salvaged and stockpiled from the project area or it may be furnished fromareas outside the project area. Topsoil shall be the original top layer of a soil profile formedunder natural conditions and it should meet the standards set forth in this specification. Itshall be reasonably free of refuse, noxious weeds, subsoil, stiff clay, hard lumps, stumps,roots, brush, stones or other litter or objects larger than 1-1/2 inches in diameter. Qualitytopsoil has the following characteristics:

a) Texture — loam, sandy loam, and silt loam are best; sandy clay loam, silty clayloam, and loamy sand are fair. Do not use heavy clay and organic soils such as peator muck as topsoil.

b) Organic matter content — (sometimes referred to as “humic matter”) should begreater than 1.5% by weight.

c) Acidity — pH should be greater than 3.6 before liming, and liming is required if itis less than 6.0.

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d) Soluble salts — should be less than 500 ppm.

e) Sodium — sodium adsorption ratio should be less than 12.

Organic soils such as mucks and peats do not make good topsoil. They can be identified bytheir extremely light weight when dry.

2. STRIPPINGStrip topsoil only from those areas that will be disturbed by excavation, filling, roadbuilding, or compaction by equipment. A 4-6 inch stripping depth is common, but depthvaries depending on the site. Determine depth of stripping by taking soil cores at severallocations within each area to be stripped. Topsoil depth generally varies along a gradientfrom hilltop to toe of the slope. Put sediment basins, diversions, and other controls intoplace before stripping.

3. STOCKPILINGSelect stockpile location to avoid slopes and natural drainageways, avoiding traffic routes.On large sites, respreading is easier and more economical when topsoil is stockpiled insmall piles located near areas where they will be used.

a) Sediment barriers — Use sediment fences or other barriers where necessary toretain sediment.

b) Temporary seeding — Protect topsoil stockpiles by temporarily seeding as soon aspossible, no more than 30 working days or 120 calendar days after the formation ofthe stockpile.

c) Permanent vegetation - If stockpiles will not be used within 12 months they mustbe stabilized with permanent vegetation to control erosion and weed growth.

4. SITE PREPARATION (Where topsoil is to be added)a) Topsoiling — When topsoiling, maintain needed erosion control practices such as

diversions, grade stabilization structures, berms, dikes, level spreaders, waterwaysand sediment basins.

b) Grading - Grades on the areas to be topsoiled which have been previouslyestablished shall be maintained.

c) Liming - Where the pH of the subsoil is 5.0 or less or composed of heavy clays,agricultural limestone shall be spread at the rate of 100 pounds per 1,000 squarefeet. Lime shall be distributed uniformly over designated areas and worked into thesoil in conjunction with tillage operations as described in the following procedure.

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d) Bonding - Immediately prior to dumping and spreading of the topsoil, loosen thesubgrade by discing or scarifying to a depth of at least 4 inches, to permit bondingof the topsoil and subsoil.

5. SPREADING TOPSOILUniformly distribute topsoil to a minimum compacted depth of 2 inches on 3:1 slopes and4 inches on the flatter slopes. Do not spread topsoil while it is frozen or muddy or when thesubgrade is wet or frozen. Correct any irregularities in the surface that result fromtopsoiling or other operations to prevent the formation of depressions or water pockets.Compact the topsoil enough to ensure good contact with the underlying soil, but avoidexcessive compaction, as it increases runoff and inhibits seed germination. Light packingwith a roller is recommended where high-maintenance turf is to be established.

Use the following table to determine the volume of topsoil required for application to variousdepths:

CUBIC YARDS OF TOPSOIL REQUIRED FOR APPLICATIONTO VARIOUS DEPTHS

Depth Per 1000 Per(inches) Sq. feet Acre

1 3.1 1342 6.2 2683 9.3 4034 12.4 5365 15.5 6726 18.6 807

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10.03.1.4 - TREE PRESERVATION AND PROTECTION

Definition

Practices to preserve and protect desirable trees from damage during project development.

Purpose

To preserve and protect trees that have present or future value for their use in protection fromerosion, for their landscape and aesthetic value, or other environmental benefits.


On development sites containing trees or stands of trees.


Preserving and protecting trees and other natural plant groups often results in a more stable andaesthetically pleasing development. During site evaluation, note where valuable trees and othernatural landscape features should be preserved, then consider these trees and plants whendetermining the location of roads, buildings, or other structures.

Trees that are near construction zones should be either protected or removed, because damageduring construction activities may cause the death of the tree at a later time.

Trees should be considered for preservation for the following benefits:

a) They stabilize the soil and prevent erosion.

b) They reduce storm water runoff by intercepting rainfall, promote infiltration, and lower thewater table through transpiration.

c) They moderate temperature changes, promote shade, and reduce the force of wind.

d) They provide buffers and screens against noise and visual disturbance, providing a degreeof privacy.

e) They filter pollutants from the air, remove carbon dioxide from the air, and produceoxygen.

f) They provide a habitat for animals and birds.

g) They increase property values and improve site aesthetics.

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Criteria for Selecting Trees to be Protected and Saved

1. Tree vigor — Preserve healthy trees. A tree of low vigor is susceptible to damage byenvironmental changes that occur during site development. Healthy trees are lesssusceptible to insects and disease. Indications of poor vigor include dead tips of branches,small annual twig growth, stunted leaf size, sparse foliage, and pale foliage color. Hollowor rotten trees, cracked, split, or leaning trees, or trees with broken tips also have lesschance for survival.

2. Tree age — Old, picturesque trees may be more aesthetically valuable than smaller,younger trees, but they may require more extensive protection.

3. Tree species - Preserve those species that are most suitable for site conditions andlandscape design. Trees that are short lived or brittle or are susceptible to attack byinsects and disease may be poor choices for preservation.

4. Tree aesthetics – Choose trees that are aesthetically pleasing, shapely, large, or colorful.Avoid trees that are leaning or in danger of falling. Occasionally, an odd-shaped tree orone of unusual form may add interest to the landscape if strategically located. However,be sure the tree is healthy.

5. Wildlife benefits - Choose trees that are preferred by wildlife for food, cover, or nesting.A mixture of evergreens and hardwoods may be beneficial. Evergreen trees are importantfor cover during the winter months, whereas hardwoods are more valuable for food.

Construction activities can significantly injure or kill trees unless protective measures are taken.Although direct contact by equipment is an obvious means of damaging trees, most seriousdamage is caused by root zone stress from compacting, filling, or excavating too close to the tree,Clearly mark boundaries to maintain sufficient undisturbed area around the trees.

Design Criteria

The following general criteria should be considered when developing sites in wooded areas:

a) Leave critical areas (such as flood plains, steep slopes and wetlands) with desirabletrees in their natural condition or only partially cleared.

b) Locate roadways, storage areas, and parking pads away from valuable tree stands.Follow natural contours, where feasible, to minimize cutting and filling in thevicinity of trees.

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c) Select trees to be preserved before siting, roads, buildings, or other structures.

d) Minimize trenching in areas with trees. Place several utilities in the same trench.

e) Designate groups of trees and individual trees to be saved on the erosion andsedimentation control plan.

Do not excavate, traverse, or fill closer than the drip line, or perimeter of the canopy, of trees tobe saved.

Construction Specifications1. Place barriers to prevent the approach of equipment within the drip line of trees to be

retained. See Figure l.4a.

2. Do not nail boards to trees during building operations.

3. Do not cut tree roots inside the tree drip line.

4. Do not place equipment, construction materials, or fill dirt within the limit of the drip lineof trees to be saved.

5. During final site cleanup, remove barriers around trees.

Figure 1.4a - Installation of tree barriers.12

Incorrect Correct

Maintenance

In spite of precautions, some damage to protect trees may occur. In such cases, repair anydamage to the crown, trunk or root system immediately.

a) Repair roots by cutting off the damaged areas and painting them with tree paint.Spread peat moss or moist topsoil over exposed roots.

b) Repair damage to bark by trimming around the damaged area, taper the cut toprovide drainage, and paint with tree paint.

c) Cut off all damaged tree limbs above the tree collar at the trunk or main branch. Usethree separate cuts to avoid peeling bark from healthy areas of the tree.

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10.03.1.5 - TEMPORARY GRAVEL CONSTRUCTION ENTRANCE

Definition

A stone stabilized pad located at any point where traffic will be entering or leaving a constructionsite to or from a public right-of-way, street, alley, sidewalk, or parking area.

Purpose

To reduce or eliminate the transport of mud from the construction area onto public rights-of-wayby motor vehicles or by runoff.


This practice is applied at appropriate points of construction ingress and egress.

Design Criteria

Aggregate size: Use 2-3 inch washed stone.

Pad thickness: 6-inch minimum

Pad width: 12-feet minimum or full width of all points of vehicular ingress oregress.

Pad length: Not less than 50 feet.

Washing: Wheels must be cleaned to remove mud prior to entrance ontopublic rights-of-way. When washing is required, it shall be done onan area stabilized with crushed stone which drains into an approvedsediment trap or sediment basin.

Location: Entrance shall be located or protected so as to prevent sedimentfrom leaving the site.

Construction Specifications1. Clear the entrance and exit area of all vegetation, roots, and other objectionable material

and properly grade it.

2. Place the gravel to the specific grade and dimensions shown on the plans, and smooth it.

3. Provide drainage to carry water to a sediment trap or other suitable outlet.

4. Use geotextile fabrics because they improve stability of the foundation in locationssubject to seepage or high water table.

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Maintenance

Maintain the gravel pad in a condition to prevent mud or sediment from leaving the constructionsite. This may require periodic topdressing with 2-inch stone. After each rainfall, inspect anystructure used to trap sediment and clean it out as necessary. Immediately remove allobjectionable materials spilled, washed, or tracked onto public roadways.

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10.03.2 SURFACE STABILIZATION

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10.03.2.1 - TEMPORARY SEEDING

Definition

Planting rapid-growing annual grasses, small grains, or legumes to provide initial, temporarycover for erosion control on disturbed areas.

Purpose

To temporarily stabilize denuded areas that will not be brought to final grade for a period of morethan 30 working days.

Temporary seeding controls runoff and erosion until permanent vegetation or other erosioncontrol measures can be established. In addition, it provides residue for soil protection andseedbed preparation and reduces problems of mud and dust production from bare soil surfacesduring construction.


On any cleared, unvegetated, or sparsely vegetated soil surface where vegetative cover is neededfor less than 1 year. Applications of this practice include diversions, dams, temporary sedimentbasins, temporary road banks, and topsoil stockpiles.


Annual plants, which sprout and grow rapidly and survive for only one season, are suitable forestablishing initial or temporary vegetative cover. Temporary seeding preserves the integrity ofearthen sediment control structures such as dikes, diversions, and the banks of dams andsediment basins. It can also reduce the amount of maintenance associated with these devices. Forexample, the frequency of sediment basin cleanouts will be reduced if watershed areas, outsidethe active construction zone, are stabilized.

Proper seedbed preparation, selection of appropriate species, and use of quality seed areimportant in this practice. Failure to follow established guidelines and recommendationscarefully may result in an inadequate or short-lived stand of vegetation that will not controlerosion.

Temporary seeding provides protection for no more than 1 year, during which time permanentstabilization should be initiated.

Specifications

Complete grading before preparing seedbeds and install all necessary erosion control practices,such as dikes, waterways and basins. Minimize steep slopes because they make seedbed

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preparation difficult and increase the erosion hazard. If soils become compacted during grading,loosen them to a depth of 6-8 inches using a ripper, harrow, or chisel plow.

A. SEEDBED PREPARATIONGood seedbed preparation is essential to successful plant establishment. A good seedbedis well-pulverized, loose, and uniform. Where hydroseeding methods are used, thesurface may be left with a more irregular surface of large clods and stones.

1. Liming - Apply lime according to soil test recommendations. If the pH (acidity) ofthe soil is not known, an application of ground agricultural limestone at the rate of2 tons/acre is usually sufficient. Apply limestone uniformly and incorporate intothe top 4-6 inches of soil. Soils with a pH of 6 or higher need not be limed.

2. Fertilizer - Base application rates on soil tests. When these are not possible, applya 10-10-10 grade fertilizer at 700-1,000 lb/acre. Both fertilizer and lime should beincorporated into the top 4-6 inches of soil.

3. Surface roughening - If recent tillage operations have resulted in a loose surface,additional roughening may not be required except to break up large clods. Ifrainfall causes the surface to become sealed or crusted, loosen it just prior toseeding by discing, raking, harrowing, or other suitable methods. Groove orfurrow slopes steeper than 3:1 on the contour before seeding.

B. PLANT SELECTIONAnnual rye grass, wheat or oats should be used for temporary seeding.

C. SEEDINGEvenly apply seed using a cyclone seeder (broadcast), drill, cultipacker seeder, orhydroseeder. Annual rye grass should be applied at a rate of 120 lbs/acre, wheat or oatsshould be applied at a rate of 100 lbs/acre. Broadcast seeding and hydroseeding areappropriate for steep slopes where equipment cannot be driven. Hand broadcasting is notrecommended because of the difficulty in achieving a uniform distribution.

Small grains should be planted no more than 1 inch deep, and grasses and legumes nomore than 1/2 inch. Broadcast seed must be covered by raking or chain dragging, andthen lightly firmed with a roller or cultipacker. Hydroseeded mixtures should include awood fiber (cellulose) mulch.

D. MULCHINGApply mulch in accordance with Section 10.03.2.3 - MULCHING.

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The use of an appropriate mulch will help ensure establishment under normal conditions and isessential to seeding success under harsh site conditions. Harsh site conditions include:

a) seeding in fall or winter cover (wood fiber mulches are not considered adequatefor this use),

b) slopes steeper than 3:1,

c) excessively hot or dry weather,

d) adverse soils (shallow, rocky, or high in clay or sand), and

e) areas receiving concentrated flow.

If the area to be mulched is subject to concentrated water flow, as in channels, anchor mulch withnetting.

Maintenance

Reseed, refertilize and mulch areas of insufficient growth. Reseed, refertilize and mulchimmediately following erosion or other damage.

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10.03.2.2 — PERMANENT SEEDING

Definition

Controlling runoff and erosion on disturbed areas by establishing perennial vegetative cover withseed.

Purpose

To reduce erosion and decrease sediment yield from disturbed areas, and to permanently stabilizesuch areas in a manner that is economical, adapts to site conditions, and allows selection of themost appropriate plant materials.


Fine-graded areas on which permanent, long-lived vegetative cover is the most practical or mosteffective method of stabilizing the soil. Permanent seeding may also be used on rough-gradedareas that will not be brought to final grade for a year or more.

Areas to be stabilized with permanent vegetation must be seeded or planted within 30 workingdays or 60 calendar days after final grade is reached, unless temporary stabilization is applied.


Vegetation controls erosion by protecting bare soil surfaces from raindrop impact and byreducing the velocity and volume of overland flow.

The most common and economical means of stabilizing disturbed soils is by seeding grasses andlegumes. The advantages of seeding over other means of establishing plants include the smallerinitial cost, lower labor input, and greater flexibility of method.

The probability of successful plant establishment can be maximized through good planning,knowledge of the soil characteristics, selection of suitable plant materials for the site, goodseedbed preparation, adequate liming and fertilization, and timely planting and maintenance.

Specifications

1. SEEDBED REQUIREMENTSEstablishment of vegetation should not be attempted on sites that are unsuitable due toinappropriate soil texture, poor drainage, concentrated overland flow, or steepness ofslope until measures have been taken to correct these problems.

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To maintain a good stand of vegetation, the soil must meet certain minimum requirementsas a growth medium. The existing soil should have these criteria:

a) Enough fine-grained (silt and clay) material to maintain adequate moisture andnutrient supply (available water capacity of at least .05 inches water to 1 inches ofsoil).

b) Sufficient pore space to permit root penetration.

c) Sufficient depth of soil to provide an adequate root zone. The depth to rock orimpermeable layers such as hardpans should be 12 inches or more, except onslopes steeper than 2:1 where the addition of soil is not feasible.

d) A favorable pH range for plant growth, usually 6.0-6.5.

e) Freedom from large roots, branches, stones, large clods of earth, or trash of anykind. Clods and stones may be left on slopes steeper than 3:1 if they are to behydroseeded.

If any of the above criteria are not met - i.e., if the existing soil is too coarse, dense,shallow or acidic to foster vegetation special amendments are required. The soilconditioners described below may be beneficial or, preferably, topsoil may be applied.

2. SOIL CONDITIONERSIn order to improve the structure or drainage characteristics of a soil, the followingmaterials may be added. These amendments should only be necessary where soils havelimitations that make them poor for plant growth or for fine turf establishment.

A. Peat - Appropriate types are sphagnum moss peat, hypnum moss peat, reedsedgepeat, or peat humus, all from freshwater sources. Peat should be shredded andconditioned in storage piles for at least 6 months after excavation.

B. Sand - clean and free of toxic materials.

C. Vermiculite - horticultural grade and free of toxic substances.

D. Rotted manure - stable or cattle manure not containing undue amounts of straw orother bedding materials.

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3. MATERIAL3.1 Purity and Germination: The following percentages are the minimum requirements in

the acceptance of seed as per Missouri Seed Law Requirements.

Grass Purity Germination

Kentucky Bluegrass 90% 75%

Perennial Rye Grass 95% 90%

Tall Fescue 95% 85%

3.2 Mix I: Sunny locations with slopes less than ten percent (10%).

Turf Type Rye Grass: One of the following at 20% by volume.Derby Palmer PreludeManhattan Manhattan II PremierPen Fine Turf Star Regal

Blue Grass: Three of the following to total 80% by volume.Barron Adelphi TouchdownMerit Parade GladeRam I Rugby

For shady sites use Glade at 60% by volume plus 20% of one of the others.

3.3 Mix II: On sunny slopes steeper than 10%, use one of the following at 90% per volumeplus one Blue Grass from above at 10%. For shady slopes use Glade Blue Grass at 10%with one of the following:

Turf Type Fescue:Rebel Rebel II ApacheOlympic Falcon HoundogBonanza Trident

3.4 Seeding Rate:

3.4.1 Mix I: Apply the Rye Grass/Blue Grass mix at 100 lbs. of mix per acre.

3.4.2 Mix II: Apply the Tall Fescue/Blue Grass mix at195 lbs. per acre.

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4. SEEDBED PREPARATIONInstall necessary mechanical erosion and sedimentation control practices before seeding,and complete grading according to the approved plan.

Lime and fertilizer needs should be determined by soil tests. When soil tests are notavailable, the following application rates may be used:

a) Ground agricultural limestone applied at a rate of 2 tons/acre.

b) A 10-10-10 grade of fertilizer or equivalent applied at a rate of 800-1200 lbs/acre.

Apply the lime and fertilizer evenly and incorporate into the top 4-6 inches of soil bydiscing or other suitable means.

Complete seedbed preparation by breaking up large clods and raking into a smooth,uniform surface (slopes less than 3:1). Fill in or level depressions that can collect water.Broadcast seed into a freshly loosened seedbed that has not been sealed by rainfall.

5. SEEDINGAll seeding shall be performed during favorable weather conditions and only duringnormal and accepted planting seasons when satisfactory growing conditions exist. Theplanting operations shall not be performed during times of extreme drought, when groundis frozen or during times of other unfavorable climatic conditions unless otherwiseapproved by owner’s representative. The contractor assumes full and completeresponsibility for all such plantings and operations.

Seed should be labeled in accordance with U.S. Department of Agriculture Rules andRegulations under the Federal Seed Act and comply with the requirements of theMissouri ‘Seed Law. Labels contain important information on seed purity, germination,and presence of weeds. Weed seed should not exceed 1.0% by weight of the mixture.

Inoculate legume seed with the Rhizobium bacteria appropriate to the species of legume.

Apply seed uniformly with a cyclone seeder, drop-type spreader, drill, cultipacker seeder,or hydroseeder on a firm, friable seedbed.

When using a drill or cultipacker seeder, plant small grains no more than 1 inch deep,grasses and legumes no more than 1/2 inch. Equipment should be calibrated in the fieldfor the desired seeding rate.

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When using broadcast-seeding methods, subdivide the area into workable sections anddetermine the amount of seed needed for each section. Apply one-half the seed whilemoving back and forth across the area, making a uniform pattern; then apply the secondhalf in the same way, but moving at right angles to the first pass.

Cover broadcast seed by raking or chain dragging; then firm the surface with a roller orcultipacker to provide good seed contact.

Mulch all plantings immediately after seeding as per Practice10.03.2.3 - Mulching.

6. HYDROSEEDINGSurface roughening is particularly important when hydroseeding, as a roughened slopewill provide some natural coverage for lime, fertilizer, and seed. The surface should notbe compacted or smooth. Fine seedbed preparation is not necessary for hydroseedingoperations; large clods, stones, and irregularities provide cavities in which seeds canlodge.

Rate of wood fiber (cellulose) application should be at least 2,000 lb/acre.

Apply legume inoculants at four times the recommended rate when adding inoculant to ahydroseeder slurry.

If a machinery breakdown of 1/2 to 2 hours occurs, add 50% more seed to the tank, basedon the proportion of the slurry remaining. This should compensate for damage to seed.Beyond 2 hours, a full rate of new seed may be necessary.

Lime is not normally applied with a hydraulic seeder because it is abrasive. It can beblown onto steep slopes in dry form.

7. IRRIGATIONMoisture is essential for seed germination and seedling establishment. Supplementalirrigation can be very helpful in assuring adequate stands in dry seasons or to speeddevelopment of full cover. It is a requirement for fine turf establishment and should beused elsewhere when feasible. However, irrigation is rarely critical for low-maintenancevegetation planted at the appropriate time of the year.

Water application rates must be carefully controlled to prevent runoff. Inadequate orexcessive amounts of water can be more harmful than no supplemental water.

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Maintenance

Generally, a stand of vegetation cannot be determined to be fully established until soil cover hasbeen maintained for one full year from planting. Inspect seeded areas for failure and makenecessary repairs and reseedings within the same season, if possible.

Reseeding - If a stand has inadequate cover, re-evaluate choice of plant materials and quantities oflime and fertilizer. Reestablish the stand after seedbed preparation or over-seed the stand. Considerseeding temporary, annual species if the time of year is not appropriate for permanent seeding.

If vegetation fails to grow, soil must be tested to determine if acidity or nutrient imbalance isresponsible.

Fertilization - On the typical disturbed site, full establishment usually requires refertilization in thesecond growing season. Fine turf requires annual maintenance fertilization.

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10.03.2.3 - MULCHING

Definition

Application of a protective blanket of straw or other plant residue, or synthetic material to thesoil surface.

Purpose

To protect the soil surface from the forces of raindrop impact and overland flow. Mulch fostersthe growth of vegetation, reduces evaporation, insulates the soil, and suppresses weed growth.Mulch is frequently used to accent landscape plantings.


Mulch temporary or permanent seedings immediately. Areas that cannot be seeded because ofthe season should be mulched to provide temporary protection of the soil surface. Use an organicmulch in this case (but not wood fiber), and seed the area as soon as possible. Mulch aroundplantings of trees, shrubs, or ground covers to stabilize the soil between plants.


A surface mulch is the most effective, practical means of controlling runoff and erosion ondisturbed land prior to vegetation establishment. Mulch reduces soil moisture loss byevaporation, prevents crusting and sealing of the soil surface, moderates soil temperatures,provides a suitable microclimate for seed germination, and may increase the infiltration rate ofthe soil.

Organic mulches such as straw, wood chips, and shredded bark have been found to be the mosteffective. Do not use materials which may be sources of competing weed and grass seeds.Decomposition of some wood products can tie up significant amounts of soil nitrogen, making itnecessary to modify fertilization rates or add fertilizer with the mulch.

A variety of mats and fabrics have been developed in recent years for use as mulch, particularlyin critical areas such as waterways and channels. Various types of netting materials are alsoavailable to anchor organic mulches.

The choice of materials for mulching should be based on soil conditions, season, type ofvegetation, and size of the area. A properly applied and tacked mulch is always beneficial. It isespecially important when conditions for germination are not optimum, such as midsummer andearly winter, and on difficult areas such as cut slopes and slopes with southern exposures.

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1. ORGANIC MULCHESStraw is the mulch most commonly used in conjunction with seeding. The straw shouldcome from wheat or oats (“small grains”), and may be spread by hand or with a mulchblower. Straw may be lost to wind and must be tacked down.

Wood chips are suitable for areas that will not be closely mowed, and around ornamentalplantings. Chips do not require tacking. Because they decompose slowly they must betreated with 12 pounds of nitrogen per ton to prevent nutrient deficiency in plants. Thiscan be inexpensive mulch if chips are obtained from trees cleared on the site.

Bark chips and shredded bark are by-products of timber processing often used inlandscape plantings. Bark is also a suitable mulch for areas planted to grasses and notclosely mowed. It may be applied by hand or with a mulch blower. Unlike wood chips,the use of bark does not require additional nitrogen fertilizer.

Wood fiber refers to short cellulose fibers applied as a slurry in hydroseeding operations.Wood fiber does not require tacking, although tacking agents or soil binders can easily beadded to the slurry. Wood fiber hydroseeder slurries may be used to tack straw mulch onsteep slopes, critical areas, and where harsh climatic conditions exist. Wood fiber mulchdoes not provide sufficient erosion protection to be used alone.

2. NETS AND MATSNetting is very effective in holding mulch in place on waterways and slopes beforegrasses become established.

Mats promote seedling growth in the same way as organic mulches. They are very usefulin establishing grass in channels and waterways. A wide variety of synthetic and organicmaterials are available. “Excelsior” is a wood fiber mat, and should not be confused withwood fiber slurry.

When installing nets and mats, it is critical to obtain a firm, continuous contact betweenthe material and the soil. Without such contact, the material is useless and erosion willoccur underneath.


Select a material based on site and practice requirements, availability of material, and availabilityof labor and equipment.

Before mulching, complete the required grading, install sediment control practices, and prepare

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the seedbed. Apply seed before mulching except in the following cases:

a) Seed is applied as part of a hydroseeder slurry containing wood fiber mulch.

b) A hydroseeder slurry is applied over straw.

1. APPLICATION OF ORGANIC MULCHOrganic mulches are effective where they can be tacked securely to the surface.

Spread mulch uniformly, by hand or with a mulch blower. When spreading straw mulchby hand, divide the area to be mulched into sections of approximately 1,000 ft2 and place70-90 lb of straw (1-1/2 to 2 bales) in each section to facilitate uniform distribution. Afterspreading mulch, no more than 25% of the ground surface should be visible. Inhydroseeding operations a green dye, added to the slurry, assures a uniform application.

2. ANCHORING ORGANIC MULCHStraw mulch must be anchored immediately after spreading. The following methods ofanchoring mulch may be used:

a) Mulch anchoring tool - A tractor-drawn implement designed to punch mulch intothe soil, a mulch anchoring tool provides maximum erosion control with straw. Aregular farm disc, weighted and set nearly straight, may substitute, but will not doa job comparable to the mulch anchoring tool. The disc should not be sharpenough to cut the straw. These methods are limited to slopes no steeper than 3:1,where equipment can operate safely. Operate machinery on the contour.

b) Liquid mulch binders - Application of liquid mulch binders and tackifiers shouldbe heaviest at the edges of areas and at crests of ridges and banks, to resist wind.Binder should be applied uniformly to the rest of the area. Binders may be appliedafter mulch is spread or may be sprayed into the mulch as it is being blown ontothe soil. Applying straw and binder together is the most effective method. Liquidbinders shall be an overspray material consisting of virgin wood cellulose fibersor recycled slick paper. The overspray shall be green in color after application andshall have the property to be evenly dispersed and suspended when agitated inwater. When sprayed uniformly over vegetative mulch, the mulch fibers shallform an absorbent cover, allowing percolation of water to the underlying soil. Themulch fibers shall not be water soluble.

Emulsified asphalt or synthetic binders which may have

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negative impacts on the environment, may not be used as mulch binders.

c) Mulch nettings - Lightweight plastic, cotton, jute, wire, or paper nets may bestapled over the mulch according to the manufacturer’s recommendations (see“Nets and Mats” below).

d) Peg and twine - Because it is labor-intensive, this method is feasible only in smallareas where other methods cannot be used. Drive 8-10 inch wooden pegs towithin 3 inches of the soil surface, every 4 ft in all directions. Stakes may bedriven before or after straw is spread. Secure mulch by stretching twine betweenpegs in a criss-cross-within-a-square pattern. Turn twine two or more timesaround each peg. Twine may be tightened over the mulch by driving pegs furtherinto the ground.

e) Vegetation - Rye (grain) may be used to anchor mulch in fall plantings, andGerman millet in spring. Broadcast at 15 lb/acre before applying mulch.

3. NETS AND MATSNets alone generally provide little moisture conservation benefits and only limitederosion protection. Therefore, they are usually used in conjunction with an organic mulchsuch as straw.

Except when wood fiber slurry is used, netting should always be installed over the mulch.Wood fiber may be sprayed on top of an installed net.

Mats, including “excelsior” (wood fiber) blankets, are considered protective mulches andmay be used alone, on erodible soils, and during all times of the year. Place the matting infirm contact with the soil and staple securely.

4. INSTALLATION OF NETTING AND MATTINGProducts designed to control erosion should be installed in accordance withmanufacturer’s instructions. Any mat or blanket-type product used as a protective mulchshould provide cover of at least 30% of the surface where it is applied.

a) Apply lime, fertilizer and seed before laying the net or mat. If open-weave nettingis used, lime may be incorporated before installing the net and fertilizer and seedsprayed on afterward.

b) Start laying the net from the top of the channel or slope and unroll it down thegrade. Allow netting to lay loosely on the soil but without wrinkles - do notstretch.

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c) To secure the net, bury the upslope end in a slot or trench no less than 6 inchesdeep, cover with soil, and tamp firmly. Staple the net every 12 inches across thetop end and every 3 ft around the edges and bottom. Where 2 strips of net are laidside by side, the adjacent edges should be overlapped 3 inches and stapledtogether. Each strip of netting should also be stapled down the center, every 3 ft.Do not stretch the net when applying staples.

d) To join two strips, cut a trench to anchor the end of the new net. Overlap the endof the previous roll 18 inches, and staple every 12 inches just below the anchorslot.

Maintenance

Inspect all mulches periodically, and after rainstorms to check for rill erosion, dislocation, orfailure. Where erosion is observed, apply additional mulch. If washout occurs, repair the slopegrade, reseed, and reinstall mulch. Continue inspections until vegetation is firmly established.

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10.03.2.4. - SODDING

Definition

Permanently stabilizing areas by laying a continuous cover of grass sod.

Purpose

To prevent erosion and damage from sediment and runoff by stabilizing the soil surface withpermanent vegetation where specific goals might be:

a) to provide immediate vegetative cover of critical areas,

b) to stabilize disturbed areas with a suitable plant material that cannot beestablished by seed,

c) to stabilize drainageways and channels and other areas of concentrated flowwhere flow velocities will not exceed that specified for a grass lining.


Disturbed areas which require immediate and permanent vegetative cover, or where sodding ispreferred to other means of grass establishment. Locations particularly suited to stabilizationwith sod are:

a) waterways and channels carrying intermittent flow at acceptable velocities,

b) areas around drop inlets, when the drainage area has been stabilized,

c) residential or commercial lawns and golf courses where prompt use and aestheticsare important, and

d) steep critical areas.


Quality turf can be established with either seed or sod; site preparation for the two methods issimilar. The practice of sodding for soil stabilization eliminates both the seeding and mulchingoperations and is a much more reliable method of producing adequate cover and sedimentcontrol. However, compared to seed, sod is more difficult to obtain, transport, and store.

Advantages of properly installed sod include:

a) immediate erosion and dust control,

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b) nearly year-round establishment capability.

c) less chance of failure than with seedings,

d) freedom from weeds,

e) rapid stabilization of surfaces for traffic areas, channel linings, or critical areas.

Sod can be laid during times of the year when seeded grasses may fail, provided there is adequatewater available for irrigation in the early weeks. Irrigation is essential, at all times of the year, toinstall sod. It is initially more costly to install sod than to plant seed. However, the higher costmay be justified for specific applications where sod performs better than seed.

In waterways and channels that carry concentrated flow, properly pegged sod is preferable toseed because it provides immediate protection. Drop inlets placed in areas to be grassed can beprotected from sediment by placing permanent sod strips around the inlet. Sod also maintains thenecessary grade around the inlet.

Because sod is composed of living plants that must receive adequate care, final grading and soilpreparation should be completed before sod is delivered. If left rolled or stacked, heat can buildup inside the sod, causing severe damage and loss of costly plant material.

Specifications

1. Types of Sod - The type of sod selected should be composed of plants adapted to both thesite and the intended purpose. The sod should be Kentucky Bluegrass, bluegrass-tallfescue blends or zoysia grass.

2. Quality of Sod - Use only high-quality sod known of genetic origin, free of noxiousweeds, disease, and insect problems. It should appear healthy and vigorous, and conformto the following specifications:

a) Sod should be machine cut at a uniform depth of 1/2 — 2 inches (excluding shootgrowth and thatch).

b) Sod should not have been cut in excessively wet or dry weather.

c) Sections of sod should be a standard size as determined by the supplier, uniform,and untorn.

d) Sections of sod should be strong enough to support their own weight and retaintheir size and shape when lifted by one end.

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e) Harvest, delivery, and installation of sod should take place within a period of 36hours.

3. Soil Preparation - Soil tests should be conducted to determine the exact requirements forlime and fertilizer. Where sodding must be planned without soil tests the following soilamendments may be sufficient:

a) Pulverized agricultural limestone at a rate of 2 tons/acre (100 lb/ 1,000 ft2).

b) Fertilizer at a rate of 1,000 lb/acre (25 lb/l,000 ft2) of 10-10-10 in fall or 5-10-10in spring.

Equivalent nutrients may be applied with other fertilizer formulations. These amendments shouldbe spread evenly over the area and incorporated into the top 4-8 inches of soil by discing,harrowing, or other effective means. If topsoil is applied, follow specifications given in Practice10.03.1.3 - Topsoiling.

Prior to laying sod, clear the soil surface of trash, debris, roots, branches, stones, and clods largerthan 2 inches in diameter. Fill or level low spots in order to avoid standing water. Rake or harrowthe site to achieve a smooth and level final grade.

Complete soil preparation by rolling or cultipacking to firm the soil. Avoid using heavyequipment on the area, particularly when the soil is wet, as this may cause excessive compactionand make it difficult for the sod to take root.

Sod Installation

Following is a step-by-step procedure for installing sod.

1. Moistening the sod after it is unrolled helps maintain its viability. Store it in the shadeduring installation.

2. Rake the soil surface to break the crust just before laying sod. During the summer, lightlyirrigate the soil, immediately before laying the sod to cool the soil and reduce rootburning and dieback.

3. Do not sod on gravel, frozen soils, or soils that have been treated recently with sterilantsor herbicides.

4. Lay the first row of sod in a straight line with subsequent rows placed parallel to andbutting tightly against each other. Stagger strips in a brick-like pattern. Be sure that thesod is not stretched or overlapped and that all joints are butted tightly to prevent voids.Use a knife or sharp spade

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to trim and fit irregularly shaped areas.

5. Install strips of sod with their longest dimension perpendicular to the slope. On slopes 3:1or greater, or wherever erosion may be a problem, secure sod with pegs or staples.

6. As sodding of clearly defined areas is completed, roll sod to provide firm contact betweenroots and soil.

7. After rolling, irrigate until the soil is wet 4 inches below the sod.

8. Keep sodded areas moist to a depth of 4 inches until the grass takes root. This can bedetermined by gently tugging on the sod - resistance indicates that rooting has occurred.

9. Mowing should not be attempted until the sod is firmly rooted, usually 2-3 weeks.

Sod Installation in Waterways

Sod provides a resilient channel lining, providing immediate protection from concentrated runoffand eliminating the need for installing mats or mulch. The following points apply to the use ofsod in waterways:

1. Prepare the soil as described in Practice 10.03.4.1, Grass-lined Channels. The sod typemust be able to withstand the velocity of flow specified in the channel design.

2. Lay sod strips perpendicular to the direction of flow, with the lateral joints staggered in abrick-like pattern. Edges should butt tightly together.

3. After rolling or tamping to create a firm contact, peg or staple individual sod strips toresist washout during establishment. Jute or other netting material may be pegged overthe sod for extra protection on critical areas.

Maintenance

After the first week, water as necessary to maintain adequate moisture in the root zone andprevent dormancy of the sod.

Do not remove more than one-third of the shoot in any mowing. Grass height should bemaintained between 2 and 3 inches unless otherwise specified.

After the first growing season, established sod requires fertilization and may also require lime.Follow soil test recommendations when possible, or use the rates previously stated.

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10.03.2.5 - TREES, SHRUBS, VINES AND GROUND COVERS

Definition

Stabilizing disturbed areas by establishing a vegetative cover of trees, shrubs, vines, or groundcovers.

Purpose

To stabilize the soil with vegetation other than grasses or legumes, to provide food and shelterfor wildlife, and to provide windbreaks or screens.


Trees, shrubs, vines and ground covers may be used on steep or rocky slopes where mowing isnot feasible; as ornamentals for landscaping purposes; or in shaded areas where grassestablishment is difficult.


Woody plants and ground covers provide alternatives to grasses and legumes as low-maintenance, long-term erosion control. However they are normally planted only for special,high-value applications, or for aesthetic reasons, because there is additional cost and laborassociated with their use.

Very few of these plants can be dependable planted from seed, and none of them is capable ofproviding the rapid cover possible with grasses. Trees and shrubs in particular require a long timeto produce cover adequate to control erosion. Consequently, efforts must first focus on short-term stabilization using densely-growing herbaceous species or a dependable mulch.

There are many different species of woody plants and ground covers from which to choose. Mostare not as broadly adapted as herbaceous species, and care must be taken in their selection. It isessential to select planting material suited to both the intended use and site.

1. TREESAlthough trees are among the best soil stabilizers, years are required for the developmentof forest cover adequate to meet sedimentation control objectives. Efforts must first focuson establishing densely-growing species to stabilize the site and protect the area betweenimmature trees.

For areas in which tree or shrub plantings are planned, initial seedings of grasses andlegumes may need to be altered somewhat to reduce competition with the woody species.Unless the site is highly erodible, seeding rates may be reduced or

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competitive species omitted.

Two alternative approaches to establishing tree cover on disturbed sites are: (1) plantingseedlings of the desired species, usually at the earliest suitable date, or (2) allowingnatural invasion by native species.

Planting speeds tree establishment, ensures adequate stands, and allows selection ofspecies composition. Where forest production is the objective, planting is preferable tonatural invasion. Where invasion is acceptable, tree planting is not necessary if there is aseed source near the site.

2. SHRUBSShrubs vary in form from small trees to sprawling, woody ground covers. They differfrom most trees in that several small trunks arise from a common base.

As a supplement to herbaceous plantings shrubs can be used to:

a) increase the aesthetic value of plantings,

b) provide screening,

c) enhance windbreaks,

d) provide food and cover for wildlife,

e) accelerate the transition to a diverse landscape.

f) provide post-construction landscaping.

3. GROUND COVERSAs used by landscapers, “ground cover” refers to low-growing, herbaceous or woodyplants that spread vegetatively to produce a dense, continuous cover. They are used inlandscape plantings or as an alternative to turf. Typically only a few ornamental grassesare included in this category. Many ground covers, such as English ivy, are vines thatspread along the ground but also climb on buildings, fences, or other vegetation.

Ground covers differ in growth form, growth rate, and shade tolerance. They may beevergreen or deciduous. Some are suitable only as part of a high-maintenance landscape;others can be used to stabilize large areas with little maintenance.

In addition to stabilizing disturbed soil, vines and ground covers perform the followingfunctions:

a) They maintain cover in heavily shaded areas where turf will not thrive.

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b) They provide attractive cover that does not need mowing.

c) They restrict pedestrian traffic (people are likely to avoid walking through a thickbed of ivy or a planting of juniper).

Specifications

Areas planted to shrubs or trees must also be covered with a suitable mulch, or seeded topermanent vegetation, to protect the site until the woody plants become established. Do not useplants that will shade-out the woody seedlings. A circle of mulch around seedlings helps themcompete with herbaceous plants.

1. TREESA. Sources - Trees can be dug on-site with a tree spade, or purchased from a nursery.

Large trees come with their roots and the attached soil wrapped in burlap, andsmall trees and shrubs are sold in plastic containers or as bare-root stock. The soilball of containerized and burlapped trees should be 12 inches in diameter for eachinch of trunk diameter.

B. Planting bare-root tree seedlings - Bare-root seedlings should be planted whiledormant in late winter, early spring or after leaf fall in autumn.

Do not allow roots to dry out during planting by carrying seedlings exposed to airand sun. Keep moss-packed seedlings in a container packed with wet moss orfilled with thick muddy water. Cover clay-treated seedlings with wet burlap.

With a tree planting bar or spade, make a notch deep enough to accommodate theroots. Place the roots in the notch to the same depth as in the nursery, then firmsoil around roots by pressing the notch closed. Water immediately and mulch thearea within 2 ft of the plant. Several weeks after planting, broadcast a handful of10-10-10 fertilizer around each plant, at least 1 ft from the base.

C. Planting balled-and-burlapped or container-grown trees -Late fall (Nov. -Dec.) isthe preferred planting time for deciduous trees and evergreens, although they maybe planted year-round. Avoid summer planting.

Keep the soil around the roots moist until planting. Branches should be boundwith soft rope to prevent damage during transport.

Each planting hole must be deep and wide enough to allow

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proper placement of the root ball. Ideally, the hole should be twice the size of theroot ball. When digging the hole, keep topsoil separate from subsoil. If the subsoilis high in clay, allow extra room (one— half again the height of the root ball).Backfill the hole with enough topsoil or peat moss to position the base of the treeat the same level as in the nursery.

If the plant is in a container, carefully remove it, taking the soil surrounding theroots with it. This may require cutting the container. Loosen the twine and burlapat the top of balled-and-burlapped plants and check to make sure that no otherwrapping is present before planting.

Before replacing subsoil, mix it with one-third peat moss or well-rotted manure.Backfill the hole, firming the soil as it is replaced, and leave a depression aroundthe trunk within the excavated area to hold water. Cover the base of the trunk tothe same level as before it was removed. Water thoroughly and rewater asnecessary to keep the roots moist.

Stake small trees with vertical stakes driven into the ground, just beyond the rootball. Secure large trees with guy wires. Cushion wire, where it contacts the tree,with rubber hose. Wrap the trunks of young trees to protect them from sunburnand pests.

Fertilize trees in late fall or early spring, before leaves emerge. Using a punchbar,crowbar, or auger, make holes 18 inches deep and about 2 ft apart around the dripline of each tree. Distribute the fertilizer evenly among the holes to bring it incontact with tree roots, and close.

2. SHRUBSA. Selecting shrubs - The best shrubs for erosion control have characteristics such as

fast growth, ease of establishment, large lateral spread or prostrate growth, year-round foliage (evergreens), disease and insect resistance, ability of the roots to fixnitrogen, and adaptation to a broad range of soil conditions. Selections should bebased on a specific site and purpose.

B. Obtaining shrubs - Shrubs are normally planted as bareroot stock or container-grown plants. Container— grown seedlings, 1 yr. old, are usually recommendedfor their ease of planting and cost.

Planting is best done in early fall or early spring. Follow the general proceduresfor tree care and planting.

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C. Maintenance requirements depend on the particular shrub. In all cases watering isimportant in getting plants established. Once established, fertilizing every 3 yearsis generally sufficient. A heavy layer of mulch around the base of each plantreduces weeds and retains moisture. Mulch may consist of woodchips, sawdust,pine needles, or straw.

3. VINES AND GROUND COVERSA. Selecting plants - For most stabilization purposes, fast-growing, evergreen, low-

maintenance ground covers are preferable.

B. When to plant - Ground covers are best planted in early fall or early spring.

C. Site preparation - Good soil is important in establishing ground covers becausetheir dense growth requires large amounts of nutrients and water. Well-drainedsoils high in organic matter work best. When possible, apply organic matter in theform of peat, sawdust, or well-rotted manure, and incorporate to 4-6 inches.

Add lime and fertilizer according to soil tests, or add 100 lb/l000 ft2 groundagricultural limestone, and 50 lb/l000 ft2 of 10-10-10 fertilizer and incorporateinto the top 4-6 inches of soil. Add organic matter in an amount up to one-thirdthe total soil volume, either over the whole area (a layer 2 inches deep mixed intothe top 6 inches) or in each planting hole if the area is large.

On steep slopes, till the soil in contour rows, or dig single holes for each plant.Blend the needed lime, fertilizer, and organic material with the soil removed fromeach hole or furrow. Mix fertilizer thoroughly with the soil before planting, anduse it sparingly to avoid burning roots.

To eliminate harmful competition from weeds, a preemergent herbicide may beuseful if weeding is not practical.

D. Planting - Most ground covers are planted from container grown nursery stock.Planting density determines how quickly full cover is achieved; a 1-ft spacing isoften suggested for rapid cover. Large plants such as junipers can be spaced on 3-ft centers.

Transplanting to the prepared seedbed can be done using a small trowel or aspade. Make a hole large enough to accommodate the roots and soil. Backfill andfirm the

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soil around the plant, water immediately, and keep well watered until established.

E. Mulching - Competition from volunteer plants inhibits development andmaintenance of the ground cover. A thick durable mulch such as shredded bark orwood chips should prevent erosion and reduce weeds. Mulch the entire plantingarea.

On steep slopes (3:1) or highly erodible soils, install netting or matting prior toplanting, and tuck plants into the soil through slits in the net. Plant in a staggeredpattern.

F. Maintenance - Most ground covers need yearly trimming to promote growth. Trimback from trees, flower beds, fences, and buildings. Add mulch where needed andfertilize as described above every 3-4 years.

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10.03.2.6 - RIPRAP

Definition

A layer of stone designed to protect and stabilize areas subject to erosion.

Purpose

To protect the soil surface from erosive forces and/or improve stability of soil slopes that aresubject to seepage or have poor soil structure.


Riprap is used for the following applications:

a) cut-and-fill slopes subject to seepage or weathering, particularly where conditionsprohibit establishment of vegetation,

b) channel side slopes and bottoms,

c) inlets and outlets for culverts, bridges, slope drains, grade stabilization structures,and storm drains,

d) streambank and stream guides,

e) shorelines subject to wave action.


Riprap is a versatile, highly erosion-resistant material that can be used effectively in manylocations and in a variety of ways to control erosion on construction sites.

When considering riprap for surface stabilization, it is important to anticipate visual impacts,including weed control, hazards from snakes and other animals, danger of slides and hazards toareas below steep riprap slopes, damage and possible slides from children moving stones, andgeneral safety.

Proper slope selection and surface preparation are essential for successful long-term functioningof riprap. Adequate compaction of fill areas and proper use of filter blankets are necessary.

Schedule disturbance of areas that require riprap protection so the placement of riprap can followimmediately after grading. When riprap is used for outlet protection, place the riprap before or inconjunction with the installation of the structure so that it is in place before the first runoff event.

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Design Criteria

1. Materials - Material for riprap may consist of field stone or quarry stone. The stoneshould be hard, angular, of such a quality that it will not break down on exposure to wateror weathering, and suitable in all other respects for the purpose intended.

Deleterious substances which include soft friable particles, objectionable materials, andother foreign matter shall not exceed 10 percent by weight of riprap.

2. Gradation - Riprap materials shall be graded within the following limits:Weight per Stone Percent of Total

in Pounds Weight Lighter Than350 10040 10-20

Not more than 5 percent shall pass the 2-inch sieve.

3. Elongation - Stone to be used as riprap shall be approximately rectangular in crosssection and relatively free from thin slabby pieces having an elongation ratio as definedhereinafter greater than 3. In no case shall the quantity of stone having an elongation ratiogreater than 3 exceed 10 percent by weight on any one load. For elongation testing thelength of a stone is defined as the longest dimension in any direction. The thickness isdefined as the shortest dimension measured perpendicular to the line established as thelength and within the middle two quarter segments of that line. Elongation ratio is definedas the length divided by the thickness. Whenever there is reason to suspect that materialsdo not meet specified requirements, additional tests shall be performed as directed by thecity inspector.

4. Thickness - Construction techniques, dimensions of the area to be protected, size andgradation of the riprap, the frequency and duration of flow, difficulty and cost ofmaintenance, and consequence of failure should be considered when determining thethickness of riprap linings. The minimum thickness should be 1.5 times the maximumstone diameter, but in no case less than 15 inches.

5. Filter blanket - A filter blanket is a layer of material placed between the riprap and theunderlying soil to prevent soil movement into or through the riprap. A suitable filter mayconsist of a well-graded gravel or sand-gravel layer or a synthetic filter fabricmanufactured for this express purpose.

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A synthetic filter fabric may be used with or in place of gravel filters. The permeability ofthe fabric must be greater than that of the soil. The fabric may be made of woven ornonwoven monofilament yarns and should meet the following minimum requirements:

• thickness 20-60 mils,

• grab strength 90-120 lb,

• conform to ASTM D-1682 or ASTM D-177.

Filter blankets should always be provided where seepage is significant or where flowvelocity and duration of flow or turbulence may cause the underlying soil particles tomove through the riprap.


1. Subgrade preparation - Prepare the subgrade for riprap and filter to the required lines andgrades shown on the plans. Compact any fill required in the subgrade to a densityapproximating that of the surrounding undisturbed material or overfill depressions withriprap. Remove brush, trees, stumps, and other objectionable material. Cut the subgradesufficiently deep that the finished grade of the riprap will be at the elevation of thesurrounding area. Channels should be excavated sufficiently to allow placement of theriprap in a manner such that the finished inside dimensions and grade of the riprap meetdesign specifications.

2. Sand and gravel filter blanket - Place the filter blanket immediately after the groundfoundation is prepared. For gravel, spread filter stone in a uniform layer to the specifieddepth. Where more than one layer of filter material is used, spread the layers withminimal mixing.

3. Synthetic filter fabric - Place the cloth filter directly on the prepared foundation. Overlapthe edges by at least 12 inches, and space anchor pins every 3 ft along the overlap. Burythe upper and lower ends of the cloth a minimum of 12 inches below ground. Take carenot to damage the cloth when placing riprap. If damage occurs remove the riprap andrepair the sheet by adding another layer of filter material with a minimum overlap of 12inches around the damaged area. If extensive damage is suspected, remove and replacethe entire sheet.

Where large stones are used or machine placement is difficult, a 4-inch layer of finegravel or sand may be needed to protect the filter cloth.

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4. Stone placement - Placement of riprap should follow immediately after placement of thefilter. Place riprap so that it forms a dense, well-graded mass of stone with a minimum ofvoids. The desired distribution of stones throughout the mass may be obtained byselective loading at the quarry and controlled dumping during final placement. Placeriprap to its full thickness in one operation. Do not place riprap by dumping throughchutes or other methods that cause segregation of stone sizes. Take care not to dislodgethe underlying base or filter when placing the stones.

The toe of the riprap slope should be keyed to a stable foundation at its base. The toeshould be excavated to a depth about 1.5 times the design thickness of the riprap andshould extend horizontally from the slope.

The finished slope should be free of pockets of small stone or clusters of large stones.Hand placing may be necessary to achieve the proper distribution of stone sizes toproduce a relatively smooth, uniform surface. The finished grade of the riprap shouldblend with the surrounding area. No overfall or protrusion of riprap should be apparent.

Maintenance

In general, once a riprap installation has been properly designed and installed it requires verylittle maintenance. Riprap should be inspected periodically for scour or dislodged stones. Controlof weed and brush growth may be needed in some locations.

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10.03.3 RUNOFF CONTROL MEASURES

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10.03.3.1 - Temporary Diversions Dike

Definition

A temporary ridge or excavated channel or combination ridge and channel constructed acrosssloping land on a predetermined grade until permanent soil erosion control is effective.

Purpose

To protect work areas from upslope runoff and to divert sediment laden water to appropriate trapsor stable outlets.


This practice applies to construction areas where runoff can be diverted and disposed of properlyto control erosion, sedimentation, or flood damage. Specific locations and conditions include:

a) applies for drainage areas five acres or less

b) above disturbed existing slopes, and above cut or fill slopes to prevent runoff overthe slope;

c) across unprotected slopes, as slope breaks, to reduce slope length;

d) below slopes to divert excess runoff to stabilized outlets;

e) where needed to divert sediment-laden water to sediment traps;

f) at or near the perimeter of the construction area to keep sediment from leaving thesite; especially upstream of public streets and municipal boundaries,

g) above disturbed areas before stabilization to prevent erosion and maintainacceptable working conditions.

h) temporary diversions may also serve as sediment traps when the site has beenoverexcavated on a flat grade; they may also be used in conjunction with asediment fence.


It is important that diversions are properly designed, constructed and maintained since theyconcentrate water flow and increase erosion potential (Figure 3.la). Particular care must be takenin planning diversion grades. Too much slope can result in erosive velocity in the diversionchannel or at the outlet. A change of

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slope from steeper grade to flatter may cause deposition to occur. The deposition reducescarrying capacity and may cause overtopping and failure. Frequent inspection and timelymaintenance are essential to the proper functioning of diversions.

Sufficient area must be available to construct and properly maintain diversions. It is usually lesscostly to excavate a channel and form a ridge or dike on the downhill side with the spoil than tobuild diversions by other methods. Where space is limited, it may be necessary to build the ridgeby hauling in diking material or using a silt fence to divert the flow. Use gravel to form thediversion dike where vehicles must cross frequently.

Diversions that are to serve longer than 30 working days should be seeded and mulched as soonas they are constructed to preserve dike height and reduce maintenance.

Temporary diversions may serve as in-place sediment traps if overexcavated 1 to 2 ft and placedon a nearly flat grade. The dike serves to divert water as the stage increases. A combination siltfence and channel in which fill from the channel is used to stabilize the fence can trap sedimentand divert runoff simultaneously.

Build and stabilize diversions and outlets before initiating land-disturbing activities.

Compacted soil

Figure 3.la - Temporary diversion dike.

Design Criteria for Drainage Areas Less than Five Acres

1. Capacity - peak runoff from a 10-year storm.

2. Velocity - Maximum Permissible Velocities in grass-lined channels shall be based oncommon engineering practices which produce non-erodible channels such as soilcharacteristics, height and type of grass, and frequency of maintenance of the grass.

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6’ typical

12”min

2’ min.

flow

3. Ridge design - side slope: 2:1 or flatter3:1 or flatter at pointswhere vehicles cross

top width: 2 ft minimumfreeboard: 0.3 ft minimum

4. Channel design - shape: parabolic, trapezoidal, orV-shaped

side slope: 2:1 or flatter3:1 or flatter wherevehicles cross

5. Grades - Either a uniform or a gradually increasing grade is preferred. Sudden decreasesin grade accumulate sediment and should be expected to cause overtopping. A largeincrease in grade may erode.

6. Outlet - Design the outlet to accept flow from the diversion plus any other contributingareas. Divert sediment-laden runoff and release through a sediment-trapping device. Flowfrom undisturbed areas can be dispersed by a level spreader.


1. Remove and properly dispose of all trees, brush, stumps, and other objectionable material.

2. Ensure that the minimum constructed cross-section meets all design requirements.

3. Ensure that the top of the dike is not lower at any point than the design elevation plus thespecified settlement.

4. Provide sufficient room around diversions to permit machine regrading and cleanout.

5. Vegetate the ridge immediately after construction, unless it will remain in place less than30 working days.

Maintenance

Inspect temporary diversions once a week and after every rainfall. Immediately remove sedimentfrom the flow area and repair the diversion ridge. Carefully check outlets and make timely repairsas needed. When the area protected is permanently stabilized, remove the ridge and the channelto blend with the natural ground level and appropriately stabilize it.

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10.03.3.2 - PERMANENT DIVERSION DIKE

Definition

A permanent ridge or channel or a combination ridge and channel constructed on a designedgrade across sloping land which are maintained after completion of all grading and earthdisturbance activities.

Purpose

To divert water from areas where it is in excess to locations where it can be used or releasedwithout erosion or flood damage.


This permanent site development practice applies to construction areas where runoff can bediverted and used or disposed of safely to prevent flood damage or erosion and sedimentationdamage. Specific locations and conditions include:

a) above steep slopes to limit surface runoff onto the slope;

b) across long slopes to reduce slope length to prevent gully erosion;

c) below steep grades where flooding, seepage problems, or sediment deposition mayoccur.

d) around buildings or areas that are subject to damage from runoff.

e) upstream of public streets and other municipalities. Planning Considerations

Permanent diversions should be planned as a part of initial site development. They are principallyrunoff control measures that subdivide the site into specific drainage areas. Permanent diversionscan be installed as temporary diversions until the site is stabilized then completed as a permanentmeasure, or they can be installed in final form during the initial construction operation. Theamount of sediment anticipated and the maintenance required as a result of constructionoperations will determine which approach should be used. Stabilize permanent diversions withvegetation or materials such as riprap, paving stone, or concrete as soon as possible afterinstallation. Base the location, type of stabilization, and diversion configuration on final siteconditions. Evaluate function, need, velocity control, outlet stability, and site aesthetics. Whenproperly located, land forms such as landscape islands, swales or ridges can be used effectively

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as permanent diversions. Base the capacity of a diversion on the runoff characteristics of the siteand the potential damage after development. Consider designing an emergency overflow sectionor bypass area to limit damage from storms that exceed the design storm. The overflow sectionmay be designed as a weir with riprap protection.

Design Criteria

1. Location - Determine the diversion locations by topography, development layout, soilconditions, outlet conditions, length of slope, seepage planes, and need for water andsediment storage.

2. Capacity - Ensure that permanent diversions have sufficient capacity to carry the peakrunoff expected from a storm frequency consistent with the desired level of protection, asshown in Table 3.2A.

TABLE 3.2AMINIMUM DESIGN STORM FOR DESIRED LEVEL OF PROTECTION

Level of Protection Area to Be Protected Minimum Design Storm

Low All erosion control facilities. 10 yr.Open areas, parking lots,minor recreation areas.

Medium Recreation development, low- 25 yr.capacity roads and minorstructures.

High Major structures, homes, main 100 yr.school buildings, high-capacityroads.

3. Velocity - Maximum Permissible Velocities shall be based on common engineeringpractices which produce non-erodible channels.

4. Ridge design - side slope: 2:1 or flatter3:1 or flatter whenmaintained by mowing

top width: 2 ft minimumfreeboard: 0.5 ft minimum

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5. Channel design - material: to meet velocityrequirements and siteaesthetics

shape: to fit site conditionsside slope: 2:1 or flatter

3:1 or flatter whenmaintained by mowing

6. Grades - Either a uniform or a gradually increasing grade is preferred.

7. Outlet - Design the outlet stable enough to accept flow from the diversion plus any othercontributing runoff. Divert sediment-laden runoff and release it through a sediment -trapping device.

8. Stabilization - Unless the area is otherwise stabilized, provide vegetative stabilizationafter installation of the diversion. Seed and mulch disturbed areas draining into thediversion within 30 working days of completing any phase of grading.


1. Remove and properly dispose of all trees, brush, stumps, or other objectionable material.Fill and compact all ditches, swales, or gullies that will be crossed to natural ground levelor above.

2. Just before placement of fill, the base of the ridge should be disced by machinery.

3. Excavate, shape, and stabilize the diversion to line, grade, and cross section, as requiredin the design plan.

4. Compact the ridge to prevent unequal settlement and to provide stability against seepage.

5. Vegetatively stabilize the diversion after its installation.

Maintenance

Inspect permanent diversions after every rainfall during the construction operation. Immediatelyremove any obstructions from the flow area and repair the diversion ridge. Check outlets andmake timely repairs as needed. Maintain the vegetation in a vigorous, healthy condition at alltimes.

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10.03.3.3 - RIGHT-OF-WAY DIVERSION

Definition

A ridge of compacted soil or gravel, to remain for a period usually less than one year, constructedacross disturbed rights-of-way and similar sloping areas.

Purposes

To shorten the length of exposed slopes, thereby reducing the potential for erosion byintercepting storm runoff and diverting it to stabilized outlets.


Constructed across disturbed rights-of-way and similar sloping areas, until they are permanentlystabilized.

Design Criteria

The following criteria will be used:

1. Top width - 2-foot minimum

2. Height -18-inch minimum unless otherwise noted on the plans (height measured from theupslope toe to top of the dike).

3. Side slopes - 2:1 or flatter (flat enough to allow construction traffic to cross if desired).

4. Grade - Not to exceed 2%.

5. Spacing - Slope: >10% 5%-10% <5%Spacing: 150 ft. 200 ft. 300 ft.

6. Outlet - Diversions should have stable outlets, either natural or constructed. Site spacingmay need to be adjusted for field conditions to use the most suitable areas for waterdisposal.


1. Install the diversion as soon as the right-of-way has been cleared and graded.

2. Disc the base for the constructed ridge before placing fill.

3. Track the ridge to compact it to the design cross section.

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4. Locate the outlet on an undisturbed area. Adjust field spacing of the diversion to use themost stable outlet areas. When natural areas are not deemed satisfactory, provide outletprotection.

5. Immediately seed and mulch the portions of the diversions not subject to constructiontraffic. An adequately sized culvert and backfill will be required at all vehicle crossings.

Maintenance

Periodically inspect the right-of-way diversions for wear and after every heavy rainfall forerosion damage. Immediately remove sediment from the flow area and repair the dike. Checkoutlet areas and make timely repairs as needed. When permanent road drainage is establishedand the area above the temporary right-of-way diversions is permanently stabilized, remove thedike and fill the channel to blend with the natural ground, and appropriately stabilize thedisturbed area.

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10.03.3.4 - TEMPORARY PERIMETER DIKE

Definition

A dike or dike and channel constructed along the perimeter of a disturbed construction area.

Purpose

To prevent storm runoff from entering the work area or to prevent sediment-laden runoff fromleaving the construction site.


Perimeter dikes may be located at the upslope side of a construction site to prevent surfacerunoff from entering the disturbed area or at the downslope side of the work area to divertsediment-laden runoff to on-site sediment traps or basins. Perimeter dikes do not usually encirclethe entire area.

The upslope dike can improve working conditions at the construction site and prevent erosion.The downslope dike assures that sediment-laden runoff will not leave the site without treatment.


A perimeter dike is a special application of a temporary or permanent diversion. It differs fromother diversions in that the location and grade are usually fixed, and the cross section andstabilization requirements are based on the existing grade of the work boundary. Hence, thedesign cross section may vary significantly throughout the length. Give special care to avoiderosive velocities in steep areas. Identify areas where sedimentation will occur since they areoften subject to overtopping.

Immediately vegetate diversion dikes after construction, but make sure channel flow area isstabilized during construction. Exercise caution in diverting flow to be certain that the divertedwater is released through a stable outlet and that the flow will not cause flood damage.

Design Criteria

1. Drainage area - 5 acres or less.

2. Capacity - consistent with the hazard involved and design life and with a 10 yr. peakrunoff minimum.

3. Velocity - Maximum Permissible Velocities in grass-lined channels shall be based oncommon engineering practices which produce non-erodible channels such as soilcharacteristics,

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height and type of grass, and frequency of maintenance of the grass.

4. Dike design - side slope: 2:1 or flatter3:1 or flatter where

vehicles must crosswidth: 2.0 ft minimum top widthheight: 1.5 ft minimumfreeboard: 0.5 ft minimum

5. Channel design - shape: parabolic, trapezoidal, orV-shaped

side slope: 2:1 or flatter3:1 or flatter wherevehicles must cross

stabilization: based on velocity byreaches

6. Grade - Dependent on site topography. Channel should have positive grade.

7. Outlet - Divert sediment-laden water into a temporary sediment trap or sediment basin.Runoff from undisturbed areas should empty into an outlet protection device such as alevel spreader or riprap outlet structure unless well stabilized natural outlets exist.


1. Remove and properly dispose of all trees, brush, stumps, and other objectionablematerial. Fill and compact, to natural ground level or above, all ditches and gullies thatwill be crossed by machinery.

2. Disc the base of the dike before placing fill.

3. Ensure that the constructed cross section meets all design requirements.

4. Compact the dike by tracking with construction equipment.

5. Ensure that the top of the dike is not lower at any point than the design elevation plus thespecified settlement after it has been compacted.

6. Leave sufficient area along the dike to permit machine regrading and cleanout.

7. Immediately seed and mulch the dike after its construction and stabilize the flow portionin accordance with design requirements.

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Maintenance

Inspect diversion dikes once a week and after every rainfall. Immediately remove sediment fromthe flow area and repair the dike.

Check outlets and make timely repairs as needed to avoid gully formation. When the area abovethe temporary diversion dike is permanently stabilized, remove the dike and fill and stabilize thechannel to blend with the natural surface.

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10.04 RUNOFF CONVEYANCE MEASURES

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10.03.4.1 - GRASS-LINED CHANNELS

Definition

A channel with vegetative lining constructed to design cross section and grade for conveyance ofrunoff.

Purpose

To convey and dispose of concentrated surface runoff without damage from erosion, deposition,or flooding.


This practice applies to construction sites where:

a) concentrated runoff will cause damage from erosion or flooding;

b) a vegetative lining can provide sufficient stability for the channel cross section andgrade;

c) slopes are generally less than 5%;

d) space is available for a relatively large cross section.

Typical uses include roadside ditches, channels at property boundaries, outlets for diversions, andother channels and drainage of low areas.


A. LOCATIONGenerally, channels should be located to conform with and use the natural drainagesystem. Channels may also be needed along development boundaries, roadways, andbacklot lines. Avoid channels crossing watershed boundaries or ridges.

Plan the course of the channel to avoid sharp changes in direction or grade. Sitedevelopment should conform to natural features of the land and use natural drainagewaysrather than drastically reshape the land surface. Major reconfiguration of the drainagesystem often entails increased maintenance and risk of failure.

Grass-lined channels must not be subject to sedimentation from disturbed areas.

An established grass-lined channel resembles natural drainage systems and, therefore, isusually preferred if design velocities are below 5 ft/sec.

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Establishment of a dense, resistant vegetation is essential. Construct and vegetate grass-lined channels early in the construction schedule before grading and paving increase therate of runoff.

Geotextile fabrics or special mulch protection such as fiberglass roving or straw andnetting provide stability until the vegetation is fully established. These protective linersmust be used whenever design velocities exceed 2 ft/sec for bare soil conditions. It mayalso be necessary to divert water from the channel until vegetation is established or to linethe channel with sod. If sod is required, the sod segments shall be staked regardless ofdesign velocity. Sediment traps may be required at channel inlets and outlets.

V-shaped grass channels generally apply where the quantity of water is small, such as inshort reaches along roadsides. The V-shaped cross section is least desirable because it isdifficult to stabilize the bottom where velocities may be high.

Parabolic grass channels are often used where larger flows are expected and space isavailable. The swale-like shape is pleasing and may best fit site conditions.

Trapezoidal grass channels are used where runoff volumes are large and slope is low sothat velocities are nonerosive to vegetated linings.

B. OUTLETSOutlets must be stable. Where channel improvement ends, the exit velocity for the designflow must be nonerosive for the existing field conditions. Stability conditions beyond theproperty boundary should always be considered.

Design Criteria

1. Capacity - As a minimum, grass-lined channels should carry peak runoff from the 10-yrstorm without eroding. Where flood hazard exists, increase the capacity according to thepotential damage. Channel dimensions may be determined by using Manning’s formulausing an appropriate “n” value.

2. Velocity - Maximum Permissible Velocities in grass-lined channels shall be based oncommon engineering practices which produce non-erodible channels such as soilcharacteristics, height and type of grass, and frequency of maintenance of the grass.

If design velocity of a channel to be vegetated by seeding exceeds 2 ft/sec, a temporarychannel liner is required. The design of the liner may be based on peak flow from a 2-yr

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storm. Permanent channel linings must be stable for the 10-yr storm.

3. Cross section - The channel shape may be parabolic, trapezoidal, or V-shaped, dependingon need and site conditions. See Figure 4.la.

Figure 4.la - Cross section geometry of triangular, parabolic, and trapezoidal channels.

4. Hydraulic grade line - Examine the design water surface if the channel system becomescomplex.

5. Side slopes - Grassed channel side slopes generally are constructed 3:1 or flatter to aid inthe establishment of vegetation and for maintenance. Side slopes of V-shaped channelsare usually constructed 6:1 or flatter along roadways for safety.

6. Depth and width - The channel depth and width are proportioned to meet the needs ofdrainage, soil conditions, erosion control, carrying capacity and site conditions. Constructchannels a minimum of 0.2 ft larger around the periphery to allow for soil bulking duringseedbed preparations and sod buildup.

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7. Grade - Either a uniform or gradually increasing grade is preferred to avoidsedimentation. Where the grade is excessive, grade stabilization structures may berequired or channel linings of riprap or paving should be considered.

8. Outlets - Evaluate the outlets of all channels for carrying capacity and stability and protectthem from erosion by limiting the exit velocity.

9. Sedimentation protection - Protect permanent grass channels from sediment produced inthe watershed, especially during the construction period. This can be accomplished by theeffective use of diversions, sediment traps, protected side inlets, and vegetative filterstrips along the channel.


1. Remove all trees, brush, stumps, and other objectionable material from the foundationarea and dispose of properly.

2. Excavate the channel and shape it to neat lines and dimensions shown on the plans plus a0.2-ft overcut around the channel perimeter to allow for bulking during seedbedpreparations and sod buildup.

3. Remove and properly dispose of all excess soil so that surface water may enter thechannel freely.

4. The procedure used to establish grass in the channel will depend upon the severity of theconditions and selection of species. Protect the channel with mulch or a temporary linersufficient to withstand anticipated velocities during the establishment period.

Maintenance

During the establishment period, check grass-lined channels after every rainfall. After grass isestablished, periodically check the channel; check it after every rainfall event. Immediately makerepairs. It is particularly important to check the channel outlet and all road crossings for bankstability and evidence of piping or scour holes. Remove all significant sediment accumulations tomaintain the designed carrying capacity. Keep the grass in a healthy, vigorous condition at alltimes, since it is the primary erosion protection for the channel.

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10.03.4.2 - RIPRAP AND PAVED CHANNELS

Definition

Channels with erosion-resistant linings of riprap, paving, or other structural material designed forthe conveyance and safe disposal of excess water.

Purpose

To convey concentrated surface runoff without erosion or other damage.

Condition Where Practice Applies

This practice applies where design flow velocity exceeds 5 ft/sec so that a channel lining isrequired, but conditions are unsuitable for grass-lined channels. Specific conditions include:

a) Channels where slopes over 5% predominate; continuous or prolonged flowsoccur; potential for damage from traffic (people or vehicles) exists; or soils areerodible and soil properties are not suitable for vegetative protection.

b) Design velocity exceeds that allowable for a grass-lined channel.

c) Property value justifies the cost to contain the design runoff in a limited space.

d) Channel setting warrants the use of special paving materials.


Riprap or paving materials are generally employed as channel liners when design flow velocitiesexceed the tolerance of grass or where grass lining is inappropriate.

Riprap is preferred primarily on the basis of cost, but it has several additional advantages such as:

a) Riprap liners can be designed to withstand most flow velocities by choosing stablestone size.

b) Riprap adjusts to unstable foundation conditions without failure.

c) Failure of a riprap liner is not as expensive to repair as a rigid liner would be.

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d) The roughness of riprap reduces outlet velocity, and tends to reduce flow volumeby allowing infiltration.

Rigid liners such as concrete or flagstone can carry large volumes of water without eroding.However, they are most expensive to design and construct, are less forgiving of foundationconditions, and introduce high energies that must be controlled and dissipated to avoid damageto channel outlets and receiving streams.

Channels combining grassed side slopes and riprap or paved bottoms may be used wherevelocities are within allowable limits for grass lining along the channel sides, but long-durationflows, seepage, or a high velocity flow would damage vegetation in the channel bottom.

Paving blocks and gabions have some of the same characteristics as riprap and are often usedinstead of riprap to fit certain site conditions.

Channels with smooth liners, such as concrete or flagstone, usually are not limited by velocity,take up less land area, and can be constructed to fit limited site conditions. In addition, theyprovide a more formal appearance and usually require less maintenance. Exercise care to seethat foundation soils are stable and proper foundation drainage is installed. Appropriatemeasures are needed to reduce the exit velocity of the paved channel to protect the receivingchannel or outlet.

Design Criteria

1. Capacity - Design channels to contain the peak runoff from the 10-yr storm as aminimum. Where flood damage potential is high, expand the capacity to the extent of thevalue or hazard involved.

2. Velocity - Compute velocity using Manning’s equation with an appropriate “n” value forthe selected lining.

3. Cross section - The cross section may be triangular, parabolic, or trapezoidal. Reinforcedconcrete or gabions may be rectangular.

4. Side slope - Base side slopes on the materials and placement methods according to theaccepted design criteria.

5. Hydraulic grade line - Ensure that the design water surface in the channel meets thedesign flow elevations of tributary channels and diversions. Ensure that it is below safeflood elevations for homes, roads, or other improvements.

6. Depth and width - Proportion the channel depth and width to meet the needs of drainage,carrying capacity, foundation

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limitations, and specific site conditions.

7. Lining thickness - Minimum thickness of concrete lined channels shall be 5 inches.Minimum thickness of riprap channels shall be 15 inches.

8. Filter layer - A sand/gravel filter layer should be used under the channel lining to preventpiping and reduce uplift pressure.

9. Riprap - For the design of riprap channels see Practice 10.03.2.6 - Riprap.

10. Concrete - Concrete for linings should be a dense, durable product sufficiently plastic forthorough consolidation but stiff enough to stay in place on side slopes.

11. Toewalls - Toewalls are needed at the beginning and end of paved or riprapped channelsections to protect against undercutting. Expansion joints and additional toewalls mayalso be needed.

12. Outlets - Evaluate the capacity and stability of all channel outlets and protect them fromerosion by limiting exit velocity.


1. Clear the foundation area of trees, stumps, roots, loose rock, and other objectionablematerial.

2. Excavate the cross section to the lines and grades of the foundation of the liner as shownon the plans. Bring overexcavated areas to grade by increasing the thickness of the lineror by backfilling with moist soil compacted to the density of the surrounding material.

3. Concrete linings:

a) Place concrete linings to the thickness shown on the plans and finish them in aworkmanlike manner.

b) Take adequate precautions to protect freshly placed concrete from extremetemperatures to ensure proper curing.

c) Ensure that subgrade is moist when concrete is poured.

d) Install foundation drains or weep holes where needed to protect against uplift andpiping.

e) Provide transverse (contraction) joints to control

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cracking at approximately 20-ft intervals. These joints may be formed by using a1/2-inch thick removable template or by sawing to a depth of at least 1 inch.

f) Install expansion joints at intervals not to exceed 100 ft.

4. Rock riprap linings: Practice 10.03.2.6 - Riprap.

5. Perform all channel construction to keep erosion and water pollution to a minimum.Immediately upon completion of the channel, vegetate all disturbed areas or otherwiseprotect them against soil erosion. Where channel construction will take longer than 30days, stabilize channels by reaches.

Maintenance

Inspect channels at regular intervals as well as after major rains, and make repairs promptly.Give special attention to the outlet and inlet sections and other points where concentrated flowenters. Carefully check stability at road crossings and look for indications of piping, scour holes,or bank failures. Make repairs immediately. Maintain all vegetation adjacent to the channel in ahealthy, vigorous condition to protect the area from erosion and scour during out-of-bank flow.

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10.03.4.3 - TEMPORARY SLOPE DRAINS

Definition

A flexible conduit of heavy duty fabric or other material used as a temporary structure to conveyconcentration of storm water down the face of cut and fill slopes.

Purpose

To safely conduct storm runoff from one elevation to another without causing erosion of slope.


This practice applies to construction areas where storm water runoff above a cut or fill slope willcause erosion if allowed to flow over the slope. Temporary slope drains are generally used inconjunction with diversions to convey runoff down a slope until permanent water disposalmeasures can be installed.


There is often a significant lag between the time a cut or fill slope is graded and the time it ispermanently stabilized. During this period, the slope is very vulnerable to erosion, and temporaryslope drains together with temporary diversions can provide valuable protection.

It is very important that these temporary structures be sized, installed, and maintained properly,because their failure will usually result in severe erosion of the slope. The entrance section to thedrain should be well entrenched and stable so that surface water can enter freely. The drainshould extend downslope beyond the toe of the slope to a stable area or appropriately stabilizedoutlet.

Other points of concern are failure from overtopping from inadequate pipe inlet capacity and lackof maintenance of diversion channel capacity and ridge height.

Design Criteria

1. Capacity - Peak runoff from the 10-yr storm.

2. Conduit - Construct the slope drain from heavy-duty, flexible materials such asnonperforated, corrugated plastic pipe or specially designed flexible tubing. See Figure4.3a. Install reinforced, hold-down grommets or stakes to anchor the conduit at intervalsnot to exceed 10 ft with the outlet end securely fastened in place. The conduit mustextend beyond the toe of the slope.

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3. Entrance - Construct the entrance to the slope drain of a standard flare-end section of pipewith a minimum 6-inch metal toe plate. Make all fittings watertight. A standard T-sectionfitting may also be used at the inlet.

4. Temporary diversion - Generally, use an earthen diversion with a dike ridge to directsurface runoff into the temporary slope drain. Make the height of the ridge over the drainconduit a minimum of 1.5 foot and at least 6 inches higher than the adjoining ridge oneither side. The lowest point of the diversion ridge should be a minimum of 1 ft above thetop of the drain so that design flow can freely enter the pipe.

5. Outlet protection - Protect the outlet of the slope drain from erosion.


A common failure of slope drains is caused by water saturating the soil and seeping along thepipe. This creates voids from consolidation and piping and causes washouts. Proper backfillingaround and under the pipe “haunches” with stable soil material and hand compacting in 6-inchlifts to achieve firm contact between the pipe and the soil at all points will eliminate this type offailure.

1. Place slope drains on undisturbed soil or well-compacted fill at locations and elevationsshown on the plans.

2. Slightly slope the section of pipe under the dike toward its outlet.

3. Hand tamp the soil under and around the entrance section in lifts not to exceed 6 inches.

4. Ensure that fill over the drain at the top of the slope has minimum dimensions of 1.5 ftdepth, 4 ft top width, and 3:1 side slopes.

5. Ensure that all slope drain connections are watertight.

6. Ensure that all fill material is well-compacted. Securely fasten the exposed section of thedrain with grommets or stakes spaced no more than 10 ft apart.

7. Extend the drain beyond the toe of the slope and adequately protect the outlet fromerosion.

8. Make the settled, compacted dike ridge no less than 1 ft above the top of the pipe at everypoint.

9. Immediately stabilize all disturbed areas following construction.

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Maintenance

Inspect the slope drain and supporting diversion after every rainfall and promptly make necessaryrepairs. When the protected area has been permanently stabilized, temporary measures may beremoved, materials disposed of properly, and all disturbed areas stabilized appropriately.

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PLAN

Holding FlapsTop of Diversion Dike

Extension CollarAnchor Pins

Strap

Full

SECTION

ISOMETRIC VIEW

TEMPORARY SLOPE DRAINSFig. 4.3a

Standard MetalEnd Section

10.03.4.4 - PAVED FLUME OR CHUTES

Definition

A small concrete-lined channel to convey water on a relatively steep slope.

Purpose

To conduct concentrated runoff safely down the face of a cut or fill slope without causingerosion.


Where concentrated storm runoff must be conveyed from the top to the bottom of a cut or fillslope as part of a permanent erosion control system. Paved flumes serve as stable outlets fordiversions, drainage channels, or natural drainageways that are located above relatively steepslopes. Restrict paved flumes to slopes of 1.5:1 or flatter.


Conveying storm runoff safely down steep slopes is an important consideration when planningpermanent erosion control measures f or a site. Paved flumes are often selected for this purpose,but other measures such as grassed waterways, riprap channels, and closed storm drains shouldalso be considered. Evaluate the flow volume, velocity and duration of flow, degree of slope, soiland site conditions, visual impacts, construction costs, and maintenance requirements to decidewhich measure to use.

When planning paved flumes, give special attention to flow entrance conditions, soil stability,outlet energy dissipation, downstream stability, and freeboard or bypass capacity. Setting theflume well into the ground is especially important, particularly on fill slopes.

Paved chutes often have the upper portion of their side slopes grassed. This saves on materialsand improves appearance. The paved portion carries the design flow, and the grassed areaprovides freeboard.

Design Criteria

1. Capacity - Consider peak runoff from the 10-yr storm as a minimum. Provide sufficientfreeboard or bypass capacity to safeguard the installation from any peak flow expectedduring the life of the structure.

2. Slope - Ensure that the slope of a chute does not exceed 1.5:1.

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3. Toewalls - Provide toewalls at the beginning and end of paved flumes. Make the toewallas wide as the flume, extend it at least 18 inches into the soil below the channel, and keepit a minimum thickness of 6 inches. Reinforce toewalls with 3/8-inch reinforcing steelbars placed on 6-inch centers.

4. Anchor lugs - Space anchor lugs at a maximum of 10 ft on the center for the length of theflume. Make anchor lugs as wide as the bottom of the flume, extend them at least 1 ft intothe soil below, and keep them a minimum thickness of 6 inches. Reinforce anchor lugswith 3/8-inch steel reinforcing bars placed on 6-inch centers.

5. Concrete - Keep concrete in the flume channel at least 5 inches thick and reinforce it with3/8-inch steel bars. Ensure that the concrete used for flumes is a dense, durable productand sufficiently plastic for thorough consolidation but stiff enough to stay in place onsteep slopes.

6. Cross section - Ensure that flumes have a minimum depth of 1 ft with 1.5:1 side slopes.Base bottom widths on maximum flow capacity.

7. Alignment - Keep chute channels straight because they often carry supercritical flowvelocities.

8. Drainage filters - Use a drainage filter to prevent piping and reduce uplift pressurewherever seepage or high water table may occur.

9. Inlet section - Ensure that the inlet to the chute has the following minimum dimensions:side walls 2 ft high, length 6 ft, width equal to the flume channel bottom, and side slopesame as flume channel side slopes.

10. Outlet section - Protect outlets for paved flumes from erosion. Use an energy dissipator toreduce high chute velocities to nonerosive rates. In addition, place riprap at the end of thedissipator to spread the flow evenly over the receiving area. Other measures, such as animpact basin, plunge pool, or rock riprap outlet structure, may also be needed.

11. Flume dimensions - Where drainage areas are 10 acres or less, the design dimensions forconcrete flumes may be selected from the Table 4.4a.

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Table 4.4a Concrete Flume DimensionsDrainage1

Area(acres)

Min.BottomWidth

(ft)

Min. InletDepth

(ft)

Min. ChannelDepth

(ft)

Max. ChannelSlope(ft)

Max. SideSlope

(ft)5 4 2 1.3 1.5:1 1.5:110 8 2 1.3 1.5:1 1.5:1

1Due to complexity of inlet and outlet design, drainage areas have been limited to 10 acres perflume.


1. Construct the subgrade to the elevations shown on the plans. Remove all unsuitablematerial and replace them with stable materials. Compact the subgrade thoroughly andshape it to a smooth, uniform surface. Keep the subgrade moist at the time concrete ispoured. On fill slopes, ensure that the soil adjacent to the chute for at least 3 feet is well-compacted.

2. Place concrete for the flume to the thickness shown on the plans and finish it in aworkman-like manner.

3. Form, reinforce, and pour together walls, anchor lugs, and channel linings.

4. Take adequate precautions to protect freshly poured concrete from extreme temperaturesto ensure proper curing.

5. Provide transverse (contraction) joints to control cracking at approximately 20-ft intervals.Joints may be formed by using a 1/8-inch thick removable template or by sawing to adepth of at least 1 inch.

6. In very long flumes, install expansion joints at intervals not to exceed 50 ft.

7. Place filters and foundation drains, when required, in the manner specified and protectthem from contamination when pouring the concrete flume.

8. Properly stabilize all disturbed areas immediately after construction.

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Maintenance

Inspect flumes after each rainfall until all areas adjoining the flume are permanently stabilized.Repair all damage noted in inspections immediately. After the slopes are stabilized, flumes needonly periodic inspection and inspection after major storm events.

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10.03.5 OUTLET PROTECTION

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10.03.5.1 - LEVEL SPREADER

Definition

An outlet constructed at zero grade across the slope whereby concentrated runoff may bedischarged at non-erosive velocities onto undisturbed areas stabilized by existing vegetation.

Purpose

To convert a concentrated flow of storm runoff into sheet flow and to outlet it onto areasstabilized by existing vegetation without causing erosion.


Where storm runoff is intercepted and diverted from graded areas onto undisturbed stabilizedareas (i.e., at diversion outlets, etc.). This practice applies only in those situations where thespreader can be constructed on undisturbed soil and where the area directly below the level lip isstabilized by existing vegetation. The water must not be allowed to reconcentrate below the pointof discharge.


The level spreader is a relatively low-cost structure to release small volumes of concentratedflow where site conditions are suitable (Figure 5.la). The outlet area must be uniform and well-vegetated with slopes of 10% or less. Particular care must be taken to construct the outlet lipcompletely level in a stable, undisturbed soil. Any depressions in the lip will concentrate theflow, resulting in erosion. Evaluate the outlet system to be sure that flow does not concentratebelow the outlet. The level spreader is most often used as an outlet for temporary or permanentdiversions and diversion dikes. Runoff water containing high sediment loads must be treated in asediment trapping device before release in a level spreader.

Design Criteria

1. Capacity - Determine the capacity of the spreader by estimating peak flow from the 10-yrstorm. Restrict the drainage area so that maximum flows into the spreader will not exceed30 cfs.

2. Spreader dimensions - When water enters the spreader from one end, as from a diversion,select the appropriate length, width, and depth of the spreader from Table 5.lA.

Construct a 20-ft transition section in the diversion channel so the width of the diversionwill smoothly meet the width of

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the spreader to ensure uniform outflow.

Table 5.1A - Minimum Dimensions of Level Spreader

Entrance Width Depth End Width LengthDesign Floorcfs ---minimum dimension in feet---

00-10 10 0.5 3 1010-20 16 0.6 3 2020-30 24 0.7 3 30

3. Grade - The grade of the last 20 feet of the diversion channel should provide a smoothtransition from channel grade to level at the spreader. The grade of the spreader should be0%.

4. Spreader lip - Construct the level lip on undisturbed soil to uniform height and zero gradeover the length of the spreader. Protect it with an erosion-resistant material, such asfiberglass matting, to prevent erosion and allow vegetation to become established.

5. Outlet area - The outlet disposal area must be generally smooth and well-vegetated with amaximum slope of 10%.

Vegetate all disturbed areas.


1. The matting should be a minimum of 4 ft wide extending 6 inches over the lip and buried6 inches deep in a vertical trench on the lower edge. The upper edge should butt againstsmoothly cut sod and be securely held in place with closely spaced heavy duty wirestaples at least 12 inches long.

2. Ensure that the spreader lip is level for uniform spreading of storm runoff.

3. Construct the level spreader on undisturbed soil (not on fill).

4. Construct a 20-ft transition section from the diversion channel to blend smoothly to thewidth and depth of the spreader.

5. Disperse runoff from the spreader across a properly stabilized slope not to exceed 10%.Make sure the slope is sufficiently smooth to keep flow from concentrating.

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6. Immediately after its construction, appropriately seed and mulch the entire disturbed areaof the spreader.

Maintenance

Inspect level spreaders after every rainfall until vegetation is established, and promptly makeneeded repairs. After the area has been stabilized, make periodic inspections and keep vegetationin a healthy, vigorous condition.

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SECTION A-A

2:1 or Flatter0.5’ min

6’ min

Undisturbed Soil StabilizedBy Existing Vegetation

Undisturbed Slope

PLAN VIEW

Channel Grade 0.0%

Compacted Interceptor or Diversion Dike

Level Lip Above Undisturbed, Stabilized Area

6’ min

A

Maximum 1% Grade For AtLeast 20’ For Transition

10.03.5.2 - OUTLET STABILIZATION STRUCTURES

Definition

Structures designed to control erosion at the outlet of a channel or conduit.

Purpose

To prevent erosion at the outlet of a channel or conduit by reducing the velocity of flow anddissipating the energy.


This practice applies where the discharge velocity of a pipe, box culvert, diversion, open channel,or other water conveyance structure exceeds the permissible velocity of the receiving channel ordisposal area.


The outlets of channels, conduits, and other structures are points of high erosion potential,because they frequently carry flows at velocities that exceed the allowable limit for the areadownstream. To prevent scour and undermining, an outlet stabilization structure is needed toabsorb the impact of the flow and reduce the velocity to non-erosive levels. A riprap-lined apronis the most commonly used practice for this purpose because of its relatively low cost and ease ofinstallation. The riprap apron should be extended downstream until stable conditions are reachedeven though this may exceed the length calculated for design velocity control.

Riprap-stilling basins or plunge pools reduce flow velocity rapidly. They should be considered inlieu of aprons where overfalls exit at the ends of pipes or where high flows would requireexcessive apron length. Consider other energy dissipaters such as concrete impact basins orpaved outlet structures where site conditions warrant.

Design Criteria

1. Capacity - 10-yr peak runoff or the design discharge of the water conveyance structure,whichever is greater.

2. Apron size - The apron length, width and thickness shall be determined by the engineer. Ifthe water conveyance structure discharges directly into a well-defined channel, extend theapron across the channel bottom and up the channel banks to an elevation of 0.5 feetabove the maximum tailwater depth or to the top of bank, whichever is less.

Determine the maximum allowable velocity for the receiving

78

stream, and design the riprap apron to reduce flow to this velocity before flow leaves theapron. Calculate the apron length for velocity control or use the length required to meetstable conditions downstream, whichever is greater.

3. Riprap - Riprap may consist of field stone or quarry stone. The stone should be hard,angular, of such a quality that it will not break down on exposure to water or weathering,and suitable in all other respects for the purpose intended. See Practice 10.03.2.6 - Riprapfor the gradation of the riprap.

4. Grade - Ensure that the apron has zero grade. There should be no overfall at the end of theapron; that is, the elevation of the top of the riprap at the downstream end should be thesame as the elevation of the bottom of the receiving channel or the adjacent ground ifthere is no channel.

5. Alignment - The apron should be straight throughout its entire length, but if a curve isnecessary to align the apron with the receiving stream, locate the curve in the upstreamsection of riprap.

6. Filter - Install a filter to prevent soil movement through the openings in the riprap. Thefilter should consist of a graded gravel layer or a synthetic filter cloth. See Practice10.03.2.6 - Riprap.


1. Ensure that the subgrade for the filter and riprap follows the required lines and gradesshown in the plan. Compact any fill required in the subgrade to the density of thesurrounding undisturbed material. Low areas in the subgrade on undisturbed soil may alsobe filled by increasing the riprap thickness.

2. The riprap and gravel filter must conform to the specified grading limits shown on theplans.

3. Filter cloth, when used, must meet design requirements and be properly protected frompunching or tearing during installation. Repair any damage by removing the riprap andplacing another piece of filter cloth over the damaged area. All connecting joints shouldoverlap a minimum of 1 ft. If the damage is extensive, replace the entire filter cloth.

4. Riprap may be placed by equipment, but take care to avoid damaging the filter.

5. The minimum thickness of the riprap should be 15 inches.

6. Riprap may be field stone or rough quarry stone. It should be

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hard, angular, highly weather-resistant and well graded.

7. Construct the apron on zero grade with no overfall at the end. Make the top of the riprapat the downstream end level with the receiving area or slightly below it.

8. Ensure that the apron is properly aligned with the receiving stream and preferably straightthroughout its length. If a curve is needed to fit site conditions, place it in the uppersection of the apron.

9. Immediately after construction, stabilize all disturbed areas with vegetation.

Maintenance

Inspect riprap outlet structures after heavy rains to see if any erosion around or below the ripraphas taken place or if stones have been dislodged. Immediately make all needed repairs to preventfurther damage.

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10.03.6 INLET PROTECTION

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10.03.6.1 - EXCAVATED INLET PROTECTION (TEMPORARY)

Definition

An excavated area in the approach to a storm drain drop inlet or curb inlet.

Purpose

To trap sediment at the approach to the storm drainage systems. This practice allows use ofpermanent storm water conveyance at an early stage of site development.


Where storm drain drop inlets are to be made operational before permanent stabilization of thedisturbed drainage area. This method of inlet protection is applicable where relatively heavyflows are expected and overflow capability is needed (Figure 6.la). Frequent maintenance isrequired and temporary flooding in the excavated area will occur. This practice can be used incombination with other temporary inlet protection devices.

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Design Criteria

1. Limit the drainage area to 1 acre. Keep the minimum depth at 1 ft and the maximumdepth of 2 ft as measured from the crest of the inlet structure.

2. Maintain side slopes around the excavation no steeper than 2:1.

3. Keep the minimum volume of excavated area around the drop inlet at approximately 35yd3/acre disturbed.

4. Shape the basin to fit site conditions, with the longest dimension oriented toward thelongest inflow area to provide maximum trap efficiency.

5. Install provisions for draining the temporary pool to improve trapping efficiency for smallstorms and to avoid problems from standing water after heavy rains.


1. Clear the area of all debris that might hinder excavation and disposal of spoil.

2. Grade the approach to the inlet uniformly.

3. Protect weep holes by gravel.

4. When the contributing drainage area has been permanently stabilized, seal weep holes, fillthe basin with stable soil to final grading elevations, compact it properly, and stabilize.

Maintenance

Inspect, clean, and properly maintain the excavated basin after every storm until the contributingdrainage area has been permanently stabilized. To provide satisfactory basin efficiency, removesediment when the volume of the basin has been reduced by one-half. Spread all excavatedmaterial evenly over the surrounding land area or stockpile and stabilize it appropriately.

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10.03.6.2 - FABRIC DROP INLET PROTECTION (TEMPORARY)

Definition

A temporary fabric barrier placed around a drop inlet.

Purpose

To help prevent sediment from entering storm drains during construction operations. Thispractice allows early use of the storm drain system.


Where storm drain inlets are to be made operational before permanent stabilization of thedisturbed drainage area. This method of inlet protection is effective where the inlet drains asmall, nearly level area with slopes generally less than 5% and where shallow sheet flows areexpected. The immediate land area around the inlet should be relatively flat (less than 1%) andlocated so that accumulated sediment can be easily removed.

This practice must not be used near the edge of fill material and must not divert water over cut orfill slopes.

Design Criteria

1. Ensure that drainage areas do not exceed 1 acre per inlet.

2. Keep the maximum height of fabric above the crest of the drop inlet at 1.5 ft. This heightallows a shallow temporary desilting pool to form behind the fabric but limits the pressureagainst the fabric if overtopping occurs. The selected height of the top of the barriershould allow overflow into the drop inlet and not let overflow bypass the inlet tounprotected lower areas.

3. For fabric barriers, use stakes with a minimum length of 3 ft, and space them a maximumof 3 ft apart, and securely drive them into the ground.

4. Drive the stakes close to the drop inlet so that overflow will fall directly into the structureand not on unprotected soil.

5. To attach the fabric, make a frame around the stakes a maximum of 1.5 ft above the top ofthe drop inlet. This will serve as a stable crest for overflow during rainfall.

6. Ensure that both fabric and supporting stakes are sufficiently strong to hold a 1.5 ft headof water without failure (Figure 6.2a).

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7. Improved performance and sediment storage volume can be obtained by excavating thearea (Practice 10.03.6.1 Excavated Drop Inlet Protection).


1. As synthetic fabric, use a pervious sheet of nylon, polyester, or ethylene yarn - extrastrength (50 lb/1 inch minimum) -that contains ultraviolet ray inhibitors and stabilizers.Fabric should be sufficiently porous to provide adequate drainage of the temporarysediment pool. Burlap may be used for short-term applications. It must be replaced every60 days.

2. Cut fabric from a continuous roll to eliminate joints.

3. For stakes, use 2 x 4-inch wood (preferred) or equivalent metal with a minimum length of3 ft.

4. Space stakes evenly around the perimeter of the inlet a maximum of 3 ft apart, andsecurely drive them into the ground, approximately 18 inches deep.

5. To provide needed stability to the installation, frame with 2 x 4-inch wood strips aroundthe crest of the overflow area at a maximum of 1.5 ft above the drop inlet crest.

6. Place the bottom 12 inches of the fabric in a trench and backfill the trench with at least 4inches of crushed stone or 12 inches of compacted soil.

7. Fasten fabric securely to the stakes and frame. Joints must be overlapped to the nextstake.

8. The top of the frame and fabric must be well below the ground elevation downslope fromthe drop inlet to keep runoff from bypassing the inlet. It may be necessary to build atemporary dike on the down slope side of the structure to prevent bypass flow. Materialfrom within the sediment pool may be used for diking.

Maintenance

Inspect the fabric barrier after each rain and make repairs as needed.

Remove sediment from the pool area as necessary to provide adequate storage volume for thenext rain. Take care not to damage or undercut the fabric during sediment removal.

When the contributing drainage area has been adequately stabilized, remove all materials and anyunstable sediment and dispose of them

85

properly. Bring the disturbed area to the grade of the drop inlet and smooth and compact it.Appropriately stabilize all bare areas around the inlet.

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10.03.6.3 - BLOCK AND GRAVEL INLET PROTECTION (TEMPORARY)

Definition

A sediment control barrier formed around a storm drain inlet by the use of standard concreteblock and gravel.

Purpose

To help prevent sediment from entering storm drains before stabilizing the contributingwatershed. This practice allows early use of the storm drain system.


Where storm drain inlets are to be made operational before permanent stabilization of thedisturbed drainage area. This method of inlet protection applies to both drop inlets and curb inletswhere heavy flows are expected and an overflow capacity is necessary to prevent excessiveponding around the structure. Shallow temporary flooding after rainfall should be expected,however.

This practice must not be used near the edge of fill material and must not divert water away fromthe storm drain.

Design Criteria

1. Keep the drainage area no greater than 1 acre unless site conditions allow for frequentremoval and adequate disposal of accumulated sediment.

2. Keep the height of the barrier at least 12 inches and no greater than 24 inches. Do not usemortar. Limit the height to prevent excess ponding and bypass flow.

3. Recess the first course of blocks at least 2 inches below the crest opening of the stormdrain for lateral support. Support subsequent courses laterally if needed by placing a 2 x4-inch wood stud through the block openings that are perpendicular to the block courseneeding support. Lay some blocks on their side in the bottom row for dewatering the pool(Figures 6.3a and 6.3b).

4. Place gravel just below the top of the blocks on slopes of 2:1 or flatter. Place hardwarecloth or comparable wire mesh with 1/2-inch openings over all block openings to holdgravel in place.

5. The top elevation of the structure must be at least 6 inches lower than the ground elevationdownslope from the inlet. It is important that all storm flows pass over the structure and

87

into the storm drain and not pass the structure. Temporary diking below the structure maybe necessary to prevent bypass flow. Material may be excavated from inside the sedimentpool for this purpose.

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Figure 6.3b - Block and gravel drop inlet protection.


1. Lay one block on each side of the structure on its side in the bottom row to allow pooldrainage. The foundation should be excavated at least 2 inches below the crest of thestorm drain. Place the bottom row of blocks against the edge of the storm drain for lateralsupport and to avoid washouts when overflow occurs. If needed, give lateral support tosubsequent rows by placing 2 x 4 wood studs through block openings.

2. Carefully fit hardware cloth or comparable wire mesh with 1/2-inch openings over allblock openings to hold gravel in place.

3. Use clean gravel, 3/4- to 1/2-inch in diameter, placed 2 inches below the top of the blockon a 2:1 slope or flatter and smooth it to an even grade.

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Maintenance

Inspect the barrier after each rain and make repairs as needed.

Remove sediment as necessary to provide adequate storage volume for subsequent rains.

When the contributing drainage area has been adequately stabilized, remove all materials and anyunstable soil, and either salvage or dispose of it properly. Bring the disturbed area to propergrade, then smooth and compact it. Appropriately stabilize all bare areas around the inlet.

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10.03.7 SEDIMENT TRAPS AND BARRIERS

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10.03.7.1 - TEMPORARY SEDIMENT TRAP

Definition

A small, temporary ponding basin formed by an embankment or excavation to capture sediment.

Purpose

To detain sediment-laden runoff and trap the sediment to protect receiving streams, lakes,drainage systems, and protect adjacent property.


At the outlets of diversions, channels, slope drains, or other runoff conveyances that dischargesediment-laden water.

Below areas that are 5 acres or less.

Where access can be maintained for sediment removal and proper disposal.

In the approach to a storm water inlet located below a disturbed area as part of an inlet protectingsystem.

Structure life limited to 2 years.


Select locations for sediment traps during site evaluation. Note natural drainage divides andselect trap sites so that runoff from potential sediment-producing areas can easily be diverted intothe traps. Ensure the drainage areas for each trap does not exceed 5 acres.

Make traps readily accessible for periodic sediment removal and other necessary maintenance.Plan locations for sediment disposal as part of trap site selection. Clearly designate all disposalareas on the plans.

In preparing plans for sediment traps, it is important to consider provisions to protect theembankment from failure from storm runoff that exceeds the design capacity. Considernonerosive emergency bypass areas, particularly if there could be severe consequences fromfailure. If a bypass is not possible and failure would have severe consequences, consideralternative sites.

Sediment trapping is achieved primarily by settling within a pool formed by an embankment. Thesediment pool may also be formed by excavation, or by a combination of excavation andembankment. Sediment-trapping efficiency is a function of surface area and

92

inflow rate. Therefore, maximize the surface area in the design. Installations that provide poolswith large length to width ratios reduce short circuiting and allow more of the pool surface areafor settling. This optimizes efficiency.

Because well-planned sediment traps are key measures to preventing off-site sedimentation, theyshould be installed in the first stages of project development.

Design Criteria

Ensure drainage area for a sedimentation trap does not exceed 5 acres.

1. Storage capacity - Keep the minimum volume of the sediment trap at 1800 ft3 /acre basedon area draining into the basin. Measure volume below the crest elevation of the outlet.The volume of a natural sediment trap may be satisfactorily approximated by theequation:

volume(ft3) = 0.4 x surface area(ft2) x maximum pool depth(ft)

2. Trap cleanout - Remove sediment from the trap and restore the capacity to original trapdimensions when sediment has accumulated to one-half the design depth.

3. Embankment - Ensure that embankments for temporary sediment traps do not exceed 5 ftin height measured at the center line from the original ground surface to the top of theembankment. Additional freeboard may be added to the embankment height to allow flowthrough a designated bypass location. Construct embankments with a minimum top widthof 5 ft and side slopes of 2:1 or flatter. Machine compact embankments.

4. Excavation - Where sediment pools are formed or enlarged by excavation, keep sideslopes at 2:1 or flatter for safety.

5. Outlet section - Construct the sediment trap outlet using a stone section of embankmentlocated at the low point in the basin. The stone section serves two purposes: (1) the topsection serves as a nonerosive spillway outlet for flood flows, and (2) the bottom sectionprovides a means of dewatering the basin between runoff events.

6. Stone size - Construct the outlet using material specified for use as riprap. A 1-ft thicklayer of 1/2- 3/4-inch aggregate should be placed on the inside face to reduce drainageflow rate.

7. Side slopes - Keep the side slopes of the spillway section at 2:1 or flatter. To protect theembankment, keep the sides of the spillway at least 21 inches thick.

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8. Depth - Keep the crest of the spillway outlet a minimum of 1.5 ft below the settled top ofthe embankment.

9. Protection from piping - Place filter cloth on the foundation below the riprap to preventpiping. An alternative would be to excavate a keyway trench across the riprap foundationand up the sides to the height of the dam.

10. Weir length and depth - Keep the spillway weir at least 4 ft long and sized to pass thepeak discharge of the 10-yr storm (Figure 7.la). A maximum flow depth of 1 ft, aminimum freeboard of 0.5 ft, and maximum side slopes of 2:1 are recommended.

Figure 7.la - Temporary sediment trap.


1. Clear, grub, and strip the area under the embankment of all vegetation and root mat.Remove all surface soil containing high amounts of organic matter and stockpile ordispose of it properly. Haul all objectionable material to the designated disposal area.

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2. Ensure that fill material for the embankment is free of roots, woody vegetation, organicmatter, and other objectionable material. Place the fill in lifts not to exceed 9 inches andmachine compact it. Over fill the embankment 6 inches to allow for settlement.

3. Construct the outlet section in the embankment. Protect the connection between the riprapand the soil from piping by using filter fabric or a keyway cutoff trench between theriprap structure and the soil.

a) Place the filter fabric between the riprap and soil. Extend the fabric across thespillway foundation and sides to the top of the dam; or

b) excavate a keyway trench along the centerline of the spillway foundationextending up the sides to the height of the dam. The trench should be at least 2 ftdeep and 2 ft wide with 1:1 side slopes.

4. Clear the pond area below the elevation of the crest of the spillway to facilitate sedimentcleanout.

5. All cut and fill slopes should be 2:1 or flatter.

6. Ensure that the stone (drainage) section of the embankment has a minimum bottom widthof 3 ft and maximum side slopes of 1:1 that extend to the bottom of the spillway section.

7. Construct the minimum finished stone spillway bottom width, as shown on the plans, with2:1 side slopes extending to the top of the over filled embankment. Keep the thickness ofthe sides of the spillway outlet structure at a minimum of 21 inches. The weir must belevel and constructed to grade to assure design capacity.

8. Ensure that the stone spillway outlet section extends downstream past the toe of theembankment until stable conditions are reached and outlet velocity is acceptable for thereceiving stream. Keep the edges of the stone outlet section flush with the surroundingground and shape the center to confine the outflow stream.

9. Direct emergency bypass to natural, stable areas. Locate bypass outlets so that flow willnot damage the embankment.

10. Stabilize the embankment and all disturbed areas above the sediment pool anddownstream from the trap immediately after construction.

11. Show the distance from the top of the spillway to the sediment cleanout level (one-half thedesign depth) on the plans and mark it in the field.

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Maintenance

Inspect temporary sediment traps after each period of significant rainfall. Remove sediment andrestore the trap to its original dimensions when the sediment has accumulated to one-half thedesign depth of the trap. Place the sediment that is removed in the designated disposal area andreplace the contaminated part of the gravel facing.

Check the structure for damage from erosion or piping. Periodically check the depth of thespillway to ensure it is a minimum of 1.5 ft below the low point of the embankment. Immediatelyfill any settlement of the embankment to slightly above design grade. Any riprap displaced fromthe spillway must be replaced immediately.

After all sediment-producing areas have been permanently stabilized, remove the structure andall unstable sediment. Smooth the area to blend with the adjoining areas and stabilize properly.

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10.03.7.2 - SEDIMENT BASIN

DefinitionAn earthen embankment suitably located to capture sediment.

PurposeTo retain sediment on the construction site and prevent sedimentation in off-site streams, lakes,and drainageways.


Special limitation - This practice applies only to the design and installation of sediment basinswhere failure of the structure would not result in loss of life, damage to homes or buildings, orinterruption of use of public roads or utilities. Sediment basins are needed where erosion controlmeasures are not adequate to prevent off-site sedimentation. Specific criteria for installation of asediment basin are as follows:

a) Keep the drainage area less than 100 acres.

b) Ensure that basin location provides a convenient concentration point for sediment-laden flows from the area served.

c) Ensure that basin location allows access for sediment removal and proper disposalunder all weather conditions.

d) Keep the basin life limited to 3 years, unless it is designed as a permanentstructure.

e) Do not locate sediment basins in perennial streams.


Select key locations for sediment basins during initial site evaluation. Install basins before anysite grading takes place within the drainage area.

Select basin sites to capture sediment from all areas that are not treated adequately by othersediment traps. Always consider access for cleanout and disposal of the trapped sediment.Locations where a pond can be formed by constructing a low dam across a natural swale aregenerally preferred to sites that require excavation. If practical, divert sediment-free runoff awayfrom the basin.

Sediment trapping efficiency is primarily a function of sediment particle size and the ratio ofbasin surface area to inflow rate. Therefore, design the basin to have a large surface area for itsvolume.

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Sediment basins with an expected life greater than 3 years should be designed as permanentstructures, and may be incorporated into the design of a permanent detention facility.

Design Criteria

1. Drainage areas - Limit drainage areas to 100 acres.

2. Surface area - To provide an adequate trapping efficiency, the following relationshipbetween sediment basin surface area and peak inflow rate should be followed for thedetermination of basin size:

A = 0.03q

where A is the sediment basin surface area in acres and q is the peak inflow rate in cfs. Areais measured at the design capacity of the principal spillway.

3. Basin shape - Ensure that the flow length to basin width ratio is greater than 2:1 to improvetrapping efficiency. This basin shape may be attained by site selection, excavation, orinstalling baffles. Length is measured at the crest elevation of the principal spillway.

4. storage volume - Ensure that the sediment storage volume of the basin, as measured to theelevation of the crest of the principal spillway is at least 1,800 ft3/acre for the area draininginto the basin (1,800 ft3 is equivalent to 1/2 inch of sediment per acre of basin drainage area).

Remove sediment from the basin when approximately one-half of the storage volume hasbeen filled.

5. Spillway capacity - The spillway system (principal and emergency spillway) must carry thepeak runoff from the 10-yr storm with a minimum 1 ft freeboard in the emergency spillway.Base runoff computations on the disturbed soil cover conditions expected during theeffective life of the structure.

6. Principal spillway - Construct the principal spillway with a vertical riser connected to ahorizontal barrel that extends through the embankment and outlets beyond the downstreamtoe of the dam, or an equivalent design.

a) Capacity - Ensure a minimum capacity of 0.2 cfs/acre of drainage area, with thewater surface at the emergency spillway crest elevation.

b) Crest elevation - When used in combination with emergency spillways, the crestelevation of the riser shall be one

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foot below the elevation of the control section of the emergency spillway. If noemergency spillway is provided, the crest elevation of the riser shall be a minimumof three feet below the crest elevation of the embankment.

c) Perforated riser - The sediment basin pool shall be drained by using a perforated riseror by some other approved means. Keep the minimum barrel size at 8 inches tofacilitate installation and reduce potential for failure from blockage. To improve theefficiency of the principal spillway system, make the cross-sectional area of the riserat least 1.5 times that of the barrel. The riser shall be perforated with 1/2-inchdiameter holes spaced 8 inches vertically and 10-12 inches horizontally. Cover theperforated section of the riser with 2 feet of 1/2- 3/4-inch clean gravel.

d) Anti-vortex device and trash rack - An anti-vortex device and trash rack shall besecurely installed on top of the riser. An approved anti-vortex device is a rigidvertical plate firmly attached to the pipe and oriented normal to the centerline ofdam. The plate dimensions shall be: length = diameter of the riser plus 12 inches;height = diameter of the barrel. Another approved device is the concentric cover trashrack which also functions as an anti-vortex device.

e) Base - The bottom of the riser shall be located at the low point in the basin to insurecomplete drainage. The riser shall have a base attached with a watertight connectionand shall have sufficient weight to prevent flotation of the riser. Two approved basesare: (1) a concrete base 18” thick with the riser imbedded 6” in the base; (2) a 1/4”minimum thickness steel plate with continuous weld all around the base of the riserto form a watertight connection. The plate shall have 2 feet of stone, gravel, ortamped earth placed on it to prevent flotation. In either case, each side of the squarebase shall be twice the riser diameter.

f) Anti-seep collars - Anti-seep collars shall be installed around the pipe conduit withinthe normal saturation zone to increase the seepage length.

The anti-seep collar and its connection to the pipe shall be watertight. The maximumspacing shall be approximately 14 times the minimum projection of the collarmeasured perpendicular to the pipe.

g) Outlet protection - Protection against scour at the discharge end of the pipe spillwayshall be provided.

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7. Emergency spillway - Construct the entire flow area of the emergency spillway inundisturbed soil (not fill). Make the cross section trapezoidal with a minimum bottom widthof 8 feet and side slopes of 3:1 or flatter. Make the control section of the spillway straightand at least 20 ft long. The inlet portion of the spillway may be curved to improvealignment, but ensure that the outlet section is straight due to supercritical flow in thisportion.

a) Capacity - The minimum design capacity of the emergency spillway must be thepeak rate of runoff from the 10-yr storm, less any reduction due to flow in theprincipal spillway. In no case should freeboard of the emergency spillway be lessthan 1 ft above the design depth of flow.

b) Velocity - Ensure that the velocity of flow discharged from the basin is nonerosivefor the existing conditions. When velocities exceed that allowable for the receivingareas, provide outlet protection.

8. Sediment cleanout elevation - Show the distance from the top of the riser to the pool levelwhen the basin is 50% full. This elevation should also be marked in the field with apermanent stake set at this ground elevation (not the top of the stake).

9. Embankment - See Figure 7.2a

a) Cut-off trench - Excavate a trench at the centerline of the embankment. Ensure thatthe trench is in undisturbed soil and extends through the length of the embankment tothe elevation of the riser crest at each end. A minimum of 2 ft depth is recommended.

b) Top width - Minimum top width of the dam shall be 8 feet.

c) Freeboard - Ensure that the minimum difference between the design water elevationin the emergency spillway and the top of the settled embankments is 1 ft.

d) Side slopes - Make the side slopes of the impoundment structure 2.5:1 or flatter.

e) Allowance for settlement - Increase the constructed height of the fill at least 10%above the design height to allow for settlement.

f) Erosion protection - Stabilize all areas disturbed by construction (except the lower1/2 of the sediment pool) by suitable means immediately after completing the basin.

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1. Site preparations - Clear, grub, and strip topsoil from areas under the embankment to removetrees, vegetation, roots, and other objectionable material. To facilitate sediment cleanout andrestoration, clear the pool area of all brush, trees, and other objectionable materials.Stockpile all topsoil or soil containing organic matter for use on the outer shell of theembankment to facilitate vegetative establishment. Place temporary sediment controlmeasures below the basin as needed.

2. Cut-off trench - Excavate a cut-off trench along the centerline of the earth fill embankment.Cut the trench to stable soil material, but in no case make it less than 2 ft deep. The cut-offtrench must extend into both abutments to at least the elevation of the riser crest. Make theminimum bottom width wide enough to permit operation of excavation and compactionequipment but in no case less than 2 ft. Make side slopes of the trench no steeper than 1:1.Compaction requirements are the same as those for the embankment. Keep the trench dryduring backfilling and compaction operations.

3. Embankment - Take fill material from the approved areas shown on the plans. It should beclean mineral soil, free of roots, woody vegetation, rocks, and other objectionable material.Scarify areas on which fill is to be placed before placing fill. The fill material must containsufficient moisture so it can be formed by hand into a ball without crumbling. If

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water can be squeezed out of the ball, it is too wet for proper compaction. Place fillmaterial in 6 to 8-inch continuous layers over the entire length of the fill area and thencompact it. Compaction may be obtained by routing the construction hauling equipmentover the fill so that the entire surface of each layer is traversed by at least one wheel ortread track of the heavy equipment, or a compactor may be used. Construct theembankment to an elevation 10% higher than the design height to allow for settling.

4. Conduit spillways - Securely attach the riser to the barrel or barrel stub to make awatertight structural connection. Secure all connections between barrel sections byapproved watertight assemblies. Place the barrel and riser on a firm, smooth foundation ofimpervious soil. Do not use pervious material such as sand, gravel, or crushed stone asbackfill around the pipe or anti-seep collars. Place the fill material around the pipespillway in 4-inch layers and compact it under and around the pipe to at least the samedensity as the adjacent embankment. Care must be taken not to raise the pipe from firmcontact with its foundation when compacting under the pipe haunches.

Place a minimum depth of 2 ft of hand-compacted backfill over the pipe spillway beforecrossing it with construction equipment. Anchor the riser in place by concrete or othersatisfactory means to prevent flotation. In no case should the pipe conduit be installed bycutting a trench through the dam after the embankment is complete.

5. Emergency spillway - Install the emergency spillway in undisturbed soil. Theachievement of planned elevations, grade, design width, and entrance and exit channelslopes are critical to the successful operation of the emergency spillway.

6. Inlets - Discharge water into the basin in a manner to prevent erosion. Use diversions withoutlet protection to divert sediment-laden water to the upper end of the pool area toimprove basin trap efficiency.

7. Erosion control - Construct the structure so that the disturbed area is minimized. Divertsurface water away from bare areas. Complete the embankment before the area is cleared.Stabilize the emergency spillway embankment and all other disturbed areas above thecrest of the principal spillway immediately after construction.

Maintenance

Check sediment basins after periods of significant runoff.Remove sediment and restore the basin to its original dimensions when

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sediment accumulates to one-half the design depth.

Check the embankment, spillways, and outlet for erosion damage, and inspect theembankment for piping and settlement. Make all necessary repairs immediately. Removeall trash and other debris from the riser and pool area.

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10.03.7.3 - SEDIMENT (SILT) FENCE

Definition

A temporary sediment barrier consisting of filter fabric buried at the bottom, stretched, andsupported by posts.

Purpose

To retain sediment from small disturbed areas by reducing the velocity of sheet flows to allowsediment deposition.


Below small disturbed areas.

Where runoff can be stored behind the sediment fence without damaging the fence or thesubmerged area behind the fence.

Do not install sediment fences across streams, ditches, or waterways.


A sediment fence is a permeable barrier that should be planned as a system to retain sediment onthe construction site. The fence retains sediment primarily by retarding flow and promotingdeposition. In operation, generally the fence becomes clogged with fine particles, which reduceflow rate. This causes a pond to develop more quickly behind the fence. Anticipate ponding andprovide sufficient storage areas and overflow outlets to prevent flows from overtopping the fence.Since sediment fences are not designed to withstand high heads, locate them so that only shallowpools can form. Tie the ends of a sediment fence into the landscape to prevent flow around theend of the fence before the pool reaches design level. Provide stabilized outlets to protect thefence system and release storm flows that exceed the design storm.

Deposition occurs as the storage pool forms behind the fence. Plan deposition areas at accessiblepoints to promote routine cleanout and maintenance.

Design Criteria

1. Ensure that the drainage area is no greater than 1/4 acre per 100 ft of fence.

2. Make the fence stable for the 10-yr peak storm runoff.

3. Ensure that the depth of impounded water does not exceed 1.5 ft at any point along thefence.

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4. Provide a riprap splash pad or other outlet protection device for any point where flowmay overtop the sediment fence, such as natural depressions or swales. Ensure that themaximum height of the fence at a protected, reinforced outlet does not exceed 1 ft andthat support post spacing does not exceed 4 ft.

5. The design life of a synthetic sediment fence should be 6 months.


A. MATERIALS

1. Use a synthetic filter fabric or a pervious sheet of polypropylene, nylon, polyester,or polyethylene yard, which is certified by the manufacturer or supplier asconforming to the requirements shown in Table 7.3A.

Synthetic filter fabric should contain ultraviolet ray inhibitors and stabilizers toprovide a minimum of 6 months of expected usable construction life at atemperature range of 0 to 1200F.

2. Ensure that posts for sediment fences are either 4-inch diameter pine, 2-inchdiameter oak, or 1.33 lb/linear ft steel with a minimum length of 4 ft. Make surethat steel posts have projections to facilitate fastening the fabric.

3. For reinforcement of standard strength filter fabric, use wire fence with aminimum 14 gauge and a maximum mesh spacing of 6 inches.

TABLE 7.3ASEDIMENT FENCE FABRIC SPECIFICATIONS

Physical Property Minimum RequirementsFiltering Efficiency 85%Tensile Strength at 20% Standard Strength-(max.) Elongation 30 ib/lin in

Extra Strength-50 lb/lin in

Slurry Flow Rate 0.3 gal/sq ft/min

B. CONSTRUCTION

1. Construct the sediment barrier of standard strength or extra strength syntheticfilter fabrics.

2. Ensure that the height of the sediment fence does not exceed 18 inches above theground surface. (Higher fences may impound volumes of water sufficient to causefailure of the structure.)

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3. Construct the filter fabric from a continuous roll cut to the length of the barrier toavoid joints. When joints are necessary, securely fasten the filter cloth only at asupport post with overlap to the next post.

4. Support standard strength filter fabric by wire mesh fastened securely to theupslope side of the posts using heavy duty wire staples at least 1 inch long, or tiewires. Extend the wire mesh support to the bottom of the trench.

5. When a wire mesh support fence is used, space posts a maximum of 8 ft apart.Support posts should be driven securely into the ground to a minimum of 18inches.

6. Extra strength filter fabric with 6-ft post spacing does not require wire meshsupport fence. Staple or wire the filter fabric directly to the posts.

7. Excavate a trench approximately 4 inches wide and 8 inches deep along theproposed line of posts and upslope from the barrier.

8. Backfill the trench with compacted soil or gravel placed over the filter fabric.

9. Do not attach filter fabric to existing trees.

Maintenance

Inspect sediment fences at least once a week and after each rainfall. Make any required repairsimmediately.

Should the fabric of a sediment fence collapse, tear, decompose, or become ineffective, replace itpromptly.

Remove sediment deposits as necessary to provide adequate storage volume for the next rain andto reduce pressure on the fence. Take care to avoid undermining the fence during cleanout.

Remove all fencing materials and unstable sediment deposits and bring the area to grade andstabilize it after the contributing drainage area has been properly stabilized.

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10.03.7.4 - TEMPORARY STRAW BALE BARRIER

Definition

A barrier installed across, or at the toe of, a slope to intercept and detain sediment.

Purpose

To intercept and detain small amounts of sediment from unprotected areas of less than 1/2 acre.


a) Where it is feasible.

b) Contributing area is approximately 1/2 acre, or less.

c) There is no concentration of water in a channel above the barrier.

d) Erosion would normally occur in form of sheet erosion.

e) Length of slope above the barrier is less than 100 feet.

Straw bales must not be used on high sediment producing areas, above “high risk” areas, wherewater concentrates, or where there would be a possibility of a washout.

Design Criteria

No design required. Bales must be securely tied.

See Figure 7.4a for installation details.


1. Bales will be placed in a single row, lengthwise, on the contour and embedded in the soilto a depth of 3 inches.

2. Bales must be securely anchored in place by stakes or re-bars driven through the bales orby other acceptable means to prevent displacement.

3. Inspection must be frequent and repair or replacement must be made promptly as needed.

Maintenance

Inspect straw bale barriers at least once a week and after each rainfall. Make any required repairsimmediately.

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Should the barrier collapse, decompose or become ineffective, replace it promptly.

Remove sediment deposits as necessary to provide adequate storage volume for the next rain andto reduce pressure on the barrier.

Remove the barrier and unstable sediment deposits and bring the area to grade and stabilize itafter the contributing drainage area has been properly stabilized.

Figure 7.4a - Temporary straw bale installation detail.

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10.03.8 STREAMBANK PROTECTION

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10.03.8.1 - VEGETATIVE STREAMBANK STABILIZATION

Definition

Stabilization and protection of eroding streambanks with selected vegetation.

Purpose

To protect streambanks from the erosive forces of flowing water and provide a natural, pleasingappearance.


Sections of streambank subject to erosion from excess runoff. This practice is generallyapplicable where bankfull flow velocity does not exceed 6 ft/sec and soils are erosion resistant.Above 6 ft/sec, structural measures are generally required.


Upstream development accelerates streambank erosion by increasing the frequency and durationof bankfull full.

Streambanks may be stabilized by vegetation, by structural means, or by combinations ofvegetative and structural measures. Vegetative measures are generally preferred becausevegetation provides habitat for fish and wildlife and is aesthetically pleasing. Natural plantcommunities that are adapted to the site provide a self-maintaining cover that is less expensivethan structural alternatives. Planting vegetation is also less damaging to the environment thaninstalling structures. Therefore, vegetation should always be considered first.

Plants provide erosion protection to streambanks by:

a) reducing stream velocity,

b) binding soil in place with a root mat,

c) covering the soil surface when high flows tend to flatten vegetation against thebanks.

One disadvantage of vegetation is that it lowers the carrying capacity of the channel which maycause flooding. Therefore, maintenance needs and the consequences of flooding should beconsidered.

Evaluate erosion potential of the stream to determine the best alternative solutions, considering:

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a) frequency of bankfull flow based on anticipated watershed development,

b) channel slope and flow velocity, by design reaches,

c) soil conditions,

d) present and anticipated channel “n” values,

e) channel bends and bank conditions, and

f) identification of stable areas and trouble spots. (Steep channel reaches, higherosive banks and sharp bends may require structural stabilization measures suchas riprap, while the remainder of the streambank may require only vegetation.)

Design Criteria

The variety of plants which should be considered for use as vegetative streambank stabilizationare so numerous that a discussion in the text of this manual would not be feasible. In designingvegetative streambank stabilization, consider the natural zones of a streambank when selectingplant species, (Figure 8.la).

Following is a guide of natural zones for locating plant groups:

1. Aquatic plant zone - This zone is normally submerged and is inhabited by plants such aspondweeds and water lilies.

2. Reed-bank zone - The lower part of this zone is generally submerged for about half thetime and is inhabited by rushes, reed grasses, cattails, and other water plants.

3. Shrub zone - This zone is flooded only when flow exceeds the average high water level.The shrub zone is inhabited by trees and shrubs with high regenerative capacity, such aswillows. Shrub zone vegetation is recommended for the impact bank of a streammeander, where maximum scouring occurs. Infringement of shrub vegetation into thechannel reduces channel capacity, however, increasing the frequency of floods.

4. Tree zone - This zone is flooded only during periods of very high water.

The designer is encouraged to obtain information from other sources which would specifyvarieties of plants compatible with the location and intended use within the streambank.Recommended methods of planting and maintenance requirements should also be obtained.

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Figure 8.la - Natural zones of a streambank.

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10.03.8.2 - STRUCTURAL STREANBANK STABILIZATION

Definition

Stabilization of eroding streambanks by the use of designed structural measures.

Purpose

To protect streambanks from the erosive forces of flowing water. Conditions Where PracticeApplies

Sections of streambank that are subject to erosion due to excessive runoff from constructionactivities. Generally applicable where flow velocities exceed 6 ft/sec or where vegetativestreambank protection is inappropriate.


Stream channel erosion problems vary widely in type and scale, and there is no one measure thatworks in all cases. Many of the practices discussed here involve the use of manufacturedproducts and should be installed in accordance with the manufacturer’s specifications.

Design Criteria

Since each reach of channel requiring protection is unique, measures for structural streambankprotection should be installed according to a plan based on specific site conditions.

Develop designs according to the following principles:

a) Make protective measures compatible with other channel modifications plannedor being carried out in other channel reaches.

b) Use the minimum design velocity of the peak discharge of the 10-yr storm.Structural measures must be effective for this design flow and must be capable ofwithstanding greater flows without serious damage.

c) Ensure that the channel bottom is stable or stabilized by structural means beforeinstalling any permanent bank protection.

d) Ensure that streambank protection extends between stabilized or controlled pointsalong the stream.

e) Do not change channel alignment without a complete evaluation of the anticipatedeffect on the rest of the stream channel, especially downstream.

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f) Give special attention to maintaining and improving habitat for fish and wildlife.


1. Riprap - Riprap is the most commonly used structural material for stabilizingstreambanks. When possible, slope banks to 2:1 or flatter, and place a gravel filter or filterfabric on the smoothed slopes before installing riprap. Place the toe of the riprap at least 1ft below the stream channel bottom or below the anticipated depth of channel degradation.Where necessary, riprap the entire stream cross section. It is important to extend theupstream and downstream edges of riprap well into the bank and bottom. Extend riprapsections the entire length between well-stabilized points of the stream channel.

2. Gabions - These rectangular, rock-filled wire baskets are pervious, semi-flexible buildingblocks that can be used to armor the bed and/or banks of channels or act as deflectors todivert flow away from eroding channel sections. Design and install gabions in accordancewith manufacturer’s standards and specifications.

3. Reinforced concrete - May be used to armor eroding sections of the streambank byconstructing retaining walls or bulk heads. Provide positive drainage behind thesestructures. Reinforced concrete may also be used as a channel lining for streamstabilization.

4. Grid pavers – Modular concrete units with interspersed void areas that can be used toarmor the streambank while maintaining porosity and allowing the establishment ofvegetation. These structures may be obtained in precast blocks or mats that come in avariety of shapes, or they may be formed and poured in place. Keep the design andinstallation in accordance with manufacturer’s instructions.

5. Revetment - Structural support or armoring to protect an embankment from erosion.Riprap or gabions are commonly used. Gabions may be either stacked or placed as amattress. Install revetment to a depth below the anticipated channel degradation and intothe channel bed as necessary to provide stability.

Stabilize all areas disturbed by construction as soon as the structural measures arecomplete.

Maintenance

Check stabilized streambank sections after every flood event and make needed repairsimmediately to prevent further damage.

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erosion and sediment control specifications...effective erosion and sedimentation control requires...

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