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ALASKA POWER AUTHORITY
BEST MANAGEMENT PRACTICES MANUAL
EROSION AND SEDIMENTATION CONTROL
February 1985
Prepared by Frank Moolin &Associates,Ire.
-under contract to Harza-Ebasco
Susitna Joint Venture ARLIS
Alaska Resources
Library &Information Services
Anchorage.Alaska
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PREFACE
This manual is one of a series of Rbest management practices"manual to be used
in the design,.construction,and maintenance of Alaska Power Authority projects.
It represents a coordinated effort involving federal,.state and local government
agencies,and special interest groups.
The Alaska Power Authority intends that applicable gUidelines and state-of-the-
art techniques contained in the manuals will be incorporated where appropriate
into the contractual documents for projects constructed,maintained,or operated
.-bY'or under the direction of the Alaska Power Authority.
TABLE OF CONTENTS
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PREFACE
CHAPTER 1 -INTRODUCTION
CHAPTER 2 -GENERAL GUIDELINES
2.1 PLANNING
2.2 DESIGN
2.3 CONSTRUCTION
2.4 MAINTENANCE
CHAPTER 3 -SPECIFIC TECHNIQUES
3.1 EARTHWORK
3.1.1 Clearing and Grubbing
3.1.2 Surface Preparation
3.1.3 Borrow and Disposal Practices
3.1.3.1 Operations Plans
3.1.3.2 All Borrow Sources
3.1.3.3 Upland Sites
3.1.3.4 Floodplain Sites
3.2 DRAINAGE STRUCTURES
3.2.1 Culverts
3.2.1.1 Non-Fish Streams
3.2.1.2 Fish Streams
3.2.2 Low-Water Crossings
3.2.3 Grading and Cross Drains
3.2.4 Vegetated Channels
3.2.5 Ditch Checks,Check Dams
3.2.6 Mechanical Channel Liners
3.2.7 Outlet Protection
3.2.8 Inlet Protection
3.3 ICING CONTROL
3.3.1 Stacked Culverts and Subsurface Drains
3.3.2 Culvert Thawing
3.3.3 Channel Maintenance
3.4 STREAM PROTECTION
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3.4.1
3.4.2
3.4.3
3.4.4
Protection During Crossing and Construction 62
Bank Stabilization -Revetments 63
Bank Stabilization -Deflectors &Jetties 65
Bank Stabilization -Vegetative ~IE;66
Alaska Resources
Library &Information Services
Anchorage.Alaska
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TABLE OF CONTENTS (continued)
3.5 SEDIMENT RETENTION
3.5.1 Settling Ponds
3.5.2 Buffer Strips,Barriers
3.5.3 Trap and Filters for Inlets
3.5.4 Silt Curtains
3.6 SLOPE STABILIZATION
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71
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73
73
3.6.1 General Techniques for Non-Pennafrost Areas 73
3.6.2 Temporary Downdrains 75
3.6.3 Permanent Downdrains 76
3.6.4 Diversions and Benches 79
3.6.5 Level Spreaders and Interception Dikes 81
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3.7 THERMAL EROSION CONTROL
3.7.1 Prevention/Treatment of Disturbed Surfaces
3.7.2 Cut Slope Stabilization
3.8 REVEGETATION
3.8.1 Soil Constraints
3.8.2 Site Preparation
3.8.3 Seeding
3.8.3.1 Timing
3.8.3.2 Application Methods
3.8.3.3 Recommended Seeds and Mixtures
3.8.4 Fertilization
3.8.5 Mulches
3.8.6 Woody Plants
3.9 RECLAMATION
3.10 INSPECTION AND MONITORING
CHil1.PTER 4 -AUTHORITIES AND AGENCIES
REFERENCES
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LIST OF TABLES
Guidelines for Borrow Operations in Braided
Rivers
Guidelines for Borrow Operations in Split Channel
Rivers
Guidelines for Borrow Operations in Meandering,
Sinuous,and Straight Rivers
Minimum Flood-Flow Buffer Widths
Approximate Maximum Channel Depths -Gravel Bars
Adjacent to High-Water and Abandoned Channels
Approximate Maximum Channel Depths -Gravel Bars
Adjacent to Active Channels
Species~Velocities,and Soils for Vegetated
Channels
Soil Groups in Al aska
Cook Inlet-Susitna Area Seeding Recommendations
Interior Area Seeding Recommendations
Southeast Area Seeding Recommendations
Southwest Area Seeding Recommendations
Western Area Seeding Recommendations
Arctic and Alpine Areas Seeding Recommendations
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47
88
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FIGURE
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LIST OF FIGURES
Schematic Diagram of a Low-Flow Buffer
Schematic Diagram of a Flood-Flow Buffer
Low-Water Crossing
Cross Drains
Ditch Checks,Check Dams
Mechanical Channel Liners
Outlet Protection
Stacked Culverts and Subsurface Drains
Frost Belts
Gravel Washing Settling Pond Layout
Sediment Barriers
Temporary Downdrains
Pennanent Downdrains
Diversions and Benches
Level Spreaders and Interceptor Dikes
Treatments for Cut Slopes
Geographic Areas by Vegetative Type
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CHAPTER 1 -INTRODUCTION
This manual has been prepared by the Alaska Power Authority as one of a series
of best management practices manuals for projects constructed or operated by the
Power Authority in Alaska.The guidelines and techniques presented in this
manual for control and prevention of erosion and sedimentation represent a
compil ation of information contained in numerous publ ished sources and the
direct recommendations of public agencies and special interest groups.Whil e
the information presented will be used in preparing contractual documents for
projects,it is not all inclusive.Rather,it concentrates on commonly accepted
practices.Nor are all the techniques appropriate for a particular site.
Therefore,this manual should be used only as a guide to select appropriate
site-specific procedures.It is intended to create an awareness of the ways and
means to minimize e.ffects of construction on the natural environment,to identi-
fy potential environmental hazards that must be considered,and to suggest
methods that can be employed to avoid or minimize environmental disturbances.
Federa l,state,and local 1aw impose specific requirements on parti cul ar Power
Authority construction projects or activities.This manual is not a substitute
for case-by-case identification and compliance with all laws and regulations
applicable to the construction and operation of Power Authority projects.
Prior to the start of construction of a project component,the contractor will
prepare a detailed plan of operations.This plan will be reviewed by the
eng;neering consultants,who,in turn,wi 11 recommend action to the Power
Authority.The plan prepared by the contractor will conform with the guidelines
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presented in this manual and with any appropriate land or water use authoriza-
tion stipulations or conditions.
Summary guidelines addressing general situations and conditions are contained in
Chapter 2 of this manual.Chapter 3 discusses alternative techniques for
specific phases of a project to implement the summary gUidelines listed in
Chapter 2.Regulatory authorities and agencies involved in controlling erosion
and sedimentation are listed in Chapter 4.
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CHAPTER 2 -SUMMARY GUIDELINES
Any planned action should be conducted with forethought toward minimizing any
damage which may result.This chapter summarizes general guidelines for reduc-
ing erosion,minimizing sedimentation,and lessening water quality impacts.It
is organized according to the phases of project development:planning,design,
construction,and maintenance.Alternative techniques to implement these
general guidelines are presented in Chapter 3.
2.1 PLANNING
The planning process entails several important elements,including initial
site selection,reconnaissance studies,economic evaluations,and review of
applicable legal and permitting requirements.This development phase
offers the greatest opportunity to explore and anticipate erosion related
problems and take initial action to avoid or minimize their occurrence.
Following are general guidelines pertaining to the planning phase:
Site Selection
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o Utilize a planning team comprised of multidisciplinary special-
ists experienced in Alaska .conditions.
o Fully consider land use management probl ems and assess impacted
resources.
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o Maintain an open dialogue among government and private managers,
engineers,environmental specialists,and planners,as well as
solicit public input.
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Assemble available data concerning water quality,soils,topogra-
phy,climate and biology to determine erosion potential and other
related problems.
Consolidate related facilities to minimize environmental damage.
Utilize existing rights-of-way whenever feasible.
Identify criteria needed for selection of acceptable sites and
routes.
Avoid,when feasible,siting fac;liti~s in areas of unstable
permafrost soils,seepage zones,landslide areas,dissected
terrain,ponds,natural channels,wetlands,and critical habitat.
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a Minimize cut and fill approaches to streams and encroachment on
streams •
Reconnaissance
o Minimize surface disturbances when conducting reconnaissance
activities.
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Reconnaissance surveys shall include preliminary aerial photogra-
phy and map studies followed by extensive ground-truthing pro-
grams.
Collect sufficient data on surface and subsurface soils,geology,
vegetative type and cover,fish and wildlife,climate and topo-
graphy not only to be incorporated into conceptual engineering
design requirements,but also to estimate erosion potential and
risk,and requirements for restoration.
Areas disturbed by reconnaissance activities shall be treated to
prevent degradation.
Clearing for ground surveys shall be kept to a minimum.
Economic Evaluation
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Erosion protection should be cost justified with alternate sites,
routes and configurations.
Erosion and sedimentation control techniques should be considered
as capital costs.Projected maintenance costs of these items
should be evaluated.
Review of Project Permit Reguirements
o Identify project goals and describe proposed construction and
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other activities to implement goals.
o Determine project impact on environment.
o Identify statutes,regulations and aencies which regulate either
the proposed activity or its impacts.In particular,determine
whether existing Power Authority permits control the activities
or impacts involved.
o Compare burdens imposed by regulations and/or permits for pro-
posed activities and alternatives (incl uding costs associ ated
with modifying activities to reduce or eliminate requirements).
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o Develop and implement permitting strategy to obtain timely
issuance of permits.
2.2 DESIGN
Many problems involving erosion during and after construction can be
mitigated by proper design.Even with the design,however,some erosion
can be expected.Provi si ons shaul d be made to accommodate unforeseen
circumstances and provide for adequate protection.General guidelines
pertaining to the design phase are summarized as follows:
Configuration
o When feasible,locate facilities on well drained upland areas and
away from stream courses and wetland areas.
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o Avoid seepage areas and geologic features which may result in
instability.
o Make cuts as steep as possible to minimize surface area.In
erodible soils,incorporate slope stabilization measures.
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Fills or embankments should be well compacted and built in lifts.
Desi gn s lopes fl atter than the angl e of repose for greater
stability.
Design to reduce the amount of c1earingrequired for cuts and
fi 11 s.
Design to prevent accumulatfon of water on surfaces of temporary
or completed work areas.
Whenever feasible,maintain buffer strips of undisturbed land and
vegetation in areas adjacent to streams,1akes over 5 acres in
size,critical areas,and borrow sites.Consult resource agency
land use plans for suggested buffer widths.Unless agreed to
otherwise by the landowner,managing or licensing agency,or when
no guidance exists,buffer strips should be 500 feet wide.
Drainage Design
o Maintain natural drainage patterns where possible.
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o Design to provide interception and removal of runoff waters.
Incorporate temporary measures to protect disturbed areas.
o Give ample consideration to determining the design flood when
designing culvert installations.Provide for clean-out or use
debris collectors to prevent clogging.
o Provide sufficient cross-drainage to prevent excess accumulation
on uphill sides of temporary or permanent work areas.
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On low-use access routes,use water bars and low-water crossings
for reduced maintenance.Consider fish passage requirements
through the use of such techniques as low-flow channels.
Provide adequate protection for inlets and outlets of drainage
structures.
o Approach stream crossings at right angl es,and when feasibl e
leave a buffer strip along the stream bank until actual construc-
tion of the structure is ready to begin.
o In permafrost areas or erodible natural soils,avoid concentrated
discharges from drainage structures.Attempt to convert to sheet
flow to prevent ground erosion.
o Consider bridges where fish passage is critical and where spawn-
ing and rearing habitat occurs.Provide clearance for debris and
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to avoid icing,and stabilize banks.
In areas where the facility will be endangered,provide a means
to remove or control groundwater and seepage waters to prevent
"aufeis"buildup.
o Consult applicable federal and state agencies for fish require-
ments and other habitat features.
Permafrost Design
o Whenever possible,use overlay construction as opposed to cut and
fill.
o When practicable,use insulation beneath fills to reduce the
amount of fill material.
o When using overlay,avoid stripping of the organic layer.
o Consider winter construction to avoid melting and thermal degra-
dation.
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Provide for stabilization of cut slopes.
Avoid induced drainage or standing water over permafrost areas
which can result in rapid thermal degradation.
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Erosion Control Design
o Based on design and construction requirements,incorporate
temporary erosion control procedures into design provisions.
o Give special attention to immediate control of surface runoff
waters.
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o \~here feasible,revegetate or otherwise stabilize erodible areas
which are to be left uncompleted for the following season.
o Consider work schedules and local climatological events to insure
adequate erosion protection is provided.
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Take advantage of natural erosion control features such as
vegetative and brush buffer strips.
Provide for adequate right-of-way to perform erosion-related
work.
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Design Documentation
o Specifications shall clearly detail measures to prevent erosion.
o Insure correlation between plans,specifications and design
documents.
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o Insofar as possible,incorporate all temporary and permanent
erosion control measures into the final design and bid documents.
o Allow flexibility to resident engineers and contractors to
improve upon design or methods.
o Provide contingency to allow for unforeseen circumstances.
o Contract scheduling shall specify the appropriate time to perform
all seasonally-effected work,to result in minimal impact.
2.3 CONSTRUCTION
The construction force shoul d follow procedures to prevent erosion.The
following guidelines pertain to the construction phase:
General
o A preconstruction conference shall educate and coordinate all
involved parties towards the goals of erosion control and pro-
tection of water quality,permit requirements and stipulations,
and inspections.
o Equipment operators and other personnel shall clearly understand
and participate in safe and proper practices.
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o The Power Authority's environmental inspector shall be given
sufficient authority to be effective.
flearing and Grubbing
o Protect establ ished monuments and clearly mark work area boun-
daries on the ground prior to initiating clearing or other ground
disturbance operations.
o All trees,snags and other wood material cut in connection with
clearing operations shall be felled within the clearing bounda-
ries.
o Avoid destroying the organic mat in permafrost areas.Immedi ate
treatment shall follow any disturbances.
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o Keep clearing and grubbing operations closely in line with
subsequent activities.Avoid clearing beyond the present sea-
son's schedule.
o Dispose of clearing debris in accepted manners.Utilize avail-
able materials for brush barriers and ditch checks.
o Whenever feasible,uti 1ize non-mechanical means when clearing in
permafrost locations,wetlands and in areas such as along tops of
cut banks.
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Earthwork
o Dependent upon load-bearing capacity specifications,chipped
wood,limbs,and other organic detritus may be mixed with mineral
materials in road fill embankments.Compact fills in lifts to
reduce infiltration and settliFig.Avoid placing fill in areas
covered by snow or ice.
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Provi de temporary protecti on such as berms to the tops of erodi-
ble cut and fill slopes.
Dispose of waste spoils in approved areas away from water courses.
Preferred methods include disposal in any future impoundment area
of a reservoir,or retention for rehabilitation of material sites
or for solid waste disposal site maintenance.
Dependent upon material quality and availability,borrow areas
should be located in upland areas.
-o Provide for perimeter dikes,ditches and sediment removal at
borrow sites.
o Apply measures to control surface runoff waters throughout
construction areas.
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Borrow and Disposal Areas
a Design for phased development whenever feasible.
a Conserve stripped topsoil for respreading over completed areas.
a Provide perimeter dikes,diversions and other techniques to
prevent sediment movement from excavated areas into streams and
drainages.
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Qrainage
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Incorporate sediment removal techniques into disposal site plans.
Prepare comprehensive operations pl ans which outl ine excavation
and disposal techniques,applicable erosion procedures,and final
restoration measures.
Stabilize all slopes and embankments.Grade to stable slope
angles.
Keep sediment and debri s out of all structures.Stabi 1i ze at
inlets and outlets.
Consider using low-water crossings for both temporary and perma-
nent cross-drains on low-traffic volume access routes,particu-
larly those that do not cross fish streams.
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o Exercise care and comply with permit stipulations when rerouting
streams during bridge and culvert installation.Provide a
non-erosive temporary channel or sediment removal measure such as
silt curtains.
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o Avoid sedimentation of water courses when removing temporary
structures.
Erosion Control and Revegetation/Reclamation
o Schedule final reclamation activities to closely follow final
construction.
a Utilize temporary techniques to protect slopes until final
treatment.
o Conserve stripped topsoil for respreading over completed areas.
o Surfaces left exposed for extended periods shall be temporarily
revegetated with fast-growing native species in areas subject to
erosion or where siltation will be a problem.Encourage reinva-
sion by native species from surrounding undisturbed areas.
a Establish permanent erosion control items.Give consideration to
critical areas and erodible soils.Maintain appropriate erosion
control materials on site.
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o Abandon,block,and restore unused roads,borrow and disposal
sites and other low-use areas.Stabilize cross-drains by either
removal or adequate inlet and outlet protection~
o Inspect abandoned facilities periodically to correct any erosion
problems.
2.4 MAINTENANCE
Proper maintenance is essential to ensure that some erosion control struc,;.
tllJres function effectively.General guidelines for maintenance activities
are as foll ows:
Glenera 1
o Provide a planned,regularly scheduled maintenance program
incorporating inspection and expeditious repair.
o Develop dialogue between maintenance and design personnel.
Drainage Systems
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Inspect all drainage structures prior to wet seasons or before
winter.Clean out debris and sediment.
Remove transportable debri s upstream and downstream of drainage
structures.
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o Clean out ditches,sediment basins and other sediment retention
structures periodically.Dispose of sediments according to
approved plan design and specifications.
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Surface Maintenance
o Treat washouts and gullies on sTopes by filling,mulching and
revegetation .
o Avoid damaging treated areas with mechanized maintenance equip-
ment.
o Direct special attention to frozen cuts until stabilized.
o Keep non-paved surfaces crowned or sloped.Avoid wi ndrows along
edges to provide lateral drainage.
o Water and fertilize revegetated areas to promote growth.
a Dust control chemicals should be used carefully and only lrlitl1
accepted techniques according to local,state and federal regu-
lations.
Winter Maintenance
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o Prior to breakup,remove or level snow berms along road edges to
prevent accumulation of meltwaters.
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Use salts and other chemicals prudently,especially near any
streams containing aquatic 1 ife.Comply with applicabl e regu-
lations.
Attempt to divert aufeis-forming flows away from driving sur-
faces.Where possible,thaw culverts susceptible to erosion from
ice-buildup.
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CHAPTER 3 -SPECIFIC TECHNIQUES
This chapter presents descriptions of specific techniques to implement the
guidel ines 1 isted in Chapter 2.In most instances,site-specific conditions
will dictate the feasibility of a particular technique or the need to modify it.
Nn attempt has been made to represent all possible techniques,nor should the
te.chniques as described in this manual be considered as design standards or
contract specifications.
3.1 EARTHWORK
3.1.1 Clearing and Grubbing
Clearing and grubbing activities involve removal of vegetation and timber.
Any clearing operation must be restricted to areas marked on the ground at
the work site prior to beginning construction.All trees,snags and other
y,rood material cut in connection with clearing operations must be felled
\'jlithin the clearing boundaries.To minimize and protect erodible surfaces,
clearing should be scheduled to closely precede excavation and construction
a.ctivities in any given area.All vegetation which does not interfere with
construction activities should be left.Whenever feasible,hand clearing,
instead of mechanical equipment,shall be used to clear permafrost areas
(for summer construction),wetlands,and at the top of cut banks.Buffer
strips of existing vegetation at approaches to stream crossings should be
maintained until actual construction.Instream equipment operation in
alnadromous fish streams should be kept to an absolute minimum and as
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permitted by the Alaska Department of Fish and Game.If felled trees or
other debris unavoidably enter a stream,they must be removed within 48
hours.
Clearing and grubbing materials can be buried,burned,chipped or sold as
appropriate.
3.1.2 Surface Preparation
A variety of techniques can be used to stabil ize disturbed surface areas,
promote seed germination,increase soil moisture retention,reduce movement
of seed and fertilizer,and increase runoff infiltration.
All disturbed areas,even those which will not be revegetated,should be
scarified to a depth of 12 inches to increase aeration and moisture infil-
tration and to control runoff."Cat-tracking",which consi sts of running
tracked vehicles up and down slopes to create mini-benches,can be effec-
tive on slopes up to 2:1.Dics and harrows can also be used for scarifi-
cation.Another technique for improving infiltration is to cut or serrate
slopes into mini-benches along the contours.
The configuration of a fill area is critical to providing surface drainage
and minimizing runoff of eroded soils.For example,in roadbed construc-
tion,the final lift of each day's work should be crowned and drum rolled
to direct surface runoff to ditches,berms,or other stabilized areas.A
surface dressing of aggregate can also minimize surface erosion.
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If the surface is to remain unused for extended periods,temporary cover
may be required to stabilize soil from wind and winter erosion.This can
be achieved by applying aggregate cover or soil binders,or by establishing
temporary vegetation.
3.1.3 Borrow and Disposal Practices
Careful site planning of borrow and disposal areas is required to prevent
or minimize sedimentation.Each site will impose its own 1 imitations,
~rhich should be considered to facilitate economical and effective con-
struction techniques.
3.1.3.1 Operations Plans
A,detailed plan of operations will be required for each borrow site.The
plan should include:
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o Oust control procedures
o Final reclamation measures
3.1.3.2 All Borrow Sources
Whenever possible~borrow sites should be located in upland areas rather
tlhan in floodplains where they may degrade water quality and sensitive
habitat.
An sites should be surveyed and their boundaries clearly marked.Pre-
construction elevation controls will facilitate restoration efforts upon
site closure.It is particularly important that sites planned to be open
during winter be surveyed during the.summer months and that boundary
markings be established so they they can be found during heavy snow cover.
The 1 imits of the area worked within a site should avoid a straight 1 ine
configuration and should be shaped to blend with natural physical features.
When possible.borrow sites should be worked in phases to minimize the
amount of disturbed areas.As one segment is completed.it may besta-
bilized while the next segment is developed.Progressive upslope or
upstream work will allow use of preceding work sections for settling ponds
(see Section 3.5.1).
If operations require washing of heavy equipment.a specially designated
area must be provided to facilitate treatment of the wash water.For large
operations,treatment may require construction of a catch basin.
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3.1.3.3 Upland Sites
Borrow areas should be located away from heavy groundwater seepage path-
ways.Surface runoff upslope of the pit should be diverted with dikes to
ditches.The floor of the pit should be sloped to facilitate drainage and
any surface runoff from the pit should pass through settling ponds before
entering a waterbody.Small volumes of discharges from settling ponds can
be diverted to overland flow if ground conditions allow the water to
percolate at a rate which will not cause rills or gullies.
Spoil or waste material removed during site opening should be disposed of
in an approved manner or stockpiled.
Borrow area slopes should not adjoin steep slopes except for those slopes
composed of rock.Excavated faces of rock quarries may be left vertical,
but no face should be more than 30 feet high without an intermediate bench
10 feet wide.
All completed borrow sites should be sloped to stable angles.Further
reclamation,such as revegetation,will be performed in accordance with
stipulations of the regulatory agency or landowner.Respreading topsoil
removed during initial site opening will assist in reclamation efforts.
3.1.3.4 Floodplain Sites
Site Planning
Borrow sites within a floodplain should be developed so that disturbance of
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the following features is minimized:
o Fish spawning and overwintering habitats
o Vegetated banks and associated riparian zones
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o Springs
o Active channels in small rivers
.Projects requiring large borrow quantities (approximately 65~000 cubic
yards or more)should consider 1)scraping of unvegetated,mid-channel bars
a'nd lateral bars in braided rivers and medium and large split-channel
rivers,and 2)pit excavation in terraces or inactive floodplains.Pro-
j1ects requiring less than 65,000 cubic yards should consider 1)scraping
wnvegetated mid-channel and lateral bars in braided rivers and large and
mledium split-channel rivers,2)scrapi,ng point bars of large and medium
meandering rivers,and 3)scraping in terraces or inactive floodplains.
Specific guidelines for borrow operations in rivers of different size l )and
configuration,and for different deposit locations in each size and confi-
guration are presented in Tables 1 through 3.
D,esign of specific work area boundaries should incorporate the following
factors:
1)Small river - a river with a drainage area less than 40 square miles and a
mean annual flow channel top width of less than 50 feet.
Medium river - a river with a drainage area greater than 40 square miles but
less than 380 square miles and a mean annual flow channel top width greater
than 50 feet but less than 300 feet.
large rivers - a river with a drainage area greater than 380 square miles and
a mean annual channel top width greater than 300 feet.
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TABLE 1
GUIDELINES FOR BORROW OPERATIONS IN BRAIDED RIVERS
,...
River Site Associated
size location channel Type of deposit
l::or-.....
l::R:S (IJ r-or-r-l::(IJ "R:S c-l::l::~~l::
r-".....R:S l::R:S ~Q)R:S ~
c-O (IJ oJ::R:S .0 (IJ "r-l::
"0 l::t)oJ::"l::111 R:S
0 r-l::t)~.....l::10 or-.0
0 'i-10 ~R:S QJ R:S Q)
r-oJ::QJ "~co l::QJ e ""'i-QJ t)+.l QJ 10 l::e Q)CIJ
>Q)10 l::co r-IO QJ of..)of..)e QJ or-t)QJ 3:0 R:S oJ::(IJ "R:S 10.....~QJ >of..)10 >,"of..)~t)"'r-of..)of..)
r-'r-C'l or-t)~or-oJ::l::l::(IJ ,or-111 CIJ QJ
R:S "~of..)10 ~of..)C'l R:S "'r-of..)"tJ)of..)C'l C'leQJR:S U l::QJ t)'r-.0 QJ 0 R:S or-l::~(IJ QJ
t/):r:...J et:-l-et::::I:et:ce 0......J :r:-0 ::>::>Comments
X X X X X X 1o Crave1 may be available by
scraping or dredgingo
X X X X X X X 2o Gravel available by scraping.
X X X X X·X X X X 3.Gravel available by scraping.
X X X X X X X X X 4.Generally should not be
mined.
X X X X X X X X X 5.Banks should not be minedo
X X X X X X X X 6.Grav~l available by scraping.
X X X X X X X X X 7.Gravel avail ab1 e by scraping.
X X X X X X X X X X X 8.Crave1 available by scraping
or pit miningo
Comments
Comment 1.Glenera11y,the bed of an active channel should not be disturbed.If bed deposits are the only
......available source,.the side channel (s)should be mined rather than the main channel.Select side channel (s)that
carr'y less thilln approximately one third of the total flow·during the mining p~riod;block off upstream ends and
minEl by scraping operations.If the main channel must be mined,dredging may be an apprOllriate method.
Comment 2.G.'ave1 is available by scraping gravel deposits to near the low summer flow or no lower than the
,....,water level present during the mining operation.Maintain appropriate buffers.
Comment 3.C"ave1 is available by scraping such that the configuration of the channel is not greatly changed
and there is nota high probability of channel diversion through the mined area.
,....Comment 4.VEigetated i sl ands shou1 d generall y be exc1 uded.Exposed deposits should be considered before vege-
tatEld island deposits.If deposits in feasible alternative locations are not sufficient,and vegetated islands
are abundant in the particular reach in question,up to about 10 to 20 percent of this habitat may be removed
_from about a given 3-mi1e length of the floodplain.
Comm~.Vegetated river banks of both active and high-water channels should not be disturbed.
Comn~.G,'avel is available by scraping within the channel;but the general configuration of the channel
should be maintained.
-Comment 7.Gravel may be available by scraping in these locations,but the general configuration of the channel
should be maintained.
Comm~.Generally,pits should only be considered when more than 65,000 cubic yards are required.
Sour'ce:U.So Fish and Wildlife Service (1980)
TABLE 2
GUIDELINES FOR BORROW OPERATIONS IN SPLIT CHANNEL RIVERS
-
-
-
River Site Associated
size location channel Type of deposit
c..........c ~QJ -.....-C QJ "C
~0-C C ~~c....."C .....~c ~~QJ ~~
0-0 QJ .s:::.~.a QJ "C .....C
"C 0 C U .s:::."C c tI)~
0 .....c u ~-c ~......a .
0 t!-~~~QJ ~~......s:::.QJ "C ~c:J c QJ'"C "C
t!-QJ U .j.,,)QJ ~c E QJ QJ
>QJ ~C c:J .....~QJ .j.,,)+"
E QJ .....U QJ :::0 ~.s:::.QJI "C ~~.....::;:,QJ >.j.J ~>I "C .j.,,)~U "C ......j.,,).j.J..........C'l .....U ~......s:::.c c QJ I .,...tI)QJ QJ
~"C ~.j.J ~~+"C)~"C ......j.J "C IIlI +"C'l C'l
E QJ ~U C QJ U .,...a QJ 0 ~.....c ::;:,QJ QJ
V'):::::.....l e(.....l-e(::::J:e(c:J a.......l :::::.....0 ::::-::::-Comments
X X X X X 1•Gravel may be avail able by
scraping or dredging.
X X X X X X X 2.Gravel available by scraping
X X X X X X X X X 3.Some gravel may be avail abl e
by scraping or pit.
X X X X X X X X X 4.Generally should not be
mined.
X X X X X X X X X 5.Banks should not be mined.
X X X X X X X X X X 6.Gravel available by scraping.
X X X X X X X X X X 7.Should not be mined.
X X X X X X X X X X X 8.Generally avoid,but much
available.
X X X X X X X X X X X X X X 9.Gravel avail abl e by scrape or
pit.
X X X X X X X X X X X 10.Gravel available by scraping.
Comment 1.Generally the bed of the active channel should not be disturbed.If bed deposits are the only
available source,the side channel (s)should be mined rather than the main channel.If the site contains a side
channel that carries less than approximately one third of the total flow during the mining period this channel
can be blocked at its upstream end and mined by scraping.If channels approximately this size are not available-then either the side or main channel can be mined using dredging.
Comment 2.Gravel is available by scraping deposits to near the low summer flow,or no lower than the water
level present during the mining operation.Maintain appropriate buffers.
-.Comment 3.Gravel is available if suitable buffers are maintained to protect against channel diversion.
Comment 4.Exposed deposits should be considered before vegetatl~d island deposits.If deposits in feasible
alternative locations are not sufficient,and vegetated islands are abundant in the river system in question,
r'"about 10 t02C percent of this habitat may be removed from about a 3-mile reach of floodplain.
Comment 5.Vegetated river banks of both active and high-water channels should not be disturbed.
Comment 6.Gravel is available by scraping in the high-water channel,but precautions must be taken to avoid
channel diversion.
Comment 7.Mining is not recommended in or near the active channel of small split channel rivers because there
is not must material available.
Comment 8.There generally is not much material avail able in these deposits and they should be avoided.If
--only a small amount (13,000 cubic yards)of gravel is needed,these deposits may be considered for scraping.
Comment 9.Pits should be considered when more than 65,000 cubic yards.
Comment 10.Some gravel is available by scraping,but the general configuration of the channel should be main-
,....tained.
Source:U.S.Fish and Wildlife Service (1980)
TABLE 3
GUIDELINES FOR BORROW OPERATIONS IN MEANDERING,SINUOUS,AND STRAIGHT RIVERS
-
River Site Associated
size location channel Type of deposit
~....r-
~ttS OJ ............~0)"'C
ttS 0-~~s-s-~...."'C ....ttS ~ttS s-O)ttS .:::.!.
0-0 OJ .s::ttS .Q 0)"'C ....~
"'C 0 ~u .s::"'C ~1Il ttS
0 -~u s-....~ttS ......0
0 ~ttl s-ttS 0)ttS OJ.....s::OJ "'C s-..0 ~~E "'C "'C
~OJ U 01->OJ ttS ~0)OJ
>OJ ttS ~.Q ....ttS OJ 01->01->
E OJ ....U OJ 3 0 ttS .s::<ll "'C ttS ttS....::::5 OJ >01->ttS >I "'C 01->s-U "'C ....01->01->
r-....Ol ....U s-.....c ~~0)I ....1Il OJ OJ
~"'C s-ol->ttS s-ol->t:)1 ttS "'C ....01->"'C 1Il 4->Ol Ol
OJ 1tI U ~<ll U ......0 OJ 0 ttS ....~::::5 OJ OJ
V)%....J <t .....l-<t ::c:<t co c.......J %.....0 :>:>Comments
X X X X X 1•Some gravel may be available
by dredging.
X X X X X X X 2.Gravel avail able by scraping.
X X X X X X X X X 3.Some gravel may be available.
X X X X X X X X X 4.Not recommended in these
systems.
X X X X X X X X X 5.Banks should not be mined.
X X X X X X X X X X 6.Gravel available by scraping.
X X X X X X X X X X X X 7.Should not be mined.
X X X X X X X X X X 8.Generally aVOid,but much
available.
X X X X X X X X X X X X X X 9.Gravel available by pit or
scrape.
Comment 1.Generally the bed of an active channel should not be disturbed.If bed deposits are the only avail-
able source,the gravel should be taken by dredging only under strict work plans and stipulations •
.....Comment 2.Gravel is available by scraping deposits to near the low summer flow or no lower than the water
level present during the mining operation.Maintain appropriate buffers.
Comment 3.Gravel is available if suitable buffers are maintained to protect against channel diversion.
~Comment 4.Vegetated islands should not be disturbed.
Comment 5.Vegetated river banks of both active and high-water chalnnels should not be disturbed.
Comment 6.Gravel is available by scraping in the high_ater chcrnnel,but precautions must be taken to avoid
channel diversion.
"""l'Comment 7.Mi ni ng in the acti veor hi gh-water channel s of these small rivers is not recommended because there
is not much material available.
Comment 8.There generally is not much gravel available in these deposits and they should be avoided.If only
a small amount (13,000 cubic yards)is needed,scraping may be considered.
Comment 9.Pits should be considered when more than 65,000 cubic yards are required.
Source:U.S.Fish and Wildlife Service (1980)
-
-
o
o
o
o
o
o
Site configurations should be shaped to blend with natural
physical features
Slopes and contours resembl ing those of natural bars should be
maintained when scraping point bars of meandering and sinuous
systems
Natural gravel bar shapes should be maintained when scraping
mid-channel and lateral bars of bll'aided systems
Pits should be excavated to provide irregular shore1 ines wi th
curved configurations,islands,spits,and diverse shorel ine
depths
When vegetated areas cannot be avoided,it is usual1ydesirab1e
to locate material sources in large stands of homogeneous mature
vegetated areas
The site should be located on the same side of the floodplain as
the material use point tom;nimi;~e the need for crossing active
channels.
-
Site Preparation
Design of floodplain access should avoid vegetated habitats.If it is
necessary to traverse vegetated areas,ice roads should be used for winter
operations and gravel should be spread over the organic layer for summer
operations.Floodplain access should occur at the inside of a meander to
avoid trafficking incised banks at outside meanders.Crossing of other
incised floodplain banks should also be avoided.If incised banks must be
crossed,a removeable fill ramp should be constructed instead of cutting or
-28-
......
notching the bank.If active channels must be crossed,crossing should be
via temporary bridges,low-water crossings,or properly cu1verted access
roads.
Any vegetation and organic overburden cleared during site preparation should be
removed from the active floodplain and eithe!r stockpiled for restoration activi-
ties or disposed of in an approved manner.
Buffer areas of undisturbed ground surface are required for most floodplain
borrow sites to maintain the integrity of active channel s.Where natural
buffers do not exist or are too low to be effective,man-made buffers in the
form of river-training structures and bank protection devices may be necessary.
low-flow buffers are recommended for scrapirtg operations on unvegetated gravel
bars adjacent to active channels.A low-flow buffer is a strip of undisturbed
ground surface extending up the bank and beneath the water surface from the
water1s low summer flow level (Figure I).The upper limit ofa low-flow buffer
is that point on the bank that is the lesser of the following:1)having an
elevation that is 0.5 meters (1.6 feet)above the low summer flow surface
elevation,or 2}having a horizontal distance to the low summer flow water's
edge wh i ch is equa 1 to one-half the norma 1 top wi dth at channe l-fu11 flow
conditions.The lower limit is that point on the bed that has a horizontal
distance to the water1s edge which is 10 percent of the top width of the
low summer flow channel.
Flood-flow buffers should be used for scraping or pit-mining operations
that are separated from active channels (Figure 2).The purpose of this
-29-
Lo'w Summer Flow Water's Edge
Lower Buffer Boundary
-
....
O.5W
w
•••.QJt~!l!l ~1.•f.y.IJ••~!!£l~••••••••52 •••
•5m
'il low Summer Flow Stage
w
ALASKA POWER AUTHORITY
SCHEMATIC DIAGRAM OF
A LOW-FLOW BUFFER
FIGURE 1
.-
-
ALASKA PO WER AUTHORITY
SCHEMATIC D'A FLOOD IAGRAM OF
-FLOW BUFFER
FIGURE 2
""."
I
undi sturbed,often vegetated t area is to prevent the active channel from
diverting through the material site.
In scraping removal operations t the site shoul d be protected by a flood-
flow buffer for at least 5 to 8 years to allow re-establishment of vegeta-
tion.The height of the buffer should be at least as high as the water
level during a 5-year flood.Table 4 Hsts minimum flood-flow buffer
widths for different sites.The width can be reduced to half the recom-
mended minimum at the downstream end of the scraped site.
For pi t removal operations,the si te s hou 1d be protected by a fl ood-fl ow
buffer for at least 20 years to provide long-term protection of this newly
created habitat.The elevation of the buffer should be at least as high as
the water level during a 20-year flood.Minimum flood-flow buffer widths
for pit operations are listed on Table 4.The width can be reduced to 20
percent of the recommended minimum at the downstream end of the pit.
Temporary dikes should be constructed around borrow sites that would be
inundated during operation.Dikes should be impermeable,high enough to
prevent overtopping t and protected from ernsion.They are often construc-
ted of stone and/or earth.Side slopes should be stable and riprapped
(generally,a 2:1 slope is recommended).The dikes should be constructed
to minimize disturbance to low-flow channels and avoid fish entrapment.
Borrow Operation -Scraped Sites
Gravel bars adjacent to high-water and abandoned channels can be scraped to
-32-
TABLE 4
MINIMUM FLOOD-FLOW BUFFER WIDTHS
-
Scraping Operations
River Size
Small
Medium
Large
Pit Operations
River Size
Small
Medium
Large
Source:U.S.Fish and Wildlife Service (1980)·
-33-
Minimum Width
(ft)
50
115
165
Minimum Width
(ft)
250
500
800
-.
a specified level at the edge of the channel and should be sloped toward
the channel to provide proper drainage.An average maximum depth (the
distance between the average thalweg profile line and the channel-full
stage at a point along the channel)should be maintained in the channel to
provide for flow containment during periods of high flow within the chan-
nel.Approximate values of maximum depth that should be maintained for
three ranges of channel-full width ~re listed on Table 5.
Gravel bars·adjacent to active channels can be scraped to a specified
minimum level and should be sloped toward the channel to provide proper
drainage.The recommended lowest elevation of gravel removal is controlled
by the greatest of the following three elevations:
F"",
-
-
o
o
o
The upper elevation of the low-flow buffer
The elevation corresponding to 6 inches above the average water
level expected during the gravel removal operation
The elevation that will maintain a specified average maximum
depth in the active channel (approximate values of maximum depth
for three ranges of channel-full width are listed on Table 6)
Scraping in high-water and abandoned channels should follow the alignment
of the channel.Side slopes should be stabilized for flow conditions
during a 2-year recurrence interval (annual)flood.The channel-full top
width should not be increased.Longitudinal slope into the material site
at the upstream end should not exceed 10 times the average slope of the
-34-
-
TABLE 5
APPROXIMATE MAXIMUM CHANNEL DEPTHS
GRAVEL BARS ADJACENT TO HIGH-WATER AND ABANDONED CHANNELS
Braided Configuration
Approximate maximum depth (in)
Channel-full
width (ft)
o -15
15 -100
100 or greater
High-water channel s.
12
20
30
Abandoned channels
2
6
20
.-Split,Meandering,Sinuous,and Straight Configurations
Approximate maximum depth (in)
-
Channel-full
width (ft)
o-15
15 -100
100 or greater
High-water channel~
15
24
40
Abandoned channels
6
12
24
-Source:U.s.Fish and Wildlife Service (1980)
-35-
-
TABLE 6
APPROXIMATE MAXIMUM CHANNEL DEPTHS
GRAVEL BARS ADJACENT TO ACTIVE CHANNELS
Braided Configurati.Q.!l
-
-
-
Channel-full
width
(ft)
a -15
15 -100
100 or greater
Approximate
maximum depth
(in)
12
20
39
F""
I Split,Meandering,Sinuous,and Straight Configurations
,....,
-
.,....
Channel-full
width
(ft)
o-15
15 -100
100 or greater
-36-
Approximate
maximum depth
(in)
20
39
51
-
.....
.-
-
.-.
channel.longitudinal slope out of the material site at the downstream end
should permit channel drainage during a flow recession to prevent against
fish entrapment.
Scraping in active side channels that have been diked and dewatered should
follow the alignment of the channel and be confined between the low-flow
buffers.Slopes of the material site should be stabilized for flows having
a 5-year recurrence interval.Existing pool-riffle sequences should be
retained.If water is present in an active channel scheduled for winter
scraping,the site should not be operated.
Horrow Operation -Excavated Sites
When appropriate,pits should be long and narrow in shape,be aligned
parallel to the river,and provide an irregular configuration.At least 30
to 50 percent of the shoreline should have a gradual slope.
Borrow pits connected to a river and those planned for restoration as fish
management areas shoul d have a mean depth of at 1east 8 feet to ensure
winter survival of fish.Those pits connected to a river should include an
outlet channel for a path of low resistance when the pit is inundated.All
outlet channels should be located on the downstream end of the pit and
connect to a scour area of an active channel.While outlet channels should
be angled downstream,they should not be of straight line configurations.
Channels should be deep enough to allow fish passage during low flow
conditions.Outlet channels should be constructed at the end of site
closure to minimize siltation in the river •
-37-
-
Borrow Operation -Dredged Sites
Active channels scheduled for winter dredging that contain flowing water
should not be disturbed as these areas may provide overwintering habitat
for fish.Depth of excavation in an active channel during any season
shaul d be confi ned to the wi dth of the surrmer low flow channel mi nus the
low-flow buffer.The length of excavation in a pool of the active main
channel should be confined to the length of the pool.Length of excavation
in a riffle should not exceed the average lengths of the pools within 3
miles up and downstream of the site.Slopes of the active channel site
should be designed to remain stable during 5:-year flood flows.
Borrow Site Restoration
Floodplain borrow sites should be returned,as closely as is possible,to
natural conditions immediately following completion of operations.The
work area should be sloped and contoured to minimize ponding and to blend
with surrounding features.Access roads,culverts,and bridges should be
removed.All cut slopes should be stabilized to prevent thermal,fluvial,
and wind erosion.Water in the settling ponds should be released by
pumping or lowering dikes.Silt from settling ponds may be 1)left in
place in inactive floodplains and terrace locations (dikes should be
lowered to the level of the impounded silt),2)used in revegetation
activities (see Section 3.8),or 3)removed to an approved disposal area.
At side-channel sites which were diked to allow scraping in a dry
condition,the downstream di ke shoul d be removed and the upstream di ke
should be lowered to correspond to the river stage of a 1.25-year flood to
-38-
-
"'"'
-.
-
....
-
prevent large quantities of sediment from being washed from the site into
the river at low flow conditions.Outlet channels from pits should be
constructed during the final phases of site closure.
3.2 DRAINAGE STRUCTURES
The follo\'/ing paragraphs di scuss al ternative techniques to facH itate
drainage and their respective advantages and limitations.Detailed design
guidelines,particularly for culverts and bridges,are·presented in a
report prepared for the Power Authori ty by the Harza-Ebasco Sus itna Joint
Venture entitled nDrainage Structure and Waterway Design Guidelines".
3.2.1 Culverts
Culverts are used to provide streamflow and fish passage where continuous
access across a stream is required"and where flow,gradient and/or length
of span do not mandate bridging.Crossings should be 90 degrees to the
direction of stream flow.In permafrost areas,culverts should be designed
to prevent ponding.
Culvert installation should occur nin the dry"whenever possible.Stream
diversion or fluming may be possible in special situations.The use of a
temporary dam and pumps to route water around a cul vert site often is a
practical method for small streams.If culvert installation occurs in
flowing water,the upstream end should be sandbagged or back.filled first to
immediately direct flow through the culvert.Culvert installation should
not occur during frozen conditions unless channel alignment,thalweg slope,
-39-
-
-.
.....
3.2.1.1 Non-Fish Streams
The culvert should match the gradient of the natural channel and the depth
of headwater at design flow (QSO)should be no greater than Ii times the
culvert diameter.If the grade is steep or the culvert outlet is above the
streambed,energy dissipators (see Section 3.2.7)may be required •
3.2.1.2 Fish Streams
Velocity of water within a culvert is one of the primary considerations in
ensuring that culvert design is adequate to permit upstream movement of
fish.The velocity criteria applied to any installation must generally be
adequate to protect the weakest swimming upstream migrant at the time that
migration occurs.The culvert velocity through which a fish can success-
fully swim is dependent on the length of time that the swimming speed must
be sustained and,therefore,dependent on cul vert length.Where the
velocity criteria cannot be met,reducing the width of the road or pad at
the crossing to shorten the length of the culvert may achieve compliance.
The slope of the culvert may match the natural river or streambed slope up
to a slope of 0.5 percent,provided that the velocity criteria can be
attained.Culverts may be installed in a natural streambed having a slope
greater than 0.5 percent,provided that the culvert can reasonably be
-40-
-
-
installed to maintain the appropriate velocity without danger of excessive
erosion and perching.
The design flow for purposes of fish passage design must be at least the
mean annual flood (Q2.33).Headwater depth must be less than or equal to
culvert diameter at the intake for the design flow (Q2.33).
At least one-fifth of the diameter of a round pipe culvert at the outlet
end must be set below the lowest elevation of the natural stream bottom.
At least 6 inches of all pipe-arch culverts should be similarly set.Depth
of burial of the inlet for circular or pipe-arch culverts will depend on
the slope of the culvert relative to the streambed slope.The use of
oversized~deeply buried culverts should be considered in situations where
stream gradients make culvert velocity criteria difficult to meet or Where
unusually low velocities are required.
Where alignment and other conditions allow,stream crossings should be
located in reaches of lower gradient.Culverts can then be placed as near
horizontal as possible,allowing lower in-pipe velocities.All bank cuts,
slopes,fi lls and exposed earth work attributable to cul vert install ation
must be stabilized to prevent erosion during construction and the culvert1s
operational life.Inlets and outlets must be stabilized with riprap or
other appropriate method.Hand labor should be utilized to the greatest
practical extent when armoring culvert inlet and outlet areas.
-41-
3.2.2 low-Water Crossings
Low-water crossings (Figure 3)may be used to provide passage of stream
flow on roads or workpads having low traffic volumes.They are not suit-
able for use on high-flow streams t deeply incised streams t and areas of
heavy traffic.While low-water crossings are inexpensive to install,they
frequently result in more maintenance costs than initial installation costs
for temporary bridges.Periodic (perhaps frequent)grading,fish blockage t
sedimentation t traffic lane failure,and icing are common problems.
The intent of the low-water crossing is to match the natural geometry as
closely as possibl e.Therefore,they are only appl icabl e where stream
banks are low and approach grades are fl at.The depth of the crossing
should be comparable to that in the stream.Low-water crossings in streams
having intermittent or seasonably low flow should be trapezoidal.On fish
streams,a minimum water depth of 4 inches must be maintained.Average
water velocity within the crossing should not exceed the average velocity
in adjoining stream sections.The banks and bed of the excavated crossing
should be protected with rock armor sized according to the maximum flow
velocity and the anticipated traffic loading.Where applicable,the
streambed should be sealed to prevent dewatering through excessive
subsurface flow by employing sufficiently fine material or an impervious
membrane.
When constructing a low-water crossing,water flow through the disturbed
streambed should be minimized.Stream diversion or fluming may be
possible.The use of a temporary dam and pumps to route water around the
-42-
-
FLOW
"
PLAN
":.,a G11;0
(.0
~• i1',.01
I 00 I
I 0 ~Ol
I ~~I 0
I (J
'-'e ~?
r-
I
PROFILE
.-
ALASKA POWER AUTHORITY
LOW-WATER CROSSING
FIGURE 3.
.....
-
-
~,
crossing site is a practical method for small streams.Temporary dams
should be composed of sandbags,fill contained in visqueen,or other
non-erodible materials.Bypass pumps should be adequate to avoid buildup
of water behind the darn and to assure sufficient flow downstream.Pump
discharge points should be naturally or artifical1y armored to dissipate
energy and prevent erosion.
3.2.3 Grading and Cross Drains
Temporary and other unpaved roads,'especially in areas of steep slopes and
highly erodible soils,must be provided with adequate drainag.e to prevent
gullying.Careful grading,using dips and pools in the grade,will break
up surface flows on or parallel toa road.A cross fa 11 of 3 percent is
recommended.Berms and tracks which prevent croSs drainage should be
graded out.Snow berms should be removed before breakup to permit lateral
drainage.
Cross drains,such as box or pole culverts (illustrated on Figure 4),can
be installed across the surface of temporary roads to collect surface
runoff.Round culverts can be used to intercept flow in ditches upstream
of a bridge or culvert crossing,carry it across the road,and discharge it
on the downstream side of the crossing to prevent erosion.
The distance between dips or crossdrains should usually be less than 100
feet for slopes over 5 percent.In silt soil areas,intervals should
usually be as noted below.
-44-
1"Pipe
;'1'·'••••.•"~}'\I t ~.-.-;..:.~.:-:1/:'"~#..-•.:-I'.:'--.lit...:....-.......: •.......-......
. •••:,.\I 4"I"\~too_:
I ••,..1 ••3"X 8'1/is'=_.
iII,-"..J -.~-1'-11 •
•;:.~.TL"L :3"x 12"
::.~.,.:~:1/.....:~.::-•.;11
BOX CULVERT
8"Dia.
POLE CUL VERT
Spikes
.........DOWNGRADE
.....-..'..'.:-.
......
I,
I,,
--I
I
r-r
I
Riprap
CROSS DRAIN CULVERT
ALASKA POWER AUTHORITY
CROSS DRAINS
FIGURE 4
-
-
Slope (%)
10
8
6
4
2
3.2.4 Vegetated Channels
Cross Drain
I nterva1 (feet)
55
65
70
80
95
-
-.
Vegetation can be used to protect man-made 0'"natural channel s from erosion
where soil conditions,flow velocities,and slope will allow adequate
stabilization with grass.While grass lined channels are the least expen-
sive method to carry surface runoff flow,they require careful design and
good maintenance to prevent gully erosion.
Generally,grass channels are not suitable for flows greater than 5 to 6
feet per second or gradients more than 10 percent.Nettings (Section
3.2.6),ditch checks (Section 3.2.5),or other techniques can be used in
the channels to decrease flows or reduce gradients.Table 7 shows allow-
able velocities for various species of grass in erodible and erosion
res i stant so il s•
While expensive,sodding may be required where rapid cover and protection
are necessary.Overlapping sod strips parcillel to the water flow can be
used in relatively flat ditches that carry large volumes of water.Shin-
gling,where grass strips are laid perpendicular to the flow,can be used
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TABLE 7
SPECIES,VELOCITIES,AND SOILS FOR VEGETATED CHANNELS
-47-
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on short grades that are steeper than 10 percent.In both methods,staking
the overlapped portions will increase effectiveness .
Channel sections may be V-shaped,trapezoidal,or parabol ic.Parabolic
cross sections have proven to be the most satisfactory.Trapezoidal
sections tend to revert to a parabolic shape.Due to flow velocity distri-
bution,V-shaped channels should not be used if channel side slopes would
exceed 6:1.
Provision should be made to divert flows during construction of the channel
and to avoid excessive compaction of soils.A tile drain placed offset
from the center of the channel by at least one-quarter of the channel width
will assist in turf maintenance.Regular mowing and a yearly application
of fertilizer will increase the effectiveness of the grass channel.
3.2.5 Ditch Checks,Check Dams
Ditch checks and check dams (Figure 5)are temporary structures used during
construction to protect natural channels from construction-induced sedimen-
tation,or to protect man-made ditches until permanent liners,such as
vegetation,can be established.They are aha used in steep channels as a
gradient break to reduce slope.These inexpensive structures,which can be
built with scrap or native materials,are used to reduce flow velocities,
trap eroded sediments,and prevent gullying of the channel.They may
require periodic clean-out or replacement due to accumulation of silt which
will reduce flow pereol ation through the structure and may cause water to
overtop channel banks.
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STRAW BALE CHECKS
VIEW FROM DOWNSTREAM
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QI
<3
I
I
Rip-Rap Apron
to Prevent Formation
of Scour Hole
I
I
I:t 4'
~I I
I ....f:!l J
E::J III
I_~I
J E:J I
STRA W BALE CHECK FOR
CHANNELS OVER 9 FEET WIDE
STRA W BALE CHECKS
FOR SMALL CHANNELS
WIRE FENCE CHECK WITH STRAW OR BRUSH
BUNDLES WIRED J.
TO FENCE·,FLOW
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I J c .,"\I I
I .Rip-Rap Apron to Prevent I
I Formation of Scour Hole
Wire Upstream I 1 I
of Posts I .'FLOW ISTRAW BALES~.3.I :'..•.WIRED TO FENCE4/1 x 4".,....Cc::::r t::::J I
Posts -......a -til.lll
4'Min.
§:_2.5.Z!fiI_
!!!!E lilt ]II!~..iliE 3IR 3iiiir
...---...~.-.-..-,..--&I
cccccc
Use Rip-Rap on Downstream Side
WOODEN STAKES ,4/'Dia.Poles
~
i
BRUSH BETWEEN TWO ROWS OF STAKES
4"Dia.Stakes on 2'Centers
~.\,~~",.
lJ \'~
Use Rip-Rap Apron
ALASKA POWER AUTHORITY
DITCH CHECKS
AND CHECK DAMS
FIGURE a
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Straw bale checks in channels over 9 feet wide consist of bales staked with
two 2!-foot wooden or metal stakes and tied with nylon cord or wire.A
riprap apron is placed downstream of the bales for a minimum of 4 feet and
at the edges of the bales to bring the structure to the crest of the
.channel.On channels less than 9 feet wide,small checks consisting of two
bales may be used without riprap.They should be spaced approximately 50
feet apart.
A wire fence/straw bale check consists ofa 3-foot cyclone fence nailed to
the upstream side of 4-inch diameter wooden stakes which are driven across
the width of the channel.Straw bales are wired together and to the
upstream side of the fence.A riprap apron is placed downstream for a
minimum of 4 feet.
On sites with large quantites of brushwood,bundles approximately 2 feet in
diameter can be substituted for straw bales.The bundles should be tied
with #9 wire,laid in staggered formation upstream of the fence,and wired
together and to the fence.
Two rows of 4-inch diameter stakes with brush packed between them is
another inexpensive check.The brush should be secured by criss-crossing
#9 wire between the stakes.
A semi -permeab 1e check may be constructed elf rock.01 ameters of 9 inches
are sufficient for velocities of up to 8 feet per second.One-hundred
pound sand bags may be used as a check in areas where rock 1s not
available.A riprap apron should extend at least 4 feet downstream.
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3.2.6 Mechanical Channel Liners
Methanical channel liners are used where runoff quantities,velocities,and
soil conditions require greater protection than can be afforded by vegeta-
tive means.They may often be used temporarily when vegetative liners are
becoming establ ished or permanently in conjunction with vegetative 1iners
to slow velocity and increase infiltration.The initial costs may be
higher than vegetative channel liners but,with proper design and con-
struction,mechanical channel liners have long life effectiveness.Some
will require maintenance due to scour.
Nettings made of biodegradable materi al s are often used to stabil ize newly
vegetated channel s.Theyal so offer some protection on their own and are
effective for medium velocities up to 6 feet per second.In large
channels,where several widths of netting are required,strips of netting
should overlap 2 inches at all edges and should be stabilized with hairpin-
shaped wire staples.The top end of the netting shoul d be buried in a
4-inch trench.Equipment should roll the c:hannel to assure that the net
makes contact with the soil.
A fiberglass mat (Figure 6)embedded in a l--foot deep trench perpendicular
to a drainage swale can function as a spreader to avoid the formation of
gullies,allow subsurface flow without migration of sediments,and aid in
establishing vegetation.Once the mat is installed in the trench and
secured with staples,the trench is backfilled and compacted.Another mat
or netting is centered on top of the vertical strip to form a cap extending
-51-
FIBERGLASS MAT
SECTION A-A
STONE CENTER DRAINS
.-
WATERWAY WITH STONE CENTER DRAIN
"Y"SECTION SHADED
Design Depth4~-----~-~
Gra'al B.ddl~I':'
WATERWAY WITH STONE CENTER DRAIN
ROUNDED SECTION SHAPED BY BULLDOZER
4"'2'~
Gravel Bedding
BRUSH SPILLWAY (PERSPECTIVE 8&SECTION)
Sod Crest'
10'Min.I,..,
Tamped Fill
:.:.[;":;;;:,.';,;1'
~~~I ,
Original Stream Bed
Straw or ulch
DROP STRUCTURES
DRY ROCK SPILL WA Y
Sod Crest
':::4-'Tamped Fill...
.'.,..•:...:,;.r-0riginal Stream Bed
'qIIj~r.>-;12"Min.
ALASKA POWER AUTHORITY
MECHANICAL CHANNEL LINERS
FIGURE.
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"""
!foot beyond the lateral limit of the design flow.This technique is not
appropriate for permafrost soils.
Stone center drains (Figure 6),consisting of a gravel bedding and packed
stone in the center of a grassed swale,are used in drainage channels
that experience prolonged flow and wetness.Acceptable flow velocities and
gradients are determined by standard riprap specifications.
Methods of stabil izing banks in waterways that experience high velocity
floW's include 1atticework concrete blocks (gaps in the blocks are back-
filled with soil,compacted and seeded with grass),gabions (enclosed wire
bask.ets filled with riprap),paving,sacked sand,and concrete filled
mattresses.
Drop structures (Figure 6)and check dams are used to counteract gully
erosion by reducing the channel gradient and are preferred over impermeable
concrete or asphalt linings when physical conditions are too severe for the
establishment of a vegetative cover.Materials can consist of timber,
rock,gabions,concrete,brush or sod.Energy dissipators in drop spill-
ways will collect silt and debris and require cleaning.
3.2.7 Outlet Protection
A variety of techniques (Figure 7)can be used to slow the velocity of flow
at drainage structure outlets.The choice of protection depends on 1)soil
and topography,2)anticipated flows,and 3)height of fill or outlet.
None of these techniques discussed below should be used where fish passage
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RIPRAP APRON FOR
SHALLOW FILLS
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DOWNDRAIN AND ROCK DISSIPATOR .DOWNDRAIN AND SEDIMENT BASIN
PLUNGE POOLS
CANTILEVERED CULVERT CULVERT WITH CUT-OFF WALL
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STILLING BASIN
'WITH BAFFLES TO
DISSIP ATE ENERG
~f[:AT BASE OF
::CONCRETE CHUT
SPILLWAY}
LOG CRIB FILLED
WITH ROCK
ALASKA POWER AUTHORITY
OUTLET PROTECTION
FIGURE 1
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is required.Structures which impound water should not be used in
permafrost soils.
Outlet protection for culverts in shallow fills can be accomplished with
protective aprons of dumped rock,hand-placed riprap or rock-filled
gabions.The width of the apron shaul d be three times as wi de as the
culvert.Height should be to or above design high water.Depending on
soil conditions,filter layers may be required under the apron.
Flows from culverts in high fills can be directed through a downdrain to a
rock dissipator or to a sediment basin.
Plunge pools should be used only for free outfall.An armor layer,perhaps
underlain by filter layers,is required for the base of the pool to prevent
the flow from undermining the toe of the embankment.While aesthetically
undesirable,the end section of the culvert can be cantilivered and
supported with wood or concrete.A second method is to support the end of
the culvert with a cut-off wall that extends into the ground below the.
anticipated depth of scour •
Stilling basins with energy dissipators can be used at the outlets of
chutes,spillways,flumes,or downdrains.The outlet should be shaped to
conform to the receiving channel.
log';'rock cribs can be used for free outfalls and at downdrains.If soil
conditions permit,the cribs can disperse the discharge to overland flow.
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3.2.8 Inlet Protection
Inlet protection consists of a variety of structures located upstream from
a culvert.The devices protect the culvert from debris accumulation that
may cause flooding and erosion.Regular removal of debris is required to
allow full culvert capacity during high flow.These devices should not be
used on fish streams.
o Debris Deflectors--usua lly "V"shaped structures pl aced upstream
from the culvert to prevent the major portion of the debris from
entering the culvert.The apex of the "V"is upstream.
o Debris Racks--rails placed across the stream channel to collect
debris before it reaches the cul vert entrance.Usually vertical
and at right angles to the streamflow.
o Debris Risers--closed-type structures,usually of metal piping,
placed directly over the culvert inlet in log-cabin fashion to
prevent inflow of coarse bed load and light floating debris.
o DebriS Crib--open crib-type structures placed vertically over the
culvert inlet in log-cabin fashion.
o Debris Fins--walls built upstream of the culvert and aligned with
the direction of flow to direct debris through the culvert.
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o Debris Dams and Basins--structures pl aced across well-defined
channels to form basins which impede the stream flow and provide
storage space for deposition of debris.
3.3 ICING CONTROL
3.3.1 Stacked Culverts and Subsurface Drains
Stacked culverts (Figure 8}provide a relief route for meltwater at an
ice-dammed culvert,thus eliminating the need to thaw the culvert at
breakup.The drainageway requires a de!ep fill section and enough
storage area for ice accumulation during \'linter,without plugging the
upper culvert.Offsetting the upper culvert reduces the amount ·of
fill required.Offset culverts also provide for fish passage in
streams which experience wide fluctuations in flow •
Subsurface drains {Figure 8}are used where topography is steep to allow
diversion of subsurface stream flow and exit downstream of the structure to
be protected.The subdrain is for low flow only and should not be used to
repl ace the conventi onal drainage structure.Perforated pipes are pl aced
upstream of the icing area and in a trench across the stream to intercept
sub-bed flow and allow filtration of low stream flow.Within the stream
channel,the trench should be backfilled with coarse material to allow
infiltration.Outside the channel banks,insulation should be placed over
the subdrain to prevent freezing.Subdrain outlets must be designed so
they will not freeze or so they can be periodically thawed.
-57-
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Natural Ground ~
Area of Known Icing
Embankment
//
Anticipated Icing Level
STACKED CULVERTS
SUBSURFACE DRAIN
ALASKA POWER AUTHORITY
STACKED CULVERTS AND
SUBSURF ACE DRAINS
FIGURE 8
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Subsurface drains also can be used to reduce artesian head at the roadside
beneath seasonal ice.For a subdrain to function effectively,surface
flows must be intercepted at the source (since the icing layer is imper-
meable)and the drain must be buried below maximum freezing depth.Outlets
arle downslope from the road embankment.
3.3.2 Culvert Thawing
Culvert thawing may be required to maintain winter flow or provide passage
of spring meltwater.
Tha\'l cables are electrical heat cables used to maintain an open passageway
through a culvert.An electrical resistance-type cable is either buried
be~low or suspended inside the culvert.
Steam thawing is suitable for ice-blocked culverts that are accessible to a
tl'UC!<mounted boiler.Thawing can be done by probe or by permanent piping.
3.3.3 Channel Maintenance
TI:!chniques to maintain winter flow through a channel or to induce icing at
sl:>me location that will not require maintenance include frost belts,
air-ice covers,and ice fences.
Frost belts (Figure 9)are constructed by excavating a ditch in the ice 10
to 12 feet wide to the streambed.The ditch progresses downward as the ice
--59-
River Ice
PARTIALLY-COMPLETED
FROST DAM
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PERMAFROST
OPERATING FROST DAM
PERMAFROST
ALASKA POWER AUTHORITY
FROST BELTS
FIGURE 9
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below the ditch thickens.A drainage ditch may be required to remove
acc;umu1 ated water downstream.Frost bel ts must extend well beyond the
stl'°eam edges.Extension ditches on the banks may be excavated before
frE~eze-up at the selected site,which should be between 600 and 900 feet
from the structure.Additional dams should be at least 60 feet apart.
Frost bel ts are best constructed where stream ice usually freezes sol id to
the bed,as in shallows or near rapids.
Air-ice covers are created by temporarily damming the stream early in the
winter and allowing the water to back up through the culvert.The dam is
placed a short distance downstream from the culvert and should retain a
degree of permeabili ty.After the ice cover freezes to a depth of 5 to 6
inches,the dam is removed.With free flow restored,the water level drops
so that an 8 to 15 inch air gap remains.The intervening layer of air
usually will insulate the flowing water sufficiently to prevent freezing.
Insulation,such as snow,peat,brush or other available materials,may be
a~/plied to the ice layer and removed in the spring.Where a broad channel
is encountered,additional support for the ice cover may be prOVided in the
form of short wooden or concrete posts acting as columns.Temporary check
dams may be reqUired at large icing sites.
A wide variety of materials can be used to form a fence upstream from a
culvert or bridge to store ice accumulation.Upstream storage area must be
large enough for a winter's accumulation of ice.If avenues open below the
flence for water to pass upward through the ice,the fence will be ineffec-
tive.
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3.4 STREAM PROTECTION
3.4.1 Protection During Crossing and Construction
Whlen construction activity repeatedly crosses active streams,particularly
fish streams,or when construction is immediately adjacent to streams,
stream protection from erosion and turbidity is required.
Seasonal timing of construction may reduce the impact of construction.
Where construction schedules or habitat sensitivity create conflicts,
techniques for stream protection should be employed.Periodic inspection
for erosion or sedimentation may be required.
CClnstruction dikes and cofferdams can be used to separate the waterbody
fY'om the construction area.Construction dikes are placed on the stream
slide of a construction area.Placement of these structures must not
constrict the channel to avoid increasing velocities that could cause
channel erosion and obstruct fish passage.Cofferdams completely enclose
an instream work area while permitting flow to continue through the
channel.While cofferdams cause minimal disturbance to the channel,they
are usually expensive to build.
Stream channel diversions should be avoided whenever possible.Temporary
diversion channels must be capable of carrying flows anticipated to occur
during the construction period.The average water velocity within the
channel should not exceed the average velocity in the natural stream.The
bed of the diversion channel must be stable at expected flows.During
-62-
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construction and excavation,the channel should be isolated from the stream
to be diverted by natural plugs left in place at the upstream and
d01r'mstream ends.Diversion of water flow into the temporary channel is
accomplished by first removing the downstream pl ug,then removing the
upstream plug,then closing the upstream end and then the downstream end of
the natural channel of the diverted stream.Abandoned diversi on channel s
must be backfilled or plugged and stabilized.
During ditching operations across small streams,it is often practical to
pipe (flume)stream water over the ditch while excavation is in progress.
With this procedure,a culvert or other pipe is installed in the stream
pr'ior to ditching with all stream flow directed through the flume.The
diitch is then excavated underneath the flume and the structure to be pl aced
in the ditch is installed.'After installation,the stream channel is
rf~stored prior to removing the flume.
T1emporary culverts can be installed under temporary roads and work pads to
clontain stream flow and allow fish passage.low-water crossings {Section
3.2.2}may be a practical method for small streams.
3.4.2 Bank Stabilization -Revetments
Mechanical streambank stabilization is for the prevention of erosion at
critical areas where velocities are too great for vegetative stabil ization.
Materials consist of riprap,concrete,grouted stone,gabion baskets,and
bagged concrete.Genera 11 y,most fa i 1ures occur at the toe,where scour
c:an undermine the lining.
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Planning for permanent bank stabilization must consider the following:
o Controlling the grades of the banks either by natural or
artificial means,before permanent stabilization is feasible
o Debris or obstructions that may deflect flow toward the bank
o The greatest depth of scour
"""'
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o
a
Additional stabilization measures,i.e.vegetative cover on the
top of slope banks
The physical and biological impact the modifications will have on
the stream
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These permanent techniques have high costs.Construction may require hand
labor and may be particUlarly difficult in deep water.Maintenance may
b~=come expensive for obstruction inspection and clearing.
Tlhe smooth lining of rigid concrete revetments will accelerate the velocity
of stream flow that may induce scour·downstream.Rigid revetments require
good access and dewateri ng of the streambed for construction.To prevent
settling and cracking,they should be used only on well compacted soils.
The revetment lining should extend beyond the top of the bank where it is
stabil i zed with vegetative.The toe shaul d be extended to the maximum
scour depth anticipated and be protected with riprap.Each concrete joint
requires reinforcement to prevent leaking and undermining.
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Concrete-filled nylon blankets are revetments consisting of nylon fabric
shleets that are stitched together as a quilt,fixed in place,and filled
with concrete.These blankets are capable of withstanding small movements
and are 1ess susceptibl e to undercutting than rigid concrete revetments.
Installation requires dewatering of the channel.This technique is not
recommended for slopes steeper than 1:1.
Dumped stone fonns a flexible lining that slumps into scour holes.The
rough surface of the stone dissipates the stream's energy,thus minimizing
sc:ouring problems at the ends of a revetment or lining.Linings and
re!vetments of hand-pl aced riprap genera11y consist of IOO-pound stones
pl aced in a single 1ayer.Any shifting of the stone exposes bare soil and
is therefore,more subj ect to damage than dumped stone.Grouted stone
rE~vetments are sometimes used when large stones are unavailable to stabi-
Hze dumped stone linings.This technique will reduce the roughness of the
l"ining and increase flow velocity which may enlarge any holes or flaws in
the grouting and lead to failure.
lrJlhen large stone for a dumped stone or riprap lining is unavailable,wire
ba.skets or wire mattresses filled with smaller stone may be acceptable.
G,abions are easy to install with minimum instream disturbance.Gabion
baskets may be placed on steeper streambanks than gabian mattresses.
Gabion mattresses may be placed in deep water by sliding them off a raft .
3.4.3 Bank Stabilization -Deflectors and Jetties
Deflectors and jetties are placed on the outside bends of streams to
-65-
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deflect stream flow away from an eroding bank or to prevent meandering and
encourage the stream to increase channel capacity by scouring its bed
rather than by lateral cutting.Jetties and deflectors should not be used
where the stream cannot compensate for restriction in channel width or in
fish spawning areas.Because jetties produce excessive eddying,they
should not be used in very sinuous channels.
3.4.4 Bank Stabilization ~Vegetative
Vegetative bank stabilization is applicable for small streams and low
gr'adient streambanks to prevent or control erosion and sedimentation.
Little maintenance is required especially after the first few years when
vE!getation is well established.If soils and flow dictate,vegetative bank
stabilization can be supplemented with mechanical techniques.Vegetation
shoul d be incorporated behind revetments,jetties,gabi ons,etc.on the
bcmks behind the design flow.
3.5 SEDIMENT RETENTION
3.5.1 Settling Ponds
S,ettling ponds are used in non-permafrost areas for retaining runoff waters
tiD remove sediments generated from construction and borrow activities.
They can range from large pennanent-type basins to temporary measures such
as ditch checks.Generally,a settling pond consists of a dike,a pit,and
an outlet for clean water.The effectiveness of a settling pond depends
upon:
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o
o
o
o
o
o
o
Surface area of the pond
Rate of flow through the pond
Grain size distribution of the incoming sediment
Specific gravity and shape of incoming solids
Water temperature
Turbulence within the pond as a result of wind or rainfall
Entrance and exit effects
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To the extent possible,settling ponds should not be located in streambeds
01'floodplains.The ideal site is on or underlain by a thick layer of
fclirly impervious soil.
Sl!ttling ponds must be sized so that the effluent is in conformance with
A'laska Water Quality Standards.Removal of suspended soi ls particl es
liirger than 0.02 millimeters is usually necessary to consistently meet this
limitation.The maximum surface overflow rate (the flow rate through the
plDnd,divided by the surface of the pond)to permit sedimentation of
0.02-millimeter particles is 3,700 gallons per minute per acre (0.011
ft/minute).Ponds should be constructed with a length that is at least
tlrlice the width.A length-to-width ratio of 5:1 or greater is desirable.
Depth ?f a pond,while not a factor in settling efficiency,must be
considered for sediment storage.Use of flocculants to enhance the
settling process to subject to approval from regulatory agencies.
Containment dikes for settling ponds should usually not exceed 10 feet in
height.They should have a crest width of at least 12 feet and upstream
a.nd downstream slopes of 2:1 or flatter.The core of the dike must be
-67-
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impermeable and should extend through surficial pervious foundation soils
into underlying bedrock or other impervious soils.
Outlets should be constructed to limit the level of the water surface to at
least 1 foot below the top of the dike.Outlet structures may be
constructed as overflow spillways or culvert pipes with risers.At least
one overflow or riser should be provided for each 150 feet of pond width to
limit nonuniform flow velocities through the pond.
Erosion protection on the downstream slope of the containment dike and at
the toe of the overflow should consist of a minimum 2-foot thickness of
arlgular rock,averaging 8 inches in diameter.The crest of the overflow
should be protected with at least a I-foot thickness of 4-inch angular
rock.The width of the overflow should be at least 1 foot for each 400
gclllons per minute of f1 ow through the pond .
R"iser outlet pipes should have a diameter of at least 18 inches.At least
1 inch of pipe diameter should be provided for each 100 gallons per minute
of flow through the pond.Several cutoff collars should be installed
around the portion of the pipe that passes through the containment dike to
prevent erosion of fill materials by seepage along the pipe.Collars may
consist of sheet metal,polyethylene sheeting or other impervious materials
and should extend at least 2 feet beyond the pipe.An apron of large rock
should be placed at the pipe outlet to prevent erosion at the toe of the
dike.
Settl ing ponds used in borrow operations to contain water from gravel
-68-
.,."
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washing (Figure 10)may be more effective if sluiced material is discharged
to a meandering tailrace that leads to the pond.Construction of a small
pr'esettl ing pond at the pond entrance wi 11 reduce inflow velocities and
result in additional deposition of coarse sediment before it reaches the
pond.The surface area of the presettling pond shoul d be about 1 square
foot for each gallon per minute of flow through the pond.Frequent removal
of coarse sediments from presettling ponds may be necessary.
R€!use of process water 'can reduce the quantity of water to be treated.
Normally,presettling of the sluice discharge would be desirable to remove
C(larse sediments before the water is recirculated back to the sluice.
C"lleaning of settling ponds should be accomplished when the pond is filled
wHh sufficient sediment to lower the quality of water discharged below
acceptable standards.Monitoring pond effluent with an Imhoff cone is the
usual method to determine if the pond is becoming ineffective.Gleaning
can be performed with a dragl ine.Removed sediment should be transported
to an approved waste area.
If clearing is impractical,or if the pond is to be abandoned,it should be
d'rained and covered with granul ar material.Draining can be accompl ished
by breaking the containment dike,prOVided that a lower containment dike of
p,ermeabl e material is constructed downstream of the pond outl et to prevent
accumulated sediments from entering a stream.
-69-
Emergency
Overflow
Riser Type-~~~~~~"""'"
Outlet Structures
Emergency
Overflow
e'r ~-~~
~
\,\M.eandering
\ \ \Trailface
~
Containment Dike --_.Ii.\...
Easily Adjustable
Bypass Gate
Presettling Pond ----~~
Area of Breaching Containment __~~~~--~
Dam for Pond Dewatering
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ALASKA POWER AUTHORITY
GRAVEL WASHING
SETTLING POND LAYOUT
FIGURE 10
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3.5.2 Buffer Strips,Barriers
Buffer zones of undisturbed ground and vegetation,and man-made barriers,
aIre techniques to retard runoff,increase infiltration,and contain
slediments eroded from construction areas .
Man-made barriers constructed at the toe of a slope are shown on Figure 11.
Some maintenance is required to remove accumulated sediments,especially if
these techniques are intended to be permanent.
3.5.3 Traps and Filters for Inlets
Traps and filters are normally applied as temporary measures during con-
struction to prevent eroded sediments and debris from entering natural or
constructed drainages.Vegetative or mechanical techniques are used
depending on the size of the structure,the anticipated flows and sediment
quantities,the maintenance requirements,as well as cost.
Examples of these techniques are discussed in Sections 3.2.5 and 3.2.8.
-71-
Dispose of Slash and
Brush Along Toe of Hill
Cut I)r FiJI
Slope
""'"
I~••OUNDS OR DEPRESSIONS BRUSH BARRIERS
Scari!fy Surface.
Fertilize and
PI~lce Sod
Ditch Of S ....
SOD STRIPS
h~
~'V SEDIMENT FENCES
STRAW-BALI!BARRIERS
-
ALASKA POWER AUTHORITY
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SEDIMENT BARRIERS
FIGURE 11
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3.5.4 Silt Curtains
Silt curtains are temporary measures used to intercept sediment from
ccmstruction activities adjacent to waterbodies.They are installed in the
wtllterbody.The intent of the curtain is to prevent muddied water caused by
construction activity from spreadi ng over the entire body of water.They
are not affective for streams where turbulent flow will prevent settling,
dE!ep lakes,or where there is wind induced mixing.
The curtain can be constructed of heavy plastic,canvas,or other suitable
material that is of sufficient strength and density to withstand wave
action and infiltration of fine-grained material.The curtain is generally
fastened to the shore at both ends and fitted with anchors and flotation
d.~vices so that is remains in a vertical position.
3.6 SLOPE STABILIZATION
3.6.1 General Techniques for Non-permafrost Areas
Listed below are vegetative and mechanical techniques available to provide
temporary or permanent stabilization of slopes.The selection of the
appropriate technique is determined by the soils,ground water,and precipi-
tation.In soils where a saturated condition results in liquification or
slumping,preferred methods could include paving slopes or ditches and
constructing diversion ditches for maximum non-erodible velocities.If
soils are not saturated and slumping ;s not anticipated,methods should be
selected to maximize infiltration.
-73-
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o
o
Serrated Cuts--reduce the velocity of runoff and collect
sediment.They are not recommended for saturated slopes where
sloughing may occur.Serrated cuts are appropriate in fragmented
rock or shale materials.
Pavement or Riprap--appropriate in high risk slopes of saturated
soils where immediate protection is required.Pavement and rip-
rap are expensive and may be difficult to install and maintain.
o Diversion Ditch--appropriate for cut slopes in erodible soils
where there is sufficient slope to prevent ponding and satura-
tion.These ditches divert runoff through·stable channels and
outlets.
o Benches or Fill Benns--reduce the angle of the slope to slow
runoff and facilitate seeding and other maintenance programs.
o Slope Drains--prevent gullying erosion by carrying runoff down
the slope in a drain.Energy dissipators may be required at the
outlet.
o Diversion Berms--made of stable non-erodible material placed
temporarily or permanently at a slope crest to divert runoff away
from the face of the slope.
o Sodding--immediate,permanent and expensive cover for critical
cut or fill slopes.
-74-
o Seeding and Mulch--provide a permanent or a temporary cover on
cut or fill slopes (see Section 3.8).
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o Temporary Cover--netting,plastic sheeting,or other material
used on steep cut or fill slopes for stabilization until perma-
nent measures can be taken.Plastic sheeting may be difficult to
secure.
3.6.2 Temporary Oowndrains
T1emporary downdrains can be effective methods during construction to safely
C!Dnvey runoff from one elevation to another until permanent stabil ization
is established.These downdrains can be used on cut or fill slopes or as a
channel gradient break to reduce velocities.Temporary downdrains can be
extended as construction of the slope progres.ses,and can serve as an inlet
to channels or as a transition from grassed to cpen waterways.
These structures usually require a diversion and a collection system to
intercept and direct runoff to the downdrain.Energy dissipators are
usually required at the outlet of the downdrain.
Each structure should be periodically inspected and any damage repaired
immediately.Inlets should be examined for undermined slopes.If snow
removal equipment is used,care must be taken to prevent damage to the
buried structure.When the temporary downdrains are removed,the slopes
should be restabilized.
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Sl~ctional downdrains (Figure 12)are normally constructed of one-half to
olne-third of round culvert sections which are secured together and fastened
tiD the slope to prevent leaking and erosion underneath the downdrain.
Slectional downdra ins can eas;ly be extended as slope construction
progresses.
Paved ch"utes (Figure 12)are generally constructed of asphalt.They are
most successful on cut slopes.An asphalt apron should extend at least 3
feet beyond the toe of the slope.The inlet should be designed and con-
structed to prevent runoff piping underneath the chute.
A flexible downdrain (Figure 12)consists of a flexible conduit (i.e.heavy
fabric)that is anchored to prevent movement.They are especially
appropriate for benched or terraced slopes.Fahri c conduits are not
f'ecommended for winter use as freezing could damage the fabric and result
in leaking.
3:.6.3 Permanent Downdrains
Permanent downdra ins (Fi gure 13)are used to transport runoff down cut and
fill slopes,as inlet or transition structures to transport water from a
c:hannel at a higher elevation to a lower one,and to provide non-erosive
9radient breaks to reduce channel velocities.They are usually used when
flows are continuous or runoff quantities dictate a permanent level of
protection.Corrugated pipe,bituminous concrete,or cement are often the
materials used for permanent downdrains.The cross section can be trape-
:i:oidal,parabolic or U-shaped.Energy dissipators are usually required at
-76-
PERSPECTIVE VIEW OF FLEXIBLE
DOWNDRAIN FLOWING FULL
Ruri-Oft
Tabs &Anchor Pins for
Securing Pipe in Position
at 20"Centers
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Run-Off:cc~m~~~~~
"ERSPECTIVE VIEW OF TEMPORARY ........
PAVED ASPHALT DROP CHUTE
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SECTIONAL DOWNDRAIN
ALASKA"POWER AUTHORITY
TEMPORARY DOWNDRAINS
FIGURE 12
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SECTION A-A Typical Concrete
Chute or Flume
ALASKA POWER AUTHORITY
PERMANENT.DOWNDAAINS
FIGURE 13
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t1'1le outlets.Inlets and outlets of downdrains should be checked for
undermining and erosion.Accumulated debris should be removed.
3.6.4 Diversions and Benches
Diive.rsions and benches (Figure 14)are intended to divert runoff water and
s~~diments away from critical areas and convey them to a stable outlet.
They maybe a temporary measure to protect exposed construction sites or a
pHrt of a permanent stabilization plan.Diversions and benches,such as
those listed below,can break up concentrations and velocities of water on
long,gentle slopes or divert runoff from steep,erodible areas.
--
o
o
o
Diversion Channel--a channel with a confining berm downslope
constructed laterally across sloping areas.Runoff is conveyed
laterally at slow velocity to protected area or outlet channel.
Diversion Levees--compacted earth ridges placed laterally along
the top of steep slopes or cut sections.Often constructed with
a diversion ditch upslope to convey runoff to a downdrain or
stable outlet.
Benches--flat areas built along the contours of a slope and
parallel to one another.If wide enough,equipment access may be
provided.Benches are built with a natural or reverse fall,
often with a swale at the lowest point.
-79-
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PERSPECTIVE
DIVERSION CHANNEL
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Swale or DitchJ Swale or Ditch\:.-,,-!-\~~-""
DIVERSION LEVEES
BENCH TERRACES
(REVERSE FALL)
BENCH TERRACES
(NATURAL FALL)
r ALASKA POWER AUTHORITY
DIVERSIONS AND BENCHES
FIGURE 14
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DE~sign is usually based on a 10-year frequency storm.If overflow would be
a hazard to water resources or structures,a design frequency of 50 years
milY be needed.location and spacing of diversions will depend on slope
soils and estimated runoff.Channel gradients are usually 0.5 to 1.0
percent but can be greater in resistant soils.The diversion outlets can
bl~vegetated cnannels,natural waterways,level spreaders,etc.If flows
are carrying sediment eroded from the si te,sediment retention techniques
(Section 3.5)may be required.
Miaintenance requirements include removal of sediment in the channel and the
establishment of any vegetation used for stabilization and erosion control.
3.6.5 level Spreaders and Interceptor Dikes
l,evel spreaders and interceptor dikes (Figure 15)intercept runoff flow and
convert it to sheet flow with non-erodible velocities over stable areas.
Spreaders are used to disperse sheet flow onto undisturbed,vegetated areas
where much of the flow will infiltrate the ground.Soils must be well
drained and stable;this technique is not appropriate for permafrost areas.
Care must be taken to ensure that the outlet 1ip is level.length of the
spreader can be determined from the inflow (0)in cubic feet per second
(cfs)as shown below.
Design Q (cfs)Length (ft)
less than 10 15
10-20 20
20-30 26
30-40 36
40-50 44
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LEVEL SPREADER
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,...,.
.....,
SECTION
SECTION
~~
6 Foot Minimum
2 To 1 Or Flatter
INTERCEPTOR DIKE
_STABILIZE
OUTLET SLOPE
ALASKA POWER AUTHORITY
LEVEL SPREADERS
AND INTERCEPTOR DIKES
FIGURE 15
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Interceptor dikes,or water bars,are used to divert flow from roadways or
work pads,particularly on long steep grades.The spacing of the dikes is
glenerallyas follows:
Grade (%)
less than 5
5-10
more than 10
3.7 THERMAL EROSION CONTROL
Spacing (ft)
300
200
150
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3.7.1 Prevention/Treatment of Disturbed Surfaces
Prevention and/or treatment of disturbed surfaces is required in areas of
poorly drained permafrost,or wherever disturbances of the active layer
could result in melting of underlying ice-rich soils and cause ponding,
gully erosion,and other self-aggravating conditions.Disturbed areas
should be inspected periodically and treatment of damaged areas should
commence immediately after discovery.Treatment also requires periodic
inspection until the area is completely stabilized.As access to the
disturbed area may be limited and a large amount of hand labor may be
required,prevention of damage is a more economical approach in permafrost
areas.Prevention measures include:
o Overlay construction,rather than cut and fill
o Use of insulation beneath fills
-83-
-o Maintaining the organic layer;conventional wheeled or tracked
vehicles should not be used
o Winter construction
Ditch checks and water bars can be used to convey melt and runoff waters
away from a disturbed area or to control the water within the area.
Revegetation of a disturbed area,once establ ished,will insulate the
underlying soils and help retard melting.Seeding and fertilizing should
be done immediately by hand or aerial application to prevent additional
dlisturbance.Sodding and transplanting trees or brush may be favorable in
some areas for quick cover and erosion control.In small areas where rapid
thawing may be occurring due to removal of the active layer,materials such
alS straw,excelsior blankets,slash,and styrofoam can be used for insula-
tion •
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o Avoiding induced drainage or standing water and concentrated
discharges from drainage structures
3.7.2 Cut Slope Stabilization
The general practice for frozen cuts is to ,make a fairly steep slope (1.5:1
to 1:4)and allow the slope to self-stabilize.While this technique will
,·esult in thawing of ice-rich soils,release of melt waters,and some
degree of sloughing,the cut will eventually return to a stable condition.
In implementing this technique,the vegetated mat should not be damaged and
should overhang or drape the cut for insulation.Trees in back of the cut
-84-
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slhould be cleared by hand to prevent them from tearing the mat as the bank
rletreats due to melting.Ditch checks or sediment filters should be
"installed to trap sediment eroded from the cut.If it appears that a cut
will not self-stabilize t the slope should be treated with either a filter
buttress or insulation (Figure 16).
A filter buttress is constructed by re-dressing the slope and placing
free-draining gravel fil ter material.The filter material can be pl aced at
an angle steeper than natural repose to eventually settle to a stable
r1epose.Sediment filters should be placed along the toe to contain silts
from melt flows.The buttress can be dressed with topsoil and revegetated.
Insulation is installed by dressing the slope to 2:lt overlaying it with 12
inches of free-draining sand or gravel t and placing urea foam insulation.
The insulation can be covered with topsoil and revegetated .
3.8 REVEGETATION
Revegetation of sites disturbed by development activities can provide an
effective erosion control mechanism.Whenever possible t reestablishment of
native vegetation should be promoted rather than introducing non-native
species which may be less hardy and more expensive to maintain.In addi-
tion t areas which do not have potential for erosion problems necessitating
vegetative cover should be left to revegetate naturally after receiving
site preparation.
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Sand &Gravel Filter-...r;..-t
Insulation
FIL TER BUTTRESS
INSULATION TREATMENT
ALASKA POWER AUTHORITY
TREATMENTS FOR CUT SLOPES
FIGURE 18
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3.8.1 Soil Constraints
Soil texture is an extremely important factor in the restablishment of
vl~getation in disturbed areas.Each of the six soil groups identified in
Alaska have unique properties which restrict root development and will
influence a revegetation program.Table 8 ill ustrates the properties in
each of the six soil groups and suggests the type of plant species suitable
f()r each soil group.Soil information for specific sites may be available
in soil survey reports published by the u.S.Department of Agriculture
(IUSDAL Soil Conservation Service.
3.8.2 Site Preparation
Proper seedbed preparation is essential to encourage revegetation through
planting or natural reinvasion.Whenever possible,surface materials
removed during construction should be segregated,stockpiled and reapplied.
In arctic and alpine areas,the largest component of soil nutrients is in
the surface organi c 1ayer.If these nutrients are not retrieved after
stripping by replacing the surface materials,large amounts of nutrients
are lost which can necessitate use of additional fertilizer.
Restoration grading should avoid creating overly smooth surfaces and
surface mater;a 1s shou 1d not be replaced over a Rha rdpa nn of compacted
material.All disturbed areas should be scarified to a depth of 12 inches
to increase aeration and moisture infiltration and to control runoff.
-87-
TA8LE 8
sorLS GROUPS I~ALASKA 1
Croup 1 -son.with Few or Ho ll..itlltion.
Hajor Soil
Lim;tat ions
None
Drainage
Cl aS5
Well and moderately
well drai ned.
Depth
(inche.)
More than 20 ...
USDA
Texture
Silt loam"Hne
sandy loam,.sandy
10....
Available
Water Holding:
Capacity (inchesl
5 to 8
Moderately
pef"lfte-able"
Substratum Porous gravel,
moderately fine
textured sed;-
ments t bedrock
or rock fill
A wide range of cl'imati-eally ada~ted pl ant species are suited to these 5011s if soil nutrients are
adequate or fertilized for establishment.
Croup 2 -Sons "Ith _rate limitation.Due taL-Water Holding Capacity -
"'jar Soil
Ll.mltatioftS
Drainage
Cll$.
We1t drained-.
Up to 20\aTop ..
Depth
(Inche.l
HI to 20
USDA
Te,xt-ur-e
Silt loam.fine
sandy loam,sandy
loam.
Available
Water Hal ding
Cap.clty (Inchea)
3 to 5
Maderately
p"r.....ble.
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Sub.tr.t....V..ry gravelly
sand,.shattered
roc-k t b:e:dr.ocf(
Group 3 -Salls with Sa""""ll"ltGtionl _ta Ve.,.low lIater Holding CapacitY or Steep Slope.
"ajar Soil
I..f..;tatio-na
Drougtltiness or
high ero$;on
haz.rd.
Drainage
Class
We 11 and exces-
sively drained.
Depth
(Inchea]
tess than 10,
or steep and
deep or shallow.
USDA
Texture
Silt loam,.sandy
loam,sand.
A"afl.bl e
W.t..r Hal dIng
Capacft)'.[Inches)
Less than -3,.
or excessive
runoff •
Substratum Gravel,.sand,
bedrock ...
Drought tolerant plants ttlat form a-dense root mass are -optimal for I"'evegetatl"q disturbed sites in
Group 3 soils.
9I'l!VI!..-Soils "itll H'od....e~lillritations Due to Exces.Holstllt'..-
Hejar SofT
limitations-
Dra;nage
CTa.a
Somnhat poorly
drai ned or poorly
drained~
Depth
(inches)
USDA
Texture
Silty clay 10....
silt loam,.sandy
loam,fine s-andy
loam.
Avaiilable
lletor Holding
Capac;ty (f nchesl
Hore than 5.H.y
be waterlogged
f-ar short peri-ods.
Only plants tolerant of -cooT,.
ad.pted to Croup 1 soi Is can be
mol 51:cor.ditiol'1S are adaptable to these 1.Indra;nad 50il s.
suitable to Croup -4 soils when the surface remains drained.
Pl.nts
Group S -SoHs with So........lllOitationl Due to Exc....Moi.ture
Haitlr Soil
Limitations
Wetness
{high ..ahr table]
Drainage
Class-
Poorly dra;ned..
Depth
(Inches)
More than 20 ..
H.y h.ve up to
16 of peat on
surface.
USDA
Texture
Very "ide range.
Available
Water HoT di nq
Capacity (fnches)
Usual I y "aterloqged
water'tabl e wi thin
Z feet ,of su-rface.
Plant choices in this group are limited due to the difficulty
condititlns.Selected plants :should be adapted to cold,wet soils.
drained soi I
Major Soi I
Limftations
'Drainage
C1 ass
Depth
(Inchea)
USDA
Texture
Water Hal ding
capacity (i nchesl
Wetness
{water tabl e
at surface J.
Very poorly drained.More than 16...Peat
drained.
Substratum Very n,de range
Waterlog-ged.
The choice of plants is limited.
avoided whenever -possible.
Damage to the existing vegetation over these soils should be
1 Source:Rural Development Council,1983.
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Scarification will result in cooler,looser,more moist soil for seed
germination and will increase seed-to-soil contact.
3.8.3 Seeding
3.8.3.1 Timing
Seeding should be done as early in the growing season as possible.Avail-
able moisture is the limiting factor necessitating early planting because
many areas dry rapidly following spring melting and summer precipitation ;s
low.Early planting also facilitates earlil:!r germination and growth which
results in less winterkill than later sowing.Optimum seeding dates for
most areas of Alaska are from May 15 to June 15,depending on temperature
and soil moisture.
3.8.3.2 Application Methods
There are several seeding methods available depending upon the size,slope,
and accessibil ity of the area to be seeded.On large areas to be planted
with grass for erosion control,unseeded stY'ips or areas should be dispersed
among the seeded areas to allow for reinvasiion and restabl ishment of native
species.
Drill seeding,which results in uniform seed distribution and placement at
the proper depth,is the most successful me~thod for achieving a productive
density rate.However,it has disadvantages for use in widespread revege-
tation programs.It is not applicable to rocky areas and must be limited
-89-
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1
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to use on areas having a slope of less than 3:1.It is also expensive and
slow.
Broadcast seeding is faster and less expensive than drill seeding,but is
less effective and requires more seed.The seed should be covered by
harrowing,packing,dragging,or mulching.Aerial broadcasting is advanta-
geous for large or inaccessible areas.Low lrlind speeds (below 2 mph)and a
uniform height are necessary to achieve an even distribution of seed.
Hydroseeding is a good technique,particularly for steep slopes where
drilling is not feasible and aerial seeding is not necessary.A water
source is necessary for mixing the slurry of 100 to 150 pounds or less of
seed with 100 gallons of water.Hydroseeding may be followed by mulching
to prevent seed runoff and retain moisture,but the operations should be
done separately to ensure·sufficient contact between the seed and soil to
enable germination.
3.8.3.3 Recommended Seeds and Mixtures
The most successful revegetation programs iare designed around the use of
native grasses,preferably the same species as those adjacent to the site.
Barring this,species should be from similar latitudes and,at worst,those
adapted to similar weather conditions.One of the greatest advantages of
the use of native plants is that once they areestabl ished they can grow
vigorously and persist without the management and maintenance so necessary
for cultivars.
-90-
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Traditionally,annual ryegrass (Hal ium mu1tiflorum)has been used as a
temporary measure for erosion control.Its very fast growth rate,exten-
sive root system,high seedling vigor,and good acidity tolerance are
particularly suited for this purpose.While~annual ryegrass may provide a
good initial cover for erosion control,it is not a permanent solution to
erosion problems.It is an annual plant and will not persist in areas
where it is seeded even though abundant seed may be produced.In addition,
it discourages the establishment of native species which would provide
long-term cover for site stability and requires reseeding and fertilization
maintenance treatments to perpetuate its cover.Where annual rye is used,
small areas within the site should be left bare to allow for the reinvasion
of native plants which can eventually take over the function of erosion
control and obviate the need for indefinite maintenance of non-native
grasses.
In general,grass seed mixes are preferable to monocultures because they
provide different species for microsite differences in soil,moisture,and
fertility.However,mixes can result in competition between species which
may result in less cover,particularly if high seeding rates are used or if
annuals and perennials are mixed.
Using the geographic regions as determined by type of vegetation (depicted
on Figure 17)and the soil groups listed in Table 8,alternative seeds and
mixtures are presented on Tables 9 through 14.Excluded are recommenda-
tions for Soil Group 6 in the Cook In1et-Susitna,Interior,Southwest,and
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•ARCTIC &ALPINE AREA
COOK INLET-SUSITNA AREA
D INTERIOR AREA
SOUTHEAST .AREA
SOUTHWEST AREA
•WESTERN AREA
Q -100 200 300 MILES
ALASKA POWER AUTHORITY
GEOGRAPHIC AREAS
BY VEGETATIVE TYPE
FIGURE 17
TABLE 9
COOK INLET -SUSITNA AREASEEDINGRECoMMENDATIONS
Soil Groups land 2
Pure Live Seed
Mixtures and Species Vari ety Name Drill Seeding Broadcast
in order of in order of Seeding Rates Seeding Rates
Preference Preference lb.per acre lb.per acre
l-Red Fescue Arctared or 5 10
Boreal 5 10
Alsike or White
Dutch Cover 1 2
Annual Ryegrass 2 4
2.Kentucky Bluegrass Nugget.4 15
Merion or Park 4 15
Alsike or White
Dutch Cover 1 2
Annual Ryegrass 2 4
3.Red Fescue Arctared or 5 10
Boreal 5 10
4.Hard Fescue Ourar 5 10
5.Kentucky Bluegrass Nugget.5 10
Merion or Park 5 10
6;Smootf1Brome Polar or 10 20
~Mancflar 8 16
7.Polargrass Alyeska 10 15
8.Bluejoint Reedgrass Sourdough 4 8
Soil Group 3
Mixtures and Species
in order of
Preference*
Variety Name
in order of
Preference
Pure t ive Seed
Drill Seeding Broadcast
Seeding R:ates Seeding Rates
lb.per a.cre lb.per acre
1.Red Fescue Arctared
White Dutch Clover
or Sweet Clover
Annual RYeeJrass
2.Hard Fescue Durar
Annual Ryegrass
3.Streambank
Wheatgras!Sodar
5
1
2
5
2
6
10
2
4
10
4
12
,.Watering.is generally required at least for establishment and preferably for
the first 2 years.
Sen Group 4
Mixtures and Species
in order of
Preference*
Variety Name
in order of
Preference
Pure Live Seed
Drill Seeding Broadcast
Seeding R:ates Seeding Rates
lb.per a.cre lb.per acre
1.Creeping Foxtail 4 8
2.Meadow Foxtail 4 8
3.Red Fescue Arctared or -5 10
Boreal 5 10
4.Reed Canarygrass Frontier 10 20
5.Polargrass Alyeska 10 15
6.Bluejoint Reedgrass Sourdough 4 8
NOTE:If land ha~been drained.use recommendations for Group 1.
,.Alsike clover at 1 lb./acre drilled or 2 lbs./acre broadcast may be added
to any of the following.
Soil Group 5
Mixtures and Species
in order of
Preference
Variety Name
in order of
Preference
Pure live Seed
Drill See!ding Broadcast
Seeding Rates Seeding Rates
1b.per a.cre 1b.per acre
1.Polargrass
Alsike Clover
2.Bluejoint
Reedgrass
Alsike Clover
Alyeska
Sourdough
10
1
4
1
15
2
8
2
10
10
20
16
15
15
15
8
Broadcast
Seeding Rates
lb.per acre
Pure Li ve Seed
5
10
8
4
4
4
4
Drill Seeding
Seeding Rates
lb.eT'acre
TABLE 10
INTERIOR AREA
SEEDHlG RECOMMENDATIONS~
Soil Group 1
Variety Name
in order of
Preference
Re Fescue rctare or
Boreal
Polar or
Manchar
Park or
Merion
Polargrass Alyeska
Bluejoint Reedgrass Sourdough
Smooth
Brame
Kentucky Bluegrass
Mixtures and Species
in order of
Preference
2.
3.
4.
5.
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!
Soil Group 2
B
S
20
16
10
8
5
5
8
4
2.5
10
8
5
4
2.5
2.5
4
Pure Live Seed
Drill Seeding Broadcast
Seedinl~Rates Seeding Rates
lb.e!r acre lb.er acre
Variety Name
in order of
Preference
Po ar or
Manchar
Durar
Polar or
Manchar
Polar or
Manchar
Arctared or
Boreal
SourdoughBluejointReedgrass
Red Fescue
Hard Fescue
Smooth Brome
Smooth Brame
4.
2.
3.
SoOOr
Polar or
Manchar
Soil Group 3*
10
8
5
10
10
12
20
16
Seed
Broadcast
Seeding Rates
lb.per acre
4
2.5
5
5
Pure Live
Drill Seeding
Seeding Rates
lb.pSr acre
Variety Name
in order of
Preference
Polar or
Manchar
Durar
Durar
Arctared
L Smooth Brame
Mi xtures.and Sped es
in order of
Preference**
Hard Fescue
2.Hard Fescue
3.Red Fescue
4.Streambank
Wheatgrass
5.Smooth Brome
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I
NOTE:If the soils of this group are irrigated.us;e seeding recommendations for
Soil Group 1.
*Watering is generally required at least for establishment and preferably for
2 years •
**YeT1ow or white sweet clover may be added at a nte not to exceed 2 lbsfacre
drilled or 4 lbs.facre broadcast.
Soil Group 4
8
8
6
6
10
10
2
5
5
20
16
15
8
Seed
Broadcast
Seeding Rates
lb.per acre
II
/I
1l.5
1.5"..1
".1
:[
:~.5
:1.5
10
8
10I'
Pure Live
Drill Seeding
Seedi ng Ra tes
lb.pE!r acre
Mixtures and Species Variety Name
in order of in order of
Preference Preference
1.Creeping Foxtail Garrison
2.Creeping foxtail Garrison
KentUcky Bluegrass Park or
Merion
3.Red Fescue Arctared or
Boreal
4.Timothy Engmo
Red Fescue Arctared or
Boreal
5.Smooth Brome Polar or
Manchar
6.Polargrass Alyeska
~7.Bluejoint Reedgrass Sourdough
8
2
6
6
15
8
Seed
Broadcast
Seeding Rates
lb.per acre
4
1
1.5
1.5
10
4
Pure live
Drill Seeding
Seeding Rates
lb.per acre
son Group 5
Variety Name-
in order of
Preference
Garrlson
Engmo
Park or
Merion
Polargrass Alyeska
Bluejoint Reedgrass Sourdough
Mixtures and Species
in order of
Preference
3.
4.
1.Creep,ng Foxta 11
2.Timoth'l
Kentucky Bluegrass
-
NOTE:The permafrost conditions common to these soils will recede to greater
depth after clearing of the native vegetation but usually will return to
its original depth if grass is grown continuously for 5 years or more.
TABLE 11
SOUTHEAST AREA
SEEDING RECOMMENDATIONS
So11Groupsl,2 and 3
-Mixtures and Species
in order of
Preference
Variety Hame
in order of
Preference
Pure Live Seed
Orin Seeding Broadcast
Seeding Rates Seeding Rates
lb.per acre lb.per acre
Arctared or
Boreal
1.Red Fescue
White Dutch or
Alsike Clover
Annual Ryegrass
2.Kentucky Bluegrass Nugget,Park
or Merion
White Dutch or
Alsike Clover
Annual Ryegrass
3.Meadow foxtail or COlllllOn
Creeping Foxtail Garrison
4.Bluejoint Reedgrass Sourdough
White Dutch or
Alsilce Clover
AnnUll Ryegrass
5 10
5 10
1 2
2.5 5
4 15
1 2
2.5 5
4 8
4 8
4 8
1 1
2 I"5.:)
Pure Live Seed
Drill Sl!eding Broadcast
Seeding Rates Seeding Rates
lb.per acre lb.per acre
-
Mixtures and Species Variety Name
in order of in order of
Preference Preference
1.Meadow Foxtail or COll'lllon
Creeping Foxtail Garrison
2.Red Fescue Arctared or
80real
3.Reed
Canarygrass Frontier
4.Bluejoint
Reedgrass Sourdough
5
5
4
10
4
10
10
15
10
8
,A>
-
Soil Groups 5 and 6
When drained refer to Soil Group 1
Undrained refer to Soi 1 Group 4
tABtE 12
SOUTHWEST.AREA
SEEDING RECOMMENDATIONS
Soil Groups 1 and 2-i
-Mixtures and Species
in order of
Preference
Variety Hame
in order of
Preference
Pure Live Seed
Orin Seeding Broadcast
Seeding Rates Seeding Rates
lb.per acre lb.per acre
Soil Group 3
1.Red Fescue Arctared or
Boreal
Alsike Clover
2.Creeping Foxtail Garrison
Al si Ite Clover
3.Kentucky Bluegrass Nugget.Park
or Merion
Alsike Clover
4.Bering Hairgrass Norcoast
Alsike Clover
S.Bluejoint
Reedgrass Sourdough
-Mixtures and Species
in order of
Preference
Variety Name
in order of
Preference
5 10
5 10
1 2
4 8
1 2
4 15
4 15
10 15
1 2
4 8
Pure Live Seed
Drill SE!eding Broadcast
Seeding Rates Seeding Rates
lb.per acre lb.per acre
1.Hard Fescue Dural"
White Dutch'Clover
2.Red Fescue Aretared or
Borea~
White Dutch Clover
5
1
S
5
1
10
2
10
10
2
son Group.4
.-
Mixtures and Species
in order of
Preference*
Variety Hame
in order of
Preference
Pure Live Seed
Drill SE!eding Broadcast
Seeding Rates'Seeding Rates
lb.per acre lb.per acre
8
8
10
10
2
IS
2
8
2
IS
2
8
2
4
4
5
5
1
4
1
4
.1
10
1
4
1
COllll1On
Garrison
Arctared or
Boreal
Rorcoast
Nugget~Park
or Merion
Engmo
Alsfke Clover
Kentucky Bluegrass
Alsike Clover
Tfmothy
Alsike Clover
Bering Hairgrass
Alsike Clover
81uejoint Reedgrass Sourdough
Alsike Clover
Meadow Foxtall or
Creeping Foxtail
Red·Fescue
1.
2.
3.
4.
S.
6.
*NOTE:These recommendations are for undrained soil..For drained soil
recommendations refer to Group 1 soils.
5011 Group 5-Mixtures and Species
in order of
Preference
VarietyHame
in order of
Preference
Pure Li ve Seed
Drill S~!eding Broadcast
Seeding·Rates Seeding Rates
lb.per acre lb.per acre
1.
2.
3.
4.
Meadow Foxtail or
Creeping Foxtail
Bering Hairgrass
Alsike Clover
Bluejoint Reedgrass
Alsike Clover
Reed canarygrass
Alsike Clover
C011lDon
Garrison
Norcoast.
Sourdough
4
4
10
1
4
1
10
1
8
8
15
2
8
2
20
2
TABLE 13
WESTERN AREA
SEEDING RECoMMENDATIONS
So11 Groups 1 and 2
Mixtures and Species
in order of
Preference*
Variety Name
in order of
Preference
Pure Live Seed
Drill Seeding Broadcast
Seeding Rates Seeding Rates
lb.per <lcre lb.per acre
Bluejoint Reedgrass Sourdough
1-
2.
3.
4.
5.
6.,-.
Red Fescue
Meadow Foxtail
Creeping Foxtail
Bering Kairgrass
Potargrass
Arctared
CORDllon
Garrison
Norcoast
Alyeska
5
4
4
10
10
4
10
8
8
15
15
8
NOTE:The above recOIIIIendations are based on judgemel~t and.not on actua 1 tti a1s
in the area.*Alsfke clover should be added to any of the fonowil~g at a rate not to exceed
1 lb/acre drilled or 2 lbs/acre broadcast.
$011 Group 3
-Mixtures and Species
in order of
Preference
Variety Name
in order of
Preference
Pure Live Seed
Drill Se1eding Broadcast
Seeding IRates Seeding Rates
lb.per i!Cre lb.per acre
_.
r
1.Red Fescue
Als.ike Clover
2.Hard Fescue
Ahike Clover
3.Meadow Foxtail
Alsifce Clover
Aretared or
Boreal
Dura.r
C01IIIlOn
5
5
1
5
1
4
1
10
i.o
2
10
2
8
2
NOTE:The above recOllllle1'ldations are based on judgement and not on actual trials
in the area.
Soil Groups 4 and 5
Pure Live Seed
Mixtures and Species Variety Name Drill Seeding Broadcast
in order of in order of Seeding Rates Seeding Rates
Preference Preference lb.per acre lb.per acre
1.Meadow Foxta it C01llllOn 4 8
AlsitceClover 1 2
2.Creeping Foxtail Garrison 4 8
Alsike Clover 1 2
3.Bering Hairgrass Norcoast 10 15
Alsike Clover 1 2
4.Polargrass Alyeslca 10 15
Alsilce Clover 1 2
5.Bluejoint Reedgrass Sourdough 4 8
Alsike Clover 1 2
Mixtures and Species Variety Name Drill Seeding Broadcast
in order!of in order of Seeding R,ates Seeding Rates
Preference*Preference 1b.per a<cre lb.per acre
1.Glaucous Bluegrass*Tundra 10 15
Polargrass Alyeska 7 10
Alsike Clover 1 ·2
2.Red Fescue Arctared 10 20
Alsike Clover 1 2
3.Bering Hairgrass Norcoast 10 15
Alsike Clover 1 2
4.Bluejoint Reedgrass*Sourdough 4 8
Alsike Clover 1 2
-
TABLE 14
ARCTIC AND ALPINE AREASSEEDINGRECOMMENDATIONs
Soil Groups 1 and 2
'Pure Live Seed
NOTE:Disturbed sites may be revegetated by sodding or spreading freshly cut
native cottongrass~sedges,or other native tundra from adjacent areas,
packing and fertiliZing according to soil tests.
*This grass is to be used only in upland sites in the Arctic area.
-This gra.S5 is to be used only in the Alpine area.
Soil Group 3
Arctared
Tundra
Variety Name
in order of
Preference
Mixtures and Species
in order of
Preference*
1.41 aucous 81 uegra5s·
Alsike Clover
2.Red Fescue
Alsike Clover
15
2
15
2
20
2
8
2
Broadcast
Seeding Rates
lb.per acre
Pure Live Seed
10
1
10
1
10
1
4
1
Drill Set:ding
Seed i ng R:a tes
lb.per acre
Alyeska
Arctared
No rcoas t
Variety Name
in order of
Preference
Mixtures and Species
in order of
Preference*
NOTE:Disturbed sites may be revegetated by sodding 01'1'spreading freshly cut
native cottongrass,sedges,or other n,atiYe tundra from adjacent areas,
packing and fertiliZing according to soil tests.
*This grass is to be used only in the Alpine area.
Soil Group 4
1.Beri.ng Rairgrass
Alsike Clover
2.Polargrass
Alsike Clover
3.Red Fescue
Alsike Clover
4.81uejoint Reedgrass*Sourdough
Alsilce Clover
15
2
15
2
8
2
Broadcast
Seeding Rates
lb.per acre
Pure Live Seed
10
1
10.
1
4
1
Drill Seeding
Seeding Flates
1b.per alcre
~orcoast
Alyeslca
Variety Name
in order of
Preference
Mixtures and Species
in order of
Preference*
NOTE:Disturbed sites may be revegetated by sodding or spreading freshly cut
native cottongrass,sedges,or other native tU~ldra from adjacent areas.
packing and fertilizing according to soil tests:.
*Tbis grass is to be used only in the Alpine area.
Son Group 5
1.Bering Hairgrass
Alsike Clover
2.Polargrass
Alsike Clover
4.Bluejoint Reedgrass*Sourdough
Alsike Clover
NOTE:Disturbed sites may be revegetated by sodding (Ir spreading freshly cut
native cottongrass,sedges.or other native tundra from adjacent areas,
packing and fertilizing according to soil test~;.
*This grass is to be used only in the Alpine area.
-!
-
Western regions where seed recommendations are not yet available.Seed
sources for large revegetation programs should be developed several years
in advance of project construction.
3.8.4 Fertilization
Fertilizers basically consist of nitrogen,phosphorous,and potassium
(N-P-K).While fertilization is normally imperative for plant establishment
at disturbed sites,specialized fertilizers with micronutrients are not
necessary as part of an Al aska revegetation program.Use of a standard
-
N-P-K fertilizer (e.g.8-32-16,14-30-14)is usually sufficient and yields
a considerable cost savings to revegetation programs compared to use of
fertilizers containing micronutrients.
A standard N-P-K fertilizer should be applied to all disturbed sites.On
sites which receive general site preparation but no seeding,appl ;cation
should be at a rate of 300 to 500 lbs{acre.For seeded areas,application
rates should be 450·to 600 lbs{acre.Fertilization should include periphe-
ral areas of undisturbed natural vegetation to stimulate seed production
and dispersal.
Fertilizer treatments should be applied in the early spring.Maintenance
treatments should be applied in the second year after planting.
3.8.5 Mulches
The use of mul ches has advantages and di sadvantages.Mul ches moderate
-99-
rr-
I
-
temperature extremes,conserve moisture,protect surface soi 1s from ero-
sion,improve conditions for germination,and can be used to improve soil
quality.The use of organic mulch (e.g.straw,woodchips),however,can
result in depletion of available nutrients~,particularly nitrogen,which
becomes tied up in the decomposition process.Mulches may also inhibit
germination or result in premature germination after early rains and
seedling mortality.In general,the indisc:riminant use of mulch is not
recommended for environmental conditions where nutrients are limited and
decomposition is a slow process.
3.8.6 Woody Plants
While extensive use of woody plants for revegetation is not expected at
Power Authority project sites,they may be appropriate in areas of
disturbed riparian habitat where annual flooding does not occur.Stem
cuttings can be used to propogate many of the deciduous tree and shrub
species in Alaska.Willow and poplar arle particularly widespread and
frequent invaders of disturbed areas.
Cuttings,approximately 8 to 10 inches long,should be conected when
plants are dormant,preferably March or early April.They should be stored
at freezing temperatures in plastic bags wi th a wet paper towel wrapped
around the bases to prevent drying.Cuttings should be planted as early in
the growing season as possible by pushing them into the ground.Approxi-
mately 2 to 3 inches of the cutting should be left exposed above ground.
-100-
3.9 RECLAMATION
Reclamation of disturbed sites should be ul1ldertaken whenever the intended
use is complete and for those areas which will remain unused for extended
periods.
o Slopes,borrow areas,and waste al'eas should be graded to stable
conditions and provided with permanent drainage
o Open culverts and culverts in natural drainages should be removed
o Fill material in streams should be removed down to the origina1
stream contour
o Roadways should be shaped to drain by crowning or outsloping and
water bars,checks or drainage str'uctures should be installed
o Abandoned roads should be removed or put to bed (i.e.stabilized,
scarified and fertilized in place)
o
o
Disturbed areas should be treated for revegetation or reinvasion
by native species
Access blocks such as berms or ditches should be installed to
prevent access and damage to stabilized areas.
-101-
-
.-
3.10 INSPECTION AND MONITORING
An environmenta 1 i os pector wi1l be ass i gned to Power Authori ty proj ects •
This individual will be thoroughly familiar with the various portions of
the work and with the environmental requirements as they relate to con-
struction operations.Before any activity is begun,the inspector will
review the work requirements,make a physical survey of the area,and
verify that construction boundaries are clearly marked.The inspector will
review the contractor's proposed methods and procedures wi-th special
attention to environmental protection.The inspector will then monitor the
actual construction activities to ensure that environmental requirements
are met.Special attention will be given to equipment movements,excava-
tion,cl earing and grubbing,embankments,quarry and borrow operations,
ditching,stream diversions,stockpiling,access roads,drainage and
revegetation •
Monitoring will be required for some projects to provide documentation that
water quality standards are met.The location of upstream and downstream
sampling stations will be pre-determined through consultation with the
applicable regulatory agency.Considerations include the hydrology of the
stream,the allowable mixing zone,and effec:ts of upstream feeder streams.
-102-
-CHAPTER 4 -AUTHORITIES AND AGENCIES
Any component of a project may require one or more permits from federal,state,
or local authorities.The following list of federal and state permits empha-
sizes those most frequently required from thle standpoint of erosion and
sedimentation control.Legal requirements appl'icable to individual projects
should be thoroughly examined on a case-by-case basis.
Federal
U.S.Corps of Engineers
Section 404 permit -required for dredge and fill operations in navigable
waters and wetlands
Section 10 permit -required for obstructions,alterations or improvements
in navigable waters
Bureau of Land Management
Pl an of operations for mineral operations and land use leases,permits,
easements
u.S.Coast Guard
Section 9 permit -for construction,modification or removal of a bridge or
causeway in navigable water
U.S.Environmental Protection Agency
National Pollutant Discharge Elimination System (NPDES permit)-required
for point source discharges
-103-
u.s.Fish and Wildlife Service
Special use permits for activities on lands under its jurisdiction
u.S.Forest Service
Special use permits for activities on lands ILlnder its jurisdiction
State of Alaska
Office of Management and Budget
Coastal zone management consistency determination
Department of Environmental Conservation
Section 401 certification (water gUidelines)-required for activities
subject to federal permits and licenses
Wastewater discharge permit
Water quality standards
Department of Fish and Game
Anadromous fish protection permit
Habitat protection permits
Department of Natural Resources
land use permit
Permit to construct or modify a dam
Water rights permit
Material purchase
Right of way
~Easements
-104-
REFERENCES
Alaska Department of Environmental Conservation,1979.Transportation
corridors water quality management study.
Alaska Department of Environmental Conservation,1980.Transportation and
water quality.
Alaska Department of Environmental Conservation,1983.Placer mining
settling pond design handbook.
Bell,F.G.,1975.Methods of treatment of unstable ground.Newnes-
Batterworths,London.
Brian,Curran,H.J.and H.M.Etter,1976.Environmental design for
northern road developments.Environmenta 1 Protecti on
Environment Canada.
Service,
Brown,J.andR.L.Berg (eds.),1980.Environmental engineering and
ecol ogicalbaseline investigations along tlhe Yukon River -Prudhoe Bay
haul road:Cold Regions Research and EngineE!ring laboratory.
Dabbs,D.l.,We Frieson,and S.Mitchell,1974.Pipeline revegetation.
Prepared by Northern Engineering Services Company limited for Alaskan
Arctic Gas Study Company.
Down,C.E.and J.Stocks,1977.Environmental impact of mining.Halsted
Press,N.Y.
Harza-Ebasco Susitna Joint Venture,1984.Drainage structure and waterway
design guidelines.Prepared for Alaska Powel"Authority.
Kubanis,S.A.,1982.Revegetation techniques in arctic and subarctic I
regions.Office of the Federal InspectOl",Alaska Natural Gas Trans-
portation System.
lotspeich,F.B.and A.E.Helmers,1974.Environmental guidelines for
development roads in the subarctic.U.S.Environmental Protection
Agency.
Murfitt,A.W.,W.B.McMullen,and J.F.McPhail,1975.Design and
construction of roads on muskeg in arctic and subarctic regions.16th
Annual Muskeg Research Conference.
Rural Development Council,1983.A revegetation guide for Alaska.
U.S.Environmental Protection Agency,1975.l099in9 roads and protection
of water quality.
U.S.Environmental Protection Agency,1975.Methods of quickly vegetating
soils of low productivity,construction activities.
r-
I
......
I
I
-I
I
u.s.Fish and Wildlife Service,1980.Gravel re~moval guidelines manual for
arctic and subarctic floodplains.
U.S.Forest Service,1979.Roadway drainage guide for installing culverts
to accommodate fish.
Vee,C.S.and T.O.Roelofs,1980.Planning fOrE!st roads to protect
salmonid habitat.USDA Forest Service General Technical Report
PNW-109 .
Younkin,W.E.,1976.Revegetation studies in the northern Mackenzie Valley
region.Prepared by Northern Engineering Services Company Limited for
Canadian Arctic Gas Study Limited.