HomeMy WebLinkAboutBradley Lake Hydroelectric Project Summary 1983>-IT:
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BRADLEY LAKE
HYDROELECTRIC
___ PROJECT __ _
A laska En ergy Allthority
SUMMARY
By ASCE
EVA LUATION CRITERIA
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Alasiul Resourcc~ Uhrlllj' & loronnation Sc:Mcc:5
Li bnlry OuH d ins. Su ite III
3211 PhwidcOl.'C Drive
Ancflora1,'C , AK W~14
SYNOPSIS
THE BRADLEY LAKE HYDROELECTRIC PROJECT
exemplifies the responsible' development of a natural resource
ill all e'llvirol1l1lelltally se'l1sitiv(' area.
It de1l1ollstrates that quality el1gineering makes it possible to
protect tlie el1virol1lllCllf while devclopillg our re'sOllrccs.
The project provides clean, low cost power to three-quarters of Alaska's population and
will help stabilize power rates for decades. In addition to the economic benefits of this rene\'lable
resource, the project pro\'ides recreational opportunities and public access to a wilderness area.
Construction in the remote, subarctic, seismically active and sensitive environment required
resourceful planning and design. Utility and public coordination groups were created to provide
input on project Extensive modeling, numerous environmental studies and a
geotechnical interpretive report \'lere developed. Optional tunnel configurations, use of onsite
materials, and the use of an open-cut intake channel helped reduce project costs and expedite
construction.
Pioneering efforts in the relocation of nesting prevented potential delays during initial
construction. State-of-the-art designs for the dam facing, powerhouse substation, and
transmission line foundations were used to cope with Alaska's harsh winter climate. Additional
design features facilitated \".'inter construction and provide future expansion capabilities. Special
seismic features enable the project to withstand earthquakes up to 8.5 on the Richter scale.
The remote site and short construction seasons resulted in innovative construction techniques
and efficient use of onsite materiaL Pre-assembly of the tunnel boring machine expedited
construction, and two tunnel boring records ,vere set. Tunnel muck was used as the dam face
bedding and the placement of the concrete face ,,,'as sped with a paving machine and conveyor
system. Due to access restrictions, a skycrane helicopter was used as an air freighter for
construction of the transmission line and river diversions.
Throughout development, extra efforts were taken to protect the area's ecology and natural
beauty. Project features were designed to minimize visual impact and surface disturbance. To
maintain its wilderness setting, no road was constructed to the site and extensive measures vvere
taken to protect and enhance wildlife resources.
C011tillucd development of our nation '5 resources to lIIeet
the gnnuillg /leeds of society will depend IIpon
the ability of ciuil c11gillcers to protcct tlle cl1viro111l1Cl1t.
The succcssflli tech11iques used at Bradley Lake'
provide l1ew cngineering! cOllstructiolllll1d 111l11/{/gcl11ellt 1110dels
for future project de''()cloplIlcnf,
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Library Du:!Jing . .::iu;lc III
3211 Providellce Drive
Anchorage, AK 99508-t614
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Chris Aretuf I AIJlska Stock Imngt'S
IONS
TO THE VvELL-BEING PEOPLE AND COMIVfUNITIES
o RENEW ABLE RESOURCE DECREASES DEPENDENCY ON FOSSIL FUELS
Fossil fuels previously generated 95 percent of electricity in Alaska. Bradley Lake
is a renewable hydroelectric resource that reduces this dependency by 10 percent.
• PROVIDES A LONG-TERM, LOW-COST, STABLE POWER SOURCE
The cost of Bradley Lake power will be stable, relative to fluctuating prices for fossil fuels.
Power will be available at knmvn, low-cost rates for 50 to 100 years, or more.
• SERVES THREE-QUARTERS OF THE ST ATFS POPULATION
The project is located in the southcentral area of Alaska, which is the core population center.
Power from the project is distributed over a distance of more than 500 miles, reaching
72 percent of the state's population.
• CREATED THOUSANDS OF JOBS
During the five-year construction period, thousands of jobs were created.
At the peak of construction, more than 400 workers were directly employed.
• IMPROVED LOCAL ECONOMY
The Bradley Lake Hydroelectric Project was built during an oil recession in Alaska.
During this critical time, the creation of jobs and the influx of project money helped mute
the recession's devastating effect on Alaska's oil dependent economy.
• INCREASED RECREATIONAL OPPOI{TUNITIES
The project provides a point of entry to the surrounding wilderness for hiking, skiing,
mountain biking, hunting and fishing. A small boat dock and six campsites ,\'ere constructed
at the project site for public use.
• DEVELOPED DESIGN, CONSTRUCTION
AND ENVIRONMENTAL PROTECTION TECHNIQUES
The techniques used to meet the challenges of this remote, seismically active and sensitive
subarctic elwironment provide models for managers, and contractors for future use.
• DEMONSTRATES THAT IIYDROELECTRIC DEVELOPMENT
AND ENVIRONMENTAL PROTECTION ARE COMP ArIBLE
The project demonstrates that environmental '-aIUl's can be protected while developing
natural resources.
ADVE SE EFFEC
• SHORT-TERM POWER RATE INCREASE
Bradley power will be slightly more expensive than gas generation for several years.
Cost for fossil fuel generation is projected to rise continuously, hmvever, while
hydropower remains stable. Bradley power is projected to be less expensive than existing
generation by 1994 or 1995.
• POSSIBLE INCREASED ICING IN THE BAY
Local fishermen expressed concern that the release of additional fresh water during the winter
months could increase icing in Kachemak Bay, causing potential interference problems with
fishing gear and boats. The Alaska Energy Authority conducted two studies and gathered
baseline data, which will be used to help determine if increased icing occurs. If it does,
plant operations can be adjusted to avoid impacting fisheries.
• DEVELOPMENT IN A PRISTINE AREA
Although the Bradley Lake Hydroelectric Project was developed in a pristine area,
planning, design and intensive mitigation efforts minimized environmental
and esthetic impacts.
RESOUI<.CEFUL ESS
IN PLANNING AND SOLVING DESIGN PROBLEMS
• EXTENSIVE ENVIRGNMENT AL STUDIES AND MODELING
As part of project design, numerous environmental studies were undertaken including:
fisheries, goats, moose habitat, eagle nesting, icing studies and tprrestrial impacts studies.
Many of the studies are multi-year programs which began beforp construction and will continup
for several ypars into project oppration. Engineering designs for the spillway, intake structure
and turbine units ,\'ere verified through the use of physical models.
• ESTABLISHED UTILITY AND PUBLIC COORDINATION GROUPS
The Bradley project served as a catalyst bringing together six of Alaska's largest electric utilities.
The utility group addressed design and operational aspects of the project, as well as joint plan-
ning for improved service to the entire southcentral region. A citizen's advisory group was also
established to interface with area residents, receive public input and address local concerns.
• GEOTECHNICAL INTERPRETIVE REPORT
A geotechnical interpretive report was llsed to predict tunnel conditions and established a
baseline for measuring changed conditions. The report assisted both designers and
contractors in choosing the most cost-effective and efficient 'way to excavate through
the mountain, and helped avoid costly claims.
• CONTRACT DISPUTES REVIEW BOARD
A Disputes Review Board was utilized to provide an alternative means of disputes resolution.
Its creation vvas effective in facilitating open dialog between the contractor and owner,
resulting in the speedy resolution of disputes. No unresolved contract disputes remain
on the project.
• ROAD USED AS PERMA="JENT AIRSTRIP
As a result of local input, the planned project airstrip was redesigned and integrated into a
section of the permanent access road, resulting in substantial cost savings.
• MULTIPLE USE OF MATERIALS
Rock blasted from the tunnel intake area was used for dam fill and material excavated from
tunnel boring was used as the bedding layer to support the dam's concrete face. Riprap
from temporary roads and tunnel shut rock were used in constructing fisheries enhancements
and the 'waterfowl nesting area.
• OPEN CUT INTAKE CHANNEL
The simple open cut intake channel design allowed the intake structure and upper tunnel to
be exca\'ated in the dry. As the intake was excavated, the material was placed directly into
the dam fill, thereby reducing handling costs and expediting construction.
___ . ________________________ . ______________________ COlltillll('d
RESOURCEFULNESS
IN PLANNING AND SOLVING DESIGN PROBLEMS
continued
• DAM FILL DESIGN
The dam is a simple three zone design, with excavated shot rock as the core of the dam.
The downstream riprap layer is oversized material from the core. The flattened side slopes
increase stability to ,vithstand major earthquakes.
• OPTIONAL TUNNEL CONFIGURATION
Multiple tunnel alignment configurations and optional tunnel diameters were designed to
aJlm'>' contractors the flexibility of choosing construction methods and equipment which
were the most efficient and cost effective.
• SPECIAL SEISMIC DESIGN FEATURES
Design criteria were developed for structurat safety and operational considerations based on
three levels of seismic disturbance. The dam fill design, continuo liS reinforced concrete dam
facing, tunnel lining and powerhouse design will help the project withstand earthquakes
up to 8.5 on the Richter scale without catastrophic failure.
• COLD WEATHER DESIGN AND CONSTRUCTION FEATURES
To facilitate construction and long-term operation requirements in subarctic winter conditions,
the design included special features such as: the use of two-stage concrete for construction of
the powerhouse to allmv embedment of the turbine units during winter, the usc of a pile
clamp design for transmission tower foundations to provide vertical adjustment in the event
of future frost heaving, the use of an ungated spillway to minimize icing problems, and
the use of an indoor substation design.
• DESIGNED FOR FUTURE EXPANSION
The installation of a third penstock and rock excavation for the foundation at the time of initial
project construction allow for cost-efficient expansion to meet future capacity needs without
requiring a lengthy shutdmvn of the plant.
PIO E RI GUSE
OF IV1ATERIALS AND METHODS
" MAN-MADE EAGLE NESTS AND RELOCATION OF CHICKS
A unique experiment to dc\'clop alternate nesting sites and relocate nesting bald eagles
minimized conflicts between construction actidties and eagles. The program provides nc,\'
knowledgc for ,vildlife managers on how to protect bald t:'agles.
• CONTINUOUS REINFORCED CONCRETE SLAB FOR DAM FACING
The dam's impervious layer consists of a state-of-the-art continuous reinforced concrete
facing. The concrete slab will control shrinkage and help maintain the integrity of the dam
facing in the event of settlement due to seismic activity.
• COMPACT GAS INSULATED SUBSTATION
A compact gas insulated substation design ,vas used to reduce the amount of \vetland fill
required for powerhouse construction. The indoor substation is protected from salt water and
cold temperatures, making it easier to maintain. This is the first such technology to be
used in Alaska.
• PILING DESIGN FOR TRANSMISSION LINE
The use of pile foundations and the pile clamp design for the transmission lines facilitated
construction and will reduce future maintenance cost. The pilings allowed for winter
construction of foundations and provide resistance to frost jacking. The pile clamps provide a
means of simple vertical adjustment.
• HELITORCH CONTROLLED BURNS
A helitorch ,vas llsed on an experimental basis for the controlled burning of downed timber in
remote sections of the transmission line right-of-way to eliminate spruce bark beetle habitat.
INNOVATIONS
IN CONSTRUCTION
• PAVING MACHIJ\JEjCONVEYORS FOR DAM FACING
The use of a conveyor system and paving machine to place the concrete dam facing sped
the process, enabling the contractor to pour each 50-foot slab in just four hours.
• USE OF TUNNEL MUCK FOR DAM FACE BEDDING
The use of tunnel muck for the dam face bedding eliminated the need to process screened
materials, providing a cost-effective use of material that would otherwise have been wasted.
• PRE-ASSEMBLED TUNNEL BORING MACHINE
The contractor's ingenuity in pre-assembling the tunnel boring machine at the factory
substantially reduced onsite set-up time. The boring machine was in full production within
four weeks of its arrival onsite.
• TUNNEL BORING RECORDS
Effective pre-planning of the tunnel drilling and the use of a modified tunnel boring
machine resulted in excavation of the tunnel in just six months --more than three months
ahead of schedule --and the setting of two tunneling records: 116 feet bored in 8 hours,
and 275 feet bored in 24 hours.
• SINGLE PASS, RAISE BORE VERTICAL SHAFT
The use of a raise bore machine for the vertical shaft excavation allowed easy removal of
tunnel debris and provided for speedy completion of the vertical shaft. The 760-foot shaft
was completed in a single pass in only four weeks.
• USE OF SKYCRANE FOR REMOTE CONSTRUCTION
Due to limited accessibility and to minimize environmental damage, a skycrane helicopter
was used to set towers for the transmission line and to transport equipment for construction
of the two river diversions. Contractors coordinated use of the same skycrane to gain
efficiency in construction.
ENVIRONMENTAL IMPACTS
UNUSUAL ASPECTS • ESTHETIC VALUE
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• NO ROAD ACCESS TO
As part of the commitment to maintain the wilderness character of the area and to minimize
destruction of wildlife habitat, no road access v\'as constructed to the project site.
• MINIMIZED SURFACE DISTURBANCES AND VISUAL IMPACTS
Every aspect of project design and construction was evaluated for environmental impacts, and
solutions were developed to minimize impacts. Examples are: an intake which is covered
by reservoir waters, underground placement of penstocks, removal of temporary roads, and
rehabilitation of the temporary camp and other areas.
• ASSURED WATER RELEASES
To alleviate concerns of the National Park Service, water flows to the Nuka River will be
maintained at or above pre-established minimums through the use of a self-regulating
control structure.
• EXTENSIVE MITIGATION EFFORTS
SPRUCE BARK BEETLE CONTROL
During clearing operations, special care was taken to dispose of cut timber along the
transmission line and access roads to protect against spruce bark beetle infestation.
FISH WATER BY-PASS SYSTEM
A series of pipes was installed at the diversion tunnel to allow controlled release of ,,,'ater from
the reservoir to maintain river t1mvs over downstream salmon spawning beds.
MOOSE HABITAT TRUST
To compC'llsate for habitat lost due to construction, 593 acres of prime moose calving and
browsing habitat were placed in trust to protpct it from dpvciopmpnt.
CREATING WATERFOWL NESTING AREA
A formal tidal area isolated by the road was enhanced with the addition of nesting islands and
water control structures to provide 33 acres of waterfowl nesting habitat.
ENHANCED FISH REARING HABITAT
A drainage ditch, initially excavated to dewater the gravel borrow area, was enhanced to
provide additional salmon spawning habitat, and gravel pits were interconnected to prm"ide
fish rearing habitat.
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