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ALASKA POWER AUTHORITY
SUSITNA HYDROELECTRIC PROJECT
TASK 6 -DESIGN DEVELOPMENT
SUBTASK 6.02 -CLOSEOUT REPORT
INVESTIGATE TUNNEL ALTERNATIVE
FINAL DRAFT
MARCH 1981
ACRES AMERICAN INCORPORATED
1000 Liberty Bank Building
Main at Court
Buffalo, New York 14202
Telephone! (716) 853-7525
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ALASKA POWER A~THORITY
SUSITNA HYDROELECTRIC PROJECT
TASK 6 -DESIGN DEVELOPMENT
SUBTASK 6.02 -CLOSEOUT REPORT
INVESTIGATE TUNNEL ALTERNATIVE
TABLE OF CONTENTS
LIST OF TJlBLES • • ~ e • • , ~ • • • • e • • • • • • • • • • • n • • • • • • • • • • • • • • • • • • • • • • • o • •
LIST OF FIGURES ···~·~·····················~Q···········••&•••···· L I ST OF PLATES •••••• o •••• o ......... e ••••••••••.••••••••••••••••••••
1 -INTRODUCTION
1.1-Overview •••••••o••••··································· 1.2 -Devil Car~on Dam and Tunnel Schemes ••••••••••••••••••••
1.3-Report Contents ·········~······················~·······
2 -SUMMARY
2.1-Scope of Work ····················~····················· 2.2 -Conceptual Tunnel Schemes ••••••••••••••••••••••••••••••
2.3-Tunnel Design and Construction Considerations ••••••••••
2.4-Screening of Conceptual Tunnel Schemes •••••••••••••••••
2.5 Preferred Tunnel Scheme ············~···················
2. 6 --Comparison with De vi 1 Canyon Dam Scheme •• \H ......... o •••
2.7-Conclusions and Recommendations ......................... .
3 -SCOPE OF WORK
3.1 -Study Objectives • • • 0 • • • • • • • ~ • • • • Q • • • 0 • • • • • • • • • ~ • • • • • • • •
3.2-Approach .,. •••••••••••• 0 ••• , ............................. .
4 -CONCEPTUAL TUNNEL SCHEMES
4.1 -Economics of Tunnel Schemes within the Susitna
Basin ••••••••••••••••••••••••••••••••••••••••••••••••••
4.2-Conceptual Devil Canyon Tunnel Schemes .................. ..
4.3 -Scheme 1 ••••••••·~·····••••••••••••••••••••••o•••••••••
4.4-Scheme 2 ············································~·· 4.5 -SchemR 3 ............................................... .
4. 6 -Sc h ente 4 •••••••••••••••••••••••••••••••••• o ••••••••• ., ••
4.7 -Historical Precedence .................................... .
5 -7UNNEL DESIGN AND CONSTRUCTION CONSIDERATIONS
5.1-Geologic Setting •••••••••••••••••••••••••••••••••••••••
5.2-Geotechnical Design Aspects ••o••·················~·····
5.3 -Seismic Considerations •••••••••••••••••••••••••••••••••
5.4-Design Considerations .................................. .
5. 5 -Construction ~let hods .................................... .
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----~--~-----------------.,.~---. ------------.------
ALASKA POWER AUTHORITY
SUSITNA HYDROELECTRIC PROJECT
TASK 6-DESIGN·OEVELOPMENT
SUBTASK 6.02 -CLOSEOUT .. REPORT
INVESTIGATE TUNNEL ALTERNATIVE
TABLE OF CONTENTS (Cont'd)
6 -SCREENING OF CONCEPTUAL TUNNEL SCHEMES
6.1-Introduction ·································~·····~··· 6.2 -Tunnel Scheme Costs ...................................... "'.
6. 3 -Power and. Energy ..................................... .,. •••
6.4-Environmental Considerations .......................... ~.
6.5-Geotechnical Considerations ..................... "' •••••••••
6.6-Preferred Tunnel Scheme···········~············~·······
7 -PREFERRED TUNNEL SCHEME
7.2-Design and Operational Assumptions •••••••••••••••••••••
7.3-Project Description ••••tt•••········· .. ······/!1 ........... .
7.4 -Cost Estimate and Construction Schedule ••• IIOOOO(!Oeoooo•
7. 5 ~-Power and Energy .......................... -•••••••••••••• ".
7.6 -Environmental Impact Assessment ..................... ~·~··
8 -COMPARISON WIT'i DEVIL CANYON DAM SCHEME
8~1 -Economic Cow.parison ..................................... .
8.2 -Environmental Comparison ···············~·~;·············
8.3 -Comparison of Construction Schedules ···············••o•
8. 4 -Summary ••••••••••• " ••••.•• a •••••••• .., .... = * ................. .
9 -CONCLUSIONS AND RECOMMENDATIONS
9.1 -Conclusions •••••••••••••••• ., ........................... .
9.2 -Recolll!nendations ••••••••••••••••••••••••••••••••••••••••
BIBLIOGRAPHY
PLATES
APPENDIX A -ROCK UNIT DESCRIPTIONS (40)
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II LIST OF TABLES
I Number
4.1
I 4.2
I 4.3
5.1
I 5.2
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5.4
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7.1
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Title Page
Assumptions ftJr Tunnel Site Comparison Index . . . . . . . . . . . . . 4-5
Information on the Devil Canyon Dam and Tunnel Schemes . . . 4-6
Historical Tunneling Precedence . . . . . . . . . ~ . . . ~ . ~ ~ ~ . . . . . . . . 4-7
Geo 1 ogic StrtA~:·ture uf Reg ion Between the Devil Can~_,on
and Watana Dam S·ites • • . . • • • . • • • • • • • . • • • • • • • • • • • • • • • • . . • • . 5-8
Effects of Se !"5mic Loading on Tunnels (11) . . . . . . . . . . . . . . . 5-9
Tunnel Cover Experience •••••••.•.••...••.•••....••......• 5-10
Regional Geology fr'iap Units ............................... 5-11
Assumed Tunnel Support . • . • . • • .. . . . . • .. . • . . • • • . . . • • • • • • • • • . • 6-5
Devil Canyoit Tunnel Schemes -Costs, Power Output and
Average Annual Energy • • • . • .• • • . . • • • • • • • • • • • • . • . • • . • • . • • • . . 6-6
Litho logy of Tunne 1 Routes • • • • • • .. . . • . • • • • • • • • • . • • . . . • .. • . • 6-7
Drilling Results at Watana and Devil Canyon Dam Sites ••.• 7'""6
Optimization of T4nnel Diameter • . • • • . • • • • • • • . • • • • • . • • • • • • 7-7
Cost Estimate for Devil Canyon Tunnel Scheme (Two 30-
Font Diameter Tunnels) •...••...•.•...• , ••..••.•••••.•••.• i-8
Cost Estimate for Dev i 1 Canyon Tunne 1 Scheme (One 40-
Foot Diameter Tunne 1) • • . . • • • • . . • . • • . . • • . . • • . • . • • . • . • • • • • • 7-9
Power and Energy Produce ion from Tunnel Scheme .•.••••••• e 7-10
Summary of Economic Eva 1 uat ions (Mi 11 ion Do 11 ars) • • . . • • • . 8-4
Summary of Economic Sensitivity Evaluations (Mill ion
Do 11 ar s ) . .• • . • . . . . . . . . . . . . e • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • a .. 5
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LIST OF FIGURES
Number
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4.1
4.2
5.1
5.2
5.3
5.4
5.5
5 .. 6
6.1
7.1
8.1
Title
Tunnel Alternative Vicinity Map .........•...............
Economic Potential of Tunnel Schemes ................... .
Schematic Represent at ion of Conceptua 1 Tunne 1 Schemes ... .
Plate Tec~onic Map (Reproduced from Reference 43) ...... .
Regional Geology with Tunnel Routes (Reproduced from
Reference 43) ..... 0 ....................................... .
Boundary Fault and Significant Feature Map for the
Site Region (Reproduced from Reference 43) ·······••u•···
Devil Canyon Area Significant Feature Mao (reproduced
from Reference 43) . . . . . . . . . . . . . . . . . . . .. . ............... .
Devil Canyon Site Significant Feature Map (reproduced
from Reference 43) .......... ~ ..............•.............
Watana Site Significant Feature Map (Reproduced from
Reference 43) . ., ................... ., ............ o ••••••••••
Typical Daily Power Produ«:tion for March ....... • ........ .
Construction Schedule Preferred Scheme 3 . . . . . . . . . . . . . . . .
Construction Schedule Comparison .•. 0 ••••••••••••••••••••
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LIST OF PLATES
.. Number
1
T ·t·l _ 1 e
2
3
Conceptua 1 Tunne 1 Schemes -Plan & Sections
Preferred Tunnel Scheme 3 -Plan Views
Preferred Tunnel Scheme 3 -Sections
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1 -INTRODUCTION
L.l -Overview
Subtask 6~02 of Task 6 Design Development studies for the Susitna Hydr·oelectric
Project is entitled "Investigate Tunnel A1ternative 11
-. The scope of this subtask
as ·originally defined in the Acres American Inc. POS dated February 1980, was
expanded in the revisions to the POS issued in September 1980o The objective of
the Subtask 6. 02 study is to undertake a preliminary assessment of the feasibil-
ity of using a major tunnel to develop hydroelectric power on the Susitna-River
between the proposed Watana and Devil Canyon dam sites (see Figure 1.1).
The scope of work i nvo 1 ves essentially a desk study uti 1 i zing av a i 1 ab 1 e data.
The limited specific geologic or geotechnical information available along the
tunnel,,route will a11ow no more than a conceptual assessment of the feasibility
of excavation of tunne-ls in the geologic structures adjacent to the Susitna
River in the region considered. Thus the assessment of the structural desi~n
requirements and the determination of feasible size and cost of such tunnels has
necessarily been based on Acres engineering judgement and experience at this
time. It is considered unlikely that goetechnical conditions would be so poor
that tunnels could not be excavated by some means in the region under considera-
tion. Nevertheless it is important to note that the worse the conditions, the
higher the cost will be. Estimates based substantially on judgement and
experience, however good, will be subject to the uncertainties.of the basic
assumptions used.
To establish the technical and economic feasibility of a tunnel alternative,. a
substantial amount of field geotechnical investigation, design, and construction
cost estimating and schedu 1 ing work waul d be required. Notwithstanding the
foregoing constraints, the study has been .tiirected towards assessing whether or
not there are sufficient grounds to consider the tunnel option in more detail as
a potentially economic, technical feasible and environmentally sound alternative
to the Devil Canyc··~ development. This report presents the results and conclu-
sions of this study.
1.2 -Devil Canyon Dam and Tunnel Schemes
The Watana-Devil Canyon \:!am scheme is compriseJ of two major dams, Watana and
Devil Canyon (Figure 1.1) .. As currently envisaged, Watana is a 840-foot high
gravel and rockfill structure with a crest elevation at 2225 feet and an 800 M\~
undernround powerhouse. The full pool surface area of Watana reservoir is
43,0QO acres and full pool storage volume is 10 million acre-feet. The large
storage volume allows regulation of river flows on bL·th a seasonal and yearly
basis. The Devil Canyon dam is a 625-foot high concrete arch structure with a
crest elevation of 1464 feet and a 400 MW underground powerhouse. The Devil
Canyon dam has a full pool storage volume of 1 mi 11 ion acre-feet and the
reservoir surface area is 7600 acres. o
A 1 arge power tunnel could be utilized to develop the head below Watana instead
of the Devfl Canyon dam. C.anceptually, this Devil Canyon tunnel scheme could be
used to develop either the total head of both dams or just that portion develop-
ed by the Devil Canyon dam. This could be achieved by locating the !11take works
either in the Watana reservoir or at some point downstream from the Watana dam ...
Based on init~a1 co~ceptui!l desi_gn corysiderations, a typical tunnel scheme would
comprise the foll:aw1ng ma,Jor componen1:s:
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Power tunnel intake works.
- A re-regt! 1 at ion dam if the i nta.~e works are 1 ocated downstream f~om Watana,
with a small hydroelectric development to utilize the available head and
flow. -
-One or two power tunnels <'f up to forty feet in diameter and up to thirty
miles in 1 ength.
-An underground powerhouse 1 .ith a capacity of_up to 1200 MW located in the·
vicinity of the Devil Canyon dam site.,
la3 -Report Contents
Section 2 of this report is a summary of the work undertaken and conclusions and
recommendations. Section 3 is an outline of the scope of work. The four basic
conceptual tunnel schemes considered are described in Section 4 and the screen-
ing process used to select the preferred scheme is outlined in Section 6. An
overview of the site geolos.,v and geotechnical design considerations are dealt
with in Section 5. The preferred tunnel scheme is described and analyzed in
more detail in Section 7 and compared to the Watana-Devil Canyon dam scheme in
Section 8. Conclusions and Recommendations are presented in Section 9.
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FOG CR.
LEGEND
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.t. DAM SITES
0 5 !!5 ,_.,
SCALE IN MilES
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TUNNEL ALTERNATIVE VICINITY MAP
FIGURE tl
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I 2 -SUMMARY
( To be written after approval of draft.
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3 -SCOPE OF WORK
l.l -Study Objective
The objectiv~s of this study are to investigate the feasibility of replacing the
currently proposed Devil Canyon dam project with a tunnel-supplied power plant
fed from the Watana dam site.
3.2 -Approach
To satisfy the study objectives, the work was organized and carried out in the
following manner:
-Four basic conceptual tunnel schemes were developed to investigate alterna-
tives for utilizing the available head between the Watana and Devil Canyon dam
sites~
-The available Information on tunnels of similar size previously constructed
elsewhere in the world was reviewed and summarized.
- A general evaluation of the topography, geology~ and seismicity of the area
was undertaken on the basis of the available information.
-Preliminary assessments v1ere made of geotechnical and structural design
assumptions and criteria for use in evaluation and comparison of
alternatives.
-A preliminary assessment of costs, energy yields, and environmental impact
associated .with the conceptual tunnel schemes was undertaken.
-Based on the information developed abov:2, a single scheme was selected as a
tentative optimtm for further study. This, more! detailed study, included:
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Develo(l11ent of preliminary engineering layouts.
More detailed assessment of capital costs and development of construction
schedules.
Monthly ·simu1 at ion of power and energy yields utilizing a computer model.
Pre 1 iminary environmental impact assessment.
-The selected tunnel scheme was compared with the Devfl Canyon dam alternative
on the basis of technical, economic, environmenta.l and construction schedule
considerations.
-The study was completed with the development of conc1us1ons on the viability
of the tunnel scheme and recorrmendations for further consideration of the
scheme as an alternative for inclusion in Susitna Basin development planning
studies.
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4 -CONCEPTUAL TUNNEL SCHEMES
4 .. 1 -Economics of Tunnel Schemes Within
the Susitna Basin
In order to put the Devil Canyon tunnel scheme into perspective. a brief study
was undertaken to assess the relative economics of tunnel schemes located in
v.:;.t"'ious portions of the basin. An essential part of a tunnel scherrte is an
upstream reservoir for seasonal and yearly flow regulation. Initially, the
Watana and Vee dam sites (see Figure 1.1) were selected as potential upstr~am
reservoir sites at which tunnel intakes would be located. An appropriate index
for initial comparison of alternatives was derived on the basis of the estimated
energy yield in kWh per cubic yard of tunnel excavation for each alternative.
The basic assumptions used in this analysis are shown in Table 4.1. The energy
yield was evaluated using the average annual discharge less 500 cfs compensating
. flow, and the net head allowing for friction losses. Preliminary studies
indicated that minimum cost of energy occurred at flow velocities ranging from
about 5 to about 7. 5 feet per second. For preliminary study purposes a uniform
velocity of 6 feet per second was adopted. Estimates of kWh/yd3 for the
alternatives considered are illustrated in Figure 4.1, from which it is evident
that the first 12 miles of a tunnel starting at Watana has lower economic
potential than the lower portion from Devil Creek downstream to Portage Creek.
The curves also indicated that the economic potential of a tunnel scheme down-
stream from the Vee dam site is much lower than that between Devil and Portage
Creeks.
The third curve on Figure 4.1 indicates the economic poten~ial of a tunnel
starting from .a re-r~:gulation dam loca·::.d downstream from Watana and just
upstream from Devil Creek. As outlined in the following section, this
re-regulation dam was ultimately chosen as the site for the intake in one of the
tunnel schemes.
4.2-Conceptual Devil Canyon Tunnel Schemes
All tunnel schemes considered assume that Watana (maximum water surface eleva-
tion 2200 feet} with an 'installed capacity of 800MW is the project's first stage
of development and that ;a minimllll of lOO'J cfs compensation flow is required in
the Susitna R1ver downstream frotl: Watana at all times.,
Four iJasic tunn.el schemes were selected for study. These involve utilizing
either the full head represented by hath the Watana and Devil Canyon dams or
just the head represented by the Devil Canyon dam and two basic operating modes,
i.e. peaking and base load power generation. The installed capacities for the
schemes are all based on a total Susitna Basin development plant factor of
between 50 and 55 percent. These schemes are depicted in Figure 4. 2 and are as
follows:
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(a) Scheme 1
This scheme involves the development of head between the Devil Car,yon dam
site and Watana and incorporates peaking operation of the tunnel power-
house.
(b) Scheme· 2
As for Scheme 1 except that the full head, including that avai·lable at the
Watana dam, is utilized.
(c) Scheme 3
This scheme involves the development of head between the Devil Canyon dam ·
site and Watana and incorporates base load operation.
(d) Scheme 4
As for Scheme 3 except that full head, including that available at Watana
dam, is utilized.
Schemes 1 and 3 require a secondary dam downstream of Watana to re~regulate
Watana releases and to control the water level at the tunnel intakes.
For Scheme 1 this re-regulation dam requires relatively little storage as the
two pow_erhouses operate essentially in series, i.e. they both peak
simultaneously. This can be proviJeci by a small re-regulation dam ·located some
2 miles downstream from Watana.
Re-regu 1 at ion storage requirements for Scheme 3 are much grea cer. To a 11 ow
peaking operations from the Watana reserve ir and base 1 c·ad o~·erat ion of the
tunnels requires a substantially larger volume. A brief economic study revealed
that this could best be provided by a re-regulation dam located some 15.8 miles
downstream from Watana. This site appears to be suitable for dam construction
and is located immediately upstream from the reach from Devil Canyon to Portage
Creek with higher economic tunnel potential, as discussed in Section 4.1. The
savings in tunnel cost at this site more than compensate for the increased
height of the re-regulation dam located this far downstream from Watana.
~more detailed discussion of the tunnel schemes is presented in the following
sections. Table 4. 2 summarizes pertinent information on each of the schemes
which are i 11 ustrated on P 1 ate 1."
4.3 -Scheme 1 (Devil Canyon Head,
Peaking Operation)
Scheme 1 consists of the Watano. dam with an 800 MW powerhouse and a re-regul a-
t ion dam approximately 75 feet in height located two miles downstream. The
tunnel intake works are located just upstream from the· re-regulation dam and a
550 MW powerhouse is located in the vicinity of Devil Canyon. Tunnel length is
about 27 miles. A minimum compensation flow of 1000 cfs is provided between
Watana and Devil Canyon. The re-regulation dam•s storage capacity is that
""
4-2
required fo~ the powerhr.uses to operate in serieso For preliminary study
purposes it has been assumed that sufficient storage to absorb approximately one
hour of peak power discharge from \tJatana will be necessary. This requires 1,600
acre-feet of storage. Peaking operations will create daily water ·level fluctua-
tions downstream from the Devil Canyon powerhouse, v-1hich will probably require
regulation.
4.4 -Scheme 2 (Full Head, Peaking Operation)
Scheme 2 consists of the Watana dam and power tunne1 intake works located
upstream of the damo Two tunnels, 29 miles long will discharge at a 1150 MW
powerhouse at De vi 1 Canyon. Upon completion of the tvr.nel stage of the over a 11
prGject, the Watana powerhouse capacity will be reduced from 800 MW to 70 MW,
just sufficient to release the required minimum compensation flow. Base load
and peak power demands will be generated at the Devil Canyon powerhouse. Water
level fluctuations downstream of Devil Canyon are s·imilar to those of Scheme 1 •
4.5 -icheme 3_1Devil Canyon Head, Base Load Operation)~
Scheme 3 consists of the Watana dam with an 800 1M powerhouse and a re-regula-
tion dam approximately 245 feet in height locat€:d 15.8 miles downstream fr·om
Watana. The tunnel intake works are upstream of th~ re-regulation dam with a
300 MW powerhouse in the vicinity of Devil Canyon. fhe re-regulation dam has a
storage capacity of approximately 350,000 acre-feet. A maximum v1ater level
fluctuation of four feet is sufficient to store the daily peak discharge from
Watana and release a constant discharge into the power tunnels. Watanats 800 MW
pO\t~erhouse wi 11 be operated as a peaking hydro ·faci 1 ity discharging into the
re-regu1ation res"rvoir. Devil Canyon•s 300 MW powerhouse: will be operated as a
base load faciliiy, and thus, no significant daily water level fluctuation will
occur downstream~
A re 1 at i ve 1y sma 11 powerhouse with a capacity of 30 M~l wi 11 f?e constructed at
the re-regulation dam. A minimum flow of 1000 cfs will be passed through the
re-regulation dam powerhouse to supply the required downstream compensation
flow.
4.6 -Scheme 4 (Full Head, Base Load Operation),
The general layout of Scheme 4 is similar to Scheme 2 with the following opera-
tional changes. The Watana powerhouse will remain at 800 MW and meet peaking
requirements. During off peak ·periods a constant base load of 35 MW will be
genel'·ated at Watana while satisfying compensation flow requirements bet\-Jeen
Watana and Devil Canyon. Th2 Devi 1 Canyon 365 t4W powerhouse and tunne 1 wi 11 be
operated as a base load facility. The full head potential for the entire flow
is not developed in Scheme 4, and thus annual energy production is less than the
other schemes. Daily water level fluctuations downstream of Devil Canyon are
similar to Schemes 1 and 2, and large water level fluctuations between Watana
and Devil Canyon wi'Il occur.
4.7 -Historical Pre·cedence
In crder to obtain a perspective of the tunnel scheme in terms of world wide
historical experience, a brief review of other tunnel schemes was undt:rtaken.
The results of this r·eview are sumJ11arized in this section.
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Table 4.3 compares on a greai;ely abbreviated basis, the Susitna tunnel
alternative with several other projects.
It is clearly evident that the propos~d tunnel concept at Susitna is unique.
However, it is important to note that tunnels of similar size, length, purpose,
and located in similar geology have been successfully completed. The Susitna
tunnel alternative is definitely within the state of the art. Larger and longer
tunnels have been driven in more complex geologi: settings. ,
. 4-4
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TABLE 4.1: ASSUMPTIONS FOR TUNNEL SITE CO~PARISON INDEX - -
(1) The tunnel powerhouse operates as a base load facility.
(2) Straight line tunnel alignments between the dam site and the tunnel tail
rane.
(3) Tunnel jischarge is the average annual discharge less 500 cfs compensation
flaw.
( 4) Tunnel size is based on an average flow velgpi.tcy of six feet per second
and one power tunnel.. •
(5) Average net head equals the gross head less head losses due to friction.
(6) Gross head is the difference between the dam tailwater level and the
tunnel tailwater level.
(7) Averr.ge head loss is based on a flow velocity of six feet per second and a
mam1ing n of 0.026.
4-5
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TABLE 4.2: INFORMATION ON THE DEVIL CANYON DAM AND TUNNEL SCHEMES
Devil Canyon Tunnel Schemf!
Dam 1 4 --
Reservoir Area
(Acres) 7,500 320 0 3,900 0
River Hiles
Flooded 31.6 2.0 0 15.8 0
Tunnel Length
(Miles) 0 27 29 13.5 29
Tunsel Volume
(Yd ) · 11,976,000 12,863,000 3,732,000 5,131,000
Compensating Flow
Helease from
5001 Watana (cfs) 0 1,000 1,000 1,000
Oownstream 2
~eservoir Volume
(Acre-feet} 1,100,000 9,500 350,000
OoMtst ream Oa~
Height. (feet) 625 . 75 245
Typical Daily
Range of Discharge
6,000 From Devil Canyon 4,000 4,000 8,300 3,900
Powerhouse to to to to to
(cfs) 13,000 ':4,000 14,000 8,900 4,200
Approximate
Maxirum Daily
Fluctuations in
Downstream
Reservoir (feet) 2 15 4
i 1,000 cfs compensating flow release from the re-regulat.ion :dam.
Downstrean from Watana.
3 Estimated, above existing rock elevation.
4-6
TABLE 4.3: HISTORICAL TUNNELING PRECEDENCE
Project Length Excavati~n Maximum Static
Name Location ~ (miles)' Shape Diameter Rock Method Depth Head b!ning
TARP Chicago Sewer Approx. Circular 18 7t-35 ft Dolomite TBM Approx. Partially C0..'1crete
140 .300 ft lined
Kemano British Power 10.1 Modified 25 ft Igneous and D&B 2200 ft 2585 ft Approx. 1}3 u:;qined,
Columbia Horseshoe metamorphics 1/) concrete li~ed
and 1/3 lined with
rock bolts and shot-
crete
Snettisham Alaska Power 1.9 t-kldified 13.5 ft Quartz-dorite, D&B 1200 ft Approx. 87 percent oolined,
Horseshoe Gneiss, Biotite~ 900 ft supported ldth rock
Schist bolts, 1 J pe:r~ent
supported ~ith rock
bolts and ~crete
Bersimis 1 Quebec Power 7.6 Modified 31.0 ft Gneisic and D&B BOO ft 875 ft Concrete lined,
Horseshoe Granitic entire length
Bersimis 2 Quebec Po we~: 0.5 Cirt!ular 36 ft Gneisic and D&B N 367 ft Concrete lured
.f::oo Granitic
.I .....;
Chute-des-~..,-dbec Power 5.6 Modified 34.3 ft Gneisic and DAJ.!, N 640 ft Concre.te lined
Passes Horseshoe Granitic
Chute-deE::t-Quebec Tail 1.7 Modified 46 ft Gneisk and D&B 250ft N Unlined
Passes Horse!'lhoe Granitic
Paijanne Sweden Water 72 Horseshoe 26.4 ft Granite. Gneiss D&B N N Unlined
Supply
Oa."le Sou~h Power l..6 Circular 24 ft Clay-Shale iBM N 210 ft, Concrete litred
Dakota (2 tunnels) 2.8 Circular 24 ft Clay-Shale TBM 272ft
Eklutna Alaska Power 4.5 Circular . 9 ft Argillite, N N 74ft Concrete lined
Graywacke
Bath Co. Virginia Power Approx. Horseshoe 32 ft Shale, Sandstone D&B N N Concrete lined
4
Susitna Alaska Power 13.~ or Modifierl 25 ft-40 ft Argillite, Gray-O&B Approx. 600 ft Suggest same as
(Tent a-29 Horseshoe wacke., Granite, 2000 ft to 1300 Kemano for study
tive) Granodiorite ft purposes
1 ABBREVIATIONS:
TBM -Tunnel Boring Hachine
D&B -Drill and Blast
N .:. Not Known
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0~01 '----""'' ---L.' --....&..' __ ...., .. •' __ ....... , __ ....... , r-_0_., __ __.,
o s 10 H5 20 25 30 as 40
TUNNEL LENGTH (MILES}
LEGEND
TUNNEL. INTAKE WORKS IS.\·:
RE'-REGULA.HON DAM S!TE LOCAT ) JUST
UPSTREAM FROM DEVIL CREEK
-· -WATANA DAM SlTE
---VEE DAM SITE
ECONOMIC POTENTIAL OF TUNNEL SCHEMES
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2200 FT. WATANA 800 MW
--+--2 MILES
:--J475 FT.
,....__..._._ RE-REGULATION DAM
3S Ft. DIAMETER
800 MW-70MW
2 TUNNELS
38 FT. DIAMETER
550 MW
1150 MW
-----RE-REGUI..ATI~~ DAM
30 MW
30 FT. DIAMETER
800 MW
365 MW
24FT. DIAMETER
SCHEMATIC< REPRESENTATION
OF . CONCEPTUAL TUNNEL SCI-!' 'ES
4-9
TUNNEL
SCHEME
#
2.
4.
FfGURE 4.2
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5 -TUNNEL DESIGN AND CONSTRUCTION CONSIDERATIONS
5.1 -Geologic Setting
Determining the geology along the tunnel alignment is critical in predicting
tunneling conditions, methods! and costs. The information acquired to date
includes several regional geology reports, site specific geology for the Devil
Canyon and Watana dam sites, and the findings of the Woodward-Clyde Consultants'
(l~CC) 1980 Seismicity Study {43).
The Susitna project is located in a tectonically active and geologically complex
region. Subduction of the Pacific plate under the North American plate (Figure
5.1) has resulted in forces which have folded, faulted, thrusted, sheared,
differentially uplifted, metamorphosed and intruded the area. The most common
geologic structures encountered include folds, faults, shear zones, joints, flow
foliation, stocks, dikes, and plutons~
(a) Litho 1..Q.9x_
As shown on Figure 5.2, three main lithologic units are crossed by the
tunnel alignments: -Argillite-Graywacke; Biotite-Granodiorite; and Schist,
Migmatite~ and Granite. ~
The Argi1'1ite-Graywacke Unit (Kag) has undergone complex folding with a
well developed axial plane cleavage and numerous quartz stringers. The
argillite is dark gray to black and in some areas has metamorphosed to a
slate OY" fine-grained phy11 it e.. Tests performed by the USBR for samples
taken at the Devil Canyon site ·indicate ·~ts unconfined compressivg strength
ranges from 12,900 to 16,850 psi, Young's modulus averages 9 X 10 psi~
and Poissons' ratio averages 0.17.
The Graywacke is dark to medium-gray, fine to medi urn grained, and is inter'-
calated with the argillite in graded beds ranging in thickness up to 16
feet. It comprises between 30 percent and 40 percent of the Ar gi 11 ite-
Graywacke Unit. Tests performed by the USBR indicate its unconfinec_ com-
pressive strength6ranges between 28,540 and 36,570 psi, Young's mo:\alus
averages 9.8 x 10 psi and Paissons' ratio ranges between 0.15 and 0.2.5 ..
The Biotite-Granodiorite Unit (Tbgd) is described as light to medium-gray,
medium to coar·se grained intrusive rock with a granitic texture. Biotite
is the chief mafic mineral~ but hornblende is occasionally present.
Although no test data is available, the average static properties for this
type of rock are generally be 1 i eved to be an unconfined compress i ve 6 strength between 20,000 and 30,000 psi, Young's modulus about 8 X 10 and
a Poissons' ratio of 0~2*
The Schist, Migmatite and Granite Unit (Tsmg} can be described as undiffer-
entiated terrain of relatively high grade pelitic schist, migmatite and
small granitic plutons occurring in approximately equal proportions with
gradational contacts.
Again, no static properties are known for this unit, but the granite and
migmatite properties are probably similar to the granodiorite. The
schistose rock properties will vary wit.h the direction they al"e loaded and
wi11 probab~y demonstr .::te a wide range of values. It is important to
determine t~1e properties of this unit and the percentage of tunnel through
it. A poor quality schistose rock may present major problems to tunneling
operations •
•
A complete descl"iption of these units is included as Apper.dix A (40).
(b) Structure
As mentioned earlier, the geologic structure in this region is complex. The
major structural -crends are NE-SW and NW-SE and major faults trend NE-SW.
Results of outcrop mapping between Dev i1 Canyon and Watana are shown in
Table 5.1 ..
(c) Topography
The topography is gener·ally rugged along the tunne 1 alignments, and the
geologic· structure exerts some topographic control. Elevations vary
. between 1300 and 3500 feet. Topographic lows, such as the locations of
streams and creeks, are areas of concern. They may represent ~;ones of
poorer rock quality and may require that tunnels be structural-ly 1 ined to
meet stability and cover requirements.
(d) Lineaments
As part of the wee study, sever·al 1 ineaments were mapped which cross the
tunnel routes. These are shown on Figures 5. 3 to 5. 6. rnese 1 ineaments
are considered significant for further investigations due to their charac-
teristics and possible problems in tunneling through them. Other lirtea-
ments may exist along the tunnel routes which were not identified due to
their distances from the dam sites. A more detailed investigation is
required if the tunnel alternative studies are continued as a preferred
scheme.
5.2 -Geotechnical gesign Aspects
I
Potential geotechn,·~.~al problems and their impact on the tunnel schemes are
reviewed in thi.s section.
Geotechnical design and hence the cost and construction schedule for a tunnel is
heavily dependent on evaluation of the geology along the potential routes. The
major tunneling problems are created by fau·lt and shear zones, joint sets, lith-
ologic contacts, water and gas. It is normally not economica1ly feasible to
undertake a comprehensive exploration program for the entire route. Therefore,
reconnaissance, mapping, and exploratory work must be directed towards locating
all potential problem areas and these ·must be. evaluated in detail.
Fault and shear zone!: may create severe problems. Special tunneling techniques
and h~avy supports may be required and decreased production rates during con-
struct ion can be expected in these areas. If the 1 ineaments identified by wee
prove to be fault and/or shear zones, l.he tunnel alignments will probably have
5-2
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to be adjusted to avoid or minimize the impact of these features. The shortest
route across these zones is preferred.
Topographic lows such as Devil Creek, Tsusena Creek and other creeks and str\'~ams
may indicate weak zones. Drilling and seismic refraction survey techniques .\\,ill
be required to determine the properties of the 1 ineaments and topographic lows.
A 1 imited amount of outcrop geologic mapping has been used to align the routes
at this time. Tunnel alignments have been oriented to cross the joints to
detre:~se support requirements and to help control overbreak.
Lithologic contacts may also present several problems. ,·f the contact is sharp
and fresh, no structural problem may exist, but production rates may change and
tunne 1 ing methods wi 11 have to be adjusted for the new rnck. Prob 1 ems wi 11 also
be encountered if the contact is sheared or brecciated. Special designs are
required if these contacts contain unconsolidated material and these contacts
may also be a source of water which can create serious difficulties. Many
joints in the Watana and Devi1 Canyon drill cores are tight and healed. Down-
hole permeabil ities vary but average less than IQ-5 em/sec be·low the
weathered zone. If this rsmains true along the tunnel alignments, water should
nut be a problem.
Gas can create both health and safety problems, i.e. asphyxiation and/or explo-
s·~on. Gas is not usually a problem in the lithologies present and good ventila~
tion will probably eliminate any potential problems. ·
5.3 -Seismic Considerations
There are several ways an ea,' thquake may adversely effect a tunnel. Three
common sources of damage are displacement, shaking, and ground failure.
Displacement is U$Ually associated with serious damage and is considered the
most severe nroblem. Small mov·ements along discontinuities are generally not
cr.,itical and only minor damage may result. However, displacements of several
feet can lead to serious damage.
Shaking may cause cracking, rockfalls, or possibly collapse. Dynamic stress
concentrations occur which increase static loadings and may result in damage.
Ground fa i 1 ure inc 1 udes liquefaction and 1 ands 1 id ing. These types of fa i 1 ures
may not damage the tunnel itself, but may seriously damage portal areas, and
thus, effect the tunnel use.
Dowding and Rozen (11) studied the effects of seismic loading on tunnels. Based
on 71 tunnels throughout Japan, Alaska, and California, they developed a corre-
lation between peak motion, particle velocity and observed damage~ Table 5.2
summarizes their findings.
They concluded that earthquakes expected to cause hea·Jy damage to surface struc-
tures cau.···~ only minor damage to tunnels. Peak motions for earthquakes usually
occur in 1... ~ 0. 4 to 10 Hz range. These low frequencies are several orders of
magnitude. lower than the natural frequencies of tunnels and not likeJy to create
diffel'·ential acceleration and damage to tunnels~ Lined and grouted tunnels are
less subject to damage than unlined ones. Under simi1a·. sei.smic loadi,ngs an
5-3
unlined tunnel may experience rockfalls while a lined and grouted tun-nel may
experience only minor cracking. ·
Seismic design considerations for tunnels usually include:
-Avoiding faults which may experier~~~ large displacements during an earthquake.
-Supporting, 1 in ing ~ and grouting areas of poor rock qua 1 ity.
-Adequately designing portals for seismic loadings.
The preliminary indications from the WCC studies indica:te that the Benioff Zone
may produce tne controlling or design earthquake in the vicinity of the Watana
and Devil Canyon dam sites. The design earthquake would, thus, be as high as
8.5 magnitude event (Richter Scale) and produce mean peak horizontal accelera-
tions in the order of of 0.4 g. Therefore, minor rockfalls and some cracking of
concrete may occur but no major tunnel stability problems are anticipated.
5.4-Design Considerations
The following preliminary de~ign considerations were adopted for purposes of
estimating t:osts of the conceptual tunnel schemes outlined in Section 4.
(a)
(b)
Tunnel Size
The power tunnels were sized to maximize the net benefit. This required
cross-section~i areas of between 700 and 2000 ft2. The geologic
information to date indicates that tunnels in the 700 to 1000 ft2 range
could be constructed without major problems;. Although it may be difficult
to economically construct very 1 arge tunnels through poor r"'ock, no
adjustments to the economically sized tunnels was made during this study as
the amount of geologic information available was not sufficient for this
adjustment.
Tunnel Shape
runnel shape is gener-ally a functi~n of hydraulics, stability and ease of
construction. In good quality, high strength rock, stability is not a
problem and the other factors govern the shape. As rock quality and
strength decrease or the rock is overstressed, shapes tend to be more
circular.
For purposes of this study, a modified horseshoe shape was tentatively
selected based on the assumptions that:
-The majority of the tunnel is in good to excellent rock requiring little
support$
-It is the easiest shape to drill and blast.
(c) Tunnel Alignment
The objective of aligning the tunnels is to have the shortest tunnel
through the best rock. Avoiding zones of poor qua 1 ity and topographic
5-4
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lows, crossing adverse geologic structures (not paralleling them),
attaining the minimum cover over the tunnel, and keeping the stresses
compressive around the tunnel are major considerations.
,,
_(d) Tunnel Grade
Tunnel grade or depth is selected so as to locate the tunnel in a competent
strata and meet cover requirements. These cover requirements vary greatly
and Table 5. 3 summarizes the cover used in several projects. It indicates
that values of between 15 percent and 50 percent of the total hydraulic
design head have been used.
For purposes of these studies, rock cover equal to the static head was
used. When the rock cover is less than this, a lining is ..tssumed neces-
sary.
It has been assumed that slopes within the tunnels will be inclined
slightly (approximately'0-.5 percent) to ease construction and haulage.
Access ad its are located so as to minimize their 1 engths. Maximum grades
are 3 percent for rai.l haulage system and 10 percent for trucks.
I)
(e) Tunnel Lining and Support
Drilling at Watana and Devil Canyon indicate that the rock is tight and
impermeable at depth. For purposes of this study it has been assurra:d that
one third of the tunnel length will require st~uctural concrete lining with
a combination of steel sets and rockbolting, one third shotcrete li-ning .and
rockbo 1 ting, and the remaining one third wi 11 require no lining or support,
except for the concrete-lined invert.
5.5-Construction Methods
'
Initially, three tunneling methods were considered for this study:
-Drill and Blast
-Tunnel Boring Machine (TBM)
·-Road Header
Based on available knowledge, drill and blast appears to be the most viable for
Susitna c.md the tunnel estimates are currently based on this method. Each
method, however, has advantages and d i sadv ant ages and is discussed briefly
below.
(a) Drill and Blast.
Drill and blast is the oldest form of rock tunneling~ Each cycle involves:
-Drilling
-Loading
-Shooting
5-5
-Ventilating
-Supporting •
-t4ucki ng.
The two most common approaches involve heading and bench or full face
excavation. Heading and bench removes a small top heading atoa higher unit
cost, then removes the bench at a lower unit cost. The full face excava-
tion ~ethod excavates the entire face at once.· In large tunnels~ heading
and bench may be more economical than full face excavation. Both methods
would be suitable for the proposed Susitna tunnel scheme.
There are several advantages to drilling and blasting:
-It is flexible and will acconmodate most rock types, tunnel shapes,
grades~ and can be adapted to rapidly changing geologic conditions.
-The initial cost is generally lower.
-Lead aYJd mobilization times are usually shorter.
-There are many experienced contractors.
Some of the d isadv ant ages inc 1 ude:
-Running costs are higher.
-Ground disturbance is high and overbreak may be considerable.
-More extensive support and/or lining may be required.
-Production, on the average, is lower than for mechanical excavators~
Considering the complex geology and the present lack of geologic informa-
tion along the tunnel routes, this method was selected. It is sufficiently
flexible to deal with any problems 1:hat may ari'e and yields a relatively
conservative ~onstruction cost estimate.
(b) Tunnel Boring Maching (TMB}
Machine tunneling has advanced greatly in the 1 ast 20 years. TBMs are
being designed to handle a variety of geologic conditions and by the time
the Devil Canynn tunnels are required machine tunneling m~y be an attrac-
tive option. Presently, this system seems too inflexible for the geologic
conditions anticipated.
The TBMs have several advantages:
-Low rock disturbance.,
-Lower support requirements.
-Lower running cost.
Q
5-6
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- A 1 in ing may not be required.
-Higher ~Jroduction rates if the rock quality is good anrl, ·"geology is
uniform.
Some major disadvantages are:
-They are inflexible, that is, grades and operating radii. are 1 imited and
only a circular shape is possible for large tunnels.
-High initial cost. These machines are unecono.;7ical for tunnels less than
several miles in length.
-Longer lecd time, probably one year.
-Longer setup time, probably six weeks.
-Prob 1 ems tunne 1 ing through poor qua 1 ity rock. TBf4s \'lork very we 1 i ... nder
the conditions they were designed for, but do not ada\pt well to geologic
. changes.
(c) Road Headers
A road header is an offshoot from the mining industry and involves a
mechanico.1 tunneling system. It ha.:s the advantages of being mere flexible
than a TBM, but presently cannot cut hard rocks efficiently. If these
machines had the capability of cutting hard rocks at reascnable prcdlJCtion
rates, they would merit serious consideration.
{d) ~ucking
Mucking is the term used to describe removal of the excav11ted materia.l from
the tunnel. Sel~cting a mucking system depends on tunnel grace, length,
.and equipment the contractor has available. Within the tunnel, two haulage
systems are conmonly used, ra'll and truck ..
Rail systems are favored for long tunnels since they can usually haul large
quantities economically. Their maximlJTl grade is 3 percent, but they may be
winched on steeper grades. Trucks ara favored in tunne 1 s less than about
4000 feet. Their maximum grade is 10 percent.
Considering the volume of material and haul distance to the access way, a
rail system has been assumed for the Sus itna tunne 1 schemes~
5-7
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A~
B.
TABLE 5.1: GEOLOGIC STRUCTURE OF REGION BETWEEN THE
DEVIL CANYON AND WATANA DAM SITES
GENERAL AREA
Orientation
Feature
Major Joint Set
Major Joint Set
Major Joint Set
Average
335° 82° sw '
Range
320°-355°, 63°-9'0° sw
300°-355c, 62°-90° NE
40°-60°, 65°-90° SE
325° 77° NE 48°: 79° SE
ARGILLITE-GRAYWACKE AND UNIT IN THE -IMMEDIATE VI!:INITY OF' THE
DEVIL CANYON DAM SITE (Based on Geologic Mapping)
Feature
Bedding . , ............. ., ...... .
Major Joint Set •••••••••
Major Joint Set •..•• ,. ••••
Minor Joint Set •••••••••
Orient at ion
53°-70°, 50°-80° SE
320°-350°, 82° NE (avera~e)
70°-105°, 15°S <~1erage)
70n-105°, 65° NW (average)
5-8
Spacing
6 in to 2 ft
6 ir: to 3 ft
6 in to 1.5 ft
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TABLE 5.2: EFFECTS OF SEISMIC LOADING ON TUNNELS (11)
Horizontal
Accelerat~on(g)
{ft/sec )
< 0.19
0.19 -0.25
0.25 -0.52
Velocitr
(In/sec)
< 8
8.16
16-32
5-·9"
Damage
None
Few instances of minor
cracking, some rock falls
in 1..11lined tunnels
One part~al collapse in
a masonry lined tunnel
associated with a landslide
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TABLE 5.3: TUNNEL COVF.R EXPERIENCE
Ratio of
Rock Cover to
Project Hydraulic Head.*
Abjors 0.4
Bersimis 2 0 .. 5
Gonda 0.2
Handek I 0.16
Handek II 0.18
Innertkirchen 0.14
Kern ana 0.4
Montpezat Ce26
South Holston 0.5
Bersimis 1 0.5
Calancasa 0.33
Chute des Passes 0 .. 5
Spray 0.24
*Hydraulic head includes both static and dynamic head.
5-10
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0
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0
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0
""" 0
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0
(J.)
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TABLE 5.4: REGIONAL GEOLOGY MAP UNITS
Qs
Tsu
Tv
Tbgd/Thr·J
Tsmy/Tkgr-
Kag
Jtr/Jgd/Jgcin
Jam
TRv
TRvs
Psv/Pls
Undifferentiated Surficial Deposits
Undifferentiated Sedimentary Racks
Undifferentiated Volcanic Racks
Biatita & Biotite-Hornblende Granodiorite
Granites and Schists
Argillite and Graywacke
Quarts Diorites & Granodiorites
Amphibolites
Basaltic Metavolcanic Racks
Me~ abasalt and Slate
Basaltic: to P.ndesitic Metavolcanogenic Racks
with Ird;erbedded Limestone
Modified after Csejtey and others, 197Bo
5-11
. . -· ~
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CT
(I .... ...
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150° 180°
\ . r~~~
\
\ ,,, NORTH
EURASIAN ',,
\
\
PLATE \
\
NOTES
1. Base map from Tarr (1974).
2. After Packer and others (1975), Beikman (1978},
Cormier (1975), Reed and Lamphere (1974),
P .Jker, and others { 1978).
PACIFIC
--- -·--- -:-.
'
150° 120°
AMERICAN PLATE
Yakutat
Block
PLATE
LEGEND
••··········•·····•·• (;' :::::::::::::::::::::Wrangell Bfock ..... " ......
~ Relative Pacific Plate Motion
----Plate Boundary, dashed where inferred
6 A 6. Shelf Edge Structure with Oblique Slip
---Intraplate Transform or Strike·Siip Fault
I
150°
Queen Chaclfotte
Islands Fauat
Q
I --·-1200 .
PlATE TECTONIC MAP
600
-~
AGURE 5.1
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EXPLANATION OF MAP SYMBOLS
-'wro•h•te CtlfttaC:t of ~rl1eta1 .deposits
-------~~~ ~ J) _.-----····· Fault
l.slll9 du.Md wben appro:d•tely located; snort duhed an tnft.n<l;
dotted ..here a~ncaleiS. U tndlc.tes upthflllljft side are dtrcttOfl
of disphee!llt'!'lt b tno.r.. .An-ows indicate rellthe lat.er11 .:~nl!l!'nt.
e • w ,_,.---.....----•• ,. •••••••
Thnnt f1ult
LOillJ dished llhere appro:d•tely locat.td. short dashed •::'1! 1!!1ferftd.
dotted .tlt!re Cl.l!ICEiled. Teeth. 1nclftate upthnMI stele.
~ ----v---.••••••• y· .••
Apprc•1•te axis of intense shear zone of variable width. possibl)l
-.rttng a thrust fault
Dotted white eonce~l!d; teeth indicate poss1bl@ upthro-r. st~ of
postulAted thrvst.
! ----..., .. --~
Antt.clhtll. showtng c:rest line ; S171C1tre, showing trough 1iM
i.oflg lbshf!d llfl>frv. llppro:~~t~Mtaly located• an"OW 1nd1e&te$ plunge.
Lcutton of Slllfllt dited by ·thl: U.S. ~log1C:.1 S!J!"l'e1 us1ng ~
patllss1~a-~rvon or the lud-alphl a!thO<S. snowSng IIIP n\JIIber, field
fillllber, alld tM tlllt1.111~ •fNrll age. et -biotite. Jb -hombll'l'l~.
J~IJ!Ibo."~tte. kt -aetJnoHte. 2r • zircor., wr -whole tuc.k. • .... .. . -... .
5-13
Loati011 of s.uple !!.ted by iumer and Slltth (1974) &~SfnlJ the potanilft-t
argon aethod. fhowin; .ap nu.btr. field nUNb!r. ind the c<u1ated
•iMnal age. 11 -1!\.,ttte~ lib -t~Urnblftlde.
x+.
Foss1l loaltt.Y in units 'llv. Pl'-and DSls.
Str1b and dt~ of bedS
-,-1AC11fle4 •»
-'"'l-u ~
-+-YerUc.al
-1-Ap~d•u• esttated froa dfstllnt oburvauons
2.0
Stnu 18\d dtp of fr1c:wre cluva;e
r--r-' Incl tned eo
.....-f-J Vfftlal
StrH.e and dip of slaty or u111 plane cleuage
,---, Inc:Hned
50
1---1 Yertial
StrUt and dip of shur plane~. •~TPhie foH&UDft or-seMst~stt.y
--v-• !nel ine.i
30
..-.-Vertical
StrUt .and dtp of igMOus flow foliation
......--Inclined
30'
-+-~erttal
learfag and plun~. or HneatfOi'l
Strht ud dip of jr.tnts
-z::r-Jncl1ned "0
-e-Yerttal
'tlfE<1£NCI: cse:JTEY,I.ET AL AfCOHHAISSAJifC£ ~Eot.oelC WAP• a CEOCIUt<*OU>C'r,
TALitlt:TNA JIIOON'!AiJI. OUAOftA)t&L,t:, HOftTHED PART Ofr ANCH~ QUADRANGLE,
&ND .SountM:IT CORNEJt Of tiE:ALY OUAPftAIUilJ:, Al!ISAA. U.S.S.S. OP'£N ,IU ftEP<Wf 71· 551A.t.,_,
REGiONAL GEOLOG,r WITH TUNNEL ROUTES
0
P!
SCALE
N01'E!
'3 6 12
-~s~~~~~~~L·
IN. MlLES
ROCK UNITS ARE LISTEO lfl! FIGURE 4.l b
FIGURE 5.2
-.·
_,.-. ...
40 ~·' .. ... . ...
. ,.., .. _~·~.s .. ;-.. _.~
..
:. .... , ..... .•' ...
~. . .. ·. .. ~<-
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........... :
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5-14
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..... .
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..;:. :--:-....__ ...
··;;:." T ~ , . ... '..... . "' ...
LEGEND
BOUNDARY FAULTS
Faults with recent displac~ment
SIGNIFICANT FEATURES
-----Indeterminate A feature
~~-~~-·-Indeterminate B feature
\
-N-
0
BOUNDARY FAULT AND SIGNIFICANT
FEATURE MAP FOR THE SITE REG!ON
0 10 20 30 40 50 Mite::
~===1~~~~==:f\~~i~~~~~~EI====~l
0 , 0 20 30 40 50 Kilometers
I
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FIGURE &3
.. -r----
...,.,. --.a ~indeterminate • A feature
-m • • ....._.~Indeterminate • 8 feature
_ .._ -.,.. Indeterminate - B L feature
-~--.. --!'""\-
rl "-.
...
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WOOOWA~D-Cl..YDE CONSULTANTS 14658A Dm!emt*r 1980 . 5-16
. .
-.
,/
··:Jo'•~
'If
.. .,
• II ..
.. .... ., ... ._.
LEGEND --Indeterminate • A feature
-......-Indeterminate-B feature -a-lndeterminalte-BL feature
DEViL CANYON SITE
SIGNIFICANT FEATURE MAP
FIGURE 5:5
-. _ _,
t
~\
;
..
·,
'
-. ... . -
]
·----~1..--""." {
l
WPOOWARD-CLYOE CONSULTANTS 14658A Def:ernber 191~
.·
... -~-. ----·-
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...
1
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.... .
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.......... ..__..,
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-!·· .-----...---.------,. ---.·
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/-·--· .-
-.
LEGEND
a •--·•----·-·----... o.-o--
.. --.
Indeterminate
lndeterminete
Indeterminate
A feature
E feature
BL feature
WATANA SITE SIGNIFICANT FEATURE MAP
. '
·FlGURE 5.6
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6 -SCREENING OF CONCEPTUAL TUNNEL SCHEMES
6.1 -Introduction
The screening analysis w~s performed to compare the four conceptual tunnel
schemes and determine the best tunnel scheme for furt~1er study s Costs, power
and energy, geology, and environmental aspects are uSied as screening criteria.
6.2 -Tunnel Scheme Costs
All costs are based on 1S80 dollars. Unit prices were applied to estimated
quantities for the various components in each tunnel scheme. The total project
cost for each tunne 1 scheme inc 1 udes the tot a 1 construct ion cost p 1 us a 20 ..
percent contingency and a 12 percent allowance for engineering and administra-
tion.
Wherever possible unit prices were developed and/or compared with cost informa-
.tion on recent projects in Alaska. Unit prices developed from projects outside
of Alaska were adjusted to Al~ska using the Handy Whitman price indices. In
general~ costs are based on the same unit pr;ces as those used for the Susitna
Basin dam alternatives outlined in the Subtask 6. 05 report on 11 0evelopment
Selection".
Tunnel costs are based on the conservative assumption that excavation will be
done by conventional drill and blast operationse Knowing very little about the
rock mass quality along the route, support requirements are difficult to
predict. Therefore, the lining and suppor-t assumptions were based largely on
experience at the Kemano Project which is similar in concept, and the results of
drilling at Devil Canyon and Watana, as outlined on Table 6 .. 1.
As mentioned previously, due to the lack of geologic information and the fact
that the tunnel is a major cost item~ total project co~t estimates must be
regarded as tentative at this time. In any event, totdl project costs are
relevant 'for a valid economic comparison between conceptual tunnel schemes.
Tunnel scheme to·~al project costs are given in Table 6. 2 for each of the four
tunnel schemes.
6.3-Power and Energy
Energy values for the tunnel schemes were determined from an annual f1ow
duration curve developed frnm the simulated monthly outflow from the Watana
reservoir (35). This curve was adjusted to all ow for a 1000 cfs minimum
discharge in the river. Allowance was made for tunnel friction and entrance
losses. Installed capacities were calculated to yield an overall p1 ant factor
of between 50 and 55 percent for the total Watana dam-tunnel system. For the
tunnel generating portions of t~1e total development p1 ant factors of about 50
perce·t~t were used for peaking tunnels and about 80 percent for base load
tunne~s ..
The resultant installed capacities and average annual energy yields are shown in
Table 6.2. Figure 6.1 illustrates in the form of simplified power durat~on
curves the operating modes of the various powerhouses in the tunnel schemes.
6o-1
I)
Of primary importance in the assessment of the tunnel schemes' potential is the
increCise in energy production over the single Watan~ development. As shown on
Table 6.2, Scheme 3 yields the largest increase in energy production with 2180
Gwh of added average annual energy. Schemes 1 and 2 would provide for an
increase in average annual energy of 2050 Gwh and 1900 G~ths respectively. Scheme
4 would have the smallest increase of only 890 Gwh.
6.4 -Environmental Considerations
A preliminary assessment of the environmental asp~cts associated with the four
tunnel schemes has been made {33). This preliminary ass.essment was done for
comparison and screening of the tunnel schemes only, and impacts common to all
schemes were not addressed. The results of this assessment are as follows:
{a) Scheme 1
The environmental impacts associated with this tunnel scheme are likely to
be greater than those of at 1 east one of the other tunne 1 ~chemes eva 1 tJated
(i .. e. Scheme 3). The main criterion for this assessment is the adverse
effects, particularly on fisheries and recreation of the variable down-
stream flows ( 4000-14000 cfs daily) created by the De vi 1 Canyon pov1erhou~e
peaking operation. Other negative impacts would result from construction
of both there-regulation dam and a relatively long tunnel. Tunnel impacts
are similar to those of Schemes 2 and 4 and include disturbance Qf Susitna
tributaries as a result of tunnel access and the potential prob~ems
associated with disposal of a relatively large volume of tunnel muck.
{b) Scheme 2
As for Schem~ 1~ this scheme involves adverse environmental impacts
associated with variable downstream flows caused by peaking operation at
the Devil Canyon powerhouse (4000-14CJOO cfs). Without there-regulation
dam, however, less land would be inundated and the impacts associated with
construction of this relatively small dam would be avoided. As for Scheme
1, the long tunnel proposed will also have negative conseouences, including
disturbance of tributaries for tunnel access and the potential problems
connected with tunnel muck disposal.
(c) Scheme 3
The overall environmental impact of this scheme is conside~ed less than
that related to each of the tv1o pre vi a us-schemes, and a 1 so 1 ess than that
related to the fourth scheme. The relatively r ·stant discharge (about
8300-8900 cfs) from the Devil Canyon powt:;•house is desirable for maintain-
ing downstream fish habitat and recreationai potential. A general reduc-
tion in river flows through Devil Canyon in this a 1 ternati ve may a 11 ow
anadromous fish access to a previou:>1,y i!1accessible 15 mile stretch of the
Susitna River, and an opportunity for enhancement of the fishet~ies
resource.
-With a compensation flow sufficient to allow minimum discharge of 1000 cfs
through Dev.il Canyon, the riverine character of the reach should be main-
tained.
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As with all of the tunnel schemes~ the wildlife habitat in the stretch of
river bypassed by the tunnel might improve temporarily because of an
increase in riparian zone vegetation. With Scheme 3, however, this stretch
of river is shorter than with the other tunnel schemes so a 'smaller area
would benefit. The wildlife habitat downstream of Devil Canyon powerhouse
may well benefit from the flow from tne hydroelectric project regardless of
the scheme chosen. With the constant flows allowed in Scheme 3, the
improvements to that habitat niay be somewhat greater than with the Vdri able
flows resulting from peaking in the other tunnel schemes.
One environmental disadvantage of this scheme compai'"ed to the others is the
larger area to be inundated by the re-regulation reservoir. This area
includes known archeological sites in addition to wildlife habitat. Never-
theless~ this disadvantage is offset by the more posit·ive environmental
factors associated with constant discharge from the De vi 1 Canyon power-
house.
(d) Scheme 4
Scheme 4 involves peaking operation at Watana with baseload operation in
the tLmne1. Since the net daily l'luctuations in flow below Devii Canyon
would be considerable (4000-13000 cfs), Scheme 4 is judged to be less
desirable than Scheme 3 7rom an environmental standpoint. Although Scheme
4 would avoid the impa~ts associated with the lower dam and its impoundment
(as planned under Scheme 3); the. adverse impacts that would result from
fluctuating downstream flows are considered to be an overriding factor.
Another, although less significant, disadvantage of Scheme 4 compared to
Scheme 3 is the longer tunnel length planned for the former, and perhaps
the proposed lccation of the tunnel on the north side of the river.
6.5 -Geotechni~al Consider1tio~s
From a geotechnical perspective, the northern and the alternative direct align-
ments for Schemes 1, 2 and 4 are similar (see Plate I). Therefore~ they will be
discussed together while Scheme 3 will be discussed separately. Table 6.3 shows
.estimates of tunnel length proportions within the various lithologic units.
The resu1ts of drilling at Devil Canyo:"J and Watana shov1 that rock quality
improves with depth. Therefore, the rock at tunnel grade for all three align-
ments should be good since the minimum rock cover is several hundreds of feet.
The geology along the northern and diret;t routes seems more complex. These
routes cross at least four lithologic contacts, three different rock units~ two
major lineaments, and several minor ones. One lineament is the Susitna Feature.
Although· it is not currently considered likely, if this feature were found to be
a fault zone, it could create a very difficult tunneling environment. The topo-
graphic 1 ow at De vi') Creek may a 1 so be a problem zone. Tu nne 1 i ng through the
schistose portions of the schist, migmatite and granite w:it may also be diffi-
cult.
Scheme 3 has several advantages. It is about half as long, crosses only 0'2
known lithologic contact, is 90 percent in the Biotite-Granodiorite unit, and
crosses one known major lineame.~nt and several mir1or ones. Being 90 percent in
an·e unit , machine t unne 1 i ng may be poss i bl e.
6-3
Various lineaments cross the alignments. None have been classified as active·
faults and most were in the doubtful category as being.faults (43). None of
these features appear to present extreme tunneling problems, but all will
require exploration to determine their characteristics. If they are faults,
strengthened linings will have to be designed and tunneling techniques may have
to be modified.
All tunnel alignments were laid out so that they crossed the known joint sets.
The northern alignment (for Schemes 1, 2 and 4) was suggested because as it
increases available cover. The tunnel length crossing topographic lows at
Tsusena and Devil Creeks is minimized, but is about two miles longer than the
direct route. The direct route has been proposed because it is the shortest.
However, the tunnel lengths crossing the topographic lows at Devil and Tsusena
Creeks are 1 anger and the cost of 1 i ni ng these. areas may make this a 1 i gnment
less attractive. Also, if these 1ows are zones of poor r·ock quality, tunneling
through them may be more costly than minimizing these lengths by avoiding them.
Scheme 3 'tas aligned to maintain the minimum cover over the entire route. The
tunnel was diverted around topographic lows. Future alignment adjustments may
decrease the tunnel length, but not significantly.
Presently, the Scheme 3 alignment appears to be preferable from a geotechnical
viewpoint. However, explorations are required on all three alignments to firm
up this judgement.
6.6 -Preferred Tunnel Scheme
It is evident from the above discussion that of the four conceptual tu~~el
schemes, Scheme 3 is preferred. The economic aspect~, environmental aspects,
and geol·ogical conditions of Scheme 3 are considered superior to the other
tunnel schemes at this time. Scheme 3 produces additional energy at by far the
lowest cost as· is shown in Table 6.2. Scheme 3 was, therefore, selected for
further, more detailed study.
6-4
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Rock Qti21lity
(RQO)
> 90
50-90
25-50
< 25
J~BLE 6.1: ASSUMED TUNNEL SUPPORT
Percent of
Tunnel
34
33
25
a
6-5
Support and Lining
None to occas.ional rockbolts
Rockbolts, shotcrete,
welded wire fabric
Rockbolts, shotcrete,
welded wire fabric,
concrete
Steel sets, sho~crete,
concrete
()
0'\
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--.. ---- ----------
TABLE 6.2: DEVIL CANYON TUNNEL SCHEMES
COSTS, POWER OUTPUT AND AVERAGE ANNUAL ENERGY
Installed Increase1 in
Ca~acit~ (MW)
Watana Oevil Canyon
Installed Capacity
(MW)
STAGE 1:
Watana Dam BOO
STAGE 2:
Tunnel:
-Scheme 1 BOO 550 550
-Scheme 22 70 1,150 420
-Scheme 3 850 330 380
-Scheme 4 BOO. 365 365
1 Increase over single Watana, BOO MW development, 3250 Gwh/yr
2 Includes power and energy produced at re-regulation dam
Devil Canyon
Average AnnuaJ
Enerfi) (Gwh
2,050
4,750
2,240
2,490
3 Energy cost is based on an economic analysis (i.e. using 3 percent intereat rate)
as discussed in Section 7-6.
Inc1•ease 1 in Tunnel Scheme
Average Total Project
Annual Energy Costs
(Gwh) ($ X 103)
.
2,050 1,979,000
1,900 2,317,000
2,180 1,221,000
B90 1,494,000
3 Cost of'
AdditiontJ.
Ener]Y' ·
(mills kWn)
42.6.
52.9
24.9
73.6
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Tli\BLE 6.3: LITHOLOGY Or TUNNEL ROUTES
Percent Tunnel Route in Each Lithologic Unit**
Scheme(s) Alignment Lithologl:
Ksg Tbgd Tsrng Qs*
1,2,4 Northern 31 11 10 48
1,2,4 Direct 13 29 31 27
3 10 90 0 0
NOTES:
* The rock units below the Quaternary soils along the alignments are mast
likely Tsmg and Tbgd.
** These percentages are based on surficial rock unit distributions. The actual
length of tunnel in each unit is unknown.
. 6-7
::.:::-
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e
-1200,..
·~ 1000 ~
-800-a::
lJJ 600 ,.. ~ ~. 400-
WATANA.
POWER HOUSE
200..-.-J
() ....... ____ __..
-.1200 I"
~. iOOO t-
~SOOt-
~ 600·
a.. 400-
200 t-
0 =======
1200,. -~· 10001-
~ 8001-
. IJJ 6001-~ 400~
2001"'
o· t: ==~--====-
....... 1200~ ~ '::E' 1000 -0: 800 I'"
lJJ ~ 6001-
Q. 4001-
200 t-
oo 24
HOU~
DEVIL CANYON
POWER· HOUSE
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HOURS
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24
TOTAL
SUSJTNA BASIN
DEVELOPMENT
--·
n
[ I ~
0 24
HOUR~
TYPICAL DAI·L Y POWER PRODUCTION FOR MARCH
FIGURE 6.1
6-8
TUNNEL
SCHEME
#
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2.
3 .
4.
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7 -PREFERRED TUNNEL SCHEME
7.1 .... Introduction
As outlined in Section 6, tunnel Scheme 3 was selected for more detailed study.
The aim of the more detailed study is to further refine the engineering con-
c~pts~ to improve the accuracy of the cnst estimate,. and to evaluate the po\~er
and energy potential in more detail. This information is used for comparison of
the tunnel scheme with the Devil Canyon da.11 $Cherne in Section 8.
7.2 -Design and Operational Assumptions
--~~----~------------·-~· ---
(a) pesign Assumption~
The design assumptions used in the mc,r~ detailed study are essentially as
previously outlined in Section 5.4 and the construction techni-que as in
Section 5. 5.
The proposed alignment crosses the known ,joint sets to minimize support arld
overbreak problems. Adequate cover is maintained along the entire route
and the minimiJm tunnel depth or 250 feet is believed to be conservative_
The 1 ining requir~ments for the tunnel are as outlined in Section 5. 4.
Table 7.1 summc.tr'izes the rock quality observed in the drill holes at the
Watana and Devil Canyon dam sites. If these rock qua'f ities remain true
along the Scheme 3 alignment, up to 50 percent to 80 percent o·r the t•Annel
could be unlined and 1 ightly supportedtt 20 percent to 40 percent may
~equire rock bolts and shot::rete., and 10 percent to 20 percer;t may require
rock bolts, shotcrete and a cast in place concr·ete 1 ining. In view of
these t"esults~ t.he 1 inin~l and support requirements suggested in Table 6.1
are conservative and wet··e retained.
As before~ the tunnel siz(: was selected on -the basis. of an economic
analysis. The optimal tunnel size was determined such that th€~ sun of the
amortized tunnel cost and the value of energy lost due to friction is mini-
mized. The value of energy was bast!d on a thermal coal-fir·ed plant in the
year 2000 .. Table 7.2 summarizes the results of the analysf!S and also
indicates that tunnel sizes would not be significantly d·ifferent fer lower
energy values or if the cost of energy produced by the tunnel had been
minimized •
The optimum sing·1e tunnel diameter was found to be 40 feet~ which is rel a-
tively large. In view of the sparsity of geotechnical data, two smallet',
~.·sarallel tunnels of similatr total capacity were conservatively selected for
study purposes. Such a ccmcept also has security advantages, the optimum
sizes of these tunnels be·fng 30 foot diameter.
For this study ;'t has bee.n assumed that the powerhouse is located crt the
downstream end of the tunnel. This does not necessarily imply that ~
powerhouseo located at thra ups,trea~n end would not bf: studied, with the
tunnels being used for tailrace discharges.. Further study would be~
required to determine the optimum location.
7-1
(b) Operational Aspects
Minimum discharge of not less than 500 cfs from Watana and 1000 cfs from
there-regulation dam were specified. No daily maximum limit on the dis-
charge from Watana was specified because of the downstream r-e-regulation
dam. Constant dai 1y discharges from the re-regulation dam and the Devil
Canyon powerhouse were specified.
The Devil Canyon powerhouse is assumed to be oper·ated as a base 1 oad power
faci 1 ity (. No daily discharge fluctuations are all owed at the Oevi 1 Canyon
powerhouse and daily peaking power .jernands are supplied by the Watana
powerhouse. Daily peak discharges-from Watana are regulated at the
re-regulation dam with a maximum fluctuation in the re-regulation reservoir
of less than four feet •. A relatively s1oall powerhouse at the re-regulation
dam operates as a base load power facility and supplies the required down-
stream compensation flow.
7.3 -Project Description
Scheme 3 is composed of a re-regulation dam, power tunr.el, and powerhouse at
Devil Canyon. Plates 2 and 3 illustrate. the detailso
The re-regulatiori dam is located approximately 15.8 miles downstream from the
Watana dam sit~. Site selection was based on regional geologic mapping and air-
photo and topographic interpretations. The 245 foot high dam ts assumed to be a
rock fill dam with an impervious core. A spillway is located on the north abut-
ment, and a relatively sma'll powerhou~e with a capacity of 30 MW on the south
side of the river. The maximum normal operating reservoir level is 1475 feet .•
Power tunnel intakes are located on the south side of the river approximately
2000 feet upstream from there-regulation dam. The optimal power tunnel dia-
meter is 30 'feet for each of the tWC? power tunnels.
The underground Devi 1 Canyon powerhouse has an ·installed capacity of 300 MW,
with an assumed four generating units. Overland access to the powerhouse access
adit area runs parallel to Cheechako Creek. A surge tank for each power tunnel
is 1 ocated, just upstream of the powerhouse. · Sma 11 cellular cofferdams are
required a I eng the south bank _of the Susitna to a 11 ow construction of the ta i 1-
race.
As part o.f this tunnel scheme~ the. installed capacity at the Watana dam is
increased by il sma 11 amount to reduce the avera ll system pi ant factor once the
base load tunnel generating plant comes on line. A provision for an additional
50 MW has been made in this study.
7.4 -Cost Estimate and Construction Schedule
(a) .Cost Estimate
The cost .estimating methodology described in Section 6.2 was employed to
develop cost estimates for the pr~ferred schemea However, as more detailed
engineering layout dra\'lings were available, it l'las possible to undertake a
more detai 1 ed cost es.timate than for the study describe<~ in Section 6.
7-2
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Tota 1 construction costs were re-estimated for both the twu 30 foot
diameter and the one 40 foot diameter schemes. These (;osts amounted to
$1.50 billion and $1.34 bill·ion~ respectively. It should be H(?;ied that
they are somewhat higher than the estimates associated with the conceptual
tunnel schemes due to. the higher level of detai: involved. Summa~'Y cost
estimates far the two schemes are shown in Tables 7. 3 and T. 4.
(b) Construction Schedule
As shown in Figure 7 .1, five years \t~ill be needed to complete c.:mstruction
of the Scheme 3 facilities. For the purposes of .this study, the schedule
is based an assumption that .access will be available frL\1 a previously con-
structed road from the Parks Highway to the Watana site. Underground work
is assumed to be pass ib 1 e throughout the entire year, and rock p'l acement
only throughout the six months of sumner. The exact timing and sequencing
of the various "noncritical .. activities will be dependent upon resource and
season a 1 1 irni tat ions and other f.actors •
Initial \oJOrk will be to construct several access r·oads of up to six· miles
in length to connect the Watana-Parks Highway to the re·-~egul at ion dam,
Devil Canyon and intermediate access sites. Zt is expected that the
construct ion of the Devil Canyon powerhouse can start shortly thereafter
with the power on 1 in e. date-approximately 52 months after work commences.
Access to the main power tunnels will be through ·inclined access tunnels at
two intermediate points .. Additional tunneling will occur at both the power
intake porta1 and at t~,;~ main powerhouse. This will enable the tunnels to
be driven from as many as six faces~ resulting in an estimated maximum
tunnel length of approximately five miles.
The complete re-rcgul ation dam will take approximately three and one half
years to construct with an estimated p 1 acement rate of approximately
640,000 cubic yards/month during the two year placement period.
As shown in Figure 7 .1, the power on 1 ine date is approximately the same
.,.,,. ' !loth the re-regul at ion cam and the Oev il Canyon powerhouses.
7.5 -Power and Energy
Power and energy have been evaluated by a demand driven computet)'> simulation
model. The model is based on monthly average derrrlnds and 30 years of histori";·a1
monthly inflows. Scheme 3 inc 'rporated with the Watana dam has been simu1 ated
to accurately represent operation .of the entire development. Pow(~rhous~es were
sized to achieve an over a 11 capacity factor>; of 53 percent which i!i with in the
des ired plant factor range of the Watana-Devil Canyon dam scheme.
Power and energy production from a Susitna basin developnent composed of \~atana
and Tunne 1 Scheme 3 is summarized in Table 7. 5.
7. 6 .. Environment a 1 Impact Assessme . .;
~~
A more detailed assessment of the environmental aspects associatf:d with Scheme 3
has been made (33). A comparative environmental analysis on the location of the
Devil Canyon powerhouse was also performed to determine the preferred powerhouse
location.
. 7-3
f : -
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(a) Locatlon of Devil Canyon Powerhouse
Alternative locations for the Devil Canyon powerhouse have been proposed.
Two altern at i\~e locations have been determined by the ease of access to the
tailrace and powerhouse access are.a. The two sites are an upstream loca-
tion about 0.3 mi1es above the Devil c,myon dam site and a downstreiln loca-
tion about 1.5 m11es below Portage Creek. The major environmental consid-
eration is that a powerhouse upstream of Devil Canyon would preserve much
of the aesthetic value of the canyon. In addition, the shorter tunnel
would confine construction activities to a smaller area and may result in
slight 1y less ground disturbance, particularly if there are fewer access
points as well as a smaller muck disposal problem.. It is for these reasons
that this powerhouse location is preferred.
A downstrecm powerhouse location, on the other hand, might create a mitiga-
tion opportunity by opening up a longer stretch of river that perhaps could
be managed to create salmon s.pawning habitat due to the lower flows through
the rapids. However, there· is currently no data to confirm this and at
this stage the downstream powerhouse location is .considered less flexible.
(b) Environmental Impacts
The major adverse environmental impacts associated with the t~.mnel scheme
are the inundation of 3900 acres by the re-regulation .'eservoir, disruption
during construction, disposal of tlmnel muck~ and bypassing the major p'i)r-
tion of river flows through the tunnel. The area to be inundated by the
r~-regulation reservoir. includes known archeological sites in addition to
wildlife habitat.
The major beneficial environment~1 impaet -is the ability to regulate ·peak
discharges from the Watana Dam. The re-regul at ion dam would store the
daily peak discharges from Watana and relea::;ce a constant downstream flow.
The re-regul at ion dam would el itninate the effects of watana peaking opera-
tions on the Susitna River. This would allow Watana to produce the maximum
amount of peak energy possible with no adverse impacts downstream ..
The compens 1tion flow in the bypassed section of the Susi·ena River is
totally controllable and could be varied seasonally. The control abi1 ity of
the -tGmpensation flow could be an asset to the fisheries and w·ildlife in ·
th~ stretch of the river bypassed by the tunnel .
. , .
/(~) Di,~·~posal of Tunnel Muck -·~ ( ________ _.,;,_
I'f;. · r~< ··important to note that cost estimates for tunnel schemes are current-
ly' =.$A~d QP minimal requirements for transportation and disposal of excav a-
ted materials by whatevet means are finally selected. If a costly disposal
method is selected, trrtal proje£t costs could increase as much as 1
percent. The total volume of excq.vated material ft"orn the two 30 foot
diameter tunnels ~aunts to 3 • .7 mill ic.n cubic yards. Allowing for a
bulking factor of 1.5 this would amount to approximately 5 .. 6 million cubic
yards of muck.
7-4
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There are a numbt:!r of options which may to be considered for environmen--
tally acceptable disposal of the rock removed in excavating the tunnel.
All of these will probab1y involve a small additional transportation and/or
d1sposa1 cost, and include: stockpiling the material for use in access
road repairS' construction of the re-regul at ion dam (total volume = 7. 7
Olillion cubic yards), or stabiliza:*:ion of the reservoir shoreline; ciisposal
in Watana reservoir· dike construction; disposal in a borrow pit created in
-dam constructions; sculpture, cover,_ and seed the pile; and disposal in a
ravine cr other convenient location. Ii. is unli-kely that the most environ-
mentally acceptable option will also be the most economical.. Because many
unkno~n factors now exist, a firm recommendation cannot be made without
further evaluation. It is quite likely, however, that a combination of
diSposal methods will be the best solution.
Stockpiling at least SO«~ of the material for access road repairs is
believed to be environmentally acceptable provided a suitable location is
selected for the stockpile. The material could poss·ibly be utilized for
construction of any of the .. access road spurs or temporary roads that are.
not already completed at the time the tunnel is excavated.
Another acceptable solut·ion might be to stockpile the material :or· us.e in
construction of there-regulation dam. This rock could also be a potential
source of material for stabilization of reservoir shorelines if required.
As with the previous option, an environmentally acceptable stockpile loca-
tion would be required. Material disposal in Watana Reservoir might also
be environmentally acceptable.. A small Jmount of tunnel muck could
possibly also be used for stream habitat development. With any of these
options, the pass ible toxicity of minerals exposed to the water should be
first determined by assay, if there is ar1y reason to suspect the occurrence
of such materials and minerals.
~-,,'0 env·ironmental problems might b~ solved by disposing of the material in
a borrow pit created in dam construct ion.
To sculpture·, cover, and seed the material is worthy of further considera-
tion~ and would require proper planning. For example, borrow areas used ir.
darn construction could, perhaps, be restored to original contour by this
method. The source of soil for cover is a major consideration as earth
should only be taken from an area slated for future disturbance or inunda-
tion"
The most economic a 1 so 1 ut ion might be to fi 11 a ravine with the materia 1 or
to dispose of it in another convenient location. Unless the chosen dispos-
al site will eventually be inundated, however, such an arrangement is
environmentally unacceptable, especially since _better· options are obviously
available ..
7-5
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TABLE 7." 1: ...
Drill Hole
l3H-4
SH-2
frrt,.1
BH-Z
BH-6
BH-8
DRILLING RESULTS AT WATANA AND DEVIL CANYON DAM SITES
Percent of Cot"e
Q!=.e~h . ( ft) ROD>~D SO<RCO<BrJ Rac<:srr
(~86 76 16 8
·. 623 89 8 3
738.4 87 9 4
391 46 28 26
732.4 78 19 3
736.7 70 21 9
7-6
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Diameter
{ft)
Two Tunnels
20
25
30
3.5
One Tunnel
30
35
40
45
50
Notes:
. (1)
tnstalled Capacity
Davi! Re~~egulation
Wat.ana Canyon Dam
(MW) (MW) {MW)
850
850
850
800
875
880
800
900
900
115
220
300
400
i90
J10
JOG
375
380
1fl0
50
30
50
30
30
30
30
TABLF 7.2 -OPTUUZATION Of TUNNEL DIAt£TER ------------------------------------
Maximum
Head loss
(ft)
97.5
!18.0
45.6
30.5
86.0
94.0
33.4
19.9
9~8
Maximum
Velocit~1 )
(fps)
5.6
6.8
5.9
5.6
8.1
9.9
6.5
6.3
5.0
Tunnel Alt2rnatl~a
Annual Net B~nefif 2 >
($ ~ 106 )
1.0
29.9
34.7*
29.4
31.9
44.7*
44.7*
42.9
35.8
Tunnel Alternative
Annual Net BenefifJ)
($ X 106 )
(17 .3)
( 1.5)-11
( 1. 7)
( 9.0)
3.1
9.3*
7.1
3.4
( 3.9)
Velocity in unlined tunnel section.
(2) 0
Cost of Energy
Produced
(mills.Jbh)
45 .. 2
30.6~
JO .. &'*
34 .. Q
28 .. ~
2$ .. ~-il'<
26 •. S
2B •. S
31.7
Based on an ener~y value of 47 mills/kwh, (i.e. the thermal system cost in the year 2000). This value used in this stucly.
(3)
Based on an energy value of 30 mills/kwh, (the average Watana-Devil Canyon Dam hydrosystem cost L"l che year 2000.
* Optimum tunnel diameter.
,1'·····
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TABLE 7.3: COST ESTIMATE FOR DEVIL CANYON TUNNEL SCHEME
(TWO 30-FOOT D1At£TER TUNNELS)
1980 ~RICE LEVELS
Item
Cost
($1 1 000)
Land and .Damages • ·• • o •••••••• , ••• ,., • .• • • • • • • • • • • $
Reservoir Clearing ••••••••••••••••••••••••••
Re-Regulation Dam ..•••.••••••••..••...•..•..•
10,200
3,300
101,900
41 '700
34,800
26,000
Spillway ...... , •.•..• __. .............. " ........•.•.•
Diversion Works ••••••••••••••••••••••••••.•••
Intake Worke -Main .......................... .
Power Tunnels· .•• .., •• Q ••••••••.••• u ••••••••.•••••
Powerhouse -Main •••••••••••.• .., ................ .
"Tailrace:__., Main ............... o••••••••o••••••
Switchy~rd ................................. o • ~ •
Transmission lines. .. ........................... .
Reacts and .6r idges • , .. __ ......... , ................... .
Recreational Facilities ...................... .
Bv.llding e.!1d Grounds • • • • l •• , ............... ..
Permanent Ope~ at ing Equi .. 11ertt •••• Q ••••••••••
Secondary Powe~~ Station ..... ,, •••• ~ ••••• ~ •••••
Ca~Jl) facilities and Suppnrt •••••••• ~ ........ .
Mobil.izat.ion ••.••. o .......•• '!" ........ , ...... ~ ••• ~.
TOTAL CONSTRUCTION COST • u .................. .
Engineering, Construction, Management and
Owner 1 s .f:osts ••••• ., ••••• e 11 •• ., ••• o."" ........ _., ••
Continge ,cies .•••••••••••••• , .•• ,, .............. .
TOTAL PROJECT COST ••••••••••••••••••••••••••
7-8
556,600
80,300
13,000
3,500
15,000
42t000
1t000
4:.000
3,000
21 t4.QQ
957,700
'130,700
_--..;,:..;...7 '000
$1,136,300
136,400
227,300
$1 ,500_.000 ,_
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TABLE 7.4: COST ESTIMATE FOR DEVIL CANYON TUNNEL SCHEME
(ONE 40-FOOT DIAMETER TUNNEL)
1980 PRICE LEVELS
!te.~
Land and Damages •••.••••••••••••••••••• _.. ••••••
Reservoir Clear~.ng ••• ? ................... .,. ••••
Re--r,egulation Daa-n •••••••••••••••••••••• a •••.••
Spillway ·~···~····,··········~···············
Diversiofi Works ·····················•••••o••• Intake W~rks-Main ••••••••••••••••••••••••••
Power Tunnel • ~ •• ~ ••••••••• t'! ................... .
Powerhouse-Main ••••••••••••••••••••••••••••
Tailrace -f.iain ............ " •••••••• ·~ ••••••••••.•
.SwitChyard ••••••••••'•••••••••····~o•••••••••
Transmission lines •••••••••••••••••••••••••••
Roads and Br idg.es ............................. .
Recreational Facilities ••••••••••••••••• ~ ••••
a·uilding and Grounds •••••••••••• ~ •••••••••• -#. •
Permanent Operating Equipm~~nt ••••••••••• " • ~ ••
Secondary_ Power Station •••••••••••••••••••• ".
Subtotal •··············~·····················
C~ Facilities and Support .................. .
Mobilization -o ................................... .
$
$
Cost
($1zDOO)
10,2iJO
3,300
101 '900.
41,700
34,800
26,000
453,100
80,300
13,000
3,500
15,000
42,200
1,000
4,000
3.000
21~400
854,400
117,000
42.%700
TOTAL CONSTRUCTION COST •••••••••••H••·····•·"$1,014,100
Engineer;.,ng, Construction? Management an:..
Owner•s· Cost ······~···*······················ 121,700 Conting~ncies .•••• : ••••••••••• ~ .••••••.•••.•••• _202,800
TiJTAl.. PROJECT COST ................. u ..... ,, ... $1 ,3.38 1 600
7-9
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TABLE 7.5: POWER AND ENERGY PRODUCTION FROM TUNNEL SCHEME
Description
Installed Capacity:
Watana Darn .•••••••.•••• G' o .•••••••
Devil Canyon········~~········ Re-regulation Dam .............. .
TOTAL .... ., .......... -~ ...... -·····
Average Annual Energr:
Watana Dam •••o••••••••~••••••
Devil Canyon ~················ Re-regulation Dam ••. , •••••••• .,
TOTAL ···················••w••
Annual Firm Energr:
Watana Dam ..................... .
Devil Canyon •••••••••••••••••
Re-regulation Dam ••••••••••••
TOTAL •••·•••·••••~•••••••co-••••
1-40 ft Diameter:
Tunnels
850 MW
300 MW
30 MW
1 '180 M'/1
3,194 Gwh
.2,064 Gwh
'195 Gwh
5,453 G\ltl
2,810 Gwh
1,927 G\'kl
127 Gwh
4,864 G\'oh
7-10
2-30 Ft Diameter
Tunnels
850 MW
300 MW
30 MW
1,180 M.W
3,192 Gwh
2,053 G\tkl
188 Gwh
5,433 G~
2,833 Gwh
1, 925 G\'ll
127 Gwh
4,885 Gwh
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'"'"EAR 1
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ACCESS
DIVERSION TUNNELS
COFFERDAMS
'RE-REGULATION DAM
PONER TUNNELS
iNTAKE STRUCTURE
.
MAIN PO\YER PLANT~ .
POWER/SURGE CHAMBER • >
POWERHOUSE
DRAFT TUBE
TAILRACE
.
TRANSFORMER GALLERY
-
TUBINE I GENERATOR
!MPOUNOMENT
-
TEST AND COMMISSION
SECONDA~ POWER PLANT
CRITICAL ACTIVITIES
IIIIIIIIDIIIIU MAIN POWER PLANT
.,411!11' ~...-FAt SECONDARY POWER PLANT
2 3 4 5 6
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'lllmi~;IGIIIIII!III IIIIIIIIUJIIIIIIIIf,lllllllllllll ••••••• 11118111!
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1 UNIT I ON-LINE ....
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"~ ,::...,.,-...-r...,...,.~..., .. ~~.,......,~...,~.IJI" . .,..,...,~AI!JI'..-r,., ... ,
" . "
EARLIE~T StART OF ACTIViTY . I EARLIEST FINISH. OF ACTIVIl'l'
-LATEST FINISH
,-f TOJAL .. ,.(OF ACTIVITY ·II(!-FLDAT -
CoNSTRUCTION ·SCHEUULE PREFERRED TUNNEL Su,iEME 3
-" --:?~--~; --
¥----------------~-=------------------....... _.......,.. ______ ,_...._::.,;,· _____ _.........,.,.._. __________ ,_. ___ .....,;__:.__"_""'''~-··' . _ ___,_ _ __;..._.....;........ ~'--"-
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FJGURE 7.1 fiil
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8 -COMPARISON WITH.OEVIL CANYON DAM SCHEME
This section outlines a brief comparison of the preferred tunnel sch~me with the
Devil Canyon dam scheme. The schemes are compared from economic, environmental,
and scheduling points of view.
8.1 -Economic Comparison
Table 8.1 summarizes the results of the comparative economics of the two
versions of the tunnel scheme involving either one or two tunnels and the Devil
Canyon dam scheme. The economic parameter·s used are as follows:
Interest rate = 3%.
-Esca1 at ion rate = 0% ..
-Economic 1 ife = 50 years .•
-Annua 1 cost factor = (3. 00. interest
+0.89 -sinking fund
+0.10-insurance}
= 3.99
-Operation and maintenance = $11/kW/year.
-Allowance for funds during construction was based on an assumed S-shaped
distribution of cash flow throughout the construction period.
The average annual energy yields in Table 3.1 represent the net increases over
the first stage Watana dam in each case. It wi 11 be noted that the on~ and two
tunnel schemes can de 1 iver energy at a cost of $27 or $31 per 1000 kWh, respec-
tively. The equivalent cost associated with tile Devil C::.myon dam is $14 per
1000 kWh. The tunnel scheme represents a 93 or 117 percent increase in cost.
It should also be noted that the tunnel schemes; :tually yield between TIC and
790 Gwh less energy than the Devil Canyon dam scheme. This represents about 26
percent.
A further factor that shou'Id be taken into consideration in the economic compar-
ison of tne t.~.mnel and dam schemes is the lower reliability associated with the
capital cost estimate of the tunnel scheme. Because of the uncertainty
associated with the geologic conditions as well as the probable availability of
more· sophisticated tunnel construction methods in the next decade; it is
conceivable that the tunnel costs estimates could vary wide1y. For purposes of
this study, sensitivities have been check(,. by assuming that tunnel costs could
be doubled or halved. Allowing for this ;;otential range in tunnel construction
costs and still incorporating a 20 pe~cent general contingency the economic
analyses shown in Table 8.1 were rspeated and the results are summarized on
Table 8. 2.
Tabie 8.2 c'fearly indicates that even allowing for the unr~rtainty associated
with the costs of the tunnel scheme, the Devil Canyon da~ scheme is st·lll
economi_cally superior.
8-l
8.2 -Environmental Comparison
At present, many gaps exist in the available environmental data. Additional
information, combined wit(l environmental field investigations would permit a
much more detailed comparison of these two development alternatives. Neverthe-
less, from what is presently understood about Scheme 3, it is believed that it
is environmentally superior to the Watana-Devil Canyon dam scheme. By virtue of
size. alone, construction of the smaller re-regulation dam (245ft) would have
less environmental impact than the Devil Canyon dam. The river miles flooded
and the reservoir area created by the Scheme 3 re-regul at ion dam would be about
half those of the Devil Canyon dam, thereby reducing negat"ive consequences such
as loss of wildlife habitat and possible archeological. sites. In addition, the
adverse effects upon the aesthetic value of Devil Canyon would be substantially
lessened with Scheme 3, particularly with the powerhouse location upstream of
the Devil Canyon dam site. Furthermore, Scheme 3 may possibly present a rare
mitigation opportunity by creating new salmon spawning habitat that could be
actively managed. With the increase in riparian zone vegetation allowed by
Scheme 3 the wildlife habitat in the stretch of river bypassed by the tunnel
might be temporarily i.mproved. It is believed that the impacts associated with
tunnel access and disposal of tunnel muck would be offset by the plan's advan-
tages.
8.3-Comparison of Construction Schedules
As shown in Figure 8.1, the construct ion duration of the tunnel scheme is
approximately one yer;.r shorter than the darn scheme. Construction startup to
power on 1 ine for the darn scheme is approximately 66 months while the tunnel
scheme is 52 months. The dam scheme's critical path is controlled by dcun con-
struction and the tunnel scheme is controlled by poNerhouse construction. There
is about a 6 month float period in the construction associated with the tunnel
and this could accormtodate some of the potential construction delays which are
mar~ likely with the tunnel than the dam Jcheme given the limited geologic
in format ion.
The construction schedule for the tunnel a1te:·nativ"e is based on the assumption
that an access road from the Parks Highway to W<r ana ·is avail able. Shouid this
not be the case, access by a new route from Watana., presumably via the Denali
Highway, will be required. The same is clearly true for construction of the
De vi 1 Canyon. However, additional costs wi 11 arise due to a considerably longer
haul distance -For equipment and materials from Anchorage and/or Fairbanks.
8., 4 -S uf11llary
The compar-ison of the tunnel schemes with the Devil Canyon dam sche1rne indicate
that the dam would yield appro,<imately 36 percent more en<!rgy at a 49 to 54
percent lower energy cost. From an environmental viewpoint, the tunnel scheme
:1as advantages, however, these do not appear to outweig.._t the economic benefits
of the dam schemes,. From a construction schedule po·in' < F view there is 1 ittle
difference between the schemes.
It should be borne in mind that the reduced environmental impact outlined in
Section 8. 2 would have to be traded off against the higher cost and lower
energy production of the tur·~el scheme. This can be quantified in two ways as
outlined bel ow.
8-2
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{a) Environmental-Capital Cost Tredeoff
The total increase in capital cost between the Devil Canyon Dam Scheme and
the more expensive tunnel scherne amounts to $500 to $700 mill ion o These
figures are derived by assuming a base fixed cost of 30 percent and
prorating the remaining 70 percent of the Devil Canyon dan costs downwards
by the ratio of the average annual energy yield of the tunnel schemes to
that of the dam s~heme. (This hypothetically results in a Devil Canyon Dam
capable of producing energy equal to the tunne"~ scheme for a capital cost
of $0.80 b i 11 ion. ) The environment a 1 benefits to be gained in terms of
about 16 miles of Susitna River and Devil Canyon which would not be
inundated, would not appear to be justified by this additional cost.
(b) Environmental-Energy Tradeoff
The tunnel schemes yield approximately 770 Gwh less energy on an annual
basis than does the dam scheme. In the long term this implied that an
additional gener"\ting facility would have to be provided to generate this
energy when required and this would create an additional source of
environmenta 1 impact and cost ·.vh i ch has not been factored into the
comparison at this time.·
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TABLE 8.1: SUMMARY OF ECONOMIC EVALUATIONS (Million Dollars)
Total Investment Cost:
Total Project Cost
Construction Period (years)
Allowance for Funds During Construction
( i = 3%, e = ~)*
\
Annual Cost:
Amortized Cost ( i = J%, 50-year economic
life)
Operation and Maintenance Cost (® $8/kW)
<}
Cost Per kWh:
Increase in Average Annual Energy (Gwh)**
Cost of Additional Energy ($/1000 kWh)
Relative Cost of Power (Devil Canyon
Dam = 100%)
* ~ = ~ntereSt rate, e = escalation rate
Scheme J
2-30 Foot Tunnels
$ 1,500
5
121
$ 1,62'
$
$
63
4
67
2,183
30.6
217
Scheme J
i-40 foot Turnel
$
$
$
$
1.339
5
108
1,447
56
4
60
2,203
27.3
193
** Increase over single Watana damJ 800 MW devel~ped with an average annual
production of 3250 Gwh
8-4
Devil Canyon
Dam
$
$
$
$
903
6
81
~
984
38
4
42
2,997
14.1
100
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TABLE 8.2: SUMMARY Of ECONOMIC SENSITIVITY EVALUATIONS (Million ._. ,llars)
Tutal Investment Cost
Including AFDC
-maximum*
-minimum**
Cost per kWh
($ per 1000 kWh)
-maximum
-minimum
Relative Cost of Power
(Devil Canyon Dam = 100%)
-maximum
-minimun
*Based on doubled tunnel costs.
*"Gased on halving tunnel costs.
Scheme 3
2-30 foot Tunnels
328
149
Scheme 3
1-40 Foot Tunr.el
-··".:-.!!If
$ 2,213
$ 1,063
39.6
19.3
281
137
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YEAR
PREFERRED TUNNEL SCHEME
ACCESS
COFFERDAMS AND DIVERSI~~N
kt:-REGULATION DAM
-
POWER TUNNELS
MAIN POWER PLANT
IMRXJNDMENT
TEST AND COMMISSION
SECONDARY POWER PLANT
DEVIL CANYON DAM
ACCESS
COFFERDAMS AND DIVERSION
SPILLWAYS
DAMS
POWERPLANT
IMPOUNDMENT
TEST AND COMMISS!ON
8 6 -
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2 3 4 5 6 7
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52 MONTHS-I
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-' UNI"f ON-LINE 1 -<
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UNIT i QN-UNEJ
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CONSTRUCTION SCHEDULE COMPARISON [Ail FH;URE B .. t
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9 -CON~LUSIONS AND R2COMMENDA.TIONS
9.1 -Conclusions
The conclusions of this study are:
-A base load tunnel scheme incorporating are-regulation dam downstream f1·om
the Watana dam site and developing the head that could be developed by th~
Devil Canyon dam is the most economic typE:' of-tunnel scheme .
.. There is no evide~ce that the tunnel scheme is not technically feasible. How-
ever, a substantial amount of additio!"lal field data. would be required to
firmly establish feasibility.
-The estimated capital cost (excl!Jding AFDC) for the selected tunnel schemes
varies from $1.50 to $1.34 billion depending on whether one. or two tunnels are
required. The rar.ge of capital costs associated with a tunnel scheme could be
as high as $2.37 billion or as low as $0.98 billion, i~e. from $1.06 to $2.37
bill ion or from $0.98 ·to $2.05 bill ion for the two and one tunnel schemes,
respectively.
-The tptal .average energy yield from the tunnel scheme is approximately 2200
Gwh over and above! that obtained from the Watana dam.
- A comparison of the tunnel scheme with the Devil Canyon dam scheme indicates
that it yie'lds less (26 percent) and more costly (93 percent to 117 percent)
energy.. The potenti~1 environmental impact associated with the tunnel scheme
is less than that of the dam scheme, but it is believed that this reduced
impact is not sufficient to outweigh the economic advant:1ges enjoyed by the
dam scheme.
9.2-Recommendations
~
The reconmendations resulting from this study are:
-In o;jer to confinn the economic comparisons with the dam scheme the prefel-red
tunnel scheme should be incorporated in the Susitna Basin development selec-
tion studies. These studies incorporate a. systemwide generation planning
model which will allow a more realistic assessment of the economics of the
tunnel scheme to be made.
-11:\dditional field or office studies of the tunnel scheme should not be under-
taken at this stage.
/
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BIRLIOGRAPHY
1. ASCE, Rock Engineering for Foundations and Sl_opes, Volumes 1 and 2, AugL'~t,
1976.
2. ASCE, Symposium on Underground Rock Chambers, Phoenix, Arizona, January ..
197lo
3. Bleifuss) De J., "Theory for the Design of UnGerground Pressure Co,tduits 11,
Powe.r division, ASCE, V. 81, July, 1955.
4. Brown, Hydroe1ectric Engineering Practi~e, Vol. 1, Blackie and Son,
Limited~ 1958:
5, Colebrook 9
11 The Flow of Water in Unlined, Lined, and Partly Lined Rock
Tunne 1 S 11 , 1958.
6. Cooke, J.B., Libby, J.W., and Madill, J.T., "Ker.tano Tunnel Operation and
Maintenance", The Engineering Journal, August, 1962.
78 Cording, E.J., Mathews, A.A., and Peck, R.B., "Design Criteria for
Permanent Structural Linings ror Station Excavations in Rock) Washington
Metropolitan Area Transit Authorityt', Prepared for DeLeuw, Cather and Co.,
July, 1976 ..
'•.
8. Cummins, A.Bo, apd Given, LA., SME Mining Engineering Handbook, The
· American Institute of Mining, I'I~Ctallurgical andPetroleum Engineers, Inc.,
· Volumes 1 and 2, 1973 .
9. Davis and .Sorensen, Handbook of Applied Hydraulics, McGraw-Hill, 1969 • . -
10. Deere, D.U .. , et al, 11 Design of Tunnel Liners and Support Systems 11
, Univer-
sity of Illinois, 1969.
11. Dowding, C.H., and Rozen, A., "Damage to Rock Tunnels from Earthquake
Shakingn, Journal of the Geotechnical Engineering Division, ASCE, February,
1978.
12. Eckenfelder, G.V., "Spray Hydroelectric Power Development", The Engineering
Journal, April, 1952.
13. Hamel, L. and Nixon, D., 11 Excavation of World's Largest Underground
Powerhouse 11
, Journal of the Con~truction Division, ASCE, September, 1978.
14. Hampton, D. and McCusker, T.G., 11 Economic Potential of Tunnel Standardiza-
tionn, Journal of the Construction D,ivision, ASCE, September, 1980.
15. Holda, J., 1'Tunnel-driving Techniques Until the Year 2000 11 , May, 1980.
16. Huber, W.G., 11 Kemano Penstocks 11 , The Engineering Journal, Nov. 1954.
BIBLIOGRAPHY (Cont'd)
17. Jaeger, C., "Present Trends in the Design of Pressure Tunnels and Shafts
for Underground Hydroelectric Power Stations", Proceedings of Inst. of
Civil Engineers, March, 1955.
18. Lawton, F.L., and Kendrick, J.S., 11 Nechako-Kemano-Kitimat Hydroelectric
Power Development and Aluminum-Reduction Pl ant 11
, "'"he Engineering Journal,
September~ 1952.
19. Maevis, A.C., and Hustl"Ulid, W.A., editors, Proc~edings-1979 Rapid
Excavation and Tunneling Conference, Volumes 1 and 2, June, 1979.
20. McFeat-Smith, I., and Tarkoy, P.J., "Site Investigations for Machine
Tunneling Contracts 11 , Tunnels and Tunnelling, Vo1. 12, No. 2, March, 1980 9
P 'JI." g. vO.
..
21. Moavenzadeh, Fo, and Markow, M.J., 11 Simulation t•bde1 for Tunnel
Construction Costs", Journal for the Construction Division~ ASCE, March,
1976.
,,
22. "~oye, D. G., 11 Rock Mechanics in the Investigation and Construction of T.l.
Underground Power Station, Snowy Mts., Australia", Engineering Geology Case
Histories, Number 3, Geological Society of Jlmerica, Inc., 1964.
23. : .Jnsey, T. E., 11 Unique Features of the Snettisham Hydroelectric Project••.
24. Obert, L., and Duvall, W. I., Rock Mechanics and the Design of Structures. in
Rock, John Wiley and Sons, 19 --
25. Parker, A.'u., Planning and E.ltimating Underground Construction, McGraw-
Hill, 1970.
26. Patterson, F.W., Clinch, R.L. and McCaig, I.W., 11 Design at Large Pressure
Conduits in Rock 11 , Journa.l of the Power Division, ASCE Proc., Vol. 83.
27. Proctor, R.V., and White, T.L., Rock Tunneling with Steel Supports,
Commercial Shearing and Stamping Co., 1946. -
28. Richardson, H.W. and Mayo, RoS., Practical Tunnel Drivi.ng, McGraw-Hill,
1941.
29. Rosenstrom, S., 11 Kafue Gorge Hydroelectric Power Project", Water Pmver~
June-July, 1972.
30. Rousseau, F .. , i•Bersimis-Lac Casse Hydroelectric Power Development", The
Engineering Journa 1, April, 1956.. -
31. Sta.gg, K. G. and Sienkiewicz, 0. C., Rock Mechanics in Engineering Practice,
John Wiley and Sons, 1968.
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BIBLIOGRAPHY (Cont•d)
I
32. Tarkoy, P. J., ;'Predicting Raise and Tunnel Boring Machine P~rf ,rmance:
State ;f the Arts 11 , 197S RETC Proceedings, vol. 1.
33. Terrestrial Environmental Specialists, Inc., 11 Pr~l iminary Environmental
Assessment of Tunnel Alternativesu, December, 1980.
34. U.S. Department of the Army, Corps of Engineers (Alaska District), Final
Environmental Impact Statement, Hydroelectric Power Development, Upper
Susitna River Basin, Southcentral Railbelt Area, Alaska, Anchorage., Alaska.
35. U.S. Department of the Army, Corps of Engineers (Alaska District),
Hydroelectric Power and Related Purposes: Southcentral Railbelt Area,
Alasl<a Opper Susitna R1ver Basin -Interim Feasibility Report, Anchorage,
A 1 ask a, 1975.
36~ U.S. Department of the Army, Corps of Engineers (Alaska District),
Hydroelectric Power and Related Purposes: Southcentral Railbelt Area,
Alaska Upper Susitna River Basin-Supplementary Feasibility Report •.. ,
1979.
37. U.3. Department of the Army, Corps of Engineers, Tunnels and Shafts in
Rock, EM 1110-2-2901, 1978.
38. U.S. Department of the Army, Corps of Engineers (Al a~ka District),
11 Snett ish am Hydroelectric Project" .
39. U.S. Department of the Interior, Bureau of Reclamation (Alaska District),
Vee Canyon Project, Susitna River, Alaska: Engine~ering Geology of Vee
Canyon Dam Site, Sacramento, Ca 1 iforn ia, 1962.
40. U.S. Department of the Interior Geological Survey, Reconnaissance Geologic
Map and Geochronology, Talkeetna Mountains Quadrangle, Northern Part of
Anchorage Quadrangle, and Southwest-:Gorner of Healy Quadrang1e!P A 1 ask a,
1978~ .
41. Vasilescu, t4. S., Benziger, C.P., and Kwiatkowski, R.vJ., 11 Design of Rock
Caverns for_ Hydraulic Projects••, Underground Rock Chambers, ASCE, 1971.
42. Wheby, F .•• and Cikanek, E.M., 11 A Computer Program for Estimating Costs of
Tunneling", Report prepared for Federal Railroad Administration by Harza
Engineering Company, Chicago, Illinois, October, 1973.
43.. Woodward-Clyde Consultants, :•Interim Report on Seismic Studies for Susitna
Hydr~electric Project ... , January, 1981 ..
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PLATES
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I APPENDIX A
I ROCK UNIT DESCRte.J.lflNS ( 40)
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ROCK UNIT DESCRIPTIONS
Tbgd
Tsmg
BIOTI1"E GRANODIORITE (Paleocene, in part may be Eocene) --Biotite
granodiorite and adamellite in approximately equal proportiuns.
Biotite is the chief mafic mineral, hornblende is occasionally
jJtesent. Color is 1 ight to medit.m gray, grain size is from medium
to coarse, texture is granitic to seriate. Very faint flow struc-
tures have developed only locally. These rocks occur in shallow,
forcibly emplaced epizonal plutons in the northwestern Talkeetna
r.tluntains. Aplitic and pegmatitic dikes are common in all the
p 1 utons. Just north of the map area, these p 1 uton ic rocks grade
into felsic volcanic rocks. Potassium-argon age determinations
(see Table 1) indicate that the biotite granodiorite and adamel-
lite of the present unit are essentially of the s~s age as the
biotite-hornblende granodiorite (unit Thgd). Thus, the rucks of
these two units, in view of their spatial proximity, probably are
the products of differentiation of the same parent magma, either
in situ or at soma deeper levels in the E:\rth's crust. The
biotite granodior·ite intrusives are also consid~red to be the
plutonic equivalents of some of the felsic volcanic rocks in the
1 ower porticn of the unit Tv.
~SCHIST, MIGMATITE, AND GRANITE (Paleocene intrusive and metamor-
phic ages) ---Undifferentiated terrane of andalusite and {or)
sillima.nite-bearing pelitic schist, lit-par-lit type migmatite,
and small graniti~ bodies with moderately to well-developed flow
foliation. These rocks occur in approximately equal proportions,
and the contacts between them are generally gradational, as is the
contact between the schist and its unmetamorphosed pe 1 it ic rock
equivalents {unit Kag) outside the present map unit.
The· pelitic schist is medium to dark gray, medium grained!! has
well-developed but wavy foliation, and contains lit-par-lit type
granitic injections in greatly varying amounts. Rock forming
mateials of the schist include· biotite (pleochroism Nz = dark
reddish brown, Nx =pale brown), quartz, plagioclase, minor
K-feldspar, muscovite, garnet, and sillimanite which locally
coexists with andalusite.
The 1 it-par-1 it type granitic injections within the schist are
medium gray, medium grained, and consist of feldspar, quartz, and
biotite. ·
The rocks of the small, granitic bodies range in composition from
biotite adamellite to biotite-hornblende granodiorite. They are
medium gray and medium grained, generally have granitic textures,
and, in addition to the flow foliation, locally display flow band-
ing of felsic and mafic minerals. These granitic bodies appe.ar to
be the source of the lit-par-lit intrusions.
Tsmg
(Cont'd)
Kag
The proximity ofthe schist to the small granitic bodies, the
occurrence of the lit-par-lit injections, and the presence of
andalusite in the schist indicate that the schist is the result of
contact metamorph·i sm. Perhaps this metamorphism took p 1 ac~ ·i r~ the
roof zone of a large pluton, the cupolas of which may be the small
granit~c bodies.
. .
ARGILLI;"~ A~~n· LITHIC GRAYWACKE (Lower Cr:-.etaceous) --These rocks
occur in a monotonous, intensely deformed f1yschlike turbidity
sequence_, probably sever a 1 thousand .meters thick, in the northwest
part of the mapped area, north of the Talkeetna thrust fault. The
whole sequence has been compressed into tight and isoclinal folds
. and probably has been complexly faulted as well. The rocks are
highly indurated, and many,are sheared and pervasively cleaved as
a result of low-grade dynamometamorphism, the intensity of which
is only locally as high as the lowermost portion of the
greenschist metamorphic facies of Turner (1968). Most of the
cleavage is probably axial plane cleavage. Neither the base nor
the top of the sequence is exposed and, because of the intense
deformation, even its minimal thickness is only an estimate.
The argillite is dark gray or black. Commonly it contains small
grains of detrital mica as much as 1 mm in diameter. Because of
the dynamometamorphi sm, in large areas the argillite is actually a
s 1 ate or fine-grained phyllite. Th .:, s sections show that some the
argillites are derived from very fine grained siltstone and that
they contain considerab1e carbonaceous material.
The. typical 1 ithic graywacke is dark .to medium gray, fine to
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medi urn grained, and occurs i nterca 1 ated with the argi 11 i te in 1·
graded beds ranging in thickness from laminae to about 1.5 m. The
individual graywacke beds are not uniformly distributed throughout
the whole sequence, of \'lhich they comrpise about 30 to 40 percent
by volume, but tend to be clustered in zones 1 to 5 m thicko Thin I
sections of graywacke samples show them to be composed uf angular ·
of subrounded detrita·t grains of lithic fragments, quartz,
moderately "fresh plagioclase, and some, generally altered, mica in 1·
a very fine grained matrix; euhedra 1 opaque grains, probab 1y
authigenic pyrite, are present in most thin sections. The lithic
fragments consist in various proportions of little altered, I
fine-grained to aphanitic volcanic rocks of mafic to intermediate .
composition; fine-grained, weakly foliated low-grade metamorphic
rocks; chert; and some fine-grained unmetamorphosed sedimentary 1 rocks possibly of intraformational origin. No carbonate grains ·
were seen. The matrix. constitutes about 20 to 30 percent of the
rock by volume, generally contains some secondary sericite and
chlorite~ and, in the more metamorphosed rocks :t biotite and I
possibly some amphibole. . ·
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Kag
(Cant 'd)
Ana lyses of pa 1 eocurrent features, ·Such as sma 11-sca 1 e cross-
,.stratification, found in several exposures near the western edge
of the mapped area, suggest that depositional currents came from
the east or northeast (A.T. Ovenshine, oral commun., 1974j.
Because fossils are extremely sparse, the exact age of the
argillite: and lithic graywacke sequence is imperfectly known. A
poor specimen of Inoceramus sp. of Cretaceous age was found just
west of the map area between the Chulitna and Susitna Rivers~ and
a block of Buchia-bearing limestone of Valanginian age was found
in float near Caribou Pass in the Healy quadrangle north of the
mapped area (D.L. Jones, oral commun., 1978).
A-3
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