United States Committee on Large Dams. U.S. Dams
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EEDPOCK
SUMMARY
OF
PRINCIPAI,
FEATURDS
Location
On
the
Cowlitz
River in
western
Washington
State
Purpose
Power,
flood control,
recreation
Owner
City
of
T'acoma,
Washington
Engineering
Harza
Engineering
Company
Construction
Dravo-Johnson
Chronology
_
Constr-uction
period:
May
1g64,
Decennber
1g68
(estimated)
Stream
flow
Drainage
area:
29
Foundation
conditions
An
extensive
foundationr
exploration
program
was
conducted
prior
to initiaution
oil co,nstruction.
The investigations
r:onsistedl
of
corro
borings,
ex-
ploratory
shafts,
georohysical
surveys,
establishment
of
groundwater
observation
'wells,
and
in-situ
bear-
ing
tests in
adits
wilbhin
the
dtam
fourndations.
The
results
of
these
investigations
were
used
for
the
design
of the
dam,
frcr
the
treatment
of its
founda-
tion and
features
associated
with
dralinage,
and
for
future
observation.
The bedrock
und,erlying
the
dam
and
reservoir
consists
of a
thick
succession
of
ancirent
lava
flows.
Those
are
overlain
almost
everywhere
by
glacial
deposits.
The
bedrock
extends
to
atrove
maximum
reservoir
levels
excerpt
for
lrbout
one
mile
of
the
reservoir
rim
beyondi
the lefl;
abutmernt
of
the
dam
where
glacial
deposiits
of ti,ll,
sands,
and
gravels
fill a buried
channel
for as
rnuch
as 250
ft
(76
m)
below reservoir
level.
The
lowest
level
of
the rock
foundation
under
ther dam in
l;he river
clhannel
was
found
to be
about 2415
ft
(7{i
m)
below
river
level.
The material
overlyirng
the roek
is
a very
compact,
almost watertight,
g)lacial
till.
The major
joint
system
at
the
darmsite
consists
of
two
sets
of
nearly vertica,l
joints.
They
are
be-
lieved
to
be
tectonic
,joints,
independent
of the
cool-
ing
joints.
The in-si1bu
bearinpl
tests in
the founda-
tion
indicated
a range in
the modulus
of
elasticity
of
the foundation
roek from 1..5
x
106
to
2.5
x 100
psi.
A value
of
1.5
x 10o
psi (105.500
kg/cm')
was
used
in
the design. .A
composite
typ,e filtl
dam
was
considered
as an
altrlrnative,
but
an
arch
dam
was
selected because
of :foundatiorr
conditions
and
eco-
nomic
considerations.
MOSSYROCK
HYDROELECTRIC
PROIECT
_-
sq mi
(m2
x
106)
1,170
Maximum recorded
flow:
o,;j;r[1i'.T:)
83,500
n"*"."%?
(m3lsec)
6'420
Reservoir volume
(total)
:
ac-ft
(mt
x 106)
--.----
l,B?2,000
Reservoir
area
at
maximum
elevation:
acres
(m2
x
ltr)
------
--
Length
of
reservoir:
(3.030)
(2.360)
(lil)
(1.6e5)
12,000 (5.000)
(38)
(84)
1,270,000
(972.000)
miles
(km)
24
Shore
line:
miles
(km)
52
Dam
Type:
concrete
arch
Dimensions-ft
(m):
Height,
above
bedrock
above riverbed
Crest
length
Thickness,
base
top ----------
Volume of
concrete:
cu
yd
(m3)
--------
Spillway:
Desigrr flood
606
(185)
366
(112)
L,260
(380)
L25
(38)
27
(9,2)
inflow:
cfs
(m3lsec)
-____--_
--
900,000
outflow:
cfs
(m3lsec)
Size of
gates (4
Tainter
gates)
length:
ft
(m)
_-_--_-__-_--__-_.
42.6
width:
ft
(m)
80.0
Diversion
tunnels
(two):
Size of each
tunnel
(unlined,
gothic)
width:
ft
(m)
height:
ft
(m)
40
Length
of conerete
plug:
ft
(m)
-
86
Outlet
works:
Penstock
(steel
lined)
diam:
ft
(m)
20.6
Size
of service
gates (three)
width:
ft
(m)
16.0
height:
ft
(m)
33.26
Maximum
discharge
each
conduit:
cfs
(m3/sec)
Power
facilities
Total
installed capacity:
300,000
kw
Number and capacity
of
generators:
2
units
at 160,000
kw
eaeh
Ultimate capacity:
three
units for a
total
capacity of
460,000
lnrr
Head, maximum
(net):
ft
(m)
----
346
minimum
(net):
ft
(m)
1?0
Turblnes: Francls
type-206,000
hp each
Power
factor-O.9
Construction costs
(8.4e0)
(7.800)
(13,0)
(
16,2)
(10,1)
(L2,21
(26,2)
(6,25)
(4,67)
(10,14)
(202)
(106)
(62)
Estimated construction
eost
-------------$116,000,000
Maximum
employment
during construction
---_--__1,200
inen
tt
(I2
m) high
and
33 ft
(10
m) wide.
The
tunnels
provide
for handling
floods
of
at
least 48,000
cfs
(1.350
m3lsec)
during
construction.
Upon comple-
tion of
construction,
the diversion
tunnels will be
closed
by
means
of
slide
gates
at
the upstream
portals.
The tunnels
will
be
permanently
sealed by
conerete
plugs.
Upstream view
of dam unriler
eonstruction.
30
MOSSYROCK
HYDROELECTRIC
PROII]CT
Design of arch
dam
The
dam
will
be
a
double-curvature, rnulti-
center, concrete arch
with
a
maximum height of
606 ft
(185
m). The
dam
is 7,250
ft
(380
m) long
at
crest
elevation
785.0 ft
(239,4
m).
The
thickness
of
the
dam at
top
is
27
ft
(8,2
m) and at the base
is 125
ft
(38
m). The
arch
abutrs
against
a
140-ft-
high
(43-m)
thrust block
on the left
abutment, and
a
l25-ft-high
(38-m)
thrust
block
on the right
abutment.
The
dam was
designed
and
analyzed by
trial load
analyses
and by
structural
model
tests
murle
ut
the Laboratorio
Nacional
de Engenharia
Civil
in Fortugal
under
the direction
of Professor
M. Rocha.
These
tests were
made
on
plaster
models
to a
scale
of
1:400.
The
allowable
design com-
pressive
stress
was
1,200
psi
(84
kg/cmr) for a
maxirqum
water
load,
dead
load,
and
temperature
load.
A rupture
test
of
a
model indicated
a safety
factor
of 8.
The
computed
factor
of safety
based
on the
ratio of compressive
strength
of concrete
at
one
year
to a
computed
maximurnr
stress in
concrete
was
4. A
series
of instruments
are
being
installed
in
the darn and
foundation
to
determine
actual con-
crete
stresses and
deflections
of the structure
and
its
foundations.
Special
design
consideration
uras
given
to
earth-
quake
because
of the seismic
history
of
the area.
A
trial-load analysis
was
made for
a
horizontal
earthquake
load
of 0.LZ
g.
The allowable
design
stresses were
increased
by
25
pe:rcent
for
this
con-
dition.
Model
tests were
made
to
determine
the
natural
vibration
frequency
of the arch.
The
model
was
also subjected
to random
elastic
and rupture
tests
performed
with
an
electromagnetic
vibrator
generator.
The
section
shown
is
of the
dam
at its
maximum
height.
Concrete
placing
temperature is limited
to
50'
F
(10"
C)
in zones
of
high
restraint
along
the foun-
dation
area, and
to
60"
F
(15'
C)
in
the remaining
mass.
River water
and refrigerated
water
is
circu-
lated
through
pipes
embedded
in
the concrete
to
in-
crease
the
rate
of
cooling
of the
concrete. All
vertical
joints
in
the
areh
and
thrust
blocks
will be
grouted
after
full
shrinkage
has
taken
place.
Foundation
treatment
No
unusual foundation
treatment
under
the dam
was
found
necessary,
The
treatment will
consist of
routine
consolidation
grouting,
curtain
girouting,
drain holes and drainage tunn,els,
with
the
latter lo-
cated
at
high level
downstrr:arm of
elach
abutment.
The drainage turnnel
in the
Ieft
aburtment was
extended for
2,000
ft
(610
nr) into
the
rock
under-
lying
the
glacial
mat;erials
oll the left; reservoir rim.
Drain holes will
extend
fro'nr the
grou.nd
sur{ace
into this drainage
tunnel.
An
extensive
area of
the
buried channel will
b'e
providercl
with wells
to
permit
observation
of
ground-water
tables
in
the
glacial
materials
of
that
area during reserv'oir
operation.
Outlet
works
and
powerhourscr
The spillway ca,pacity
oll
275,000
cfs
(7.800
m'lsec) was
deternrined
by'
routing
the
probable
maximum flood
through the
resely6rirl
taking
into
account operating
procedures
estalilished in
the
Feder,al Power
Comnnission
License.
Control wilt
tie
by four
42.5-
by 50-ft
(12,9-
by 15,2-rn)
radial
gates
located
at
the crest of the dam.
Disclharge
from
the
spillway will
plunge
into a n,atural
poo'l
ov€r
200
ft
(61m)
deep located
downstream of
the toe of the
dam in an
existing
preglacial ,ehannell.
The
areas
of
expected maximum scour vl'ill
be
lined
with
rein-
forced
concrete.
Spiillway
ogtration
is
expected
to
be infrequent.
A
separate
intake for each
unit
is
provided
at
the upstream face o:f the darnr. Eachr
int;ake
is
pro-
vided with
a single
gate
oll the fixed wheel
type
with
trashracks.
Sl;eel
penstocks
alre
elxposed
be-
tween the downstre,am
face
of the
dam and
the
powerhouse.
The
pernstocks
are
20.5
ft
(6,3
m) in
diameter
and are nrade
of T'-1
stee{. lfhe
power-
house
is
the conventional indioor
type located
just
downstream from
tlhe dam, along
the right
abut-
ment.
Space
for
thr,ee
generatbing
units will
be
pro-
vided.
Two
are
installed init;ially. The
turbines are
of
the
vertical shaft, Francirs
type
rated
at
206,000
horsepower
each, under
310
ft
(95
m)
of
net
head.
The
generators
are
rated
at
167,000
kva
each at
178.6
rpffi,
0.9
power
factor,
and
13.18
kilovolt.
The
section
through
the
intake
a:nd
powerhouse
shows
the arrangement
of
the
intake
facilities,,
Fish facilities
Elaborate fish
passing
facilities which
included
ladders,
pumping plarnt,
and tr:ucking facilities
were
initially
considered ;for
the
p:roject.
However,
fish
hatcheries
were
ado'pted insbead
becauser
they were
deemed
to be
more
effective,
to sustain
the
runs
of
anadromous
fish
on the
Cowlitz Rivr:r.
r{Ew EXCHEQUER DAt\4
31
r"
\.
b3
13
*t
Artist's
'sketch
of completed New Exchequer Dam.
Existing
dam
shown
in
insert.
Arthur R. Il,eitter,
Senior Vice
Presid,ent, Tudor
Engineering
Company,
San
Francisco,
Californi.a
The
.Merced
Irrigation
Dist;rict,
Merced,
Cali-
fornia,
recently replaced
its
olld
Exchequer
Dam
facilities
on the
Merced
River
in
central
California
with
a
leurger
New
Exchequer
Dam
and Power In-
stallation increasing
storage
f'rom 281,000
ac-ft
(347
x 1r0o m')
to 1,026,000
ac-llt
(1.264
x 100
ms).
The
old
310-ft
(95-m)
high
concrete
gravity
arch
dam had impounded
water
for ir:rigation
and hydro
power
since
1926.
The
annual
:ilow
of the
Merced
River
averages 987,100
ac-ft
(1,218
x 1.00
ms),
but
it fluctuates
widely
and
the lDistrict
needed
in-
creased
storage
to
provide
adequate
carryover
for
the water
deficient
years
and
the control
of floods
in
wet
years.
In 191i8
the District
authorized
Tudor Engineer-
ing
Company of
San
Francisco
to
develop
a feasible
design
to meet
the
objectives
of water
supply for
irrigatiorr,
power
generation,
flood
control,
and rec-
reation.
Four
proposals
were
studied:
1.
A
500-ft
(152-m)
hiigh
.on.".t.
arch
da:m
downstream
from
thLe
old
dam.
2.
An
enlargecl
concr€rte
gravity
dam
to
be
achieved
by increasing
the u,idth
and
heright
of
the
existing
dam.
3.
A
composite
gravlty-zurch
dam
consisting
of
the
existing
dam witlh
a ne''tr
concrete
&rch
atop
the
old dam.
4.
A
concrete-liaced
ror:llfill
dam
utilizing
thLe
existing
dam
as its rrpstrearn
toe.
The
first
two
pr:oposals
\\/ere
elirninated
because
of cost and
the
thirrl because
it seenrLed
unlikely
that
state
and federal
licensinpJ
authoritieil
would
ap-
prove
this
unconvenional
ap'proach.
The
rockfill
danr
as buill; :is 490
ft
(149
m) higtr,
1400
tt
(427
m)
long, and
has
a volum,e
of approxi-
mately 5.3
million cu
yd
(,4,
1 x
1()o
m'). An
up-
stream concrete far:e
providers
the
iimpervious
lbar-
rier.
The
design is,
unique in
that it
incorporat€s
the old 310-ft
(95-rn)
high
croncrete
gravity
stnuc-
ture
into
the
embankment as
an upstream
retaining
32
wall for
tLre
new
rockfill
embankrnent
and as a con-
tinuation of the upstream imprervious membrane
(see
general plan
and
section).
Incorporation
of the old
dam into
the
new
offered several advantages.
It
saved a
large
amount
of fill, shortened
the diversion-power tunnel and
permitted
storage
of irrigation
water
during
con-
struction
with
releases
of
water
for
irrigation
when
required.
The design
posed
three
problems:
1.
How
to
build a rockfill
to
minimize settle-
mrent in
order
to
preserve
the
integrity
of
the
face slab
and
insure
maintenance
of a
posi-
tive contract between
the
face slab
and the
existing
structure.
Z, How to
determine the
optimum height of
contact
of the
rockfill.upstream
surface
with
NE\M EXCHEQUER DAM
the
existing
structut:e
to attainr
minimum
cost
while assuring
starbility of
the old dam
under
all con,ilitions
of
loading.
3. How to
form
a
watertight
joint
at the
point
of contact
of the
concrete
face
sllab
and the
existing
structure.
Records of existing
du:m.ped
rockfjills
showed
average
settlements
of
1
percent
whictr were con-
sidered too
much tor
assure the
water
tightness of
the
face
slab
and
the
conlba,ct
joinrt
between
the
concrete
face
and t;he old
rilam.
It
was therefore
decided to compact
most of
l;he roclkfill.
Based on
records
of
existing
compacterl
rockfills,
it was
ex-
pected
that an
ultimate
settle:ment olf
about
0.2
per-
cent
will result"
Actual
settlernents
since completion
of the
fill in April
I.966 range from 0.16
percent
to
0.28
percent,
at
various elel'ations
on the
face.
%,
N
6f'
^d
.tJ-
ilTl*t ST|IUCT'URE
)
EXCHEOUER
DAM
o
ca
b,
6f
ITCHYARD
//
-oo
.B
//
u9o
,i
GENERAL
PLAN
roo
o
roo 200
FEET
_
20 0
20 40
60 METERS
E
t6'(4r9m)
-/
srEEL
LINED
TUNNEL
ST
ELEVATION
879I
(26Jsm)
!
I
I
NEW
EXCHEQUER
DAM
f).)
t)t)
coIP
cTED
itoct(,
YOIDS
FILLED SITII
ao-50
PEITETF|ATtOr{
FACE OF
OLD O
AS PXAL
I
FLEXIBLE
ASPHALT
-
IMPREGNATED
,JOINT
i-!Lj-tttt"
coracRErE i,Ac€
sLAa
rfi#i#t1s*
Location
On
the
Merced
River in Mariposa
County,
central
Calif.
Purpose
Power,
irrigation,
flood
control, recreation
0wner
Merced Irrigation
District
Engineering
Tudor Engineering
Company
Construction
Dravo
Corporation
Chronology
Construction
period:
1964-196?
Stream
flow
Drainage
area
(total
above
dam):
sq mi
(m2
x 106) -----.- 1,020
Maximum
flood of record
at
dam
site:
cfs
(m3lsec)
101,500
Maximum
probable
flood, regulated:
cfs
(m3lsec)
341,000
Standard
project
flood:
efs
(m3/sec)
16'7,000
Average annual flow, at
dam
site:
ac-ft
(m3
x 106)
98'7,100
Reservoir
Volume at top
of
gates,
elevation 867 ft
(264,2
m)
z
ac-ft
(m3
x
106)
------.-
1,025,000
(1.264)
Surface area:
acres
(m?
x 10r)
'1,127
(2.880)
Length
of shoreline:
miles
(km)
82
(132)
Dam
Material
and
type:
Rockfill
with concrete upstream face
Dimensions--ft
(m):
Maximum
height
490
(149)
Maximum length
1,400
(427)
Total volume:
cu
yd
(m3)
----
5,300,000
(4.100.000)
Outlet facilities:
Spillway capacity
with
gates
closed, HW
elevation 879
ft
(267,9
m):
cfs
(m3/see)
16?,000
(4.729)
zofiE 3
ICOMPACTED
ROCX}
-rc,rr9n)-l
STEEL
LINED
TUI||'EL'
/-'-
'
SECT 1 ON
!o
o !o roo rlo rfEt
ro
o
ro
a s
aoratars
ffi
SUMMARY
OF
PRINCIPAL
FEATURES
(2.642)
(2.874)
(e.656)
(4.72e1
(
1.218)
Spillway
capacity
witlh
gates
opened,
HTV
elevation 877
ft
(26?,3
m):
cfs
(m3/sec)
341,000
Six 40-
by
30-ft
(12:,,2-
by 9,.1-:m) Tainter
erated
with fixed hoist
Power
facilities
Generating capacity:
80,100 kw
Number of units: 1
(e.656)
gates
op-
Type
of
powerhouse:
se:mi-outdoon
plant
located
at
down-
stream
toe of
main ernbankment
Turbine:
Francis
type
Rated capacity-123,000
hp
at 3i97 ft
(121
nn) head
Speed-180
rpm
Governor:
Cabinet type
Draft
tube: Elbow type--two
openings
Gates-l set, 1 slide section
for
each opening
Intakc: 1-13.83- by 2',9.26-f.t
(4,2-
by
7,1,-m) bulkhead
gate
operatcd by
submerged
hydraulic
,eylinder
Tunnel:
Concrete
lined
section,
l8i-llt
(5,6-m)
diam,
385-ft
(117-m)
Two
7- by 10.5-ft
(2,L-
by 3,2-m)
sliide
gates
hy-
draulically operated
Steel lined
section,
16-ft
(4,9-m)
diam,
1,050-ft
(320-m)
108-in.
(2,74-m'S
Howell-Bunger
valve
on
bypass con-
duit
Switchyard:
One three-phase
mainr
transfo,rmer
115
kv-100,000
kva
69 kv-60,000
kva
13.8 kv-89,000
kva
Major
eonstruction
quantities
(estimnted)
Dam
cu
Yd
mr
Rockfill
5,350,000
4.090.000
Concrete 29,400
22.600
Spillway
and dike:
Concrete
26,000
19.900
Embankment fill
211,000
161.000
Powerhouse,
tunnel,
and intake:
Concrete
12,300
9.400
Construction
contract
New
Exchequer
Dam
and
power
I'ar:ilities
New
Exchequer
Dam, A:fterbay
Darn
and
power
facilities
at both dams
__.._..$26,911,034
.
..-..$31,66?,714
/
zoNE I
DUUPEO
ROCK
(
OLO
IXCXEOUER
DAI
34
I\EW
EXCHEQUER
DAM
There was no
precedent
for deciding where
the
upstream slope
of
the
new
dam should
meet
the
downstream
face
of the old dam, On the
basis of
some
50 computer-calculated
analyses using
various
assump'tions, it
was
decided
to make the
joint
175
ft
(53
m) above
the foundation
of the o,ld dam. The
decision
was
based
on
stress limitations imposed
on
the old
concrete
gravity
dam.
The
upstream com-
ponent
of the embankment
load
places
maxirnum
stress
on the old
dam
foundation
when
the reser-
voir is
empty.
To
obtain
a watertight seal be'bween the old
con-
crete dam
and
the new concrete
slab on the rock-
fill,
the
engineering
contractor designed
a
joint
which is
a
combination
of smooth contact surface
between
old and
new
concrete,
a
sliding concrete
wedge
blor:k,
neoprene
gasketing,
,copper
and rubber
waterstop, a
premolded
asphalt-impregnated
expan-
sion
joint
filler,
and a
flexible
asphalt-impregnated
rock cushion
below
the
joint
(slee
section).
The
seal had to be flexible
to accommodate movement
of
the new
rockfill
and
deflection of the
old
dam
with variation in
reservoir
wat;er level. Higher
reservoir levels
will tighten
the seal.
The face
of
the old dam was sandblasted
in
the area where
it
contacts
the edge
of
the
concrete
face
of, the new
dam.
A sand-cement mortar,
rcontaining
a
plasticized
high-polymer
resin,
'was
app,lied
to
tlhe
srandblasted
area to
provide
a srrrooth
surrf'ace.
The reinforced-concrete
fa,ce
on the 1.4:1
slope
is
made
up
of 60-ft
(18,8-m)
wide
stripsi
that vary
in length
from 2L
tct
50
ft
t[6i,4
to L5,2
m) and
in
thickness
from
18
to 34
in,
(46
to
86
em). the
paver
used
was adjustable
for
thickness
of
concrete
slab and for length
of sloping block. Plarcing
of
the
concrete
face
progressed
as rapidly
as :rock
place-
ment
permitted.
At
each abutment
the concrete facr:
bears against
a concrete cutoff slab that irs
keyerl
and
doweled
into the
rock. The final
exczlvation
linr:
to
sound
abutment rock
determined
the
exact
shape of
the
cutoff slab.
Premolderl
asphalt-irnpregnated
expansion
joint
fill,er,
styrolfloam,
and
a copper
waterstop sealed
the
joint
be1;vi'een
the concrete face
and the abutment cutoff
sla'b.
Vierv
of
nerv roekfill dam
rvitlh
concrete
faee.
Old concrete
gravity
dam
at
left serves
as upstream toe
of nerv structure.
The
principal
features
of the
New
Exchequer
project
consist
of
the main
dam,
a 60-ft
(18,8-m)
high
rim
closure
dike,
a combined
gated
and un-
gated
spillway
at a
saddle
in
the
right
rim
of the
reservoir,
a 16-ft
(4,9-m)
steel
lined
power
tunnel
through
the
right
abutment,
and
a semi-outdoor
powerhouse
at
the
downstream
toe
of
the main
em-
bankment.
The
main
dam
is
a compacted
and zoned
meta-andesite
rockfill
embankment
with
a rein-
forced
concrete
upstream
face
acting
as the im-
pervious
membrane
in
the
dam.
Ea,rly
plans
called
for
embankment
material
from
a
granitic
outcrop
about
4.5
miles
(7,2
km)
downstream
from
the
damsite.
Additional
explora-
tions
located
a confined
meta-andesite
formation
just
above
and
slightly
downstream
of
the left abut-
ment.
This
hard
gray
igneouLs
rock
was
used,
with
some zoning
adjustments.
Zone
1,
the
transition
material
under
the up-
stream
concrete
face,
is
15-in.
(88-cm)
max-size
rock
compacted
in
Z-ft
(61-cm)
lifts
by 10-ton
vibratory
rollers.
Zone
2
is 4-ft
(1,2-m)
max.
rock
compacted
in
4-ft
(1,2-m)
lifts
by
10-ton
vibratory
rollers.
Zone
3
is
4-ft
(1,2-m)
max.
rock
placed
in 10-ft
(3-m)
lifts
and
compacted
by
hauling
and
grading
equipment.
zone
4
has
the largest
rock
that could
be
handled,
with
*t least
b0
p*rce't
of
it
over 12 in.
(30
crn). It
was
dumped
from
heights
up
to 60
ft
(18
m) with
no
compaction
specified.
Sluicing
with
high-pressure
jets
helped
compact
zones
Z,
B
and
4
(see
section).
The
various
embankment
zones
were
shaped
to minimize
setilement
and
distortion
of
the concrete
face
during
the
life
of
the
dam.
The
saddle
spillway
in
the right
rim
of
the
res-
ervoir
consists
of six
40-ft-long
by
B0-ft-hieh
(I2,2
by
9,1-m)
Tainter gates
and
a
1,090-ft
(329-m)
long
ungated
section.
The
tops
of
the
closed
gates
are
at
elevation
86?
ft
(264,2
m)
or
one
ft
(0,30
m)
below
the
ungated
crest.
The
stan-
dard
project
flood
of 1GT,000
cfs
(4.729
m'lsec)
will
pass
over
the
closed
gates
and
the
ungated
crest
rvith
a residual
freeboard
of B
ft
(0,9
m).
With all
gates
open,
the
spillway
will
pass
a
possible
maxi_
mum
flood
of
341,000
cfs
(9.656
m',/sec)
with
a
re_
sidual
freeboard
of b
ft
(1,b
m)
on
the
main
dam.
A
tunnel
through
the
right
abutment
was
used
for
diversion
of
flows
during
construction
and
was
later
converted
for
power.
It
incorporates
an intake
structure
upstream
of
the
old
dam
with
a
hy_
draulically
operated
bulkhead gate,
an 1g-ft
(b,b_m)
-
diam
concrete
lined
section
Bgb
ft
(11?
m)
long
from
the
intake
to
a
gate
chamber
which
contains
twin
hydraulically
operated
slide
gates
7
by
10.b
ft
(2,1
x 3,2
m)
each,
and
a 16-ft
(4,g_m)_diam
steel
NEW
EXCHEQUEIT
DAM
35;
Iined
conduit
1,0150
ft
(3i20
m)
long leading
from
the
gate
chamber
to the
powerhouse.
The
steel
linring
varies
in
thicknress
from
.,1
in.
(2,54
rcm)
to 1.g?b
in.
(4,76
cm),
and is
backerl
up
with
concrete
to insure
composite
actiorr
with
the
surrounding
rock
througtr
which
the
tunnerl
was
d'i,ren.
Just
upstream
of
ther
powerhouse
a combined
bifurcation-transition
siec-
tion
is
utilized
to branch
off
to a 10g-in.
(2,74-m)
bypass
conduit
and
a
povser
conduit;
which
redu.cesr
from
16
to 13
frb
(4,9
to 4,0
m)
(see
general
plan),
The
most
critical
arspect
of
the
constructionr
schedule
was
tlhe
driving
of
the
power-diversionr
tunnel
and
the
installatio;n
of
the
tunnel
gates.
To,
assure
water
for
irrigation
throughout
the
con-
struction
of
the
project,,
it
was
necessary
to st61g
water
behind
thrs old
darn
during
wirnter
and
spriing,
trnd
lelease
conbrolled
srupplies
during
spring
*nd
summer.
Thus
the
intakre
structure
and
its
gate
trad
to be
completed
during
the
months
of
Septemher,
October,
and
November
when
the
reservoir
v/as
empty.
During
1;hese
m.nths,
the
tunnel
was
holed
through,
the int'ke
strur:ture
constructed,
the
bu,lk-
head
gate
installled,
and
the
ouilets
in
the
old
dam
plugged.
The
contractor
completed
t;his
first
phase
of
the
work
December
4,
1964,
and
within
thr.ee
weeks
a
major
slborm
nezrrly
filled
the
old
reservoir.
The
next
critical
step,
also
completecl
on schred-
ule, was
the installation
,f'the
tunneil
slide
gates
by
March
1965
so
tlhat
releases
for
irrigation
could
be
controlled.
once
the riv,er
flow
was
under
control,
construction
of
the main
embankment
proceeded,
The
powerhouse
coinl;ains
a
single
128,0()0-
horsepower
Francis
turtrine
with
a rated
head
of
397
ft
(121
m).
The
turlbine
drives
an
g0,100lcw
generator
at a speed
of l{10
rpm.
The
power
pla,nt
is
designed
for
manual
control,
local
automatic
con-
trol,
and remote
automatic
control.''
The
unit load
control
is
desigrred
for
rnanual
control
and
aut,o-
matic
dispatch
control
from
a remote
automatic
load
control
center.
llhe
mailn
power
transformer
is
a
115-kv
auto
transformer
u'ith
a 6g-kv
auto
tap arrd
a
13.8-kv
tertiartr
winding.
A
switchyard
adjacerrt
to the
powerhouse
distrihrutes
the
power
over
6gJrv
or 115-kv
transmission
lines.
Bids
for
construction
of
the
project
were
re-
ceived in
June of
1964,
and
the
contract
was
awarderd
to
Dravo
Corporation,
Bellervu€,
Wash:ington,
for
ap-
proximately
931,1i00,000.
36
NICKAIACK
DAM
k;r;-N
I
li
ii
,',
POWERHOUS€
,i
4units@24,3OOkv
SPILLWAY
]
Lock
Operation
8uilding
Et
633.0
-
Ramp
(tszrsln)
UAIN
LOCK
llo'x
8oo'
AUXILIARY
i
LOCK.
'
i
llo'x600'
\
XlE2r88n)
(esrsJrxzt4al^1
(
Partial
conslrucllon)
EARTH
EUEAHRUEilT
Original
ground
surface
E/ 637.O(/94r/6
n,l
2.5
,.<.
TRASHWAY 22.5'(6186n)
LOCKS
SPILLWAY
t Main
Lock
Et
652.0(t9&73
El
649.O(/97182n)
DOWNSTREAM
ELEVATION
SASE
LIHE
t:/
652.0
(/98r73n)
?.s
tt/
THOHOTEA\FLO|(
DaU
I
etnra euax
I
,ltlo'!
(l<16tn)
tOO.O'(3t7r48n)
652.0
(/g'8,73n)
Rock
surface
Orig inal ground
surface
Mnrht,flffiS)J'M:,
Pervious'
backfi//
Cofferdant
dtkc
^t^\l,A-l,F\l//l
Kock
surtace
Grave/ fi/led
c,g//s-
/tr
-
l/t
silor.
GENERAL
PLAN
ElJlll:)
(/8_0,75
nb
SEC
T
lON
-
RlGHT
EMLANKMENT
I Groul curlain
Ilova
P. La-cy,
Jr.,
Head.
Civil
Engineer
(Hydro
Design)
Tennessee
Valley
Authority
Knoxville,
Tennessee
The Nickajack
Dam
will
replace
Hales
Bar
Dam,
which
is located
6.4
miles
(lCr,B
km)
upstream
of
the
nevr
damsite.
The Hales
Bar
Dam
was
constructed
by
the
Chattanrooga
and
Tennessee
River
power
Company
and wars
completed
in
1g18.
T'he
Tennessee
Valley
Authority
acquired
it
in
1g3g.
Eleven
days after
the
dam was
iompleted,
the first
leakage
was
no-
ticed;
a few
days
later,
inle.bs
were
located
up-
stream
of
the
dam.
Numerous
efforts
were
made
and
much
money
was
spent
lby
both
the
former
owners
and
TVA
through
the
years
to reduce
the
leakage
through
the large
cavities
in
the soluble
Bangor
limestone
foundation.
lBeneath
the
dam are
two important
fault
zones
characterized
by east-
dipping
thrust
faults.
Secondary faults
and
joints
combined
to weaken
the
rock in
both
areas
so that
it
was
easily
attacked
by
solul;ion
to depths
of
90
ft
(27,4:i
m) .
Some
of the
efforts
reduced
the
leak-
iIJ
age
f,or
short
periods
of
time.
ftn
1960,
fir€zrsur€r-
ments
showed
lealkage
was
approximately
2,0(10
cfls
(56,6
m',/sec).
Power
wals
being
Jlost
and
the
danrr
foundation
weakened
by
ther
continual
flow
of wate:r
through
it.
Stud.ies
of v/a,ys
to
construct
a nev/
navigation
lock
al;
the sit;e
revealed
l;hat it
woul:l
be very
difficult
a,nd costly
to
provide
a
cofferdam.
After
a thorough
investigation
of means
of stop-
ping
the
persistent
and
extensive
leakage
ancl
strengthening
ther Hales
l3ar
foundartion,
an ap-
praisal
of
the
necr3ssary
repairs
and
the new
facili-
ties required
at
Hales
Bar
in
comparrisorn
with
a! nev,r
multipurpose
dam at
the
tNickaJack
site showed
an
economic
advantapre
for Nicikajack.
The
principal
f,eatures
of
the Nickajack
Dam
are,,
in
general,
simila.r
to
Hales
Bar.
The
major
d:if-
ferences
are:
the
volume
of the rese,rvoir
will
'bc:
increased
by 95,100
ac-f1;
(117.305.850
m')
;
the:
spillway is
being increased
so
that tlhe
maximurnr
flood
will be disc)rarged,
surcharging
the
pool
Z.tli
ft
(0,85
m) less
than
Hales Bar;
and
there will trcr
one
completed
locl<
with ar
chamberr lL10
by
600
ft;
(33,53
by 182,88
m)
and
another
partially
corn-
NICKAIACK
DAM
Aerial
view
of Nicka-jack
Dam
looking
upstream.
First
stage
constructionr
;is flooded
prior
to
earth
embankment
construction.