Indian National Committee on Large Dams. Design and Construction Features of Selected Dams in India
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power
generation
\\iill
have to be inrposed
to
the
extent
of
46
percent.
For
the
year
rvith
an annual inflow
of
493
X
103
ha m,
a cut
will have
to be imposed
on
irrigation restricting
area
under
cotton
and
wheat to
50
percent
and omitting area
under Kharif
and
Rabi
Jowar,
and
a
cut
of 70
percent
will
be imposed to
power
generatlon.
18. Power
Generation
The
Ukai
hydro
power
station is
a
peaking
station
and
has an
installed
capacity of 4
x
75
MW,
i.e., totally
300 MW being
generated
through
vertical
shaft
Kaplan type
generator.
The
power
house
as
shown in Photo
12
was
commissioned
on
8
July
1974
with
the
first unit coming
into
generation
on
that day.
The other three
generators
also followed
in
fairly
quick
succession.
It is envisaged to
generate
193MWat
35
percent load factor,
i.e.,
67.55 MW
continuous
in
a normal
year
when
75
percent
depend-
ability
of the inflou'
are
available
at
full upstream
utilisation
of
0.37
M.
ha
m
(3.0
M
acre-ft).
Presently,
however,
with lesser upstream
utilisation, larger
flows
are becoming available
and hertce,
average
annuai
generation
from
July
1974
to
November
I978 has been
about
1,050
million
units
(i.e.,
M kWh)
as against 67O
million units envisaged
in
the
plan.
The
yearly
power
generation
in
million
units
-siven
in Table
XVIII.l.
TABLE
XVIII.I
is
Year
Total inflorv in
103
ha
m
Power
genera-
Maximum u'ater-
tion in
Mlllion
level
reached
untts
In
m
t974
197
5
1976
r977
1978
6r4.801r
1233.759
r
686.9839
1220.4249
r338.ls0r
212.19
7
55.r74
1313.172
1230.400
1056.780
102.769
105.186
104.848
105.08s
104.190
A
small
generation
through the canal
bed
power
house at
H.R.
dam installing
tlo
units each
of
2.5
MW
with
80
percent
load
factor
is
also
planned.
The
intake
for this, i.e.,
penstocks,
emergency
gates
and
hoists are
presently
ready
but the
canal
power
house
for
rvhich
approval is recently
received
is still to
be
undertaken
by
the Gujarat
Electricity
Board.
289
IDT]KKI DAMT
by
C.
ETTY DARWIN
Mernbe'r
(Civil)
Kerala State
El€ctricity
Board
'
Trivandrurn
fd,akki
lDano
History
and
Description
The
Idukki
Hydro-Electric
project
is
located in
the
Western
Ghati,
80
km
from
thi, Cochin
Fort,
in
the
southernmost
Indian
State
of
I(eraia:
Kerala is
deficient
in
fossil
fuel
resources,
but,
nature
has
endowed
the
state
with
rich
potentialiti'es
for
hydro-
power.
It
is
estimated
that
-the
total
hydro-power
potential
in
Kerala
is
around
1s,000
millioir
.roim
p.t
annum.
With
the
commissioning
of Idukki
Hydro-
Electric
Ploject,
which
is
the
biggest
of its
-kind
constructed
in
Kerala
about
one
third
of
the
State's
hydro-power
potential
has
been harnessed.
,
History
of
t-he
project
dates back
to
the
year
lglg
when
a
small
and modest
scheme
to
harness
Periyar
waters
was
proposed
with
a small
dam
across
leriyar
at Idukki
arid tb lead
the
impounded
warers
thrgugh
a
tunnel
and
pipe
line
to
;
power
house
to
be located
on
the
bantis
of
the
sam6
river
lower
down,
to
utilise
a head
of
236.3
m (775
ft)
for
power
generation.
.
Later,
in
1932,
a
proposal
for
a trans-basin
diver-
sion
of
Periyar
for
-hydro-power
development
was
brought
to
the
notice
-of
the
erstwhile
dovernment
of
Travancore.
This.
scheme,
contemplated
the
cons-
truction
of
two
high
dams,
one
aclross
periyar
at
Idukki
182.9
m (0OO
f, high,
the other
across
C.heruthoni,
a
tributary
of Periyar
152.4 rn
(500
ft)
high
to create
a
common
reservoir
of
88 sq
km
(3a
sd
miles)
waterspread
and to
divert
the waters
thiougli
?
long
tunnel
zt
El.
685.8
m
(2,250
ft)
to
a
power
house
to
be
located
at Arakkulam.at
F,l.
45.7
m
(iSO
ft)
to
generate
power.
In
1937,
two Italian
Engineers,
Mr.
Angelo
Omedeo
and
Mr.
Claudeo
Maicelle
were
comiris-
generators.
Prelimin_ary
works
of
the
project
rvere
then
taken
up
and
simultaneously
it
*as posed
for
aid
assistance
from
friendly
couniries (Figuri
1).
During
the
preconstruction
surveys
and
studies by
the Kerala
State
Electricity
Board
the scope of ttri:
Part
f-Entrod,aetion
293
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fr
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lrr
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o
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294
project
was
enlarged
and
revised. Late
Shri V.
Ranganathan,
who
was
then Chief Engineer
incharge
of
the
project
was
responsible
for visualising the
project
in
its
present
form.
The Government
of
Canada agreed
to aid
the
construction
of
the
project
and appointed the
Canadian
Engineering
firm
of M/s
Surveyer, Nenniger
and Chenevert
fnc.,
as Consultants for
the
project.
During
the
pre-construction
studies made
by the
State
Electricity
Board and
the feasibility
studies
conducted
by
M/s Surveyer, Nenniger
and
Chenevert
Inc.,
the
scope
of the
project
was
revised and
enlarged.
This
resulted
in certain
modifications
to the
original
project
features relating
to reservoir
levels and
choice of
the structural
type. A
revised
Project Report
was
drawn up in 1966 and
this
was
finally
approved
by
the Planning
Commission.
An
aid
agreement
was
signed
between
the
Governments
of Canada
and
India
in 1967. The
consulting
engineers
were
assigned
the
engineering responsibility
in
respect
of
Idukki
Arch Dam,
pressure
shaft and
the
underground
power
house.
Brief
Description
of
the Project
The
qlojec^t
was planned
to
be
completed
in
two
stages.
_
The
lrst
stage
works
are
comple-te.
As
com-
pl.l.{
!t- .c9ns_is1s
of
three
major
dams,^viz.,
l6g.9l
rn
(q5l
fr)-high
Idukki
Arch
Dam,
138.38
'm
(454
ft)
n!g!
Cheruthoni
Concrete
Gravity
Dam,
gg.gl
;,
(328
.
ft)_
higb
Kulamavu
Masbnry-cum-Concrete
C-rqvj{V
_Dam
forming
the
two
billion
ionnes
capacity
Idukki Reservoir,
a water
conductor
system
consist-
ing
of 2027.53
m
(6,653
ft)
power
tunnel
and
a
pressure
shaft_ 993.34
m
(3,259
ft)
long
an under-
ground power
house
with
3
Nos.
i:O
MW
six
jet
pelton-wheels
installed.
The
tail-race
system of tunners
and
channels
er-r.y
the
Idukki
waters
after
power
generation
to
_
Valiar,
a
tributary
of
Thodupuzha
River in
the
Muvattupuzha
basin
(photo
l).
The
220
kV switchyard
which
is
overground
is
connected
to
the
power
house
by
two
cablJ
tunnels
which
accommodate
the
large
oil filled power
cables.
Th.
dpsigned
annual
power
generation
on
comple-
tion of
the first
stage
is
1,864
million
units
of
energy-
1.
Nachar
2.
R.C.C. Conduit
3. Access
tunnel
4.
Switchyard
5. Cable tunnel
6.' Tail-race tunnel
7.
Underground
power
house
Pressure shafts
^
Intermediate
adit
Penstocks
Butterfly valve
cbamber
Expansion
chamber
Surge shaft
Control
gate-head
race
tunnel
PHOTO
I
: Schemotic
profile-Idukki
Hydro-electric
project.
o
o.
9.
10.
11..
12.
13.
14.
Power
tunnel-Intake
torver
(Mornins
glory
type)
Kulamavu
Dam
Open
cut
channel
Idukki
Reservoir
Cheruthoni
Dam
Idukki
Arch
Dam
across
periyar.
15.
16.
17.
18.
19.
20.
295
e
t45
4400
2350
23@
225o-
2aoo
w-
F
lr,
rrl
tt
z
6{
$
2
t50
2too
aos0
aooo
t950
I
900
t850
re
z
,o
rF
;<
t!
J
la,
i
CROwN
SECTTON
FIGURE
2:
Geometricat
definition_Idukki
Arch
Dam.
96
by 5
large radial
crest
gates
12.19
m
x 10.36 m
made
in
the
country.
The
underground power
house
cavern
is
the
largest in India.
The
220 kY
power
trans-
formers
are housed
in
the
power
house
cavern, which
is
rather
unusual.
This
paper
aims
at
describing
the Idukki Arch
Dam
and its features.
Idukki
Dam
Geology
- .Geologically
the
formation
of
Idukki
Gorge
is
believed
to have
taken
place
during
the
formation of
'Wesfern
Ghats.
An
extract from
a
geological
report
reads
as
follows.*
"One
of the most
striking
features
of
this area is
of
the
ridge.
the interflue
and
to
the
formation
of
the
gorge".
The
site
is
situated
in
an
archean
group
of
precam-
brian
formation
of
which gneisses
and
lharnockites
are
predominant.
The
foundation
of
Idukki
Dam have
been
carved out
of
massive,
coarsely
crystalline
charno-
ckite.
The
geological
investigation
ol the
dam site
indicated
excellent
rock
conditions.
There
are no
faults
except
for
the
two
systems
of close
joints
in
the
Foundation
Treatment
The
geological
exploration
of
Idukki
Dam
site was
carried
out
in
an
extensive
way. The
exploration
consisted
ofl making
numerous
-diamond
aint
holes
und-
logging
th9m,
conducting
permeability
tests,
surface
excavation,
determinalion
of
static
and
dynarnic
modulus
.of
elasticity
of
rock
and driving
of
two
exploratory
drift
tunnels
into
the
abutments.
In Idukki Dam
contact
grouting
was
systematically
done
to consolidate
the
foundatioil
and ti, fill
in thL
the charnockite
rock
foundation
below
the dam
is
*A
note on
the
examination
of
periyar
and
cheruthoni
Dam
sites, Idukki
hydro-.Ftectric
proje6t
Uv Stri n.N.F.
Arogva
|*e*y.,.
Superintending
Geololist,
Geologicai
Su.viy""of
India
(September
I
958).
297
A
system
of
foundation
drains
are
provided
in
the
foundation
rock
to
drain
the
rock
and relieve the
uplift
pressure.
The
drainage
system
consists of
two rows
of
76
mm (3
in.)
diameter
holes
spaced at 9 m
(30
ft)
intervals,
supplemented with
local
holes
specifically
drilled
to
if,Grsect
known
fissures.
The
first
row
covers
the
middle
part
of
the
foundation
and
the
second
row
the
downstream
area. The
seepage
through
A.
River
Diversion
The
Idukki
and
Cheruthoni
Dams are
located
very close
to each other
and
are
separated by
a
hill
iknown
as Kuravan
hill.
The
two streams
are
separa-
ted by
a low
saddle.
The
problems of
diversion of
iPeriyar for
the construction
of
Idukki
Dam
and
diversion
of
Cheruthoni
for
the
construction
of
Cheruthoni
Dain
werd
planned
together
and
diversion
Part
ff-Design
During
the
monsoon
of
1967,
there
was heading
up
of
water
downstream
of
the dam
site. To
take the
end of
the auxiliary
tunnel carried
the
water further
downstream
and solved
the
problem
of backing
up
of
water
at the dam site.
The
diversion
tunnels
of
both Idukki
and Cheruthoni were
driven
through
excellent
quality
charnockite and
no
problems
were
encountered
during driving.
Idukki
Dam was
designed
to
overflow only during
the two
initial
rainy
seasons.
By
-the
time
the dam
was
planned
to be
raised
to
sufficient
height
so that
the
flood
flow in subsequent
seasons
could be diverted
over
the
low dividing saddle
in-between
and
passed
over low blocks kept
in
Cheruthoni Dam
for
the
pur-
pose.
To facilitate diversion
of flood over Cheru-
thoni
Dam,
the
level
of
the
low
blocks of
the
dam
was
always
kept
below those of Idukki
during cons-
truction.
During the
construction
of Idukki Dam,
overflow over
Idukki low
blocks happened
only in one
season.
B.
Structural Design
of Dams
Analysis
of
Stress
and
Stability
Factors
for
Dams
The Idukki
Dam as designed
and
constructed
is a
thin
double curvature,
parabolic,
assymmetrical
high
arch
dam.
The
geometry
of the
arch was finalised
by the
Consulting
Engineers,
M/s
Surveyer,
Nenni.ger
and
Chenevert
Inc.,
in
consultation
with
their
Consul-
tant,
the Late Mr. Jean
Gehin,
the
renowned French
arch
dam
expert.
The
assymmetry
of the
valley
offered a
challenge
to which
the designer's
answer
r
works
designed
accordingly.
I
,
The
summer
flow in
Cheruthoni
was
diverted
to
;Periyar
by
constructing
a
masonry
coffer
dam
upstream
of
Cheruthoni
Dam
site
and a diversion
tunnel
driven
across
the
dividing
saddle between
Periyar
and
Cheruthoni.
The combined
flow of
Rivers Periyar
and Cheruthoni
was
then
led through
another
diversion
tunnel
driven
through
the
left
bank
;of
Idukki
Dam with
suitable
stone
masonry
coffer
,dams
on
the
upstream
and
downstream
of
the
ldukki
Dam
site,
to
facilitate
construction
of
the
arch dam.
,During
the
rainy seasons
the
additional
flow
in these
,rivers
were
passed
over
the
low
blocks
left in
the
dams.
:
'
The
Cheruthoni
diversion
tunnel
is
a
309
m
(1,012
f0 long
D-shaped
unlined
tunnel of
size
'4.25
mx4.25
m
(I4
ftxl4
ft)
having
a sectional
area
iof
16.25
m2
(175
sq ft).
The
tunnel
is
driven
across
the
idividing
ridgi
between
Idukki
and Cheruthoni
Rivers.
,The
Idukki
diversion tunnel
is
driven
through
the
left
flank
of
the
dam,
the
minimum
cover
for
the diver-
sion
tunnel
from the
dam
foundation
being
29
m.
The
tunnel
is
a 6.5
m
(21ft
4
in.) diameter
unlined,
horse
shoe
shaped one
having
a
length of
247.8
m
(813
f0
with
a bed slope
of I
in
100.
The upstream
coffer
dam
is
a
gravity
type
stone
masonry structure
curved
upstream
in
plan
to
reduce
the
quantity
of
masonry.
The
crest
of
the
coffer
dam
was
shaped
to
an
approximate
ogee
crgst
to
pass flood over it
smoothly.
i2gg
;
]vls -an
assymmetrical
arch
with
a
wing
wall on the
left
bank
to relieve
a
part
of the water-load on the
arch
dam.
The
wing
walfwas
later
omitted
and
instead
a
mass
concrete
filling placed
integral with
the
dam
was
finally
adopted.'
^ -.Thg
design
of
the
arch dam
was
analysed
by
the
toilowrng
methods
:
(l)
Trial
Load
Method.
(2)
Finite
Element Method.
(3)
Model
Test.
Tnrel
Loen
Mernoo
For
the
trial load
analysis
of
Idukki Arch
Dam,
the grid
chosen
consisted
of
:
(1)
8
arches
at 19.5
m
(65
ft)
centres,
the top
one
Iocated
along
the crest
and the bottom one at
Er.
597.4 m
(1960
ft).
(2)
14
cantilevers
located
at the
intersection of
the
upstream
face of
the
arches with
the foun-
dation
contour
line.
(3)
Crown
cantilever
in
the
planb
of
arch
centres.
With
this
grid
stresses
were
obtained
at
g
l
locations
on
each face
of
the
dam.
The
load
combinations
investigated
in
the.trial load
analysis'
are
given
below
:
(a)
Dead
load
only
:
(b)
Dead
load
:
Maximum
waterJevel
734
m
(2409.5
ft)
Maximum
silt level
-
640
m
(2100.0
ft)
(c)
Dead
load
:
Normal
water-level
732.4
m
(2403.0
ft)
FrNlre
ErruBNr
Merqoo
(a)
Fixed
supports
at
rock
interface
and
at left
bank
intersecrion
with
*i"g
*;lJ
bl";t:
(b)
Flexible
support
modered
by
independent
spring
response.
r
-----r
Maximum
silt
level
Earthquake
640
m
(2100.0
ft)
0.02 g
(d)
Dead
load
:
Normal
water-level
.
732.4
m
tZ+Of
.O
ft)
Maximum
silt
level
640
m
(2100.0
ft)
Earrhquake
0.1
g
Deflections
were
adj_ust-ed
for
radial,
tangential
and
twist
loads.
Arch
cdrculations
included
deformation
299