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| OPINION |
DAM
DISASTER: Kulekhani And West Seti By Dr. A.B.
Thapa In 1970s,
the construction of the Kulekhani High
Dam Project was about to begin. I had
horrible suspicion that the geology of the
Kulekhani dam site area could be problematic. I
published an article about that in the newspaper
“ The Rising Nepal”. Some other local and
foreign newspapers also carried partially the
content of my article shortly thereafter. That
news was very seriously taken up by the
World Bank and the government. Much later on,
I learnt that I was going to be charged
with criticizing the government decision The case
was dropped, when few of my colleagues stepped
in to plead on my behalf. It is
said that extra concrete grouting works
and other measures were taken up to
protect the riverbed and the terraces
just adjacent to the dam to ensure
safety. Despite such limited measures,
few years after the completion of the Kulekhani
dam news came out of the blue
that very wide cracks have already developed
over an wide area adjacent to the
intake structures on the right bank. It
appeared that the Kulekhani dam was on
the verge of collapse. An
Ironic Twist To The Story The
misgivings I had about the poor
geological conditions turned into the gravest
reality. At that time, I was heading the
monitoring section of the Water Resources Ministry. Dr.
John Cooper and Mr. Deepak Gyawali from WECS had visited
the Kulekhani dam site to spend the weekend.
They were shocked to find that the Kulekhani
dam was at the risk of being washed away. I
got the full reporting from them It was
feared that at any time in near future a
very big portion of the right bank
terrace along with the intake structure could
plunge into the reservoir setting in
motion a huge big mass of the
reservoir water to overtop the dam. In a
similar type of Vajont dam incident in
Italy, the loss of life was
significant even though the dam
was left standing after the overtopping
because it was a concrete dam. However,
the whole project was rendered useless
after that incident. In case of the
Kulekhani dam made of earthen core the
whole dam body would have been completely
washed away after the overtopping. I had
to play the lead role on behalf of the ministry in
expediting the civil works to save the Kulekhani
dam Leading experts from the USA,
Australia and Japan were called in
for consultation shortly thereafter. On
their recommendations works such as
the clearing of large volume of
weathered materials, anchor bolting of
huge masses of rocks to
prevent sliding into the reservoir,
provision of underground drainage system were
carried out. Nepal was guided all
along by the advice of the
donor agency. Their timely assistance
helped to preclude the possibility of Nepal
being hit by a big disaster. Dam
Failures Insensitivity
to advise from outsiders could have
terrible consequences. A case in point could be the
Malpasset dam near Frejus in Southern France.
It is reported that the decision makers
were cautioned in time. They were told
that the dam site was not suitable so
it was recommended that the dam be built
elsewhere. However, for reasons of engineering
convenience, the advice was disregarded. The
dam failed on 2nd December, 1959, causing death
of a large number of people. Construction
of the high dam without full study
of the environs led to the catastrophe of
the Vajont Dam in Italy. The Vajont Dam is 261
meters high and the volume of the water contained in
its reservoir is 150 million cubic meters ( the
volume of the West Seti reservoir would
be about 1500 million cubic meters). In September,
1963 the reservoir level reached a height of 180
meters, and an earth movement started along the
slope of Mont Toc. That movement accelerated in October
and caused a landslide which gave rise to
a giant wave that flooded the valley beneath, wiping
out several villages and killing more than
2,000 people. Shoddy
workmanship and poor quality of materials
are often the prime cause of dam
failures. The failure of St. Francis dam in
California has been attributed to faulty
foundations. Design errors were apparently
largely responsible for the collapse of the
Teton dam. In our own region, ‘over-topping’ occurred
with the Machau II dam in India in 1979 and
caused the death of 1,500 people downstream. In
this case, the malfunctioning of equipment
contributed to the failure, as the spillway
gates could not be opened in time. The failure
of spillways to function properly also led
to the near failure of the 140 m high Tarbela dam
in Pakistan in 1975-6. It is reported that
in this case design errors and possible poor
construction materials were also involved. Nepal’s
laissez-faire hydropower development policy
could have adverse effect on dam safety.
It is difficult to visualize how we
can be assured that the private
developers would be sincerely interested
in maintaining the high standard of
workmanship and superior quality of materials
which are fundamental prerequisite for dam
safety that would invariably lead to
higher cost. What is the guarantee that
the private developers would not be tempted to
cut a lot of corners in order to
make hefty profit that could be
disastrous in long run. West
Seti Dam Safety Now talks
are going on about the direct involvement of
the private developer in the implementation of
the mammoth West Seti storage dam project
Everybody is at a great loss
to understand who would be actually
responsible to ensure that this highly
sensitive project would be planned and
implemented fully complying the well
established internationally accepted engineering
practices. The West
Seti dam project appears to be
ridden with very serious technical problems
that concern the safety of its most
important structure, the high dam itself. The
WECS had few years back sent its
opinion to the Water Resources Ministry stating
that the type of the high dam
proposed for the West Seti by the
private developer could be risky. Some
of the evidences put forward by the
developers to justify their selection do not
appear to tally with the information
contained in the recently published
scientific documents. So it was suggested to
constitute a panel of few renowned
international experts recognized to be the
authority on their respective discipline to
seek their opinion. Any further action in
the direction of taking the decision
to award the project to the private
developer should be deferred until the
panel gives its absolutely positive
opinion. It is not known who
had approved the technical design
of the West Seti project on behalf
of the government to vouch for the
correctness. Unfortunately, the developers were
allowed to go ahead to find buyers for
the electricity. Every sensible man will agree
that the West Seti dam should be
completely safe. The incident of the
Kulekhani High Dam should not be allowed
to be once more repeated. At that time
the Kulekhani dam could be saved which
was on the verge of collapse resulting
into one of the biggest man
made disasters in the world In case
of the West Seti reservoir the magnitude
of such disaster would be far greater
because the volume of the West Seti
reservoir might be about 15
times greater than the volume of
the Kulekhani reservoir. Why
West Seti Dam Could Be Unsafe? The West
Seti Project will have a 195-m high concrete face
rockfill dam ( CFRD ). This type of dams are found to be very competitive
in cost but until recent time they were considered
risky for heights above 150 meters. This
type of dam could have also been
considered as one of the alternatives in
selection of the high dam for the Kankai
Project. The French expert called in to
advise on Kankai dam appears to have
dissuaded the German study team from
considering the CFRD as a viable option.
It was considered that it could be
unsafe to build the CFRDs. So finally at
the end an embankment type dam with
an asphaltic concrete face was selected. The CFRD
is very sensitive to settlement and deformation of
the rock-fill supporting the upstream face. These
deformations produce movements of the concrete slab joints
by opening them and if the movements exceed
certain limits then the resulting leakage is
difficult to control. The deformations of CFRD
for dynamic loading are even more difficult to
evaluate. In the Michigan Convention of ASCE in
1985 on CFRDs papers were presented to establish Earthquake
Severity Index (ESI) with relative vertical settlement. In
the ICOLD meeting of 1988 it was suggested that
future research should be focused to correlate ESI
and the relative settlement as function of yield
acceleration. There
is no Precedent Needless
to say that there is a need for
great caution in adopting very high
CFRD. According to J. Barry Cooks, Consultant USA
( Development in High CFRDs, Hydropower &
Dams, Issue Four 1997), this type of dams are of
empirical design and based on precedent
design and experience. Unfortunately, only very
recently relatively high CFRDs have been introduced. The
proposed developer of the West Seti Project has cited
as precedent in their report two CFRDs close to
the West Seti dam in height. It is
claimed that they are already in
good service. They are the Tiensingquiao of China
with a height of 180 meters and Aguamilpa of Mexico
with a height of 185.5 meters. Unfortunately, both
these CFRDs can not be satisfactory example to
justify the selection of CFRD for the
West Seti Project. The Tiensigquiao dam of
China might be still under construction.
According to the original schedule the dam
was expected to be completed towards the
May of 1999. So nobody might be yet
knowing how that dam would be going to perform.
The Aguamilpa reservoir was first filled in
August 1993. Since then two abnormal peak seepage
values have been observed. These events were of
great concern, and several hypothesis were made to explain
this behaviour although none has been satisfactory.
Now underwater inspections are in progress to
try to identify any factor, which could explain
the observed behaviour. There are
not any other examples in the world of CFRDs in
service with heights close to 195 meters. It is
a fact that very high CFRDs are yet
to be tested in practice. So a great
deal of caution is required to adopt this
type of dam. Let us not take the risk
of unnecessarily endangering the life and
property of innumerable people by
recklessly deciding to implement the West Seti
Project. In
Conclusion Nepal’s
laissez-faire hydropower development policy
could have adverse effect on dam safety.
Until now, our government’s performance in
handling private developers of hydropower projects
has been extremely shocking. Government
endorsed whatever the private developers proposed.
There is nobody from the government side
to check the works of the private
developers at the site. As a result, in
case of the Bhotekosi Project the
concerned Department and the Ministry came to
know that the installed capacity of that
hydropower project had been raised from
35 MW to 45 MW completely defying the power
purchase agreement only after the completion of the
construction works. Government learnt about it
only after a claimed was lodged by the
private developer with the government to compel
the NEA to buy extra power to be
generated entirely during the monsoon season which
is going to be totally wasted. It is
difficult to visualize how we can be
assured that the private developers would
be sincerely interested in maintaining
the high standard of workmanship and
superior quality of materials which are
fundamental prerequisite for dam safety that
would invariably lead to higher cost.
What is the guarantee that the private
developers would not be tempted to cut a
lot of corners in order to make
hefty profit that could be disastrous in
long run. Institutions like the Electricity
Department, Ministry of Water Resources and National
Planning Commission should take full responsibility
to guarantee that the storage dam projects
have been planned, constructed and operated in
accordance with internationally accepted norms
and practices. (Dr. Thapa
writes on water resources) |
Send your feedback to the
editor: spot@mail.com.np |
