Safety of Bhasha Dam may be at high risk
11
11
2008
By B. A. MALIK
Courtesy and Thanks: The Nation
The writer is a chief technical advisor World Bank/UNO
Construction of Bhasha Dam will start in September 2009, according to a press statement of the Minister of Water and Power (published on Oct 14). In an earlier report it was claimed that “Pakistan is going to set another record (after Tarbela Dam) in hydropower engineering by building the world’s highest roller compacted concrete Diamer Bhasha Dam” (April 6). The press report, however, was silent on the fact that the world’s highest adam on the Indus River may also be vulnerable to some of the highest risk factors.
In this regard one may refer to the 485 feet high Tarbela Dam on the same river which was the world’s largest when built in 1976. It was later termed as “perhaps the world’s most problem-stricken major dam” in technical terms (The World Bank and large dams, failure to learn from history. World Bank Report # 4).
Bhasha with a maximum height of 922 feet would be one of the world’s highest dams, as compared to the famous 642 feet high Itaipu Dam in Brazil/Paraguay and the 607 feet high Three Gorges Dam in China. Furthermore, Bhasha site being located in the highly unstable seismic zone in a narrow valley of the upper Indus, could be vulnerable to some extraordinary safety hazards. What follows highlights some of the risks that may not have received full attention in the feasibility study of Bhasha Dam.
Regarding its background name of Bhasha Dam did not appear in the list of sites identified for storage dams at Kalabagh, Tarbela and Mangla etc in the mid 1950s. Nor it figured in the World Bank study of 1967 on Water and Power Resources of West Pakistan. It also did not form part of Wapda Revised Action Programme 1979.
Bhasha probably did not attract attention as it was not a natural site for a large storage reservoir. The wadi above the site was narrow instead of being wide, spreading out like a fan to form the lake. Nor there was any scope for side-channel storages as at Kalabagh, Tarbela and Mangla. It required a higher dam to obtain equivalent storage.
For instance, Bhasha Dam with its height of 982 feet would yield 6.4 million-acre- feet (MAF) live storage as compared to 6.1 MAF at Kalabagh with a height of only 260 feet. Moreover, the site lacked access. Power transmission line to load centres 250 miles away was to run over a very rough mountainous terrain in an active seismic zone.
Bhasha was said to have been included as a storage dam in the list of hydropower sites identified by Montreal Engineering Company (Moneco) of Canada, on cue as a counter weight to Kalabagh Dam. A feasibility study of Bhasha Dam was drawn by Moneco in 1984. It proposed a rock-fill dam 660 feet high with 5.7 MAF live storage and 3360 MW hydropower generation. Kalabagh Dam for which detailed designs and tender documents were ready by 1987 was opposed by NWFP ostensibly on the fear of flooding of Nowshera town and waterlogging of farmland. As the afore said fear technically was found to be untrue it is widely believed that the opposition to Kalabagh Dam was based on the grounds of loss of hydel royalty to NWFP since Kalabagh Dam and the power house happened to fall in Punjab. On the other hand, Bhasha site was located in NWFP rendering the province eligible for hydel royalty. This was borne out from a resolution of the NWFP Cabinet passed on April 20, 2005 wherein the Cabinet resolved as under:
“In the case of Kalabagh project NWFP would not be eligible to get net hydel profit in accordance with the constitutional provisions because the power house(s) would be established at a place falling under the jurisdiction of Punjab.”
A local government minister added that: “…the Cabinet had resolved that Bhasha Dam had more benefit than the Kalabagh Dam project” (May 1, 2005).
Sindh also objected to the construction of the Kalabagh Dam primarily for the fear that it would enable Punjab to divert unauthorised Indus flows into its canals.
In the face of a political log-jam in the efforts to obtain provincial consensus for Kalabagh Dam, Wapda in 2002 retained NEAC CONSULTANTS (a consortium comprising two national and two international firms) with NESPAK as the lead firm, as project consultant to update feasibility study of Bhasha Dam. Name of the dam was changed to Diamer Bhasha to mollify people of Northern Areas who contended that the site was situated in their Diamer district. For the sake of brevity Diamer Bhasha Dam will henceforth be referred to as Bhasha Dam. Here Project Feasibility Report completed in August 2004 recommended Bhasha Dam to be located on the lndus 197 miles upstream of Tarbela. Height of the dam was increased from 660 to 922 feet (40%
and its type changed from rock-fill to roller compact concrete (RCC). Effective storage was increased from 5.4 to 6.7 MAF (28%) and power potential enhanced from 3360 to 4500 MW (34%) yielding about 16,800 GWH annually.
Dams are an instrument of development. Yet every dam small or large carries an inherent risk of failure. In the case of a larger dam it could be catastrophic for life and property down the valley. Large dams are therefore planned and designed with utmost care to preclude as far as possible any risk of a failure. Following features of Bhasha Dam are considered important for addressing safety concerns with due regard to unacceptable increase in costs and period of project implementation:
” Seismic risk to the dam structure and the reservoir rim stability
” Maximum probable flood and spillway discharge capacity
” Under-estimation of costs and project implementation period
The dam will be located in a highly active seismic zone in the Kohistan region which fact is recognised in the Project Feasibility Report as under: “The region (of Bhasha Dam) is seismically very active due to its position near the collisional boundary of the Indian and Asiatic tectonic plates….The proposed dam site is located in the northern mountainous area of the Kohistan region. The Kohistan terrain represents an intra oceanic “Island Arc” which was formed as the result of the collision process of the Indian and Eurasian plates. Kohistan Island Arc is bounded by the Main Karakoram Thrust (MKT) in the north and west (Northern Suture) and by the Main Mantle Thrust (MMT) to the south and east (Southern Suture).”
The high seismic risk was demonstrated by the earthquake of extraordinary intensity of 7.6 on the Richter scale on October 8, 2005 causing widespread devastation in the region. After the earthquake, public and press were apprehensive of the safety of Bhasha Dam. A local English newspaper expressed fear in its editorial Is Bhasha Dam no longer an option? (Nov 13, 2005).
Sources in the Ministry of Water and Power said: “There are chances that it (Bhasha Dam) is declared unfeasible project or may be re-located due to the seismic zoning as the studies are going on for reconsideration about Bhasha Dam’s suitability. The fresh seismic studies are in progress but according to initial assessments, the site of Bhasha Dam is highly dangerous when huge water quantum is to be stored very close to Bisham-Battagram major earthquake fault line,” (The Nation Nov 11, 2005)
Large reservoirs also cause induced seismicity as observed during the filling and impoundment operations at the world’s highest 984 feet Norukh Dam in Kajistan, Effects of induced reservoir seismicity have to be catered for in dam safety concerns.
Bhasha Feasibility Report adopted, on the basis of seismic data then available, peak bedrock acceleration of 0.4g for maximum design earthquake and 0.21g for the design basic earthquake (DBE). In order to adequately address safety concerns of the dam the seismic data emanating from the earthquake of October 2005 is likely to result in a higher than 0.21g DBE Bhasha Dam will form a reservoir some 65 miles long spread over an area of 30,000 acres. Width of the glaciated Indus Valley forming the lake will range from less than 1/2 mile to 1.5 miles.
Mr Kenneth Hewitt a Canadian Glaciologist who studied glaciers of the Northern Areas for over 40 years has observed about the nature of the valley as under: “But you also see extensive areas of scoured, streamlined and pot-holed bed rock between Chilas and Bhasha, recording the water’s fury when it finally removed these impediments. …formed of rock slides or rock avalanches long in the past” (Sep 2005).
The study of landslides in the reservoir rim by US Geological Survey highlights the significance of slope movements induced by the storages. Rockslides related to reservoirs likely to be large and very rapid, generally have been more destructive than slope movements. The Grand Coulee Dam impoundment on the Columbia River in USA has been the site of hundreds of reservoir-induced landslides since its filling in the early 1940s.
A review of Three Gorges Dam on the Yangtze in China by a panel of experts found that the conclusion reached in the Feasibility Study that the reservoir would result in “no significant change in slope stability” is highly questionable considering that wide fluctuations in storage levels are likely to have a destabilising effect on potential slide areas. Erosion has already been noticed along the reservoir rim in some regions.
Bhasha Feasibility Report discussed the risk of landslides in the reservoir. But it did not investigate the effect of earthquakes, including those induced by the reservoir itself, on activating landslides in areas rated as stable. Nor did it evaluate the impact of landslide waves on spillway gates at the time of rapid drawdown in the reservoir immediately prior to the flood season. The report noted potential hazards of the large masses of moraine deposits upstream of Chilas becoming unstable on coming in contact with lake water generating dynamic waves, local blocking of the reservoir and increase in sediment loads. It concludes, however, that “these will not cause unusual problem.” This conclusion is open to question, The report did not seem to investigate effects of earthquakes, including those induced by the reservoir itself and the submergence and pore pressures in the gorge slopes on activating landslides in the rim rated as stable.
The Vajont disaster was a classic example with regard to risks of failure due to landslides in the reservoir rim. Vajont Dam is located in the south-eastern part of the Dolomite Region of the Italian Alps. The 870 feet tall world’s highest thin arch dam was completed in 1960 with storage of barely 0.1 MAF. The dam was built across a deep, narrow gorge in the Vajont Valley. The geological setting of the valley was characterised by massive near-vertical high cliffs.
During construction of the dam concern was expressed about stability of the left flank of the dam. Investigations identified a possible prehistoric slide on the right bank. Whilst there was considerable discussion of the stability of the valley walls it was concluded that deep-seated landslides were extremely unlikely. However during filling of the reservoir a gigantic block of rock detached from one rim slid into the lake at unimaginably high velocities. As a result an 820 feet wave over topped the dam and swept onto the valley below causing large loss of life and property. Remarkably the dam structure remained unbroken by the flood wave.
There are topographical similarities of a narrow valley at the Bhasha and Vajont Dam sites. Whereas geology at Bhasha comprises more competent rock formations than at Vajont, its proximity to earthquake faults could result in the possibility of similar disastrous events. Bhasha spillway with radial gates will have a discharge capacity of 640,000 cusecs. It was based on the record flood of August 1929 with peak discharge of 837,000 cusecs adopted as the Basic Design Flood. The 18th Century historic Biafo Glacier flood discharge estimated at 1,744,000 cusecs is assumed as the Probable Maximum Flood.
The spillway capacity should be examined with regard to the drainage characteristics of the upper Indus catchments in the mountain ranges of the Great Himalayas, Karakoram and the Hindu Kush. The region is largely covered by glaciers and snow. Avalanches, massive rock slides, land slides and snow dams blocking stream flow and lake bursts are not unknown in that region. A major event of this nature occurred in 1841 when the mighty Indus ran dry for 6 months. A battalion of Sikh army crossed it on foot above Attock.
This was caused by an earthquake which triggered a massive rock avalanche from a side of the Nanga Parbat blocking Indus flow for 6 months forming a lake. When the rock and snow dam barrier across the river burst open, it unleashed a devastating flood wave of highest discharge ever recorded at Attock. According to Hewitt incidence of catastrophic rock slides, avalanches or snow dams was not confined to the past but is a continuing albeit unpredictable feature of the terrain.
A dam can be designed to withstand the impact of an earthquake of any estimated magnitude. But a surge caused by major rockslides, avalanches or snow dams could be much higher than design flood resulting in serious risks to dam safety due to limited discharge capacity of the spillway. And Bhasha site topography presents severe limitations on the spillway discharge facilities.
It may warrant freeboard higher than 10 feet though it may not be able to cater for a flood of higher magnitude nor in the event of concurrent occurrence of a seismic tremor. Type of dam structure has been changed from rock-fill to RCC masonry. Earth/rock fill embankments besides being relatively economical are more resilient than masonry dams. They can effectively dampen to a large extent seismic tremors and impact of high floods.
It was because of such technical and economic considerations that dams at Mangla, Tarbela, and those proposed at Kalabagh and the original Bhasha were rock-fill embankments. World’s two highest dams namely 1100 feet Rugan and its older sister 984 feet Nurukh are not masonry structures as would expect but rock-fill embankments. Both are located on the Vakhash River in a seismic region of Tajikstan.
Further more RCC is relatively a new material for dam construction. Nowhere in the world it has been used for construction of dams higher than about 700 ft as at Longtan in China. It may be possible to design a fail proof dam. But no state of the art technology is yet available to predict precisely occurrence much less magnitude neither of a Probable Maximum Flood nor of a Maximum Design Earthquake. To use RCC for construction of 922 ft high Bhasha Dam located in a seismic zone and at the mouth of a hazardous valley terrain would be like sailing in untried waters with risks of catastrophic proportions.
Construction period of Bhasha Dam has been taken at 7 years compared to 10 for the far lower original rock-fill dam. Keeping in view severe constraints of access to site, right of way and affectees’ problems and procedural delays including mobilisation of funds etc implementation schedule of the dam is obviously over optimistic.
According to the Feasibility Report cost of Bhasha Project has been estimated as US$4.6 billion against $6.7 billion of the lower original dam estimated by Moneco in 1984. Without going into a detailed review total cost presented by NEAC would appear to be a gross underestimate. Cost of 40% higher RCC dam is shown to be about the same as of a lower rock-fill embankment. In particular provision of US$572 million for relocating 66 miles of Karakoram Highway, acquisition of right of way over 32,000 acres and relocating some 24,000 persons including other facilities appears to be too low.
If the cost of original Bhasha Dam estimated by Moneco in 1984 was adjusted for inflation over the past 20 years, the updated figure at current rates would exceed $10 billion. Price tag of $6.5 billion in 2004 for the higher Bhasha Dam Project should therefore need to be reassessed.
In the light of foregoing paragraphs it seemed its water and power benefits were upgraded and cost and time frame reduced albeit questionably and disregarding its safety aspects, as if to rank Diamer Bhasha Dam superior to Kalabagh,. The bid apparently did succeed in January 2006 when the govt gave priority to Bhasha Dam over Kalabah to be built first.
A consortium of consultants with Lehmeyer International of Germany as the lead firm has been retained for review of feasibility studies, detailed engineering designs and preparation of contract documents for Bhasha Dam Project. But the lead firm had been black listed by the World Bank after being found involved in cases of corruption and kickbacks while executing the Losotho Highlands Project in 1997.
Lehmeyer International was also a consultant to India’s controversial 4500 mw Baglihar hydropower project on the Chenab in IHK. The Bank notified India of this decision. The Government of India notified J&K State of the Bank’s decision on Nov 24, 2006 that Lehmeyer International was not qualified to be retained as consultant for any project. But the Bank’s decision appears to have been ignored.Lehmeyer helped India’s Indus Waters Commission in preparing its case for the Neutral Expert Prof Raymond Laffite appointed by the Bank in connection with Pakistan’s complaint with regard to Baglihar Project. Lehmeyer also appointed Dr Schwartz. He was said to be a consultant to the Norwegian Construction Company engaged as a contractor for building Baglihar Project.
Prof Laffite as the Neutral Expert “gave a win-win verdict (in favour of India) on February 12, 2007″ (Jun 24, 2007). One can only wonder why Pakistan government chose to retain a consultant blacklisted by the World Bank and known for supporting India in its case against Pakistan’s complaints on Baglihar Project.
Certain concerns about safety of Bhasha Dam have been highlighted so that they are addressed
P
