Diamer Bhasha Dam : An overall view

There have been few concerns about Diamer Bhasha Dam. Foremost is that Roller Compacted Concrete (RCC) Dam is a rigid structure and has no flexibility against earthquakes. Bhasha Diamer Dam has been under review since the early nineteen eighties by various panels of international consultants and experts including the World Bank’s experts. In eighties Roller Compacted Concrete Dams (RCCD) were in early stages of development. In fact Pakistan at Tarbela was the pioneer in using RCC on a mass scale on replacement of damaged right bank hill and building right bank tunnel intel portals. Tarbela created a record in which a large quantity of RCC material was placed in shortest possible time. Quantities equivalent in volume of Warsak dam were placed in 43 days observing all technical requirements of Roller Compacted Concrete and has performed well over 5 decades since its placement. This innovative action at Tarbela was a technological breakthrough and RCC dams construction took precedent all over the world where geotechnical, hydrological and seismological uncertainties dominated the design of large dams

Another criticism was cost of RCC structure would be exorbitant as compared to other types of dams. With such technological advancement and experience available, the international consultants and panel of experts were compelled to review the type of dam most suitable at Diamer Bhasha site along with final selection of dam alignment. Based on such reviews and keeping in view the geotechnical, hydrological and seismological aspects prevailing at Diamer Bhasha site and in depth cost analysis of various type of dams it was finally agreed by all experts that RCC dam would be most suitable, cost effective and with the breakthrough in the construction technology it can be built faster than other types of dams

Third concern was construction period of RCC structure would be more than other type of dams. It can well be argued that proposing Earth Core Rock Fill Dam on Indus River one has to keep in mind the problems we faced at Tarbela where both foundation and blended core material resulted in severe damages to the core of auxiliary dam and foundation of main dam due to piping of material creating major holes in the dam core and over 350 sink holes were formed in the upstream impervious blanket. Tarbela reservoir was emptied and large cost was incurred in repairing the sink holes. A vertical shaft was driven in the core of the dam for repairs. A step never attempted in the history of dams anywhere in the world. It took more than four years before the sink holes in the u/s blanket under 400 feet of water depth (again an unprecedented process) were fully treated by dumping specially designed fitter material through HydroKLAPP 200 tones bottom dump barges using sophisticated sonar and ocean research equipment (ORE) for under water location of sink holes. Motorola communication equipment was used for navigation, location and positioning of barges over the sink holes. The cost of such repairs runs into millions of dollars. Had the technology that is available now if available at the time of construction of Tarbela dam, we would have opted for RCC dam at Tarbela instead of constructing ECR type of dam using blended core material. The fitter designed which was practiced over the last 100 years failed to effectively stop internal erosion of core material responsible for sink hole in the core of auxiliary dam. Again Tarbela taught the dam engineers all over the world to be careful in the design of filters. A new set of filter design criteria were adapted which are now being used by Dam builders all over the world

Concerns have been raised that seismic parameters adopted for the design of DBD need to be reviewed. In the light of advancement in technology, economy in cost and rapid method of construction the RCC type dam would be preferable than any other type. Proposing ECR type of dam, the safety and stability issues with extremely high associated hazards cannot be proposed at Diamer Bhasha dam site due to non availability of core material, inherent shortcomings in creating seepage barrier with blended core material. Tarbela experience should be enough to avoid blended core material, with 50 meter deep alluvium over the bedrock in the foundation, the estimated settlement of 7.5m cannot be handled by core of ECRD without very high risks, liquefaction risk of the river alluvium in case of earthquake, possibility of cracks in non-plastic erodible core due to earthquake and doubtful integrity of concrete cutoff wall through 50m river over burden containing very large boulders and skip graded alluvium deposits. One must keep in mind that cutoff walls and grout curtains in type of foundation that we have at Diamer Bhasha dam site would be impossible to provide an efficient barrier to foundation seepage. An open space ration of 0.1% would have only 29% cutoff efficiency and this would allow 71% of flow under large head and steep gradient. These conditions would tantamount to foundation failure and also catastrophic damage by overtopping through glacial lake outburst floods (GLOFS).

About site of dam it may be noted that Montreal Engineers Company Ltd. during its ranking and feasibility studies in 1984 identified Bhasha dam site as feasible site for large dam and proposed two types of dams , Earth Core Rock fill Dam (ECRD)  and Concrete faced Rock fill Dam (CFRD).

During their preliminary assessment, they preferred a zoned earth-rock fill dam with  emphasis to select a better method for under seepage control.

In September 1988, Wapda appointed a panel of experts to review the feasibility report of Montreal Engineering Company Ltd. The panel consisted of Professor Fiedrich-Karl EWERT, Professor Francesco ILICETO, Mr Syed S. KIRMANI, Mr Ernest L. PEMBERTON ,Mr Nelson L.de S. PINTO, Professor Walter WITTKE, Mr Alfonso POSADA (Chairman). The panel raised serious concerns on type of dam and its stability including over topping potentials.

Based on above concerns, Wapda appointed another joint venture of consultants to review and upgrade the Montreal’s feasibility report in the light of POE’s comments and concerns. The new joint venture NEAC consultants (NESPAK, ACE, Bennie Black, Veatch, UK, MWH, USA) under took detailed review of consultant reports and POE’s comments.

The consultant considered four types of dams for their suitability assessment, Earth Core Rock Fill Dam (ECRD), Concrete Faced Rock Fill Dam (CFRD),Roller Compacted Concrete Dam (RCCD), Arch Gravity Concrete Dam (AGCD).

From above the four types of dams ECRD is not considered due to non-availability of suitable core material and serious other safety issues. NEAC consultant had proposed AGCD, which POE (2003) did not endorse and instead suggested a RCC gravity dam along a slightly curved axis. The panel also included CFRD for comparison. Wapda appointed another international panel of experts in March 2003 to review the recommendation of NEAC. This panel consisted of Barry Cooke U.S.A ,Brian Forbes Brisbane Australia, Amjad Agha Pakistan, Nelson L.de S.Pinto Brazil.

The POE in first assignment endorsed the Bhasha dam site for major dam project and asked the consultants (NEAC) to consider RCC gravity dam moderately curved along with CFRD alternative where auxiliary structures are separate from the rock fill embankment. The panel allowed NEAC consultant 4 months to develop optimized layout to a more complete degree of definition of structures, schedules and costs for RCC dam and CFRD. After this study is completed, the POE will make final decision on dam type and layout .

NEAC consultants completed the feasibility report in early June 2004. Wapda appointed the POE for review of the feasibility report consisting of BERNARD TARDIEU-FRANCE,BRIAN FORBES-AUSTRALIA ,AMJAD AGHA-PAKISTAN, OIVIND NICOLAYSEN-NORWAY. POE concluded that RCC dam as presented in the feasibility report is technically feasible 

Wapda next appointed DB (Diamer Bhasha) consultants in 2005 a joint venture of Lahmeyer International Company, NDC, Barqaab, PES in association with ANEC Canada. During their tenure from 2005-2008, the consultants reviewed the feasibility, detailed engineering design/tender documents.

Wapda appointed another panel of experts consisting of following international experts, WALTER WITTKE – GERMANY, BRIAN FORBES – BRISBANE- AUSTRALIA, FOBIO VILLEGAS – MEDELLIN – COLOMBIA, ABDUL SHAKOOR – KENT STATE UNIVERSITY- KENT.

POE during their final meeting in May 2006 considered RCC type dam viable and implicitly endorsed it. Based on some observations of the POE, BD consultants then proceeded with refinement of the design addressing POEs observations.

Selection of type of dam at Bhasha site went under vigorous reviews. Four types of dams were considered at various stages of investigations and studies by different joint ventures consultants, which were independently reviewed by international panels of experts. Based on investigation and studies and as additional facts brought into light consensus on types of dams narrowed down, and both earth-rock fill type and rock fill with concrete facing were dropped.

In the final stages Roller Compacted Concrete Dam (RCC) and Arch Gravity Concrete Dam (AGCD) were considered for further review. The POE in its review pointed out that with advance technology available in design and construction of RCC dam they are superior to (AGCD) type dam having no layer joints, fully monolithic ensuring water tightness and resistance to cracking and are lower in cost and faster to construct.

The projects consultants namely NAEC consultant and DB consultant preferred RCC type dam, which was further supported by two international panels of experts appointed by Wapda to review the consultants’ recommendations. The two international panels of experts were, Bernard Tardieu, France, Brian Forbes, Australia, Amjad Afgha, Pakistan, Oivind Nicolaysen, Norway. Another panel of experts included Walter Aittke, Germany, Brian Forbes, Australia, Fobio villegas, Colombia and Abdul Shakoor, Kent State university, Kent.

Both international panels of experts recommended RCC dam to be built at Bhasha dam site and design of RCC dam was finalized by B.D consultant.

It needs to be appreciated that appointment of various joint ventures of consultant comprising foreign and local technical experts and four different panels of international experts over a span of decades cost Wapda millions of dollars before final type of dam, its alignment location and design were finalized. At least in my life time with over a half century of working on large dams, I have not come across such a through and exhaustic study as I witnessed on DB dam.

About Seismic Parameters adopted for the design of Diamer Bhasha Dam, it may be understood that we may look into the seismic parameters adopted in the design of DBD. Before I touch upon the parameters I would like to mention my own experience on seismic design of large dams. Since July 1962 to date my association with large dams construction in Pakistan, Malaysia, Indonesia, Sri Lanka and UK, I have seen seismicity as an emerging science developing from is infancy to quite advance stages but still its has not achieved the maturity to blindly rely on it.

The advancement in seismic monitoring instrumentation has help out tremendously to study local as well regional tectonic settings of the project area. Some advance theories and equations have been developed to assist the dam engineers in adapting safe parameters but still they have to be reviewed during construction and post construction operational stage of large dams. There are a lot emphasis to establish micro-seismic network around large dams located particular in the seismic active regions. In case of DBD site, microseismic network has been already established and data being collected and analyzed. Such data is extremely important in giving real time data of the region in which dam is located.

It is critical to monitor around the clock the seismic activities during first filling and draw down and see if there is any seismic activity related to reservoir loading and unloading i.e. Reservoir Triggered Seismicity (RTS). Such monitoring of seismic instrumentation along with other structural monitoring instruments would continue during life span of the dams. Any additional seismic information which becomes available during post–construction period of a large dam with high hazard potentials would necessitate the review of seismic design and if required the structures would be strengthened accordingly. Tarbela dam structures were strengthened three times during the post-operational period as more seismic information became available along with revised international design standards and safety parameters.

In case of Diamer Bhasha dam project, Wapda has already referred the original seismic design to M/s Tractebel Engineering GMBH of Germany for their review of seismic hazard study in accordance with ICOLD Bulletin 148 published in 2016. M/s Tractebel Eng. reviewed the seismic design. Wapda had certain technical observation which needed further clarification. M/s Tractebel has taken Wapda’s observation into consideration and submitted the final reply. They updated their previous report of 2010. 

The consultants latest report is an update of the previous report of 2010, considering, study updated based on revised guidelines on the selection of seismic parameters given in recent ICOLD Bulletin 148, published in 2016, the updated earthquake database, including the new earthquake data after 2009 and updated attenuation relationships used in the previous report by the same authors in 2014, as a part of NGA West2 project.

For the new earthquake data, two sources were adopted, the tele-seismic catalogue compiled by Khan et al (2018) for Pakistan and the local network data provided by WAPDA, covering earthquake records between 2007 and 2019.

The review concluded that the best local seismicity data is that supplied by the Bhasha network within the area inside of the array, which has a 50 km radius around the project site. The density of epicenters in this map is clearly far greater indicating the statistical analyses based on this data set is more accurate and more robust than that of other earthquake data relating to the Diamer Bhasha dam site.

For constructing a dam that resists possible strong shaking by large earthquakes it is important to examine known major faults in the region. The first important point regarding major faults is that no geologist who has mapped the area at and near Diamer Bhasha dam has found an active fault. This significant observation precludes large and great earthquakes near the Bhasha dam because these can only occur on faults that reach the surface of the Earth, can be seen, and have been mapped.

The map of the surface rupture of the 2005 M7.6 earthquake clearly shows the location of this earthquake and the Kohistan seismic zone (Kanea et al., 2008) in relation to the Diamer Bhasha dam site. The dam site at is located 75 km from the NWerly end of the 2005 M7.6 rupture. The observed intensity, I, generated by this earthquake in the area of Diamer Bhasha was I = VI, which corresponds to an acceleration of 0.1 g, on average (e. g. USGS website).

The conclusions regarding the tectonic setting, and specifically the relationship of the project site w.r.t. the Himalayan mega thrust are the following. The Diamer Bhasha project site is not located in the Himalayan mega thrust. Instead it is located near the center of an area that shows a remarkable absence of great faults and exhibits low seismicity rates. The absence of mapped active faults in the vicinity of the dam site, as determined by project geologists, further supports the fact that no large or great earthquake can be expected near the dam site. The nearest possible large earthquake is one that extends the 2005 M7.6 rupture into the Kohistan seismic zone, at a distance of 75 km from the dam site. Due to this large distance, the ground motion levels caused by even an M=8.0 magnitude earthquake in the Kohistan seismic zone would be significantly less than the abovementioned PGA values.

The ICOLD Bulletin 148 (2016) suggests two different earthquake levels for design of large dams, namely Operating Basis Earthquake (OBE) and Safety Evaluation Earthquake (SEE, formerly referred to as maximum design earthquake, MDE). ICOLD suggests to consider, a ground motion level with a return period of 145 years for OBE, a ground motion level with a return period of 10,000 years for SEE (which should also be evaluated by a deterministic approach).

In the light of these results, the PGA for OBE and SEE are suggested as 0.16 g and 0.48 g respectively based on the probabilistic results.

This rupture would be located at a distance of 75 km from the dam site.

The largest earthquake ever triggered by impounding a reservoir occurred in 1967 near the Koyna dam. Its magnitude has been estimated as in the range of 6.3 ≤ M ≤ 6.6. The distance from the dam was 15 km with an estimated depth of 15 km. In the present seismic hazard analysis we modelled the worst case of an earthquake very close to the dam as having M6.5, distance = 0 km, and depth =12 km. This means that our model calculation would generate a much larger PGA at the Bhasha dam than any known earthquake triggered by reservoir impounding. Therefore, the present seismic hazard analysis covers the possibility of a triggered earthquake.

The revised study concludes that the seismic hazard assessment for Diamer Bhasha dam location was performed by using both deterministic and probabilistic methods. A previous seismic hazard study of 2010 was updated, using new earthquake data after 2010, and the latest attenuation relationships. The new earthquake data included a recently published tele-seismic catalogue and also earthquake hypocenters from a local seismic network for the years 2007 to 2016 provided by WAPDA.

•          PGA = 0.16 g (for a return period of 145 years) is suggested for Operating Basis Earthquake (OBE).

•          PGA = 0.48 g (for a return period of 10,000 years) is suggested for Safety Evaluation Earthquake (SEE), considering that it is more critical than the PGA obtained by deterministic analysis.

The PGA values obtained with the updated earthquake data, new seismic sources and updated attenuation relationships are similar to the results in the previous report by Wyss and Trendafilovski dated 2010.

Questions have been raised on the height of the DBD as unprecedented. It should be noticed that to go down to competent rock levels for placing the foundation, we have to start placing dam material 50 meters below river bed level. Therefore the exposed structure above the river bed would be (272-50M) 222 meters only. Designing of a tall dam of 272 meters with modern technological advancement taking into consideration all safety aspects is not an issue. The designers for high hazard potential structures consider all types of possible risks and the margin of safety incorporated into the structures bear a direct relationship to the magnitude of potential losses and also takes into account the range of uncertainly involved. These facts have been acknowledged and adequate factors of safety have been incorporated. We also need to appreciate that Pakistan’s water security has become a national security issue. Every drop of water has to be conserved and used most judiciously. As per decision of the Supreme Court of Pakistan and National Water Policy, Pakistan has to build 10 MAF of storages on fast track. The 6.4 MAF of live storage at Diamer Bhasha Dam is part of the 10 MAF required for additional storage. If we compare the storage potential at Diamer Bhasha Dam site it is much less than the Tarbela dam original storage. Tarbela dam with a height of 450 ft i.e. 137 meters, above bed levels stored 9.69 MAF whereas Diamer Bhasha Dam with a height of 222 meters above river bed stores only 6.4 MAF

In other words Tarbela stored 70,073 acre feet/meter against this Diamer Bhasha Dam storage per meter is only 28,829 acre feet. The reason being Tarbela had wide valley with mild bed slope whereas DBD valley is narrow with steep bed slope. Therefore, any dam built upstream of Tarbela would be a tall dam. On other hand if we look into potential benefits of Diamer Bhasha Dam they are tremendous in terms of storage and cheap renewable energy. With judicious use of stored water at Diamer Bhasha Dam, and adapting to high value crops IMAF would give a return of US $ 1.5 TO 2.0 billion to the agriculture GDP. Similarly DBD can enhance energy generation of Tarbela, Ghazi Barotha, Jinnah HP and Chasma HP to tune of 2520 GWH and once other hydro projects on main Indus downstream of Diamer Bhasha Dam are completed at Dasu, Pattan and Thakot would give additional energy of 7500 GWH. Therefore on D/S of Diamer Bhasha Dam total energy enhancement would be to the tune of 10,020 GWH which would definitely bring about major change in the existing energy mix and would help lower the tariff. We should be aware of the facts that energy price shocks have high risks for economic development.

In 1980 after Mangla and Tarbela the energy mix was 72% hydro and 28% thermal and over 3000 industries were established and the number kept on increasing with the result that GDP growth of Pakistan was progressing handsomely.

It is also pointed out that unprecedential height has been adopted at DBD with a gain of only 1 MAF of storage. It is absolutely not true. The designer looked into aggregate storage potential within the safe limits of design. I would just like to mention here that every acre foot of storage has tremendous benefits in terms of agriculture GDP and production of cheap renewable energy. 1MAF of storage if used in production of high value crops would generate US $ 1 billion and 6.4 MAF of storage at Bhasha could add to agriculture GDP to the tune of US $ 6.4 billion.

We should also be aware being one of the most arid countries of the regional with extreme distorted availability of water during one complete hydrological cycle storages become a vital question of National water security, food security, energy security and provides impetus to national development. Presently we get 80% of water during Kharif season against requirement of 40% and get 20% during Rabi season against a requirement of 60%. With such distortion storages become inevitable for National water security, food security, energy security and economic development. In an arid country like Pakistan, the required storage capacity is 40% of the total water availability –our storage capacity is only 9% and that is also depleting fast. We should also appreciate that storage sites in Pakistan are extremely limited. Therefore whatever storage sites are available, we should try to utilize the full potential of positive storage within the technical limitations. Reducing height of DBD would tantamount to under exploitation of storage potential inspite of technical viability. Certain friend suggests that we should build DBD to lesser height and in case its performance is satisfactory we should raised it in future. My answer to it is that with sophisticated safety monitoring instrumentations which are installed on large dams, the structures are vigorously monitored around the clock for their safe performance. In case of any alarms the most effective tool available with the project operator is to lower the reservoir level through spillways, and low level outlets. DBD has these outlets built into the body of the dam. My second reason against the argument on future raising is the cost component. I quote the example of Mangla raising. I was responsible for carrying out stability analysis to study the impact of raising Mangla dam in the design office of M/s Bennie and Partners in London. This was my exclusive assignment in 1965. I completed Mangla dam raising project in mid 1966 in all respects which included stability analysis, detailed design and preparation of raised Mangla dam drawings. We were hoping the Mangla raised project would be completed when contractors were fully mobilized at nominal additional cost. However this was not done and the project was delayed for decades. We all know the astronomical cost that we have to bear to execute Mangla raising project. It is absolutely not advisable to attempt to raise mega projects at later stages. The cost associated with such options render the project cost wise unfeasible.

Vulnerability of access road to frequent landslides and blockage would delay the project with cost escalation is again a reasonable concern. It is not only the Diamer Bhasha dam issue that such landslides along KKH access could disrupt, the vital communication link to the supply chain. There are number of hydropower and storage projects upstream and downstream of BD site. Presently identified projects which are included in the list of Wapda’s Master plan are Bunji HPP of 7100 MW upstream of DBD and Dasu HPP of 4320 MW (under construction), Pattan HPP of 2400 MW, Tahkot I,ii,iii of 4866 MW on the downstream of DBD site located on main Indus stem along KKH would also get affected. Realizing the grave issue of disruption to communication to these vitally important projects which Wapda wants to undertake on priority basis, the Chairman Wapda took up the issue with the National Highway Authority (NHA). The traffic of KKH the only all weather road to these projects shall also be highly congested due transportation of huge quantity of construction materials and M&E equipments. Wapda proposed an alternate all weather route to DBD through Naran valley via Babusar pass through a tunnel to increase its current utility of 6 months to round the year. Chairman Wapda is keeping the Prime Minister’s office, Registrar Supreme Court of Pakistan, relevant Ministries informed and hopes the decision would be taken soon by the Prime Minister.

The writer is former Member Water WAPDA, EX-Member President Technical Committee, Former Chair Technical Committee – GWP South Asia, Former Chair Regional Council GWP South Asia.

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