Tuesday, December 21, 2010


Keeping Dams Safe
India ranks third in the world after China and USA in terms of number of dams.  The country has about 4711 completed large dams with 390 under construction. These dams play a very important role in the water resources development. In India most dams are constructed and maintained by the State Governments with a few manned by organizations like Bhakra Beas Management Board (BBMB), Damodar Valley Corporation (DVC) and National Hydro Electric Power Corporation (NHPC). Private sector is also poised to own and operate dams.

India follows International Commission on Large Dams (ICOLD) norms, where large dams are those with maximum height of more than 15 metres (from its deepest foundation to the crest).  Those between 10 and 15 metres height also are large dams if they comply with one of the following: 
  • Length of crest not less than 500 metres
  • Reservoir capacity not less than one million cubic metres
  • Maximum flood discharge not less than 2000 cubic metres/second 
  • Has specially difficult foundation problems, or 
  • Is of unusual design.
Being a critical infrastructure facility with wide ramifications, information needs for dam safety have to be available in an understandable format with all concerned. Several of dams are half-a-century old with the Centre planning legislation for Dam safety. The Mullapperiyar dam is more than 100 years old and concern about its safety is not misplaced. A proposed bill on safety of large dams called "the dam safety bill 2010" is slated for introduction during current budget session of parliament. It will "provide for proper surveillance, inspection and maintenance of dams to ensure their safe functioning"

"We have prepared a legislation which aims to establish an institutional system to regularly monitor the safety of large dams," Water Resources Secretary U N Panjiyar said. He said while some states like Bihar have their own dam safety laws, West Bengal and Andhra Pradesh have authorised Parliament to enact a law in this regard.

"As per constitutional provisions, if two or more states authorise Parliament to make a law on a state subject, the Centre can pass a law," he said, adding that "other states can pass a resolution in their legislatures to adopt the Central law. Water is a state subject".

With several private players now involved in operating dams, they would also be covered under the proposed law. Under the new bill, a Dam Safety Cell will be set up at the project level, a Dam Safety Organisation will be constituted at the state level and the Centre will carry out the overall monitoring. The owner could either be government or a private operator with obligation to allow inspections by experts to ascertain safety of the structure.

The Backdrop: In the 20th century, around 200 notable dam failures have occurred in the World, killing about 8000 people. It is notable that dam failures do occur in developed countries too. The biggest catastrophe recorded in this century had occurred in Vaiont in Italy in 1963. The accident killed about 2600 people. Another accident of nearer proportions occurred in India in 1979 about 2000 persons lost their lives when the Machhu II dam gave way. Other dam failures in the country included Ashti in Maharastra (this dam gave way twice-- in 1883 and 1933), Tigra in Madhya Pradesh (1970), Panchat (1961), Kadakwasala (1961), Nanak Sagar (1967) and Chikkahole (1972). The failure of the Malpasset dam in France in 1959 killed 421 persons and the Baffalo Creek dam in USA in 1972 claimed 125 lives.

These failures have caused severe devastation in the valleys downstream both in terms of lives lost and widespread damage to infrastructure and property.  The most common cause is extreme inflow events, exceeding the capacity of the spillway, but structural failures have also occurred at inflows less than the design flood. 50 per cent of dam failures in the World are from inadequate capacity of the spillways.

Why Dams Fail: Dams are artificial barriers designed to be capable of impounding water (wastewater, or any liquid) for the purpose of storage or control of flow. Either one or a combination of the reasons Cited hereunder can be attributed to Dams failure:
  • Overtopping meaning water levels that exceed the capacity of the dam. Due to,
  • Inadequate Spillway Design
  • Debris Blockage of Spillway
  • Settlement of Dam Crest
  • Structural failure of materials used in dam construction.
  • Foundation Defects Movement and/or failure of the foundation supporting the dam due to,
  • Differential Settlement
  • Sliding and Slope Instability
  • High Uplift Pressures
  • Uncontrolled Foundation Seepage
  • Settlement and cracking of concrete or embankment dams.
  • Piping and internal erosion of soil in embankment dams due to,
  • Piping and Seepage
  • Internal Erosion Through Dam Caused by Seepage-"Piping"
  • Seepage and Erosion Along Hydraulic Structures Such as Outlet
  • Conduits or Spillways, or Leakage Through Animal Burrows
  • Cracks in Dam
  • Conduits and Valves
  • Piping of Embankment Material Into Conduit Through Joints or Cracks
  • Inadequate maintenance and upkeep.
  • Deliberate acts of sabotage.
  • Any Other
Global Estimations: On apportioning principal causes of dam failure seen worldwide the findings are quite revealing. See below:

Overtopping: 1/3 of all dam failures globally Overtopping occurs when the level of a reservoir exceeds the capacity or height of the dam. It could be an inadequate or dysfunctional spillway or due to settlement of the dam crest. This is a direct consequence of water levels rising rapidly, without enough reaction time for operatives to take corrective action. Flashfloods, incessant heavy rains, landslide in the reservoir leading to a tsunami, or the upstream of dam collapsing can be causes. The net effect is structural failure, or   land erosion on either side of the dam, dam losing connection with its river slope embankments.

Failure by overtopping or a failed spillway is prevalent in earthen dams as seen in the Banqiao Dam. Landslides falling into storage reservoir Sending a wave of water over the top of the dam may cause dam failure. Concrete dams may survive but result in floods downstream. The Vaiont Dam in Italy in 1963 had 1900 people killed.

Foundation defects: 1/3 of all dam failures Foundation Defects due inadequacy in design might cause differential settlement of the soil underneath leading to failure. Dams built on slopes should avoid issues of instability and take care of landslides. The point  is, compromising foundation's integrity is invitation to failure. An earthquake may cause the movement of a foundation, which could trigger off failure.

Geological problems with the dam foundation Post failure findings in a case found some of the foundation rock, a conglomerate, disintegrated when immersed in water showing rock lost all its strength when saturated. This is exactly what happened as a new dam filled with water for the first time failed. The Malpasset Dam in France, which failed in 1959, is an example of foundation failure making it the first collapse of a modern, thin concrete arch dam.

Foundation failure is the main cause of concrete dam failure. A high uplift pressures and foundation seepage that goes uncontrolled may lead to dam's foundation failure. St. Francis Dam is an example. Piping and seepage: 1/5 of all dam failures Embankment dams - are generally semi-permeable. This means that high and therefore can be compromised when too much water seeps or leaks through the structure. Dam failure can occur when the structure becomes weakened from internal erosion, an effect referred to as piping. This can occur along hydraulic structures, spillways, conduits, or cracks. An animal burrowing in and around earthen dams can even cause such seepage or leakage. (Example of dam failure due to piping and seepage: Kelly Barnes Dam)

Other Reasons: Dams, which are improperly maintained or built with inadequate materials or unsound design, can result in structural weaknesses that lead to catastrophic dam failure. (Dam failure due to improper maintenance and structural weakness: Val di Stava Dam) Faults in construction methods:(Eg inadequate compaction of fill) or use of the wrong type of construction materials (eg silt) may lead to internal erosion or piping failures of embankment dams. An example is the Teton Dam failure in Idaho, USA in 1976.

Failures - Bad Dreams of the Past?
It would be worthwhile to stop and glance at these facilities that we built. Starting from the industrialized economies that have been ahead of all in most events in history. We can take a close look at the U.S.A. As on date, the National Performance of Dams Program (NPDP) stats show that, "at least 85% of the more than 75,000 dams in the US will be in excess of 50 years old by 2020." Further it adds that, "Perhaps more significantly, most of the large dams throughout the US are also approaching old age. Other nations are not far behind even if exposure scale is much lower. The message is loud and clear. Dam safety needs to be addressed on an urgent basis.

Dam Safety: Dam safety is the art of scientifically applying the resources to ensure the operation, maintenance, modification in a safe and techno-economically viable manner while meeting the social and environmental needs. Risks to the general public, property, and the environment being on stake,  dam safety is not a matter that can be compromised. This puts a great responsibility on all interfaces in the hierarchy of dams' managements as well as the governments. Thus it is imperative to put in place collective application of engineering principles, experience, right risk management practices. While doing so the realization that should dawn on each individual and organization finding berth anywhere in this hierarchical chain is that,

Dam is a structure whose safe function is not explicitly determined by its original design and construction.Dams safety and life is dependent on it's "As on date status" which is determined by a host of factors post construction too. This includes punctual and planned actions taken towards identification or prediction of deficiencies and consequences related to failure, documentation of these, sharing information with all stakeholders in order to mitigate to extent possible, unacceptable risks.

Dam Safety Programs 
: The purposes of any dam safety program are to protect life, property, and the environment by ensuring that all dams are designed, constructed, operated, and maintained as safely and as effectively as is reasonably possible. Accomplishing these purposes requires commitments to continually inspect, evaluate, and document the design, construction, operation, maintenance, rehabilitation, and emergency preparedness of each dam and the associated public. It also requires the archiving of documents on the inspections and histories of dams and the training of personnel who inspect, evaluate, operate, and maintain them.

Programs must instill an awareness of dams and the hazards that they may present in the owners, the users, the public, and the local and national decision-makers. At every forum periodic reporting on the progress or conformance to plan should figure alongwith remedies for non-conformities. The only way to realize these objectives is to have the resource in terms of adequate:
  • Manpower proficient in dam design.
  • Equipment & instrumentation for monitoring & maintenance
  • Financial allocation
  • Accountability at all levels of hierarchy within Technical, Bureaucratic and political regimes.
Dam Break Risks: Dam owners world wide are strengthening disaster preparedness for potential dam failures. The need for modernized emergency action plans, revised dam operation &Maintenance strategies etc has gained momentum in light of today's realities like terrorist strikes. Real time evaluation mechanism is the order of the day. To instantly apprise stakeholder of his risks exposure in case of effected modifications, or effect of meteorological changes etc. letting him to assess the consequences of possible dam break in terms of the affected areas, the time available to evacuate people, and the damage, which the flood wave will cause. For this we need possible models that can simulate perceived conditions and instantly come back to the stakeholder with not only the effects but also with plausible alternative solutions (eg: MIKE FLOOD of DHI used for Machhu II study). Flood mapping empowers professionals to devote more time in thought process than mundane calculations, which can be off loaded to the machine.

A wealth of intellectual capital is available in the country and if requisite monitoring in the right way with properly calibrated instrumentation located at appropriate locations is made part of dam safety programs it would be a great service to the experts to use their intellect and experience to be able to make right predictions on dam safety measures to be taken from time to time.

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