A dam is considered as the most hazard prone man made structure, amongst all the civil engineering structures. Failure of a single large dam can cause loss of thousands of lives, billions worth of property and priceless environment instantly. So it is the sole responsibility of engineers to ensure safety of these dangerous structures, by preparing continuous safety plans, emergency preparedness plans and sharing the information with other stakeholders.

Many countries, including developed countries, have faced this horrendous experience. From the ancient times, Sri Lanka experienced many episodes on dam failures of which evidence can be found from ancient chronicles. Some historians believe that the end of Sri Lanka’s hydraulic civilization by 12th century would have been due to breach of many reservoirs simultaneously during a heavy flood or any other natural disaster. The unprecedented floods in 1957 December in dry zone specially in NCP, NP,NWP and SP caused breaching of 35 large dams, 53 medium dams and 1500 small dams within a 3-5 days’ time period causing a heavy damage to the irrigation infrastructure. Luckily Sri Lanka was financially and technically capable of handling this massive disaster at that moment and irrigation engineers could restore almost all the dams by 1958 November. Sufficient time was there for issuing pre-warning and hence live lost reported to be very few.

In contrast, a single dam breach, the Kantale dam failure, in April 1986, made a heavy toll and it happened without warning. During that incident 130 lives lost, nearly 600 private and government buildings totally destroyed, another 630 buildings partly damaged, agriculture, roads and other infrastructure washed away. Cost of relief work and rehabilitation of infrastructure was Rs 525 million during that time, which would be approximately nine thousand million rupees at present value. Reliability placed by the society for those responsible for safety of dams shattered, especially of the engineers after this incident, in spite of the fact that some of the critical decisions were made by outsiders were responsible for jeopardizing the safety of Kantale dam.

Can anyone ensure that similar disaster in future will not happen? Whose responsibility is prevention or mitigation of such disaster? Let us get some idea about causes of dam disasters and responsibilities of various sectors in minimizing the risks.

A dam can fail with or without prior warning due to an inherited weakness, a gradually developed weakness or as a result of a natural phenomenon such as heavy storm, land slide or earthquake. Hence it is difficult to design a dam with a zero probability of failure.

How vulnerable those who are living under the shadow of dams is a question frequently asked specially during stormy seasons when the reservoirs are full. It is very common that rumors get spread during bad weather conditions over breach of dams specially located in higher elevation of populated cities such as Anuradhapura or Polonnaruwa, which make people panic and looking for authentic information. One basic issue is that people have not been made aware about the danger prone area in case of a failure in advance.

Whether a dam is earthen, concrete or rockfill, it is susceptible for aging, similar to any living being. It has a certain life span, which can be extended with proper maintenance, upgrading and correct operation of associated structures. If not proper attention is given, the life span will become less than the specified. Very much similar to human beings, dams too should go through proper examinations/ surveillance by specialists, need to provide with periodic healthy treatments and continuous testing to be done to track illnesses.

Statistics shows that highest no of dam breaches had occurred globally due to hydrological failures. Excess incoming water has to be released safely through the spill in properly controlled manner. Water release from a breach of small village reservoir will be sufficient to trigger a large dam failure. This is inevitable with the topographical conditions in our river basins, in which the dams are located in close proximity. Spillways in Large dams were upgraded after 1957 floods, by incorporating radial gates after finding that large dams were overtopped due to sudden inflow to the reservoirs from breached small reservoirs in upstream. However vulnerability for failure does not end with the provision of the gates as these gates need to be maintained and even upgraded to meet the changes in climate and ecology. With the changing hydrological conditions due to climate change variations, it has been observed that the intensity of the rainfall getting higher and within a short time water level in reservoirs too raises very fast. The reduction in forest cover in catchments has escalated this process. Hence the adequacy of the spillways have to be studied by the authorities periodically to ensure safety of dams during floods.

What is the first step the engineer should take to minimize the risk of disaster? It is to take care of it at the very initial phase of planning, designing and construction. Decisions on selection of the dam site, materials, dam type, construction technology, instrumentation, and quality control during the construction have to be carefully made by the engineers.

Next is a carefully planned dam safety program for existing dams. The program should separately address single dams, group of dams in a single river basin and cluster of reservoirs and ancillary structures in trans-basin systems which are common in Sri Lanka. The safety plan should be a collective effort of all the organizations involved in managing the reservoirs and disaster responsive teams in above scenarios. . Not only the dam managing organizations, but also the other organizations making use of the reservoirs, (such as inland fishing, domestic water supply, tourism etc) too have a responsibility for safety of the dams, realizing the vulnerability.

Normally this program shall consist of

• Dam Inspection
• Dam Monitoring
• Reliable and Planned Operation and Maintenance
• Periodical Safety Reviews (in-house and by independent panel)
• Timely Implemented Remedial Works -
• Capacity Development of Inspectors, Operator and Field staff
• Emergency Management Plan

Prior warning also to be handled by engineers operating the dams and mechanisms have to be put in place so that in case there are signs the people in the vulnerable areas could be informed in the shortest possible time. It is also necessary to identify the evacuation centers and paths and people be made aware of those facilities.

The safety guidelines and practices should have a uniformity, irrespective of the ownership of the dam/ reservoir. In Sri Lanka there are many organisations responsible for operation of the dams, still having their isolated plans, starting from farmer organisations to large dam owners such as ID, MASL, CEB, PC etc. It is high time for us to come under a shade of one umbrella and adopt a mutually benefitted dam safety program to serve the society better. Prevention of disaster and mitigation of impacts can be achieved only through such a collective action.

Setting up a regulatory body could be the first step, drawing people from agencies having competence and exposure in dam safety. The organization should then put uniform standards and guidelines in place. The technical analysis of risks associated with a dam cannot be the sole criterion on which such standards and guidelines should base upon. Decisions during emergencies need to be taken with the consideration of economic, environmental, social, and cultural impacts. As such regulatory body should also have disciplines outside engineering.

Engineers should not compromise safety standards and practices to any outside pressure as the cost of consequences especially the loss of lives cannot be compensated in monetary terms. Hence the holistic approach in dam safety is the need of the hour.