1 Former Chairman, CWPC & Ex-Officio Secretary, Govt. of India; Ex-Senior Consultant World Bank; Ex-Vice President, International Commission on Large Dams (ICOLD).
2 Secretary General Honoraire, ICID; Former Engineer-in-Chief and Head of Irrigation Department, U.P.; Former Projects Coordinator, Govt. of Mauritius
Failures and accidents of several large and even small dams in the world have caused great tragedies. Lessons from the failures have led the dam engineers to focus special attention and study the modes and causes of failures ICOLD have published case histories. After intensive study of the accidents and incidents of failures, guidelines for dam safety evaluation have also been formulated. However, relative risk and hazard factors have to be determined and apportioned to plan the rehabilitation.
Some years ago in the summary of progress in Iraq war, U.S. politician Donald Rumsfeld developed the concept of ‘Known-Knowns’, ‘Known-Unknowns’ and ‘Unknown-Unknowns’ which was not appreciated at that time in USA but the concept has been found to be helpful and appropriate to be used by dam safety review engineers for apportioning the risk in dam safety evaluation. It also can lead to constitute a properly qualified and capable Dam Safety Review Panels (DSRP) to identify the degree of risk and recommend economical and site-specific rehabilitation measures. India has also been giving serious attention to Dam Safety Evaluation particularly after World Bank initiated and funded a Dam Safety project in 1991.
The causes of distress and defining the risks to plan remedial measures for ensuring risk free performance of the dam which can be classified under three categories of Rumsfeld's concept. These have been briefly outlined with appropriate examples and case histories to illustrate the principle with special emphasis on the category ‘Unknown-Unknowns’.
