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| Fig. 1. Distribution of Ages of Large Dams in Canada and The United States (source: The 1998 ICOLD Registry of Large Dams) |
| As dams age, owners face major decisions about the allocation of finite financial and human resources to ensure continued safe operation. With the introduction of the National Dam Safety Program in the United States, a process of reporting dam failures and dam safety incidents was made an integral part of dam safety practice. The results of this monitoring program have shown that, since 1993, 421 dam failures of varying degrees of severity have occurred (Hydro Review 1999) which translates to an overall probability of failure in the order of 6 x 10-4 failures per dam year (Figure 2). |
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| Fig. 2. Occurrence of Dam Failures and Dam Incidents in the United States |
As shown in Table 1, numerous other researchers throughout the world have reported similar dam failure rates with the overall average equivalent to about one dam failure every 2500 years.
Table 1. Frequency of Occurrence of Dam Failures
Reported in the Literature
On the basis of these data, it is apparent that dams can
be expected to continue to fail unless actions are taken to systematically
assess and maintain the structures.
To protect the public, and the asset itself, the concept of a structured
dam safety program is becoming widely accepted worldwide. This involves
a regular comprehensive review of the performance and integrity of a dam
at intervals that are defined by the hazard the structure presents to
the public. In a general sense, a dam safety assessment involves the following
steps:
- Collect and review all available data
- Undertake a comprehensive site inspection
- Assess the consequences of a dam failure in terms of loss of life,
economic losses and environmental losses
- Classify the dam according to the hazard it presents
- Select the design parameters (i.e., the magnitude of the flood and
earthquake the dam must resist) according to the dam classification
- Undertake hydrotechnical analyses to determine the capability of the
flow control structures top to pass the design flood
- Assess the stability of the structures under the design loading conditions
- Document the results of the assessment and recommend the measures
needed to upgrade the dam so as to satisfy dam safety requirements
- Prepare a plan to implement the recommended measures
- Implement the plan
- Document the results of the dam safety improvements
- Repeat from step 1 at intervals established on the basis of the dam classification.
 Acres Dam Safety Experience in Ontario, 1998 to Present (click image to open a PDF) |
Acres is a leader in the field of dam safety. We participated in the development of Canada’s national Dam Safety Guidelines and, within the last few years in Ontario alone, have performed over 250 dam safety assessments for various clients (Figure 3). We also have extensive international experience in dam rehabilitation and assessment projects. For example, Acres recently assisted the major utilities in El Salvador and Costa Rica in the preparation of national dam safety standards and regulations, and to train local staff in the performance of dam safety assessments. Acres was also recently awarded assignments to train Chinese engineers and to work with Khuzestan Water and Power Authority in Iran to develop a comprehensive set of dam safety standards and procedures. |
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Rick Donnelly, Division Manager Acres International, Niagara Falls, ON 905-374-5200 rdonnelly@acres.com |
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