The Four Pillars of Dam Safety
Dams have been around for millennia and are common throughout the world. Originally, earth dams consisted of little more than earthen embankments while concrete dams tended to be mortar and rock structures. These structures evolved into reinforced concrete, timber and other core type earth dams in the nineteenth century. In the past half century, dams have been developed as part of the hydroelectricity and mining industries, using improved technology to become much larger and more sophisticated. With increased sophistication in construction came a parallel requirement for sophistication in engineering and management.
While the line is often blurred, professionals working with dams and related hydraulic impounding structures make a distinction between dam safety and dam engineering; the latter forming a subset of the former. At Mitchelmore Engineering Company (Meco), we resist the duality of the two definitions, referring to the profession as dam safety engineering and concentrating on the four pillars of dam safety; owner commitment, regular dam safety reviews, effective operations, maintenance & surveillance (OM&S) practices and effective emergency preparedness (see Figure 1).
The first pillar, owner commitment, involves ensuring the dam is designed to current acceptable practice, is classified according to the consequences of failure, adequate annual resource allocations for continued safe performance, and that staff is adequately trained. Sometimes overlooked is the importance of defining tasks related particularly to dam safety to an individual operator or manager. Specific task assignments have a two-fold positive impact; they imply ownership to the staff member and they underline the importance attached to the task by management. In effect, the more committed the owner is to dam safety, the more committed their staff.
The second pillar, regular dam safety reviews, involves six components, a site visit, review of classification, review of design & construction, review of Operations, maintenance & Surveillance (OM&S) practices, review of emergency preparedness, and a review of previous reports and the owners implementation of the recommendations. Depending of the classification of the structure, an independent reviews scope of work can vary from design checks on critical sections to full redesign. Generally, some place in the middle is adequate unless deficiencies are noted requiring further investigation. The Canadian Dam Association (CDA) publishes guidelines outlining the recommended content of a review but, in practice, most owners can influence the content of a review to their unique circumstances. To be most effective, reviews should be performed by trained professionals from outside your organization. This independence implies objectivity and provides better assurance of impartial, objective opinions and analysis. Reviews are suggested at five to ten year intervals, depending on the classification of the dam.
The third pillar, effective OM&S practices include operating rules that do not compromise safety, maintenance schedules that are followed, multi-level surveillance and monitoring with regular review of surveillance reports, and effective communication of objectives. Dams, like any structure, can fail if allowed to deteriorate despite good initial design. Likewise, regular surveillance can detect a design deficiency that may not have been apparent during design but that can be remedied prior to any catastrophic event. Effective OM&S practice is closely related with owner commitment in terms of resource allocation and training.
The fourth, and not least or last, pillar, effective emergency preparedness planning involves having a formal written plan to implement in the event of an emergency situation at the dam. The plan needs to include contact information for responsible individuals, resource procurement procedures and identification of the population at risk of flooding. To be effective, a plan needs to be regularly tested and updated, current to operators, management and emergency response agencies. While nobody thinks their dam will fail, experience has shown that emergency plans save lives during dam failures.
In Atlantic Canada, dams are largely regulated by the respective department of Environment within each province. None of the provinces have specific legislation regarding dam safety, and only Alberta, British Columbia and Quebec have legislation in Canada. Ontario is set to introduce similar legislation next year. The current de facto guideline in non-legislated provinces is the Dam Safety Guidelines of the Canadian Dam Association (CDA). These guidelines espouse the four pillars, although it is not always obvious.
The Nova Scotia Department of Environment and Labour (DOEL) estimates there are between 400 and 600 dams in Nova Scotia. By international standards, many dams in Nova Scotia are considered small to intermediate in size. Your typical conventional dam is an earth fill embankment, or maybe a concrete or timber structure, although smaller dams sometimes have less conventional designs. All should be equipped with discharge facilities for operational flows and flood discharge. Dams in Nova Scotia are regulated by DOEL through the Environment Act, but, as noted, there is no specific dam legislation. In the absence of specific dam legislation, the DOEL often cites compliance with the CDA Guidelines as a requirement for obtaining or renewing an operating license for a dam.
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Dartmouth, Nova Scotia, B3B 1S8
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