etc . As such , it is difficult to obtain a good understanding of the historical performance , inherent condition , characteristic behaviour and potential failure modes of the dam . In some cases , the dam instrumentations are damaged and the instrumentation data is not available .
The causes and processes of dam failure are varied . Case histories of dam failures reveal many remarkable similarities in antecedent conditions and processes of deterioration . Often deficiencies have developed over extended periods of time , yet these conditions have either gone undiscovered or were incorrectly interpreted . Surveillance programmes should be capable of detecting such conditions and processes early enough for corrective action to be taken .
Safety Reviews Dam owners must recognise that there are uncertainties associated with natural destructive forces , material behaviour and construction processes associated with their dams . These must be balanced with competent technical judgement to deal with the uncertainties .
Dam safety reviews are required for assessing the safety of a dam , and comprise where relevant , detailed structural , hydraulic , hydrologic , geological and geotechnical design aspects and the records and reports from surveillance exercises .
A safety review should assess the integrity of a dam against known failure modes and mechanisms for the various types of dams in terms of safe acceptance criteria such as engineering standards and dam safety guidelines in order to recommend remedial or maintenance works .
Special Safety Review A special safety review may be required on short notice if any inspections , monitored results or unusual events such as flooding , earthquake or landslide indicate that an adverse trend or condition exists . A safety review should also be undertaken to update the risk profile of a dam ( See figure 1 ).
Emergency Preparedness The standards used for design , construction , operation , maintenance and surveillance of dams minimise the risk of dam failures . However , unusual circumstances could result in dam failure . Dam owners should establish a formal internal emergency action plan that describes the procedures that operation staff should follow in the event of an emergency at the dam .
Two types of emergency plans might be required :
1 . A dam safety Emergency Action Plan ( EAP ) developed by dam owner ; and
2 . A separate Disaster Plan , developed by State or local disaster management agency to provide protection for downstream communities in the event of a dam safety emergency .
It is important that these two plans be linked in a compatible manner . An EAP is a formal plan that :
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Identifies emergency conditions which could endanger the integrity of the dam and which require immediate action ;
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Prescribes procedures which should be followed by the dam owner and operating personnel to respond to , and mitigate , any emergency conditions at the dam ; and
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Provides timely warning to State or local disaster management agencies for implementation of their protection measures for downstream communities .
It is essential that an EAP be tested periodically by conducting a drill simulating emergency conditions . For high hazard rating dams , an annual in-house review should be conducted and , at least once every five years , a drill should be conducted that is co-ordinated with all State and local disaster management agencies .
Identifying and Managing Dam Safety Issues The identification and management of dam safety issues is an essential part of dam safety management by dam owners . Dam safety issues include physical infrastructure issues , dam safety deficiencies and non-conformances .
Information Management In the context of dam safety in a dam ’ s lifetime , the importance of careful record keeping and preservation of all dam information cannot be overstated .
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