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20 ANCOLD Guidelines on Selection of an Acceptable flood Capacity for Dams I I I I I I I I I I I I I I I I I I I additional areas and PAR involved, and evacuation routes; . time for the emergency authority to issue a warning to the relevant PAR to evacuate, In some cases, to provide effective lead time for warning and evacuation, the operator alert may need to be at an early stage such as the 1:100 AEP flood phase when it is not possible to assess whether the flood will reach darn break proportions, It is also likely that there will not be any significant difference in the flood hydrograph, rising stage between a nonhal flood and the PMP design flood making it difficult to identifY the potential ultimate flood condition, The historical records are unlikely to include extreme floods, 7.3.5. Dam Safety Emergency Plans (DSEP). The DSEP should include an assessment with the emergency authority of the relevant lead times required to determine at what stage an alert should be given of a potential dam break situation to provide sufficient time to warn and evacuate the PAR (ANCOLD, 1994). As indicated above this could identifY that the alert from the dam operator may have to be made well ahead of firm data that the dam could faiL The community would require education that such advance warnings and evacuation would be conservatively made to protect the community, and that the dam may not subsequently faiL 7.3.6. Non Structural Risk Options If dam break warning and evacuation plans are proposed as non-structural options to reduce loss of life, a number of factors need to be considered. (i) Proposals to use warning and evacuation plans as a risk reduction option should be coordinated with the regional and local emergency authorities for their agreement on the practicability and preparation of appropriate plans consistent with good emergency management practice, with clear lines of responsibility. (ii) The community concerned should be advised of the implications of using the warning 'system as a risk reduction measure, and the plans should be discussed at public meetings, with public involvement in design and agreement to implementation of the system. (iii) Regular follow up, with review and updating off plans and community education and involvement (with at least paper trials) are essential to maintain effectiveness of plans, '7.3.7. Effectiveness of Emergency Plans. (Refer Appendix 2, sub-section A2. 6.) It can only be stated that an appropriate plan, consistent with emergency practices, has been developed with the emergency authority, discussed and accepted by the community concerned, and will be regularly reviewed with all parties. (Legal liability has not been tested), ~. f . , 1c In the case of warning systems in the homes, as has been used for a number of dams, current references indicate a resistance from home owners following longer term experience with the warning system and malfunctions. A dam break warning and evacuation plan cannot guarantee outcomes such as a specified reduction in loss of life, or that there will be no loss of life, as with any risk-reduction solution. 8. AFC SCREENING PROCESSES. A deterministic fallback option can be considered as an alternative to a risk study, or preferably during a phased risk assessment that has identified the critical issues. A review during a phased risk study could indicate further detailed risk studies may not be cost effective compared with a conservative deterministic fallback option. Traditional practice has generally been to adopt PMF where lives were at risk, While not compatible with the risk concept, PMF can be considered as a fallback upper limit. I I i j i