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<br />.i" <br />.' <br />II <br />,I <br />. I <br />I <br />I' <br />. I <br />I, <br />II <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br /> <br />This will indicate the relative criticality of the <br />flood load cases and the order of risk reduction <br />to bring the cumulative risk to life within the <br />criteria, (Refer the indicative examples in the <br />Risk Supplement, Appendix 3, A3.5.). <br /> <br />It may not be practicable in all cases, due to <br />design, construction and cost limitations, to <br />propose remedial risk reduction options for <br />existing dams which will meet the ANCOLD <br />risk to life criteria, including in some cases <br />even the Limit. <br /> <br />The options then have to be considered for the <br />specific case using an ALARP type principle, <br />with the risk criteria as a reference rather than <br />a prescriptive requirement, in conjunction with <br />deterministic standards. <br /> <br />Alternatively, the question of legal <br />responsibility should be considered if options <br />based on risk to life criteria would pose a <br />higher risk than the established deterministic <br />standards. <br /> <br />7.3. Warning and Evacuation Plans, & <br />Non-structural options. <br /> <br />7.3.1. General <br />Flood warning plans should be developed, <br />with the relevant emergency authority and <br />the community, for all dams. Dambretrk <br />warning and evacuation plans should be <br />arranged within these plans, not as stand <br />alone plans, (AEMI, 1995). <br /> <br />The warning system may include radio and TV <br />Bulletins, direct telephone, or radio contact, <br />house-to house contact, public alarms such as <br />fixed sirens and mobile loud speakers, and in- <br />home alarms (NWS, USA, 1997). <br /> <br />7.3.2. Dam break Warning & Evacuation <br />Plans. <br /> <br />For effective warning and evacuation, plans <br />need to consider number, distribution and <br />elevation of the populated areas for effective <br />warning and evacuation, noting the dambreak <br />dynamic flood wave and debris could impact <br />to metres vertically above the natural flood <br />levels. <br /> <br />The plan should in<:lude identification of <br />available escape routes under flood conditions <br />prior to dam break and under dambreak; this is <br />critical for evacuation. <br /> <br />In many cases significant natural flooding will <br />have already taken place before the flood <br />reaches the dam failure stage, and phased <br />emergency actions should have started, which ' <br />has advantages, but may lead to panic and <br />chaos, making the further dam break warning <br />and evacuation more difficult, <br /> <br />However, with small catchment dams, the <br />flood rise, and time to peak, can be so short as <br />to preclude practical pre-warning and effective <br />evacuation. <br /> <br />7.3.3. Warning Time. <br /> <br />The warning time is the time elapsed between <br />initiation of a formal warning by public <br />safety officials through radio, TV, direct <br />warning, or otherwise, for a selected PAR to <br />evacuate, and the time at which the leading <br />wave of the failure flood reaches the PAR <br />(USBR,1989). <br /> <br />The warning time is measured from the time at <br />which the official dissemination to the PAR of <br />the warning begins, not the time when a <br />potential dam break is recognised, or the <br />emergency authority receives an alert from the <br />dam operator. <br /> <br />It relates to the time at which the first section <br />of the PAR receives the warning, not the time <br />to when all individuals are warned, <br /> <br />7.3.4. Warning Lead Times. <br /> <br />When assessing waming time for loss of life <br />estimates, include effective lead time in regard <br />to: <br />. The operator/owner threat recognition <br />time, from rain, inflow and reservoir <br />level information, of a potential <br />dambreak flood; <br />. time to make a decision to alert the <br />emergency centre (already under <br />stress); <br />. emergency centre decision time to <br />decide if the alert is correct, and the <br /> <br />ANCOLD Guidelines on Selection of an Acceptable flood Capacity for Dams 19 <br />