Table 4. Flood Severity and Incremental Fatality Rate Based on Graham Method Severity Warning/Travel Time (min) Fatality Rate Dam Failure1 Fatality Rate Flood Only2 Incremental Fatality Rate Description Low < 15 (no warning) 0.01 0.0002 0.0098 Appropriate where no buildings are washed off the foundations (Water depths less than 3.0 m; DV values less than 4.6 m2/s) 15-60 0.007 0.0002 0.0068 > 60 0.003 0.0002 0.0028 Medium < 15 (no warning) 0.15 0.03 0.12 Applied to locations where homes are destroyed but trees or mangled homes remain for people to seek refuge on (Water depths larger than 3.0 m; DV values larger than 4.6 m2/s) 15-60 0.04 0.005 0.035 > 60 0.03 0.005 0.025 High Instantaneously arrived in seconds 0.75 N/A3 0.75 For locations flooded by the near instantaneous failure of a concrete or earthfill dam (where the dam fails in seconds rather than minutes or hours) Notes: 1. The fatality rate for dam failure is based on the suggested rate in DSO 1999 (Ref. 23). 2. The fatality rate for flood events without dam failure is according to the guidance in Section A5 of Appendix A of ANCOLD Guidelines (Ref. 24). 3. The scenario is generally not applicable for natural flood.
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