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<br />5.A.(5)(CI The Increoental Damage Analysis (IDA) used to <br />justify In Inf ow Design Flood (loF) less than the .Inl.um <br />requirements of Rule 5.A.(5)(b) or Rule 6.A.(4), shall be based upon a <br />comparison of two floods: first, a base flow flood of a .agnltude <br />which will cause overtopping failure of a dam and routing it down- <br />stream assu.ing no dam Is In place and second, the dam failure flood <br />due to overtopping, Imposed upon the base flow flood. The spillway <br />capacity and 10F will be acceptable where it can be shown that the da. <br />failure flood would cause nO expected additional loss of life and <br />would ~ot cause significant incremental flood da.ages downstream. <br /> <br />5.A.(5)(c)(I) For comparison of the two types of floods, no <br />additional loss of life nor 'significant' da.age is expected in the <br />incremental lone If the increoental increased depth of flow is two <br />feet or less and the product of the average floodplain flow velocity <br />(in feet per second) and the incremental depth .of flood (in feet) is <br />less than seven; <br /> <br />5.A.(5)(C)(JI) Documentation for the IDA shall include but <br />not be l1.ited to: a dam break flood plotted. on topographic .aps. of <br />the affected areas; hydraulically appropriate cross-sections of the <br />downstream channel showing flood stages with velocities and discharges <br />for the two floods; Incremental damage and loss of life determina- <br />tions; and a sUlllllary of all hydraul1c parameters. oocu.entatlon shall <br />also Include, If deemed necessary by the State Engineer, channel <br />profiles with the various flood stages; aerial photogra~hs of the <br />affected areas; and computer printouts showing flood discharges, <br />stage, and velocities with respect to time. <br /> <br />5.A.(5)(d) The Inflow Design Flood (loF) shall range between <br />the Probable Haxlmum Flood and the 25-year flood, with the Inflow <br />DeSign Flood determined by the following methods: <br /> <br />5.A.(5)(d)(I) When the 100-year flood event Is the <br />appropriate Inflow Design Flood, the probable future flow shall be <br />determined by one of the following methods: <br /> <br />5.A.(5)(d)(I)(A) Whenever the records basic to a deter- <br />mination of probable future water flows extend for a period of one <br />hundred or more years at reliable gaging stations, the calculation of <br />the 10F based upon those records shall be deemed conclusive. The <br />records however, must be adjusted for historic diversions and the <br />effects of upstream storage. If such records do not extend for a <br />period of 100 or more years, then the determination shall be made by <br />interpolation and correlation to a full 100 years of records by <br />relating the. to known records of known basins as similar as <br />reasonably possible to the basin under consideration. A stream gaging <br /> <br />- 16 - <br />