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<br />6.A.(4) The inflow design flood (IDF) require..nts for existing <br />dllDs sh.ll be determined in .ccord.nce with the principles of Rule <br />5.A.(5){cj .nd (d). .xcept those structures whose splllw.ys wtre <br />designed .nd .pproved in ,ccord.nce with the methods publish.d . in the <br />U.S. Dep.rtment of the Interior. Bure.u of R.cl....tlon..Design of <br />Small Dams'. Second Edition. 1973, sh.ll be considered .dequ.te for <br />. the cl.ssific.tion (formerly referred to .s h.z.rd r.ting) for which <br />they w.re designed. If the cl.ssific.tion h.s ch.nged. then the <br />provisions of Rules 5.A.(5)(c) .nd (d) .pply. <br /> <br />6.A.(4)(.) Wh.never the methods of Rule 5.A.(5)(c) .nd (d) <br />.pply, the requirements for determining the spillw.y capacity .re <br />sunn.rlzed. in the following table. These requirements maY.be waived <br />for good cause shown. Spi llways designed in accordance With ' these <br />rules will not be required to enlarge the. due to subsequent revisions <br />in PMP estim.tes. unless. in the opinion of the State Engineer. there <br />Is a substantial threat to public s.fety. <br /> <br /> INFLOW DESIGN FLDDDREgUIREMENTS <br />0.1111 (1 ass II III IV <br />Dam Size <br />Large .75 PHP . 50 PMP 100 YR 50 YR <br />Intermediate .75 PHP .50PHP 100 YR 50 YR <br />Small .75 PHP .50 PHP 100.YR 25 YR <br />Minor . 50 PH? .100 YR 50 YR 25 YR <br /> <br />6.A'.(4)(a)(I) Existing Large, Intermediate, and <br />Sm.ll Class I dams shall have. spillways capable of passing. as a <br />minimum. the IDF generated by 75 percent of the probable maximum <br />precipitation. unless an incremental damage analysis demonstr.tes a <br />lesser flood is applicable. <br /> <br />6.A.(4)(a)(lI) Existing. Hinor Class 1 dams. and <br />Large, Intermediate, and Small Class II dams shall have spillways <br />capable of passing as a minimum, the IDF generated by 50 percent of <br />the probable maximum precipitation. unless an incremental damage <br />analysis demonstrates a lesser flood is applicable. <br /> <br />- 28 - <br />