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<br />( <br />. <br /> <br />( <br />. <br /> <br />~ <br /> <br />3. Private (Rining, hydroelectric, .griculture, <br />developllents) <br /> <br />I. Cl.ssific.tion by Location <br /> <br />1. Con.tructed to obstruct flov of a natur.l vater <br />cour.e. <br /> <br />2. Hot sited acro.. . natur.l vater course. <br /> <br />P. Classification by Ba.ard Rating <br /> <br />Bazard rating is a ....ure of pot.ntial hazard <br />rather than dam condition. <br /> <br />1. 1Qw bazard dams are expected to produce no loss <br />of human life and little property loss, should a <br />failure occur. <br /> <br />2. Moderate b.zard dams .re expected to produce <br />significant property daaage but no loss of human <br />life, should a failure occur. <br /> <br />3. Jigh hazard dams are expected to produce loss of <br />buman life, .hould a failure occur. <br /> <br />G. Classified by Safety Rating <br />Safety rating is a measure of potential for failure. <br />1. JAtl dams are unlikely to fail. <br />2. Inadeouate dams may fail as the result of an <br />extreme event. <br /> <br />3. Unsafe dams are in i.-inent danger of failure. <br /> <br />In 1978 the Rocky Rountain States contained 5,600 <br />non-federally owned dams with hazard ratings of moderate <br />and high. Twenty-two percent of these dams were rated as <br />unsafe in 1980. The corresponding national average is <br />twenty-nine percent. <br /> <br />II I. CAUSES OF DAM FAILURE <br /> <br />The first known dam failure occurred in Egypt around .2900 <br />B.C. Surviving evidence indicates that the 350 foot long <br />aasonry dam failed by overtopping shortly after it vas built. <br />.Iven today, approximately 50' of dam failures occur during <br />initial filling. <br /> <br />The Hational Dam Inspection Act (PL 92-367) specifies <br />overtopping, .eepage, settlement, erosion, sediment, cracking, <br /> <br />-3- <br />