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I- '-\ ~~1 STATE OF COLORADO OFFICE OF mE STATE ENGINEER DIVISION OF WATER RESOURCES DAM SAFETY BRANCH PROCEDURE FOR HAZARD DETERMINATION FEMA JWVS 8/31/84 Introduction The State of Colorado roster of dams contains entries for over two thousand separate structures of jurisdictional size as defined by Colorado Revised Statutes Section 37-87-105, C.R.S. (1983) (amended 1984). Colorado Revised Statutes Section 37-87-107, C.R.S. (1973) (amended 1984) tasks the State Engineer, through his representatives, with the determination of the safe storage level of these reservoirs. The intended purpose of the legislation is to promote public safety. To achieve the goal of public safety while recognizing the limited resources of the State Engineer's Office, a procedure had to be established to identify darns with the greatest potential to cause loss of life should they fail. The word ''Potential'' is used here in the probablistic sense. We recognized that a dam could fail under circUlllStances such as overtopping by a rare flood event, or structural collapse during an earthquake, but that these mechanisms are considered rare events. In contrast, the forces which could cause failure by piping, an embankment slide, or deterioration of the outlet works, are present on a continuing basis for reservoirs which normally impOlmd water. The significant dam failures in Colorado for the past decade (Lower Latham - 1973, Prospect Valley - 1980, furse Creek - 1981, Lawn Lake - 1982), resulted from piping of embankment materials or a structural slide, during otherwise "Normal operating conditions." "Normal" in this case means non-storm conditions, with reservoir waters stored at or near the crest elevation of the emergency spillway. Failures under "Normal Operating Conditions" are frequently preceded by observeable symptoms often identified during routine visual inspection of the structure. ].