The existing Vail Dam was constructed in 1948 and 1949 and was acquired by the District in 1978. The results of hydrologic and seismic evaluations of the existing dam indicate that the dam’s spillway is insufficient to pass the Probable Maximum Flood (PMF) without overtopping the dam and that the existing concrete arch dam would not resist the stresses induced by the Maximum Credible Earthquake (MCE). The hydrologic evaluation also indicated that the outlet works do not have the capacity for the District to lower the maximum storage depth of the reservoir by ten percent (10%) within seven (7) days to meet regulatory requirements for emergency drawdown. The existing arch dam will be replaced with a straight-axis gravity roller compacted concrete (RCC) dam immediately downstream of the arch dam. New inlet/outlet facilities will be incorporated in the new gravity dam. The new dam will be higher than the existing dam, such that the PMF will be routed entirely through the existing spillway. Once the new dam and outlet works are operational, the existing gates will be removed, the arch dam will be partially demolished, and an underwater penetration will be constructed near the base of the arch dam to provide a hydraulic connection to the new dam. Project draft figures are included in Exhibit D of this Notice, which is attached hereto and incorporated by this reference. These draft figures are included as an example of the type of work required for this Project and are not intended to be final construction documents.
