2004-02-11_HYDROLOGY - M1977493 (3)

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Mr. Blair, P.E. February 11, 2004 Page 4 Upstream Piping and Valves As shown on the as -built drawings, the outlet control consists of a 24 -inch butterfly valve with a hydraulic actuator and a 12 -inch diameter gate valve with a manual operator on the crest of the dam. The 24 -inch diameter valve was installed in 1970 when the original 24 -inch diameter gate valve was abandoned in place. The date of installation for the 12 -inch diameter valve is unknown, but may have been in 1954 when the dam crest was raised. The attached photos 5 and 6 show the condition of the two valves. The body and seat of the 24 -inch diameter valve were in fair condition, with minimal corrosion observed. However, the edges of the disc was pitted and worn, and it is likely that the valve will not seal completely when closed. It is recommended that this valve be replaced when the outlet is put back into service. As part of the inspection, the valve was successfully operated using the hydraulic system. The 12 -inch gate valve was coated with a thick layer of what appeared to be coal tar or asphalt coating, which made it difficult to assess the condition of the metal body of the valve. The seats of the valve were in fair condition but would likely not ✓ seal drip- tight. Although the valve is not in bad condition, it is recommended that this valve also be replaced when the outlet it put back into service. The existing configuration of the outlet piping is such that the outlet discharges into the pump header piping in the decommissioned Robinson Pump Station. In order to discharge from the outlet to the stream channel below the dam, it would be necessary to open several valves in the pump station that used to serve as intake lines to the pumps. This water would then flow through the drain system in the station to the stream. During an emergency release, it is likely that the flow rate would exceed the capacity of the drain system and water would flow onto the floor