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CONSULTANTS. INC. MEMORANDUM Project 11119 Performed: August 23 & 31, 2011 CLIENT: Catlin Canal Company By: Michael L. Graber, P. E. SUBJECT: Mt. Pisgah Dam and Reservoir Outlet Inspection Section 1 Background The original dam was constructed in 1911 with dual 16- inch - diameter outlet pipes that had downstream control gate valves installed at the toe of the dam. In 1928 a slide on the upstream slope of the dam covered the intake of the dual 16 -inch pipes with embankment material rendering the outlet unusable. A rehabilitation approach was developed in November 1928 by H.I. Reid, a consulting engineer from Colorado Springs. The rehabilitation approach included blowing a hole in the 16 -inch pipes with "powder" to drain the reservoir and then constructing a tunnel through the right (west) abutment of the dam. A plan prepared by H.I. Reid indicated that the majority of the upstream portion of the tunnel was to be constructed of concrete in the shape of a horseshoe, which was 5 feet high and 3 feet wide with a grated intake structure. Water in the concrete tunnel flowed into two 30- inch- diameter gate valves located in a rockcut tunnel near the transverse midpoint of the dam. A vertical rockcut shaft was shown to the dam crest in which the valve stems and operators were to be located. The valves discharged into an open rockcut tunnel, which was to be excavated to daylight. The 16 -inch valves were to be plugged and then abandoned once the new outlet works was complete and functional. Section 2 As- Constructed Outlet There are no known as- constructed plans for the new outlet works that were prepared after the construction was completed in 1929. RJH measurements and inspection of the outlet works discovered some significant changes made to the original plan prepared by H.I. Reid in 1928. The intake structure had both low level and upper level intake openings that were covered by trashracks. The original plan indicated only a upper level intake opening. The current inflow control elevation of the intake structure is at Elevation (El.) 7928.8 and the maximum reservoir elevation, which corresponds to the emergency spillway flowline elevation, is at El. 7984.35. The horseshoe tunnel was generally constructed to the cross section dimensions shown in the original 1928 plan but the length and alignment were found to be significantly different. The intake structure was generally located so that it was parallel to the longitudinal axis of the dam but the tunnel was not perpendicular to the intake structure having a skewed alignment of approximately 15 degrees to the right (southwest). The tunnel followed this alignment for approximately 100 feet where it began a circular curve to the left (southeast). After the curve, there was a short tangent section which terminated in an open rockcut tunnel. A short rockcut tunnel section downstream of the concrete horseshoe tunnel of 11119 11 -11 -01 Outlet Inspection Memorandum Draft