To the Tune of a Piano-Key: Analysis of Alternatives for Curtis Dam and Hydraulic Design of a Piano-Key Spillway

Curtis Dam, initially constructed in 1887 as a water supply dam by the Scranton Gas and Water Company, consists of a homogeneous earthfill embankment with a masonry core wall and a masonry gravity dam which serves as the spillway. The existing spillway has a capacity of approximately 36% of the regulatory spillway design flood which is the PMF. Therefore, the Pennsylvania American Water Company (PAWC) initiated the rehabilitation project consisting of an alternatives analysis for increasing Curtis Dam’s discharge capacity and the design of the preferred alternative.
The initial design criteria included maintaining the dam crest and normal pool elevations, due to permitting constraints; and not increasing the dam’s discharge for all flow scenarios up to the 1% annual exceedance probability (AEP) storm event. Alternatives that were evaluated included RCC armoring of the embankment, a new auxiliary spillway at the right abutment, fusegates at the existing spillway, and a new weir crest via a labyrinth or piano-key weir at the existing spillway. With the compact existing spillway footprint and various site limitations, many of these alternatives were dismissed. (Continued)