INSTALLATION OF GATES ON THE SPILLWAY OF THE PUEBLO VIEJO DAM

摘要

The 300 MW Pueblo Viejo - Quixal hydroelectric scheme, located in central Guatemala and completed in 1986, includes a 130 m high rockfill dam with an ungated spillway of 3 900 m~3/s maximum capacity. A severe flood occurred in 1979 during the dam construction leading to a re-evaluation of the design flood hydrograph from 1 000-years to a 10 000-years event. As part of the design modifications, it was suggested, for safety reasons, to complete all civil works according to the original design, but to postpone the installation of the radial gates on the spillway. The report presents the analyses and the characteristics of the finally adopted solution including a description of the construction details insuring an appropriate gate operation under any condition. The project mainly consists in an increase of the spillway capacity by lowering the weir crest elevation of the fixed weir combined with the installation of three 4.5 m high and 12.00 m wide radial gates equipped with concrete counterweights. The design of the spillway modification works and the selection of the hydromechanical equipment characteristics were dictated by unusually severe safety requirements. Shortly after completion, the hurricane "Mitch" affected in November 1998 the watershed of the Chixoy river, resulting in relevant floods safety discharges by the new spillway structure.