Rehabilitation of Plane Nine Dam

Plane Nine Dam, an earthen water supply dam near Altoona, Pennsylvania, was constructed in 1907. The dam performed satisfactorily for more than 80 years but it deteriorated with time and its spillway capacity was inadequate according to modern criteria. Geotechnical investigations of Plane Nine Dam conducted from 1988 to 1990 developed the geotechnical framework of the dam site and the dam and demonstrated adequate stability for the dam. Dam modifications, including a floodwall and spillway capable of accommodating the Probable Maximum Flood, were designed in 1989 and 1990, then constructed in 1991 and 1992. When a new water treatment facility, now under construction downstream from the dam, is completed in 1994, the service life of the project will extend well into the twenty-first century.