National Dam Inspection Program. Speedwell Forge Dam (NDS-PA-00345, DER-36-257), Susquehanna River Basin, Lancaster County, Pennsylvania. Phase I Inspection Report.

Speedwell Forge Dam, formerly known as Hammer Creek Dam, is a zoned earthfill dam with a maximum height of 35 feet above the streambed. The embankment length is 830 feet and the top of dam has a width of 18 feet. A cutoff trench was excavated along the centerline of the dam to the top of solid rock. A 120 foot long trapezoidal spillway weir is located in the right abutment at an elevation of 10 feet below the top of the dam. The concrete spillway ends in a stilling basin, from which the water flows through a riprap lined discharge channel to the original creekbed. A concrete control tower is located upstream just off the breast of the dam. Discharge through a 4-foot square concrete conduit is regulated either by stop logs or by opening a 30-inch sluice gate. Based on the visual inspection, past performance and the available engineering data, the dam and its appurtenant structures appear to be in good condition. The hydrologic and hydraulic calculations indicate that the spillway for this dam has the capacity for passing 47 percent of the Probable Maximum Flood PMF without overtopping the embankment.