National Dam Inspection Program. Larsen Dam (NDI ID Number PA-00367, DER ID Number 35-30), Delaware River Basin, Lehigh River, Lackawanna and Wayne Counties, Pennsylvania. Phase I Inspection Report

Abstract

Abstract : Based on visual inspection, available records, calculations, past operational performance, and according to criteria established for these studies, Larsen Dam is judged to be in fair condition. Based on the size and hazard classification of the dam, the Spillway Design Flood (SDF) at the dam varies between 1/2 the Probable Maximum Flood (PMF) and the PMF. Based on the downstream conditions, the selected SDF is the 1/2 PMF. Under existing conditions, the spillway will pass about 12 percent of the PMF without overtopping of the dam. If the low areas on the top of the dam were filled to the design elevation, the spillway would pass 16 percent of the PMF. It is judged that Larsen Dam could not withstand the depth and duration of overtopping that would occur during the 1/2 PMF. However, it is judged that a high hazard dam located immediately downstream would fail due to overtopping prior to the overtopping failure of Larsen Dam. Therefore, the spillway capacity of Larsen Dam is rated as inadequate. No immediate stability problems were evident at the time of the inspection, but deficiencies do exist that could eventually affect the stability of the dam and appurtenances if they are not corrected.