National Dam Safety Program. Lake Grinnel Dam (NJ00289). Wallkill River Basin, Tributary to Wallkill River. Sussex County, New Jersey. Phase I Inspection Report.

Abstract

Abstract : Based on available records, past operational performance, visual inspection and Phase I engineering analysis, Lake Grinnel Dam is assessed as being in fair overall condition. Based on investigations of the downstream flood plain made in connection with this report, it is recommended that the hazard potential classification be downgraded from high to significant hazard. Hydraulic and hydrologic analyses indicate that the spillways are inadequate. Discharge capacity of the spillways is not sufficient to pass the designated spillway design flood (100-year storm) without an overtopping of the dam. The spillways are capable of passing approximately 1 percent of the SDF. Therefore, the owner should engage a professional engineer experienced in the design and construction of dams in the near future to perform more accurate hydraulic and hydrologic analyses relating to spillway capacity. Based on the findings of the analyses, the need for and type of remedial measures should be determined and then implemented. The owner should, in the near future, develop an emergency action plan together with an effective warning system outlining actions to be taken by the operator to minimize downstream effects of an emergency at the dam.