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Washington Dams No. 3 & 4 Spillway Rehabilitation


CONSOL Energy, Inc.

Project Location

Washington, Pennsylvania

Related Markets

Dams Hydropower

Bergmann Location

Cranberry, PA

Washington Dam No. 3 Spillway

Hydrologic & Hydraulic analyses, final design & construction documentation for two dams south of Pittsburgh.

Bergmann performed a hydrologic and hydraulic analyses of Washington Dams No. 3 & 4 in South Franklin Township as a result of a significant rainfall that required an upgrade to the dams’ existing spillway. Constructed in the early 1900s, the dams are inspected annually in accordance with the Pennsylvania Department of Environmental Protection (PADEP)and Bureau of Dams and Waterway Regulations. Each dam includes a concrete ogee weir and spillway chute and current Pennsylvania dam hazard classifications require the spillway system to convey the peak discharge associated with a Probable Maximum Flood (PMF).

Bergmann determined the PMF, evaluated the existing spillway capacity, designed a 3-cycle labyrinth spillway that met PADEP freeboard requirements, analyzed and designed a stilling basin at the end of the modified chutes and designed channel protection armoring downstream to the end of the stilling basin.

Bergmann also developed both annual and monthly watershed yield analyses for water withdrawals, performed calculations to assess construction conditions flooding risk using a pumping system to reduce reservoir water surface elevations and developed preliminary drawings that allowed for the determination of construction quantities and the preparation of an opinion of engineer’s cost estimate. In conjunction with the estimate, Bergmann prepared a Phase I report summarizing the design and information developed. Following client and PADEP approvals, the final design was completed and construction documents were prepared for both dams.

Project Highlights

  • Hydrologic modeling using HEC-HMS to determine PMF
  • Labyrinth spillway hydraulic design
  • Stilling basin hydraulic design
  • Mixed flow HEC-RAS modeling of spillway chute
  • Reservoir water yield analysis
  • Construction flooding risk analyses
  • Preliminary and final design drawings
  • Specifications and cost estimates

Washington Dam No. 4 Spillway Shoot