Spruce Run Reservoir on a cloudy day in winter.

Spruce Run Reservoir Outlet Vault Emergency Repair


Serving two million residents, the New Jersey Water Supply Authority (NJWSA) operates the Spruce Run Reservoir, one of two reservoirs at the Spruce Run/Round Valley Reservoir Complex.

The available release capacity of the reservoir’s outlet vault is normally 170 to 180 million gallons per day (MGD), including duplicate east and west discharge points, each with 12- and 30‐inch discharge mains. When the west 12-inch discharge main exhibited a leak, it necessitated a shutdown of both west mains that significantly decreased the available release capacity until a repair program could be completed.

NJWSA turned to Gannett Fleming to prepare the design of the outlet vault repair for bidding as an emergency contract. Because the same failure condition was suspected in the east 12-inch discharge main, and a site investigation found thinning pipe in the same area, the east 30-inch main became the sole discharge option.

A permanent solution needed to be implemented quickly to restore the original discharge capacity of the Spruce Run outlet vault to meet summer demand.

What We Did

The Gannett Fleming team conducted a site investigation to gather critical information on the piping and valves, determine access, and identify potential limitations on the sequence of construction. At the same time, we conducted a unique hydraulic computational fluid dynamics (CFD) model of the existing piping to confirm the root cause of the thinning pipe wall.

Modeling indicated that the sudden transition from low to high velocity in the 12-inch east and west discharge main was a source of high-velocity gradients and potential cavitation. We designed a reducer fitting with a long radius transition elbow to eliminate this high-velocity transition. We also provided a corrosion-resistant lining for the interior of the new piping and the existing transition for added protection against cavitation.

Along with the design, Gannett Fleming provided construction management services for the project, conducting construction inspections each week, and full-time construction inspections during welding operations. By completing all work to meet the client’s schedule, our firm significantly bolstered water system resiliency, restoring the outlet vault’s full release capacity when needed.

Key Features

  • Site investigation facilitated the development of a successful construction sequence.
  • CFD modeling identified the source of pipe wall damage, enabling the design team to mitigate the risk of future issues.
  • Reducer fitting with a long radius transition elbow reduced the potential of cavitation.
  • Corrosion-resistant lining for the interior of the new piping provides long-term protection against damage.


  • Restoration of outlet vault’s total available release capacity.
  • Mitigated risk of future pipe wall thinning.
  • Extended service life for crucial water infrastructure.
Spruce Run Reservoir on a cloudy day in winter.


New Jersey Water Supply Authority


Hunterdon County, N.J.


Design, Repair, Construction Management Services

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