Lee Hall Dam
NEW SPILLWAY AND RAISED EMBANKMENT KEEP KEY RESERVOIR OPERATING SAFELY TO SERVE 400,000 VIRGINIA RESIDENTS
With a storage capacity of 960 million gallons, the Lee Hall Reservoir is a key part of a water supply system that serves 400,000 people on the Virginia Peninsula. A change in the regulatory requirements applicable to the reservoir’s lower impoundment dam meant that its spillway needed to be upgraded to handle the maximum amount of rain that could fall in a given time period for the area. As well, the upper impoundment dam needed significant rehabilitation to comply with the requirements. To ensure safe dam operations and extend the facility’s service life, Newport News Waterworks embarked on an ambitious dam rehabilitation effort.
Gannett Fleming provided design and construction services for the project. The work involved decommissioning the upper dam, raising the main portion of the lower dam embankment, and installing a two-stage labyrinth spillway, allowing the facility to maintain a higher water level. A new auxiliary spillway created by armoring part of the embankment with articulated concrete blocks further increased spillway discharge capacity. Now complete, the upgraded dam enables Newport News Waterworks to maintain reliable water service while protecting the surrounding community.
What We Did
Our firm provided alternatives analysis of possible solutions during the project’s first phase and preliminary and final design as well as bidding assistance for the second. Because the Lee Hall Reservoir is the terminal reservoir in the area’s water-supply system, maintaining near-full water levels throughout design and construction was critical for system operation. Our firm developed a construction sequencing plan so the water could be diverted during the work without interrupting water supply to Waterworks customers, and without affecting the adjacent municipal park.
Gannett Fleming completed hydrologic and hydraulic modeling to develop inundation mapping required to update the facility’s emergency action plan for a dam break scenario. Our firm also provided geotechnical services, including subsurface exploration to assess underlying conditions and soil testing to confirm suitability for construction. Detailed analyses of embankment overtopping, slope stability, and potential seepage, as well as the abandonment or relocation of a number of utility pipelines from the embankment, ensured that the rehabilitated dam was safe and stable.
Key Features
- New labyrinth spillway and raised embankment increased capacity in accordance with state guidelines.
- Construction sequencing plan maintained water service to customers throughout the project.
- Analyses of overtopping, slope stability, and seepage facilitated safe and sound dam design.
- Subsurface investigation and soil testing confirmed site and material suitability for construction.
- Decommissioning the upper dam removed it from regulatory purview.
Outcomes
- Capacity for full probable maximum flood without overtopping.
- Compliance with applicable state regulations after hazard reclassification.
- Updated emergency action plan details safety procedures.
CLIENT
City of Newport News Waterworks
LOCATION
Newport News, Va.
ROLE
Concept Development, Design, Construction Services, Geotechnical Services
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