Lenihan Dam Outlet Modifications

The project site operates as the Lexington Reservoir County Park and will remain open during construction, scheduled for completion in 2009. The design includes a 54-inch-diameter steel pipe installed within a 13-foot, cast-in-place concrete horseshoe tunnel. The outlet design, containing intake, pipeline and outlet works, includes an intake control building, five independently operated sluice gate inlets, conveyance pipeline in tunnel, outlet structure with four fixed-cone valves for controlled releases. Other features include an RTU-based SCADA system, hydraulic power system for intake gates and electric control for outlet discharge valves.

The multi-port sloping intake, together with four fixed-cone energy dissipation valves in the outlet structure, will provide variable releases up to 410 cfs, based on reservoir operations and future sedimentation projections. A second phase of construction will connect the intake and tunnel through a shaft constructed during a reservoir drawdown.

Our scope of services includes:

• Inlet and outlet design
• Conveyance
• Hydrology and hydraulic analysis
• Bid support
• Engineering support during construction
• California Division of Safety of Dams coordination support

In addition to design services, MWH will provide quality assurance/quality control and risk management plans, and a complete construction cost estimate and schedule.