A new pumped storage project in Kauai requires rehabilitating existing infrastructure and new construction. We are modifying three reservoirs and dams and associated ditch systems, access roads, and diversion structures, and we are building six miles of pressurized penstocks, two new hydropower stations, gate and intake structures, and a pump station. McMillen is leading design, procurement, and construction to get the facilities up and running.
The project comprises three dams:
Puu Opae, Puu Lua, and Mana. Our team is rebuilding Puu Opae and Mana embankment dams following analyses of hydraulics, dam stability, loading conditions, seismic conditions, seepage, and drainage. We conducted a preliminary stability analysis on the Puu Lua earthen dam using a 2D model, drilling, and sampling.
These analyses guided our team in developing plans to modify each dam. Our design includes all civil, structural, mechanical, electrical, hydraulic, and geotechnical disciplines, and our team will self-perform construction and commissioning. Puu Lua will undergo construction of a new outlet structure and spillway, reconstruction of the embankment dam, sediment removal from the reservoir, addition of a toe buttress to address liquefaction concerns, and installation of new dam safety and instrumentation systems. The upstream face of the Puu Opae and Mana dams and the base of the Puu Opae and Mana reservoirs will be fully or partially lined with a geomembrane to help limit water loss via seepage.
In addition to the dam modifications, McMillen will build two new powerhouses and lay 32,000 feet of pressurized penstock. The Puu Opae powerhouse features a 4.25 MW Pelton turbine generator. The Mana powerhouse and pump station includes a 20 MW Pelton turbine and a 32 MW pump station consisting of ten 3.2 MW vertical turbine pumps. Our team is providing all electrical and control systems design and will be self-performing the systems controls and integration. In addition, our fire protection engineers provided a life safety analysis and detailed fire suppression and fire alarm designs. The design of the powerhouses accommodates challenging water supplies and a remote location from municipal utilities.
Other critical features of the project include:
• A 56 MW photovoltaic solar field to pump water uphill
• Underground medium-voltage power distribution along the penstock alignments
• A several-mile-long fiber optic ring-network backbone
• Power distribution and controls stations for the reservoir outlets, penstock intakes, and penstock flow
metering
• Four rugged terrain stream diversion structure control stations that must operate fully non-grid powered
using solar arrays, batteries, and thermal-propane generators, communicating via satellite to the controls
network
• Grading, stormwater, and roadway design
• Inlet and outlet closure gates at all three reservoirs
• Installation of gauging equipment at each diversion location with remote monitoring
We anticipate completing construction in December 2027.
