Lenihan Dam Outlet Modifications
Submitted by Flatiron
At the foot of the rugged Santa Cruz Mountains stands the 50-year-old Lenihan Dam — a 1,000-ft-long earthen barrier holding water stored at the Lexington Reservoir in Los Gatos. Surrounded by pristine wilderness, the trail system around this reservoir is one of the most scenic in Northern California.
The 2.5-mi-long reservoir is the second-largest reservoir under the Santa Clara Valley Water District’s authority, with a capacity of 19,044 acre-ft and a surface area of 412 acres. Over the past few decades, the dam’s old outlet structure, a 50-in. steel pipe, had begun to buckle and corrode. Despite repairs, the aging pipe continued to deteriorate and a new outlet structure was required. Construction included a new 2,000-ft horseshoe-shaped tunnel 14 ft wide by 13 ft tall to house a 54-in.-diameter outlet pipe. A 37-ft vertical shaft was also constructed down the backside of the dam that intersects with the tunnel.
The $39-million Lenihan Dam and Outlet Structure project included a significant amount of underground and confined space work with the tunnel excavation and the abandonment of the existing outlet pipe. It is a testament to the way this construction site was run that with more than 155,000 hours worked there were no recordable or lost-time incidents that resulted in a lost day of work. Thanks to all parties involved, this project was completed safely, under budget and ahead of schedule.
One of the major differentiating factors on this project and the reason the Lenihan Dam project should be recognized was the early and crucial decision by the Santa Clara Valley Water District to commission Hatch Mott MacDonald as the construction manager and two full-time design personnel from Jacobs and placing these technical experts on site where they could interact with each other and the contractor, Flatiron. This resulted in an immense amount of collaboration and understanding — understanding by designers of what it took to build the structure and understanding from the contractor as to what the designers intended so that they could arrive at the best way to achieve both partners’ goals.
Developer/Owner: Santa Clara Valley Water District, San Jose
General Contractor: Flatiron, Benicia
Construction Management: Hatch Mott MacDonald, Pleasanton
Civil Engineer: Jacobs Associates Engineers/Consultants, San Francisco
MEP Engineer: MWH, Broomfield, Colo.