A small steady stream of water flowing out of the new 54-inch-wide outlet pipe will be the official signal of completion for the Santa Clara Valley Water District’s Lenihan Dam Outlet Replacement Project at Lexington Reservoir.
Later this summer, the district board of directors will host a first-flow ceremony to mark the end of the two year construction project that began in fall 2007. The project provides a resolution to the dam’s deteriorating outlet pipe which has buckled several times since this was first detected during an inspection in 1989.
The Lenihan Dam structure remained safe, but because the durability of the outlet pipe was in question, state regulators limited the water district to releasing just a little more than one-seventh of the outlet capacity. The outlet restriction posed a risk to the towns of Los Gatos and Campbell, as the reservoir wouldn’t be able to release significant amounts of water prior to heavy winter storms if needed.
As the public agency responsible for the continued safe operation of reservoir, the water district concluded that creating a new outlet pipe that ran adjacent to the dam would be the safest, most cost-effective and efficient way to restore the operations of the dam.
The newly placed outlet pipe allows the water district to operate and regulate the water levels in the reservoir as designed. The new system modernizes the water intake system and allows the water district to make controlled releases from reserves with greater efficiency, which is particularly important during major storms.
Located at Lexington Reservoir and adjacent to Highway 17, the project was one of the water district’s most visible construction projects. Since the beginning of construction, commuters traveling along the highway, which runs alongside the project site, were given a birds-eye view of the project’s development and even some of its surprises.
Part of the construction process required that the reservoir be partially drained in preparation for excavation work needed to install the new modern drain system. During some points the low water levels were shallow enough to reveal some of the old foundations and structures of the historic towns of Lexington and Alma. The remnants of the two towns had been submerged by the waters of the Lexington reservoir since 1952. It marked the first opportunity for these old ghost towns to be viewed since the drought of 1989.
Currently, the water levels are at roughly half of normal capacity due in part to the construction project and a third consecutive dry year in the state. The reservoir will gradually refill as runoff from winter rains in the Santa Cruz mountains run into Los Gatos Creek.