PBCSD Opts to Store Irrigation Water

Nov. 26, 2007

Recently, the fabrication and installation of a high-profile and challenging water reservoir containment project for the prestigious Pebble Beach, Calif., community was completed. Originally constructed in the late 19th century, the Forest Lake Reservoir, near a scenic stretch of California's coastline, underwent a dramatic transformation and upgrade to service its irrigation needs.

Located in the Monterey Peninsula, the Pebble Beach Community Services District (PBCSD) recently commissioned the rehabilitation of the Forest Lake Reservoir to be used for the containment of recycled water. The recycled water was required for irrigation purposes for a number of courses and recreation areas, including prominent PGA tour venues such as Pebble Beach, Spyglass Hill and Poppy Hills. The project included supplying and installing approximately 950,000 sq ft of a specially produced tan-colored, five-ply, scrim-reinforced Hypalon geomembrane and a geosynthetic composite drainage system.

Mike Niccum, district engineer with the PBCSD, said one requirement of the reservoir was to accumulate and store water through the winter months when irrigation is generally not needed for the various Pebble Beach golf courses and green spaces. The stored recycled irrigation water is primarily required for the dryer summer and fall months when irrigation demands typically exceed water production.

Engineering challenges

The design of the project included a number of environmental sensitivities and engineering challenges. In particular, the California Department of Water Resources, Division of Safety of Dams, was concerned with stability issues in the event that sufficient quantities of surface water penetrated and weakened the earthen embankment.

As a result, the project was subject to stringent design and permitting requirements. Following a similar rehabilitation project design in the Los Angeles area, the project specified the use of a high-performance, ANSI/NSF 61-certified, five-ply scrim-reinforced Hypalon geomembrane with a functional exposed service life of 25 years. The material offers excellent UV and physical properties, including high tensile strengths and puncture resistance.

The scope of the Forest Lake Reservoir project included prefabricating the geomembrane at the Layfield fabrication plant located in Hollister, Calif. Based on the irregular shape of the reservoir, a pre-designed panel layout was completed to minimize material waste. This process included 175 prefabricated 34-ft-wide panels in lengths up to 200 ft.

The plant fabrication on the geomembrane started in early July 2005 and was strategically sequenced with the liner installation in August 2005. In addition to the 950,000 sq ft of 65-mil five-ply Hypalon and geosynthetic drainage composite, the project required 3,300 lineal ft of perimeter mechanical anchorage and the use of specialized cap strips to reinforce all cross seams.

The project also had a very tight leak tolerance specification requiring an electrical leak location test be conducted over the entire installed geomembrane surface. The prefabrication of the geomembrane allowed the majority of the seaming work to be completed under controlled welding conditions in the Hollister plant, which reduced the amount of field welding and overall installation time.

"This sensitive project was successfully supplied on time and on budget," said Jon Feenstra, a project manager for Layfield.

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