The Franzen project reinforced the reservoir's earthen support structure and split the reservoir into two separate lined cells.Click here to enlarge imageThe US$ 16.6-million Franzen Rehabilitation Project, which split a reservoir into two lined cells and provided both sections with floating covers, was completed for the US city of Salem, Oregon in December 2004.
The reservoir was built in the 1950s and holds nearly 100 million gallons of drinking water. Salem depends on 17 other reservoirs, but Franzen is by far the largest, serving 171,000 water customers. It holds water drawn from the North Santiam River and is treated at the city’s Geren Island facility.
The Franzen rehabilitation project reinforced the reservoir’s earthen support structure, splitting the reservoir into two separate lined cells, an east and west cell, and then providing each with a floating cover. The double cell design will provide maximum operational flexibility in that half of the reservoir can be taken out of service for repairs or maintenance while the other half continues to provide water to the city.
The floating covers will protect the water from contaminants such as dust, leaves and other debris, and prevent water loss from evaporation. The US company of Cooley Engineered Membranes of Pawtucket, Rhode Island, manufactures Coolpro®, a special 45-mil reinforced polypropylene membrane, that was used by Colorado Lining International, Inc. to make the reservoir cover and liner.
The City of Salem specified the membrane to be tan on one side and white on the other. For the liner and cover, the white side of the membrane faces the interior of the reservoir, so that a diver’s flashlight reflects the white, making it easier to inspect the reservoir when filled. The city chose the tan colour to blend harmoniously into the woodland area where the reservoir is located.
The success of the project depended upon several functional characteristics. Durability is key to the success of any membrane exposed to the elements. Ultraviolet light, the same light that causes sunburn, can degrade a membrane that isn’t properly protected and stabilised. Cooley’s polymer chemists designed Coolpro with special light stabilisers to ensure the cover will function as intended for 20 years.