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<br />'~J <br />(Yj <br />...-4 <br />o <br /> <br />:-:-i <br /> <br />other factors which have been compared for concrete and membrane <br />lining are: <br /> <br /><~=) <br /> <br />Safetv: As discussed in the "environmental consequences" <br />chapter of the EA, membrane lining is safer for two significant <br />reasons. First, with flatter sideslopes, it is easier to climb out <br />of a membrane-lined canal. with concrete lining, structural <br />modifications are required to allow an animal or person to climb <br />out of the canal. In addition concrete becomes very slippery <br />because of algae growth. The second reason is the slower velocity <br />of the water in the membrane-lined canal. The velocity in a wider <br />membrane-lined section is about 1.5 miles per hour while the <br />velocity in a concrete section is about 2.3 miles per hour. These <br />seem to be relatively low numbers, but when a person is trying to <br />get out of a canal, this 50 percent increase in velocity is <br />significant. <br /> <br />Life exoectancv: With a 35-year history of use for membrane <br />lining, to consider a life expectancy of 50 years requires <br />extrapolation of existing data. Several membrane-lined canals have <br />been found to be performing satisfactorily after 20 to 30 years of <br />service. Most of these earlier membrane-lined canals used 8 or 10 <br />mil PVC. Based upon this evidence, increasing the lining thickness <br />to 20 mils, and modifying the PVC formulation to provide a more <br />flexible lining, Reclamation feels that a 50-year expected life is <br />reasonable. <br /> <br />Concrete lining can and has lasted both longer and shorter than 50 <br />years. The major factors which influences how long concrete would <br />last is foundation stability and climatic conditions. Both of <br />these factors weigh against the use of concrete for the proposed <br />canal construction, especially in the last 9 miles of Reach 1 and <br />probably in Reach 2. It is possible to design and properly install <br />a concrete canal to better tolerate these factors, but at <br />significant additional costs as reflected in the construction costs <br />presented in Table 1 of this EA. The concrete lining alternatives <br />are thought to address these factors to a practical degree, thus we <br />feel a 50 year life is possible. <br /> <br />Ooeration and maintenance (O&M): Reclamation has found that <br />annual O&M costs for concrete-lined canals are 80 percent greater <br />than for membrane-lined canals in the Grand valley. This <br />determination is based upon data collected from 1930 through 1984 <br />on 3,000 miles of irrigation system canals in environments similar <br />to the Grand valley. It recognizes factors that make maintenance <br />of membrane more difficult than concrete such as increased care <br />needed in cleaning of the less durable membrane lining, and of <br />increased vegetative growth and weed control problems. Expensive <br />concrete maintenance problems are inherent with the climatic and <br />foundation materials in the Grand Valley. <br /> <br />43 <br />