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<br />!"j <br />('r) <br />~ <br />o <br /> <br />~:) <br /> <br />Reoair: when the canal is full of water, it is not any more <br />difficult to find a break in a membrane lining than a concrete one. <br />Once found, repair of membrane lining is significantly less <br />expensive, and it takes less time to resume irrigation water <br />service because the additional time to allow for the curing of <br />concrete is saved. During the non-irrigation season it is usually <br />easier to see a break in a concrete lining; however with membrane <br />lining there is usually an indication of surface disturbance which <br />would indicate potential leaks. <br /> <br />Comment 8: The increase in O&M costs for weed control of membrane <br />lining as compared to concrete lining should be recognized in the <br />EA. <br /> <br />::~) <br /> <br />Resoonse 8: The increase in vegetative growth for membrane vs. <br />concrete-lined canals and resulting O&M cost increases have been <br />considered. It is comparable to weed control costs for the <br />existing earth lined canal, and it is overshadowed by expensive <br />repair and maintenance anticipated for concrete lining. Increased <br />vegetative growth would result from lower water velocities in the <br />membrane-lined canal where more sediment is deposited in the canal <br />to support vegetation growth. In the concrete-lined sections, the <br />higher velocities significantly reduce the amount of sediment <br />deposition. In any of the alternatives, the GVWUA is responsible <br />for controlling vegetation according to plans which are submitted <br />for approval by Reclamation. <br /> <br />Comment 9: Concrete lining is preferred over membrane lining <br />because evaporative losses would be greater for the wider, <br />membrane-lined canal. <br /> <br />Resoonse 9: Evaporative losses would be greater from a membrane- <br />lined canal as compared to existing or concrete lined conditions, <br />but these losses are considered to be minor after taking into <br />account the amount of water that would be conserved by either <br />lining alternative. For Reach 1 the total evaporation from the <br />existing canal is approximately 240 acre-feet of water per <br />irrigation season. There would be about 200 acre-feet of <br />evaporation from a concrete-lined canal and about 320 acre-feet <br />from a membrane-lined canal. Currently, annual seepage losses from <br />Reach 1 have been determined to be about 4,600 acre-feet per year; <br />for either lining method this would be reduced to 1,000 acre-feet <br />per year. Therefore, lining of Reach 1 would conserve about 3,600 <br />acre-feet per year. The net savings considering differences in <br />seepage gains and evaporative losses for Reach 1 would be 3,640 <br />acre-feet (3,600 - (200 - 240)) for the concrete lining <br />alternatives, and a 3,480 acre-feet (3,600 - (320 -200)) for the <br />membrane lining alternatives. <br /> <br />Comment 10: The lacing of alternatives with inflexible and <br />unacceptable policies makes the EA spirit not one of cooperation. <br /> <br />44 <br />