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WSP03260
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Last modified
1/26/2010 12:49:29 PM
Creation date
10/11/2006 11:37:42 PM
Metadata
Fields
Template:
Water Supply Protection
File Number
8276.120.10
Description
Grand Valley Unit-Colorado River Basin Salinity Control Project
State
CO
Basin
Colorado Mainstem
Water Division
5
Date
9/10/1991
Title
Final Environmental Assessment: Alternative Lining Methods for the Government Highline Canal - Grand Valley Unit
Water Supply Pro - Doc Type
EIS
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<br />"" <br /> <br />:::.l <br /> <br />~ <br />o <br /> <br />Modified Alternative Ml because the proposed shifting of the canal <br />requires significantly more excavation and fill, and construction <br />would require additional temporary ROW. <br /> <br />- <br />,--' <br />~.:) <br /> <br />Concrete Lininq Alternatives <br /> <br />A second group of alternatives involve concrete lining. A March <br />1991 geological investigation of the East End Government Highline <br />Canal found that foundation materials through much of the area were <br />not stable and were dominated by a preponderance of silt-sized <br />particles which are susceptible to frost action (Reclamation, <br />1991). The unstable foundation materials dominate the last half of <br />Reach 1A west of 36.3 Road, and all of Reach lB. unstable <br />foundations cause significant cracking of a rigid concrete lining, <br />therefore concrete lining of these portions would require costly <br />installation of a suitable foundation for these reaches. This is <br />not a problem with a flexible membrane lining. Along Reach 1, the <br />irrigation of lands above the canal and high water tables increase <br />requirements for canal drainage structures for concrete compared to <br />membrane lining. These factors are reflected in increased <br />construction and O&M costs for concrete as compared to membrane <br />lining. <br /> <br />Alternative Cl - Alternative C1 (Concrete 1) would concrete line <br />the entire length of a given reach and would generally avoid the <br />need to widen the canal and purchase additional fee land. However, <br />the purchase of from 3S to 9S feet of temporary ROW would be needed <br />north of the canal for use during construction. Temporary ROW <br />width could typically be 6S feet, and might be reduced or <br />eliminated in short stretches to avoid high value areas. <br />Alternative Cl has been evaluated for Reaches lA, lB, and 2 even <br />though the feasibility of implementing it along Reaches lB and 2 is <br />doubtful without extraordinary construction measures considering <br />the prevalence of unstable foundation materials. <br /> <br />Figure 3 depicts the temporary ROW requirements associated with the <br />design and construction of a typical concrete-lined section of the <br />canal. As in Modified Alternative Ml, the design centerline of the <br />concrete-lined canal is adjusted 10 feet to the south of the <br />existing canal centerline to make better use of the existing u.S. <br />property. <br /> <br />Due to safety considerations, the concrete lining would require <br />much stricter fencing and the installation of "escape" structures <br />along the canal. These structures include ladders and deer escapes <br />and are necessary because people, deer and other animals are unable <br />to escape from the steep, slick sides of concrete-lined canals. <br />Land would need to be acquired in the area of each deer escape <br />structure and would be located where impacts to adjacent land uses <br />would be minimized. The exact number and location of these <br /> <br />14 <br />
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