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<br />" ~ . <br /> <br />the array of potential solutions too quickly since optimal solutions are <br />rarely intuitive in nature. A general c1iscussion of selecting salinity con- <br />trol options for irrigated agriculture is givenbySkogerboe et a1. (1979b). <br /> <br />o4:lo. <br />N <br />l\.j <br />c.o <br /> <br />Canal and Lateral Linings-- <br />Many unlined canals, ditches, laterals, and watercourses traverse long <br />distances between the point of c1iverdon ancl the farm. Where soils are well <br />structured and permesble, seepage loesea may be considerable. Traditionally, <br />reaches with high seepage losaes have been lined with a variety of 61 ternative <br />materials. such as concrete, asphalt, bentonite clays, compacted. earth, and <br />plastic sheeting to prevent seepage with the economic justificationbasecl on <br />the value of the water saved. Converting to a closed concluit of concrete, <br />asbesto.s-cement (A-C) or plastic is an effective alternative that .offers <br />advantages of better trafficability, reduced evapoTation, maintenance of <br />pressura clue to gTavity, ancl aesthet.ics. <br /> <br />Cost of conveyance channel lining vary with apPToximately the square root <br />of the channel cspacity, so unit oosts c1iminish with increased scale of con- <br />struction. Seepage rates per unit of channel erea, on the other hancl, tend to <br />be higher with smaller-sized channels because of less meintenance, greater <br />depths to a wster table, and larger ratios of wettecl perimeter to discharge <br />capscity. <br /> <br />A review of concrete linings costs in the western Unitecl States by Walker <br />(1978) indicated a reasonably h:tgh correlation bet1<leencapscity and cost. <br />Data presentecl by the USDI, Bureau of Reclamation (1952, 1963), ancl personal <br />communication (USDI, ER, 1976) and Evsns etsl. (1976) indicate the following. <br />general form: <br /> <br />. <br /> <br />Co. - IS. .QK2 + K3 <br /> <br />(20) <br /> <br />in which, <br /> <br />C - unit lining cost, in dollars per meter; <br />c <br /> <br />lll' <br />II <br /> <br />Q - conveyance capacity, in cubic meters per seconcl; <br /> <br />Kl encl Kz -empiricel site~a,pec:Lfiocoefficients; <br />. ,..!C3'.:" fb~d.coets, in dollarsper.meter. <br /> <br />..."...' ..:,..,;...... <br /> <br />. The slope of the canal WOuld affectvaluell .0fK . and K dpcea given dis.- <br />. charge can be conveyacl in a smaller channel if ~heslo~e" is inc1'assad.......Many. <br />large canals have fairly flat slopes and can be estimatecl with Equation 20. <br />If the channel slope is greater than 0.001, the co.efficients shoulcl be re- <br />evalustecl. <br /> <br />For conclitions in western Coloraclo end indexecl to Jenuary, 1980 time <br />hase, the value of IS. was found to be 99.34, K was 0.56, ancl K rangecl from <br />$25-$95/m with an average value of $61.60/m. tne costs includaa in the first <br />term on the right-hand sicle of Equation 20 are earthwork, relocation, lining <br /> <br />52 <br /> <br />.'. <br />