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<br />. 0 0 ~~ ~; ~ j "1 <br />j'_-C- __ -=c..-,- <br />d <br />II <br />:i <br />" <br />;1 <br /> <br />. <br /> <br />I: <br />, <br /> <br />,.' <br /> <br />~ <br />,I <br /> <br />-21- <br /> <br />penetrat~by water to reach the much more pervious materials iu <br /> <br />the buried channel. <br /> <br />We estimate that the maximum foundation seepage with no <br /> <br />cutoff or blanket aud with reservoir level at elevation 4575 would <br /> <br />amount to 31 cubic feet per second. This estimate is approximate, <br /> <br />using a transfo!"med-section flow net, but we feel that it is with- <br /> <br />ing the accuracy of the permeability tests themselves. Conser- <br />I <br />" vative asswnptions were made throughout, including those of <br /> <br />!I <br /> <br />(a) neglecting the "blanketing" effect of the Aeolian deposits <br /> <br />,; and (b) assuming ,the buried channel to be under the maximum,dam <br /> <br /> <br />,I section. More accurate calculations by eleetl'ic analogy analyses <br /> <br />I <br />" <br /> <br />. <br />. <br />.:.,. <br /> I <br /> I <br /> :1 <br /> " <br /> ! <br /> , <br /> <br />~ <br /> <br />f' <br />'" <br /> <br />" <br /> <br />" <br /> <br />" <br />, <br /> <br />could be made but these would also be subject to the same iu- <br /> <br />herent inaccuracies of the permeability determinations. We have <br /> <br />assumed the conditions indicated in Figure 10 in our analyses. <br /> <br />It is our general op~ ion that there will be substantially <br /> <br />less total seepage at the Weld County site under given cutoff or <br /> <br />blanketing treatment than there will be at the Narrows site, par- <br /> <br />ticularly in view of the fact that there is a buried channel of <br /> <br />similar size and permeability by-passing the Nau"ows site. The <br /> <br />Weld County site is subject to improvement since cutoffs through <br /> <br />the major layers could be made to reduce seepage by sub~tantial <br /> <br />Ulounts, or even cut it off almost entirely. <br /> <br />Several cutoff alternatives COUle to our mind which we believe <br /> <br />are practical: (1) a cutoff to bedrock on the abutments, and to <br /> <br />water table elevation in the channel area, which would be quite <br /> <br />economical to construct. We wou ld envision an open-cut on ap- <br /> <br />proximately 1:1 slopes with the trench backfilled with compacted <br /> <br />impervious clays. The extra costs involved over construction of <br />