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0 4.3.4.3 Crop Cover Fraction <br />Selection of crop cover fraction coefficients ranging from 0 to 60 percent resulted <br />in significant changes in the calculated net flux and as a result, crop cover fraction <br />is considered a sensitive parameter. Since undisturbed areas of the native <br />landscape adjacent to the FSL currently support a sturdy vegetative growth of at <br />least 60 percent, this value was selected for subsequent long-term analyses. <br />4.3.4.4 Root Distribution <br />Root distributions were incorporated in the analyses completed for this study by <br />simulating native shallow rooting grasses with only a few deeper rooting shrubs. <br />As modeled in the long-term analyses of the alternative design, roots were limited <br />to the upper three feet of the proposed four foot final cover profile, with 87 <br />percent of the roots assigned to the upper one foot (3 05 mm) interval, 10% in the <br />middle 2-3 foot layer and 3% for the bottom foot. As shown in Table 3, variations <br />in root distribution did yield significant variability in system performance <br />however and this parameter is therefore considered a critical variable for system <br />performance. As a result, incorporation of an intermediate root depth shrub into <br />the low-lying grass vegetation is considered an important component of long-term <br />system performance. <br />For the prescriptive analyses presented herein, though the soils were assumed to <br />yield similar performance under prescriptive and alternative cover conditions, the <br />vegetation was assumed to be limited to the 1 -foot thick vegetative layer. <br />4.3.4.5 Root Length <br />As shown in Table 3, variations in the cumulative root length (within a 2 -meter <br />square area) do not significantly alter the performance of the cover system. As a <br />result, this is not considered a sensitive parameter. A conservative 100 -meter root <br />length was selected for subsequent long-term analysis. <br />4.3.4.6 Root Flow Resistance <br />As shown in Table 3, slight variations in root flow resistance yielded insignificant <br />changes in cumulative system performance. As a result, this is not considered a <br />sensitive parameter and a root flow resistance of 1.0 was assigned for the long- <br />term analyses presented herein. <br />la <br />C:U003-033\EDOM HILL ALTERNATIVE COVER.DO06/16/2005 <br />Geologic Associates <br />