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4.3.4.2 Minimum and Maximum Root Potentials <br /> The minimum root potential is the minimum potential at which plant roots can <br /> remove water from a soil and should be within range of the wilting point <br /> (estimated around—1500 Kilopascals (Kpa)) and the hygroscopic water of a soil <br /> (estimated around—3100 Kpa) (Brady and Weil, 1996). The maximum root <br /> potential is associated with the force required by plants to access capillary water <br /> (estimated to be around 0 to—30 Kpa). <br /> Calculated net flux through several modeled profiles varied significantly when <br /> completing sensitivity analysis using minimum root potential values between <br /> -1000 and -3000 Kpa and only slightly when using maximum root potential values <br /> between—30 Kpa and 0 Kpa. As a result, it is concluded that the minimum root <br /> potential is a sensitive parameter and system performance will be enhanced by <br /> incorporation of relatively high suction and region plant communities. In <br /> anticipation of the use of high suction and plant types, a reasonably conservative <br /> minimum root potential of-2000 Kpa(relatively low for and plant types)was <br /> selected for long-term analyses. <br /> Though not considered a sensitive parameter, a conservative maximum root <br /> potential of-15 Kpa, were selected for the analyses included to simulate the water <br /> extraction capabilities of the average grass and shrub vegetative cover anticipated. <br /> 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 /> • <br /> -8- <br /> C:\20050082\FOR WARD/FonvardCOVER.DOC\7/11/2005 <br /> Geologic Associates <br />