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Aquaiic and Riparian Resource-s " <br />80 years, as discussed above, so that water yield increases produced by harvest in the first decade <br />add to increases from harvest in the second decade, and so on. <br />Modeling was not performed for the other alternatives, but because water yield increases aze <br />ronghly proportional to the proposed harvest volume for each alternative, relative changes in <br />water yield increase can be estimated by comparing harvest volume for Alternative B with the <br />planned volume for other alternatives. The average water yield increase for Alternative B is <br />0.1165 AF feet per thousand board feet (1VOF) harvested. <br />Fire, both prescribed and natural, will have a considerable effect on water yield. It is estimated <br />that wildfire will burn approximately 1,100 acres per year for each alternative except Alternative <br />H, where 3,700 burned acres are expected. An additional 6,000 acres of forested Iand will be <br />treated for fuel management through a combination of prescribed fue and mechanical treatment. <br />(For a detailed description, see the Fire section in this chapter.) For Alternatives B, E, and I, the <br />water yield increase cansed by fue will exceed that caused by timber harvest. <br />The values in Table 3.17 differ from those in the table above because they display the average <br />annual water yield generated by vegetation treatment over five decades rather ihan decade by <br />decade increases from treatments in previons decades. However, the table does allow the <br />comparison of water yield increase by alternative. <br />Table 3.17 Estimated Water Yield Increase bv Alternative (Averaae AF/ r over 5 decades) <br />Alternatives A. B C E H` I <br />Harvest Volume 17,576 6,668 19,369 2,036 1,017 14,855 <br />Water Yield-Timber 2,048 777 2,256 237 118 1,731 <br />Water Yield-Fire 1,614 1,614 1,614 1,614 2,190 1,614 <br />T'otal Water Yieid <br />Increase.(AF/yr.) <br />3,662 <br />2,391 <br />3>870 <br />1>851 <br />2,308 <br />3,345 <br />It should be noted that the present water yield of the Forest includes water yield increases from <br />; past and current veQetation manajement. While timber harvest declined under the 1984 Foresr <br />? Plan to a low of 2,244 MBF in 1995, the average harvest volume for the period 1976 to 1994 <br />, <br />was 14,647 MBF. This volume is a eater than the projected volume for all alternatives except A, <br />? C, and I. As the water yield from past harvest diminishes, water yield increases from planned <br />harvest for Alternatives B, E, and H will be insufficient to make up the difference, and total <br />water yield from the Forest will decline sli?htly. However, water yield increases from vegetation <br />? management or fire make up only a small fraction of the total water yield for the Forest. <br />?!•?t <br />' '. <br />t>? <br />?. <br />Chapter Three • 127 <br />1 <br />?