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ATTACHMENT 3 <br />_I <br />.-._ ? <br />f <br />? <br />INTERPRETATION OF WATER YIELD INCREA5E RELATIVE TO BASELINE <br />WATER YIELD <br />The projected water yield increase from timber harvest was modelled for the 1997 Routt <br />National Forest Land Management Plan Revision. Estimations were also made of the baseline <br />water yield from the Routt National Forest (RNF) based on USGS gage station data from <br />undisturbed basins. <br />The average annual baseline water yield from the entire RNF is estimated to be 1.6 million acre- <br />feet. The baseline water yield range within one standard error is 1.1 to 2.1 million acre feet. <br />Water yield increases from full implmentation of the preferred alternative were modelled for the <br />first five decades (Table 1). In the first decade water yield would increase by 7300 acre-feet, <br />which would be an average annual increase of 730 acre-feet. Water yield would increase in the <br />subsequent decades due to the effects of harvesting during the decade of interest combined with <br />the residual effects of harvesting from the previous decade(s). By the fifth decade water yield <br />would increase to 28700 acre-feet which would be an average annual increase of 2870 acre-feet. <br />The average annual water yield increase is less than 0.5 percent of baseline for the first decade, <br />and two percent for the fifth decade. This increase appears to be negligible and is well within <br />one standard deviation of the baseline water yield. <br />TABLE 1 <br />DECADE WATER YIELD INCREASE (acre-feet) <br />1 7300 ac-ft <br />2 12,800 ac-ft <br />3 18,600 ac-ft <br />4 23,100 ac-ft <br />5 28,700 ac-ft <br />LIZ SCHNACKENBERG <br />Hydrologist <br />1 Q/ 10/97 <br />N ??- <br />10