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EXECUTIVE SUMMARY <br />?, . <br />Estimating Additional Water Yield From Changes in Management of <br />National Fore;sts in the North Platte Basin <br />C.A.1 roendle & J.M. Nankervis <br />The Platte River EIS is exa:min.ing alternative approaches to improving river <br />flows in the Central Platte River for four threatened and endangered :;pecies <br />(target species). Many differe;nt approaches to increasing basin stor•age of <br />waters, management of viaters, and retiming of river flows are being <br />examined. Among the alternatives suggested during the scoping process is <br />the concept of increasing the timber harvest on National Forests in the <br />headwaters of the Platte River as a means of augmenting the water supply. <br />This study is undertaken to pr•ovide a reconn i? ssance-level analysis of the <br />water yield that might be expec;ted from such an action as well as the current <br />impact of past management activity. <br />In order for increased runaff f'rom the National Forest to lead to improved <br />Central Platte R.iver flows fc>r the target species, some fraction of the <br />additional flows must be captured and allocated to the Recovery Program. <br />The most likel y means for this is ca pture and storage in a Federally operated <br />reservoir. Due to the number of Federal reservoirs on the North Piatte, as <br />well as their relative proxirriity to the North Platte headwaters, it appears that <br />focusing this study on the North Platte forests is a good test of the vi.ability <br />of this concept. <br />Several issues stand out as a re;sult of this analysis. First, and perhaps most <br />interesting is the magnitude of the simulated decrease in flow that has <br />occurred over the last 140 years due to vegetative growth; a ecrc;ase of <br />185 000 ?cre-feet or more cTwater`from 1,107,000 acres of NFS land.1 <br />- <br />Water yield from NFS lands on the North Platte is in general quit.e high <br />because of the high precipi.tation input. Although the percentage of <br />forestland Suitable for Tinibei• Harvest is less than 50 percent of the total <br />NFS lands, sizable increa:>es in flow appear feasible using the 120-year <br />rotation and appropriate silvic;ultural techniques for each forest type with <br />lodgepole pine and spruce-:Eir being the most prevalent. Simulations indicate <br />that water yield can be increase;d by 37,000 acre-feet per year by 2015 with a <br />gradual increase, through the rotation, to sustainable 50 - 55,000 acre-feet of f <br />water per year. _