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J <br />EXECUTIVE SUMMARY <br />Estimating Additional Water Yield From Changes in Management of <br />National Forests in the North Platte Basin <br />C.A. Troendle & J.M. Nankervis <br />The Platte River EIS is examining alternative approaches to improving river <br />flows in the Central Platte River for four threatened and endangered species <br />(target species). Many different approaches to increasing basin storage of <br />waters, management of waters, 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 provide a reconnaissance -level analysis of the <br />water yield that might be expected from such an action as well as the current <br />impact of past management activity. <br />In order for increased runoff from the National Forest to lead to improved <br />Central Platte River flows for the target species, some fraction of the <br />additional flows must be captured and allocated to the Recovery Program. <br />The most likely means for this is capture and storage in a Federally operated <br />reservoir. Due to the number of Federal reservoirs on the North Platte, as <br />well as their relative proximity to the North Platte headwaters, it appears that <br />focusing this study on the North Platte forests is a good test of the viability <br />rof this concept. <br />Several issues stand out as a result 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 decrease of <br />185,000 acre -feet or more of water from 1,107,000 acres of NFS land. <br />Water yield from NFS lands on the North Platte is in general quite high <br />because of the high precipitation input. Although the percentage of <br />forestland Suitable for Timber Harvest is less than 50 percent of the total <br />NFS lands, sizable increases in flow appear feasible using the 120 -year <br />rotation and appropriate silvicultural techniques for each forest type with <br />lodgepole pine and spruce -fir being the most prevalent. Simulations indicate <br />that water yield can be increased 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 <br />water per year. <br />1 <br />