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In general, the simulated trends in stream flow whether the result of <br />historical in-growth,? sim ted harvesting, or catastrophe appear consistent <br />with observed changes measured at the streamgage for treatments with a <br />comparable impact. The hydrologic model WRENSS appeared to perform <br />well when simulating the effects of fire, insect mortality, and timber harvest. <br />Simulations of hydrologic response to both clear cutting and partial cutting <br />compare well with observed changes in flow measured at the stream gauge, <br />for similar impacts. <br />It would seem unlikely that the simulated changes in flow following timer <br />harvest simulations would be detectable at any streamgage on the North <br />Platte River. Neither is it likely that the simulated increases in flow could <br />actually be detected as they exit NFS land, assuming a gauge were present to <br />monitor them. <br />It is conceivable that decreases in flow on the order of magnitude simulated <br />for the historical trend in forest cover could be detected downstream at a <br />USGS gauge, if the gauge had an adequately long and consistent record. <br />Since most gauges (North Platte at Northgate and Mitchell, North Platte <br />?•-? ?, below Whalen, etc.) were not initiated until the early 1900's, thus making <br />detection of the flow reduction, as simulated, questionable. <br />,_...?., <br />Although we chose not to simulate the potential response to other <br />management scenarios, one can infer the relative impact of adding or <br />subtracting Suitable acres based on simulated responses for the acreage <br />currently available. One can also infer the impact of fully or partially <br />implementing the management alternatives or a modification of them. Costs, <br />in terms of water yield, can also be calculated as opportunity forgone for <br />exclusions for Wilderness, wildlife set asides, and so on. To the degree the <br />data set provided to us properly characterizes the vegetation, the historical <br />trend simulations are indicative of the cost, in water, of allowing vegeta.tion <br />density to increase., Although we did not specifically address peak flows <br />and low flows, we would expect the nature of the simulated responses to fall <br />within the frequencies and distributions observed on experimental <br />watersheds. Except following fire at lower elevations (5 - 7,000 feet), we <br />would not expect peaks or low flows to be altered. <br />?:;r;.