Estimating Additional Water Yield From Changes in Management of National Forests in the North Platte Basin

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d Coon Creek. The calibration relationship, as well as pre- and post - harvest seasonal flow values are presented in figure 8. Flow was significantly increased as a result of timber harvest, but it should be noted seasonal increases in flow only slightly exceeded the significance detection limit. Generally, it has been assumed that 20 -25 percent of the vegetation on a fully forested small watersheds has to be harvested in order to generate a detectable response at the streamgage. Approximately 24 percent of the vegetation on the Coon Creek watershed was harvested and the increase is slightly above the detection limit. In addition, in an attempt to harvest as much of the area as possible, many of the clear cuts crossed interior ridges, as they did on the Upper Basin at Deadhorse Creek, causing a certain degree of wind scour. Snow pack accumulation in the openings was not increased on Coon Creek (Troendle et al. 1998) and there may be actual decreases in net accumulation on the watershed in wetter years as a result of exposure to wind. (Troendle and Meiman (1984) observed that once slash or roughness, filled with snow, retention efficiency in openings decreased). ^ 26 24 ❑ ❑ 0 22 ❑g 20 '��/ o lg CO rn 16 U 12 -i 1983 -1990 t t t 1991 -1992 U0 10 rCO3O 1993 -1997 Fit for 1983 -1990 8 - Lower 95% CI for Mean — — - Upper 95% CI for Mean — — Lower 95% CI for 1 Pred — — Upper 95% CI for 1 Pred 6 6 8 10 12 14 16 18 20 22 24 26 28 Upper East Fork Seasonal Flow (in) Figure 8: Seasonal water yield for Coon Creek watershed (harvested) plotted over that for the Upper East Fork (control). Pre - harvest, harvest, and post-harvest data are presented. Understanding the dynamics of stream flow response to timber harvest is critical to evaluating the opportunity to increase flow via timber harvest and equally critical in assessing the effects of forest regrowth on historic flows. 16 1