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Troendle/Nankervis/Port.h Page 2 5/22/2003 <br /> <br />b) Current stand conditions (ca 1997) were then adjusted annually to reflect management <br />activities actually imposed on the forests in the North Platte basin during the period 1997 <br />to 2001. Since past 2001 activity data are not available, it was assumed a similar level of <br />activity would aontinue to occuT from 2002 to 2017 and the effect of that activity on <br />stream flow was ;also simulated. <br />c) The Forests provided additional information on "catastrophic" impacts (fire, insect and <br />disease) that ocr,urred on the forests in the North Platte drainage in 2002 and we <br />simulated the impact of those acl:ivities on stream flow as well. The Forests were asked to <br />provide data on the catastrophic impacts in 2002 by vegetation type, stand age class, and <br />an index to basal azea reduction (or burn severity). Factors such as precipitation, aspect, <br />and elevation were obtained from the GIS. <br />The requirements under Task 1 focused on starting with the forest stand conditions that existed <br />in 1997 and projecting those conditions into the future to evaluate the potential effect of <br />management on future :;tream flows. In one simulation scenario, no management intervention <br />and only natural success:ion was allowed to occur from 1997 to 2017. In the second scenario, the <br />hydrologic impact of the current level of?mana.gement activities on stream flow was projected out <br />to 2017. However, the entire analysis utilized a more refined version of the Water Resource <br />Evaluation of Non-Point Sources in Silviculture Hydrologic Model (WRENSS, see Appendix A) <br />than the DOS version of'the model useci in the earlier analysis. Therefore, the entire ana.lysis of <br />the historic trends in w;ater yield done in the first assessment was repeated to using the new <br />model and comparisons i-nade with the earlier results obtained using the DOS model. <br />Projecting stands back ui time, to deterrnine historical impacts, followed the simplistic approach <br />of starting with current stand conditions and then moving stands into and out of various age <br />classes, in 20-year increments back thni time to the yeaz 1860, as previously done by Troendle <br />and Nankervis (2000) in the initial assessment of the North Platte Basin. In the current analysis, <br />the hydrologic simulatioins were made using a revised version of the WRENSS hydrologic model <br />in SAS 8.2, programme;d by J.M. Narilcervis (Appendix B). As presented in this report, the <br />results of simulation of total water yielcl, using the new model, differ from the yields simulated <br />using the DOSS version in the initial North Platte assessment (Troendle and Nankervis 2000). <br />Simulations of the increases, or declines,, in flow that occur because of changes in vegetation aze <br />similar, however. The differences in the simulation of total flow reflect data management change <br />more so than technical change in the model (see Appendix A). The revised SAS 8.2 model (see <br />Appendix B) represents an updated stand-alone nomographic model that reflects current <br />hydrologic thinking for the Snow Zone: of the Central and Northern Rockies (a.k.a. WRENSS <br />Hydrologic Region 4). 7'his report includes validation and documentation of the consistency of <br />the hydrologic simulatio:ns done for this effort and compazes the new simulations with the earlier <br />simulations. <br />The second major task in this effort involved identifying a series of reference stream and <br />precipitation monitoring; sites that would be useful in documenting measurable long term <br />changes in stream flow that might occiu as a result of NFS Forest Management activities and <br />other land and water use changes within the Platte River Basin, both on the North and South