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I'rocndk/Nanl:crvis/Porth Page 4 5/22/2003 <br />original stand characterization (sFx:cies composition, age class, management class, aspe;ct, <br />clevatiom, etc.), monthly precipitation, and post-1997 managrment activity. <br />I I istorical 'I'rends <br />In a iixinncr similar to that donc in the in the earlic:r analysis, current stand conditions were <br />projected tackward in time, in 20 year incre;ments, to the year 1860. For each 20-year increment <br />a new adjusted age was calculated for each stand, or polygon, and a new basal area estimaled <br />tiurn the age/hasal area relationships pravided by the Forests (see fur example Figures 12a - 12c <br />in 'l'roendle and Nankervis 2000) for each torest tyEx:. As in the earlier efYort, it was assumed that <br />once the age of an existinb stand was disc:ounted tu age zero, or non-stocked, it was assumrd to <br />have; teen lully fore;sted in the prior 20 year time increment. Furest stand characteristics were <br />redetined for each 20-year increment from I860 tc+ 1997 and the SAS 8.2 versicin ot' thr <br />WRFNSti hydralogic modcl was used to simulate average hydrolugic respunse, by torest type, <br />tbr each interval. <br />A comparison ot'the historical watcr yield tnom Natianal Forest land in the Narth Plaue River <br />E3asin simulated using the earlier I)OS version ol' the WRF.NSS hydrologic mudel versus the <br />SAS R.2 version is presc:nted in Figurr l, teluw and in Figurr 2 ul'Appendix A. Although there <br />is a str„ng similarity in the simulated decline flow over tinu, the ahxolwe estimates ot' watcr <br />yield diflcr signiticantly tx;twcen the two models. "t'he causal factors ztrc explainrd in Anpendix <br />A. <br />15 <br />14 <br /> ¦ Swanson: DOS <br />' 13 ¦ Nankervis : SAS <br /> <br />? <br /> <br />y-. 12 <br />- <br />? <br /> <br />10 ? <br />9 - .? <br /> <br />1860 1880 1900 1920 1940 1960 1980 199i 2017 <br />Year <br />Figure I. ('ompariuon of the simulated stream fluw fTUm Natic+nal Forest lands in the North <br />Platte River 13asin for the period 1860 to 1997 using the f)Oti model (Troendle and <br />Nankervis 2000) and the SAS modrl (ApNndix R. this clocument). Stream flow fi?r <br />2017 was simulated using the tiAS mudel unly.