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Troendle/Nankervis/Porth Page 5 5/22/2003 <br />The simulations using the DOS version (Troendle and Nankervis 2000) of the WRENSS <br />hydrologic model indicated the average decline in stream flow from 1860 to present was about <br />3.0 area inches of water (Table 1). The SAS model indicates an average decline of about 3.4 <br />inches of water yield for the same time period (Table 1, Figure 2). In both the DOS and the SAS <br />model simulations, the dominant contributor to the simulated decline in stream flow is the <br />simulated response from the spruce-fir forest type (Figure 3). <br />Table 1. Stream flow estimates for the DOS and SAS simulations are presented for each time <br />interval along with the estimate of area in each timber size class, by yeaz. <br /> Water Yieid (in) Acres by Timber Size and Year <br />Date SAS DOS Non SeediSap Poie Saw Total <br />1860 13.4 14.8 397930 378594 297357 33712 1107593 <br />1880 12.5 13.5 55385 697522 92137 262548 1107593 <br />1900 13.1 14.4 285731 654913 156462 10488 1107593 <br />1920 12.2 13.4 35860 833308 238424 0 1107593 <br />1940 11.0 12.1 0 365292 709189 33111 1107593 <br />1960 10.4 11.9 33057 193146 789152 92238 1107593 <br />1980 10.2 12.1 133461 132 952339 21661 1107593 <br />1997 10.0 11.8 15567 133593 339430 619002 1107593 <br />2017 9.7 0 149161 9655 948777 1107593 <br />As discussed in the earlier analysis (Troendle and Nankervis 2000), the reliability of the <br />simulations of historical water yield is totally dependant on the combination of the reliability of <br />current stand descriptions (including stand age) and the assumptions we made about discounting <br />current stand ages in 20 year increments back to the year 1860. Although a high percentage of <br />current forest stands are currently classified as pole and saw timber, the average age of the stands <br />is relatively young. Given that the current average age of all stand classes is less tha.n 200 yeazs, <br />projection back in time indicates that the stands were generally quite young, with a dominance of <br />non-stocked and seedlings and saplings during the 1860 -1900 period (Figure 2). The associated <br />hydrologic simulations generate an estimate of water yield for that period that is quite high <br />relative to the current yield (Figure 2), for all forest species. As noted, the spruce-fir type has <br />probably had the greatest impact on the historical simulation of stream flow, as the simulated <br />decline in flow from the spruce-fir type from 1860 to 1997 is 6.0 azea inches of water (Figure 3). <br />Currently (ca 1997), the spruce-fir type in dominantly classed as being saw timber and <br />approximately 180 years old. Discounting those stands back to 1860 virtually eliminates the saw <br />timber component in the spruce-fir type and results in a consistent increase in the density of the <br />spruce-fir forest, from 1860 to 1997, that is associated with the uniform and very significant <br />decline in simulated stream flow. Although spruce-fir occupies only one-third of the total area of <br />forestland (Table 1), it is a high elevation species that occurs in the zones of greatest <br />precipitation, which in turn generates the most stream flow (Figure 3). The historical trends in <br />stand composition and water yield, for all other forest species, are presented in Figures 3 to 8.