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Lapse - Lapse allows the user to enter a multiplier which cot7•ects for the ettects of elevation on <br />? precipitation. It allows the use of local precipitation guage data in a watershed. Because it is <br />unlikely that local data will be available for an entire Forest and tor the reasons documented <br />above with regard to duplicating the original results of the WRENSS procedure, I recommend <br />that this be set to " 1", no coirection. <br />Elevation - The model does not allow entry of an elevation for the Rocky Mtn. Region <br />(WRENNS Region 4). <br />Tree Height - Enter the average tree height for each vegetation type. This can be provided from <br />FVS by averaging tree height for the first five decades. An exception to this is where partial <br />treatments dramatically affect the height of the remaining trees. An example from this forest is <br />for shelterwood treatments in ponderosa pine. The tirst step changed the ti•ee height fi•om 43 ft. <br />to 27 ft. In this case. I recommend using the average tree height before the fii•st treatment. The <br />Qrimary concern is the height of the trees surrounding the treated area rather than the height of <br />trees within the treated area. (Note: Tree height may be irrelevant if the adjustment to <br />precipitation is made as recommended above.) <br />Type - The only choices for the Rocky Mountain region are Lodgepole pine, Spruce-Fir, <br />Ponderosa Pine, or deciduous. Although there is a small component of Douglas Fir in this <br />Forest's suited and scheduled lands, it is so small that the forester's lumped it with ponderosa <br />pine for growth and yield modeling. I propose to do the same for water yield modeling. For <br />those Forest's who may have an aspen component and need to use the deciduous type. I would <br />recommend that they test the model and consult with Chuck Troendle before using it. <br />? Wind Speed - As suggested above, set to zero. <br />l <br />Days of no snow - As suggested above, set to zero. <br />Guage - Set to none. This variable allows the user to set the type of wind shield used on a gage. <br />It is not applicable if precipitation is not based on site specific data. <br />Exposure - Set to zero. This, in conjunction with "Guage", allows the user to adjust precipita- <br />tion. Not applicable. <br />Unimpacted vs. Impacted - This version of WRENNS estimates water yield rather than the <br />increase in water yield. I suggest that existing stand conditions be entered into the UNIlVI- <br />PACTED column and harvested stand conditions be entered into the IMPACTED column. If the <br />adjustment to precipitation is made as recommended above, change in water yield is then the <br />difference between water yield for the UNIMPACTED, unadjusted precipitation units and the <br />IMPACTED, adjusted precipitation units. <br />Max BA - Enter the maximum BA from FVS. For stands treated with shelterwood harvest, <br />maximum basal area may be found on the unharvested simulation (several entries over the <br />rotation may prevent the stand from reaching maximum basal area). <br />BA - Enter the predicted BA for the decade of interest from FVS. <br />7