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7 <br />c <br />6 <br />5 <br />:2 4 <br />2 <br />? <br />? 3 <br />c? <br />? <br />2 <br />0 <br />1860 1880 1900 1920 1940 1960 1980 2000 2020 2040 2060 <br />I ? AR o MBR o PSI <br />Figure 16. Unit area water yield, in area inches, from NFS lands in the South Platte <br />River Basin. Precipitation and water yield are highest on the AR National Forest. <br />? tlirbance I acts on Water Yield <br />? P? ?,+??,'(??Y f'M fi' <br />?i? ??i ? <br />? <br />4 ? N.? <br />For the most part, the impacts of historic wildfires on NFS land in the South Platte River <br />Basin are reflected in the characterization of the current forest conditions provided by the <br />three Forests. In 2002, however, the largest wildfire in recorded Colorado history <br />occurred in the South Platte River Basin. Known as the Hayman Fire, the boundary of the <br />burned area encompassed about 140,000 acres. Stand data indicate that about 110,000 <br />acres within that boundary were consumed by fire. The simulated water yield from the <br />burned area for the year 2020 is about 4.5 area inches and represents a 3.4-area inch or <br />30,600-acre-foot increase over the reference water yield (Table 4). Simulations indicate <br />that the water yield from the burned area will decline from 4.5 area inches in 2020 to 3.0 <br />area inches in 2060, but still represent a 1.9-area inch (17,000 acre-foot) increase relative <br />to the 1997 reference water yield. Contributions from the ponderosa pine and Douglas fir <br />lands within the burn area represent more that 80 percent of the simulated water yield <br />change. <br />Several issues should be considered regarding the simulation of water yield after the <br />Hayman Fire. First, the initial simulation of the change in water yield resulting from <br />vegetation disturbance from the fire was for the year 2020 (18 years after the fire). The <br />WRENSS Hydrologic Model simulates the annual water balance and annual water yield. <br />Although the procedure can distribute the annual change in flow using a flow duration <br />curve that includes peak flow, the procedure is not capable of simulating individual storm <br />20 2/2/2007