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<br />DRAFT 1/8/98 <br /> <br />Wildfire Flood-Hazard Mitigation and Watershed-Rehabilitation Monitoring <br /> <br />R.D. Jarrett, U.S. Geological Survey, Lakewood, Colorado <br />T.W. Browning, Colorado Water Conservation Board, Denver, Colorado <br /> <br />Abstract A basin-wide, monitoring approach provides important information to assess the effects of <br /> <br />wildfire on water and sediment runoff, assess the effects of watershed-rehabilitation activities, determine <br /> <br />watershed recovery time, and help manage forest ecosystems. The approach is flexible, requires minimal <br /> <br />resources, and complements comprehensive instrumented monitoring in a short amount of time. The <br /> <br />approach was applied to the mountain community of Buffalo Creek, Colorado, which had a catastrophic <br /> <br />wildfire in May 18, 1996. Subsequent rainstorms produced 9 floods larger than a 1 DO-year (pre-fire <br /> <br />conditions) flood as well as numerous smaller floods. Rates of flood runoff in 1997 were about the same <br /> <br />as in 1996, which indicate persistent effects from the fire. The largest rainstorm of about 130 mm in an <br /> <br />hour (about 2.5 times larger than a 1 DO-year rainstorm) on July 12, 1996 resulted in a flood about to times <br /> <br />larger than the 1 DO-year (pre-fire) flood. Unburned basins in areas of maximum rainfall had minimal water <br /> <br />and sediment runoff. Study results were used to help the National Weather Service determine threshold- <br /> <br />rainfall amounts that could produce flash flooding in the Buffalo Creek area. Large quantities of sediment <br /> <br />continue to be transported in burned-area streams since the fire. Investigations of alluvial sediments <br /> <br />indicate at least 10 wildfire-flood sequences during about the past 2,500 years in the Buffalo Creek area. <br /> <br />Study resulls indicate that prehistoric fires and subsequent increased runoff prior to fire suppression of <br /> <br />the last century contribute to cyclical, geomorphic instability. <br /> <br />RECEIVED <br />JAM 1 2 1998 <br /> <br />Colorado Water <br />conservation Soard <br /> <br />1 <br />