Laserfiche WebLink
<br />change estimates from aerial photographs taken before and after the fire. <br /> <br />Results and Discussion <br /> <br />Most efforts have concentrated on monitoring numerous floods and to provide preliminary information for <br /> <br /> <br />hazard-mitigation and forest managers. Resu~s are presented for the storm and flood of July 12, 1996, <br /> <br /> <br />the effects of the fire on flooding, and assessing watershed-rehabilitation efforts. <br /> <br />July 12, 1996 Storm and Flood <br /> <br />Maximum rainfall from bucket-survey data for the July 12, 1996 stonn was about 80 mm in an hour in the <br /> <br /> <br />community of Buffalo Creek and headwaters of Spring Creek (fig. 1). Before additional rainstonns, the <br /> <br /> <br />extent of fresh rill and gully erosion was compared to bucket-rainfall amounts. Hillslope erosion then was <br /> <br /> <br />used to estimate rainfall in areas without rainfall data. Hillslopes (bumed or unburned) with sparse <br /> <br /> <br />vegetation and less than about 25 mm rain had some sediment movement and minimal rill development. <br /> <br /> <br />Hillslopes in areas of about 50 mm of rain had rills about 75 mm deep and 50 mm wide. Hillslopes that had <br /> <br /> <br />about 75 mm of rain had numerous gullies up to 0.5 m deep and a meter wide. Numerous gullies up to a <br /> <br /> <br />meter deep and 3 m wide occurred about 5 km south of Buffalo Creek near the head of Sand Draw, <br /> <br /> <br />Shinglemill Creek, and Spring Creek were used to infer a maximum 1-hr rainfall amount of at least 115 mm <br /> <br /> <br />and then draw an isohyetal map (fig. 1). Rainfall amounts decreased rapidly outside the bumed area and <br /> <br /> <br />the storm covered about 50 to 75 km2. Henz (Henz Meteorological Services, Denver, written commun., <br /> <br /> <br />1997) analyzed Doppler radar signatures and upper-air observations for the July 12 storm. He estimated a <br /> <br /> <br />maximum rainfall of about 130 mm in about an hour with the cell located near the head of Sand Draw with <br /> <br /> <br />similar isohyetal patterns, but oriented slightly different (fig. 1). Thus, geomorphic techniques provide a <br /> <br /> <br />good estimate of rainfall amounts and spatial variability when compared with estimates from Doppler radar. <br /> <br /> <br />The 1 DO-year, 1-hr rainfall is about 55 mm for the Buffalo Creek area (Miller et aI., 1973). Thus, the July 12, <br /> <br /> <br />1996 maximum rainfall (130 mm) in Buffalo Creek was about 2.4 times larger than a 1 DO-year storm. <br /> <br />8 <br />