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<br />, <br /> <br />sizes, and watershed-rehabilitation measures. On site data also were collected for subsequent <br />storms that produced runoff. Monitoring is planned until water and sediment runoff in the burned <br />area has returned to near-normal. <br /> <br />For burned and unburned basins, data also were collected to: a.) estimate hillslope erosion; b.) <br />estimate channel agradation and degradation; c.) approximate volumes of channel and alluvial-fan <br />deposits; and d.) identify past fire and flood deposit sequences in the alluvial stratigraphy. This <br />monitoring complements sediment studies being conducted by other USGS and USFS scientists <br />and helps validate channel change estimates from aerial photographs taken before and after the <br />fire. <br /> <br />Results and Discussion <br /> <br />Most efforts have concentrated on monitoring numerous floods and providing preliminary <br />information for hazard-mitigation and forest managers. Results are presented for the storm and <br />flood of July 12, 1996, the effects of the fire on flooding, and assessing watershed-rehabilitation <br />efforts. <br /> <br />July 12, 1996 Storm and Flood <br /> <br />Maximum rainfall from bucket-survey data forthe July 12, 1996 storm was about 80 mm in the <br />community of Buffalo Creek and headwaters of Spring Creek (fig. 2); local residents stated most <br />of the rain fell in about an hour. Before additional rainstorms, the extent of fresh rill and gully <br />erosion was compared to rainfall-bucket amounts without gaged rainfall data. Hillslope erosion <br />then was used to estimate rainfall in areas without rainfall data. Hillslopes (burned or unburned) <br />with sparse vegetation and less than about 25 mm rain had some sediment movement and <br />minimal rill development (fig. 3a). Hillslopes that received about 50 mm of rain had rills about 75 <br />mm deep and 50 mm wide (fig. 3b). Hillslopes that received about 75 mm of rain had numerous <br />gullies up to 0.5 m deep and a meter wide (fig. 3c). Numerous gullies up to a meter deep and 3 m <br />wide (fig. 3d) were documented about 5 km south of Buffalo Creek near the headwaters of Sand <br />Draw, Spring Creek, Shinglemill Creek, and Spring Gulch. The gullies were used to infer a <br />maximum 1-hr rainfall amount of at least 115 mm. Rill and gully erosion data were used to <br />graphically display comparisons and to draw an isohyetal map (fig. 2). Peak-flow data (next <br />section) for small watersheds also were used to help draw the isohyetal map. Rainfall amounts <br />decreased rapidly outside the burned area and the storm covered about 50 to 75 km2. The rainfall <br />isohyetal pattern estimated from NWS-WSR-88 radar by the National Weather Service (written <br />commun., 1996) estimated the evening of July 12, 1996 storm, which was used to issue a flash- <br />flood warning to the public, is shown on figure 1. The NWS estimated the maximum rainfall was <br />at least 80 mm. <br /> <br />Henz (1998) analyzed Doppler radar signatures and upper-air observations for the July 12 <br />storm. His approach differs from the NWS radar estimate in that interpretations have been <br />validated with ground-truth rainfall data for a network in the Denver area during about the past 15 <br />years. Henz estimated maximum rainfall of about 140 mm in about an hour with the cell located <br />near the head of Spring Creek with similar isohyetal patterns, but oriented slightly different (fig. 4). <br />Henz's preliminary results had the storm footprint located about 3 km southeast of the present <br />center in Spring Creek (Henz Meteorologic Services, written commun., 1997). However, the <br />geomorphic rainfall estimates indicated a lack of rainfall (fig. 3a) and essentially no runoff in <br />Henz's preliminary estimated area of maximum rainfall. Areas having extreme flood runoff (next <br />section) were not located below Henz's preliminary storm footprint. Henz used our results to <br />better locate the storm footprint (fig. 4). Therefore, it appears that geomorphic techniques provide <br />good estimates of rainfall amounts and very good estimates of spatial variability when compared <br />with Henz's estimates from Doppler radar. The paleohydrologic rainfall data also provide <br />valuable information to assess the reliability of radar estimated rainfall, which are used for flash- <br />flood forecasting and other purposes. <br /> <br />Henz's rainfall reconstruction is very likely more accurate than NWS estimates for Buffalo Creek <br />because Henz has many years of local experience analyzing severe storms, and he has spent <br /> <br />Draft 3/30/98 <br /> <br />4 <br />