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Previous local flood insurance studies include Rio Grande county, Colorado (FEMA, 1987), Monte Vista, Colorado (FEMA, 1982a), Del Norte, Colorado (FEMA, 1982b), the vicinity of South Fork, Colorado (USDA Soil Conservation Service, 1980), Archuleta county, Colorado (FEMA, 1979), and Alamosa, Colorado (FEMA, 1978), and Willow Creek at Creede, Colorado (USDA Natural Resources Conservation Service, 2002). None of these studies addresses flooding in the Willow Creek (near South Fork) watershed. Flood hazards in the study area can result from several types of seasonal conditions or storm types. Rapid melting of the typically large snowpack in the higher elevations (>10,000 feet) can cause sustained high- water conditions during May and June. Spring or fall monsoon rains lasting hours or days could cause flooding, especially if peak snowmelt is in progress or the ground is saturated. Monsoon rains in August 2002 caused local flooding and debris flows in the Missionary Ridge burn area near Durango, Colorado. Probably the most important source of flood potential in the post-fire period will be from thunderstorms. These short rains can be intense, delivering rainfall at intensities that easily exceed infiltration (hydrophobic soils) and causing direct raindrop impacts (lack of vegetative cover) that can erode soil and add bulk to flood waters. Thunderstorms have caused floods in other burned areas in Colorado such as the Coal Seam fire near Glenwood Springs and the Buffalo Creek and Hayman fires near Deckers, Colorado. Hydrologic Analysis Hydrologic analyses done in Elliott and others (2005) and summarized here, detailed the post-fire and long- term hydrology of Willow Creek and other drainages affected by the Coal Seam wildfire. Before long-term hydrology could be computed, both the pre-fire calibration to flood-frequency discharge and the computation of post-fire hydrology had to be completed. Pre-fire Hydrology Willow Creek has a contributing drainage area of 17.7 me at the mouth at the Rio Grande River (fig. I). No previous estimates of peak-flow discharge or flood studies that included estimates for Willow Creek could be found. Estimates of the 100-year peak discharge were made using the USGS regional regression equation for the Rio Grande basin (Vaill, 2000): Q,oo = 1.19(DA)o846(P)'o74 Where QlOO = 100-year peak discharge recurrence interval; DA = drainage basin area P = average precipitation (GIS computed) Rainfall-runoff modeling was used to develop pre-fire hydrographs for each of the subbasins of Willow Creek. Six subbasins (fig. 2, app. 5a, 5b) were delineated using GIS (geographic information system) and a USGS lO-m DEM (digital elevation model) of the study area. The U.S. Army Corps of Engineers HEC- HMS computer model was used for the analysis (U.S. Army Corps of Engineers, 2001b). The 100-year, 1- hour storm was selected for analysis to represent spring and summer thunderstorms in the study area.