Probability and volume of potential postwildfire debris flows in the 2011 Indian Gulch burn area, near Golden, Colorado

This report presents an assessment of the debris-flow hazards from drainage basins burned in 2011 by the Indian Gulch wildfire near Golden, Colorado. Empirical models derived from statistical evaluation of data collected from recently burned drainage basins throughout the intermountain western United States were used to estimate the probability of debris-flow occurrence and debris-flow volumes for selected drainage basins. Input for the models include measures of burn severity, topographic characteristics, soil properties, and rainfall total and intensity for a (1) 2-year-recurrence, 1-hour-duration rainfall, (2) 10-year-recurrence, 1-hour-duration rainfall, and (3) 25-year-recurrence, 1-hour-duration rainfall. Estimated debris-flow probabilities in the drainage basins of interest ranged from 2 percent in response to the 2-year-recurrence, 1-hour-duration rainfall to a high of 76 percent in response to the 25-year-recurrence, 1-hour-duration rainfall. Estimated debris-flow volumes ranged from a low of 840 cubic meters to a high of 26,000 cubic meters, indicating a considerable hazard should debris flows occur.