Abstract

This report presents a preliminary emergency assessment of the debris-flow hazards from drainage basins burned by the Monument wildfire in southeastern Arizona, in 2011. 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 volumes of debris flows 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, 30-minute-duration rainfall, (2) 5-year-recurrence, 30-minute-duration rainfall, and (3) 10-year-recurrence, 30-minute-duration rainfall.

Estimated debris-flow probabilities in the drainage basins of interest ranged from a low of 26 percent in response to the 2-year-recurrence, 30-minute-duration rainfall to 100 percent in response to the 10-year-recurrence, 30-minute-duration rainfall. The high probabilities in all modeled drainage basins are likely due to the abundance of steep hillslopes and the extensive areas burned at moderately to high severities. The estimated volumes ranged from a low of about 2,000 cubic meters to a high of greater than 200,000 cubic meters.

First posted July 28, 2011