EBTAG Annual Workshop and Field Trip
May 16-17, 2012

¹Hydrologist, U.S. Geological Survey, 5338 Montgomery Blvd. NE Suite 400, Albuquerque, NM, 87109, atillery@usgs.gov

²Warning Coordination Meteorologist, National Weather Service, 2341 Clark Carr Loop SE, Albuquerque, NM, 87106

During the summer of 2011, wildfires burned nearly 500,000 acres of forested lands in the State of New Mexico.  Two of the fires in northern New Mexico included the Las Conchas wildfire, the largest in the state’s history and the Track Fire which burned much of the Chicorica Creek watershed, a major source of water for the City of Raton, New Mexico.  The Las Conchas wildfire burned a total of 156,593 acres including portions of the Santa Clara, Cochiti, San Ildefonso, and Santa Domingo Pueblos and also portions of Bandelier National Monument and the Valles Caldera National Preserve. Some of the Las Conchas wildfire burn area was previously burned by the Cerro Grande Fire in 2000.  Freshly burned landscapes are at risk of damage from post-wildfire erosion hazards such as those caused by flash flooding and debris flows.  The risk of hydrologic hazards may persist for years after a fire and can negatively impact water resources, ecology, businesses, homes, reservoirs, roads, and utility infrastructure in wildland/urban interface areas.  Following the Las Conchas and Track Fires, several high volume (low frequency) floods occurred in and downstream of burn scar areas as the result of otherwise typical summer monsoonal rainstorm events.  Personnel from the U. S. Geological Survey and National Oceanic and Atmospheric Administration visited significantly impacted areas in both burn areas, conducted debris-flow assessments of burned areas (http://pubs.usgs.gov/of/2011/1257/ , http://pubs.usgs.gov/of/2011/1308/) and collected data to support numerical modeling (slope-area computations) and documentation of high volume floods downstream of burn scar areas.  In response to a design storm of 28.0 millimeters of rain in 30 minutes (10-year recurrence interval), the probabilities of debris flows estimated for basins burned by the Las Conchas Fire were greater than 80 percent for two-thirds (67 percent) of the modeled basins.  In response to a design storm of 38 millimeters of rain in 30 minutes (10-year recurrence-interval), the probabilities of debris flows estimated for basins burned by the Track fire were greater than 80 percent for the majority of the tributary basins to Raton Creek in Railroad Canyon and for six basins that flow into Lake Maloya, the main water supply for the City of Raton.  Debris-flow hazard assessments and flood-frequency predictions conducted in wildfire threatened areas before fires occur could help land and resource managers plan for and mitigate the effects of post-wildfire hazards in advance of a fire occurrence.