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Scientific Investigations Report 2014–5161

Prepared in cooperation with the Bernalillo County Natural Resources Services

Potential Postwildfire Debris-Flow Hazards—A Prewildfire Evaluation for the Sandia and Manzano Mountains and Surrounding Areas, Central New Mexico

By Anne C. Tillery, Jessica R. Haas, Lara W. Miller, Joe H. Scott, and Matthew P. Thompson

Thumbnail of and link to report PDF (3.36 MB)Abstract

Wildfire can drastically increase the probability of debris flows, a potentially hazardous and destructive form of mass wasting, in landscapes that have otherwise been stable throughout recent history. Although there is no way to know the exact location, extent, and severity of wildfire, or the subsequent rainfall intensity and duration before it happens, probabilities of fire and debris-flow occurrence for different locations can be estimated with geospatial analysis and modeling efforts. The purpose of this report is to provide information on which watersheds might constitute the most serious, potential, debris-flow hazards in the event of a large-scale wildfire and subsequent rainfall in the Sandia and Manzano Mountains. Potential probabilities and estimated volumes of postwildfire debris flows in the unburned Sandia and Manzano Mountains and surrounding areas were estimated using empirical debris-flow models developed by the U.S. Geological Survey in combination with fire behavior and burn probability models developed by the U.S. Department of Agriculture Forest Service.

The locations of the greatest debris-flow hazards correlate with the areas of steepest slopes and simulated crown-fire behavior. The four subbasins with the highest computed debris-flow probabilities (greater than 98 percent) were all in the Manzano Mountains, two flowing east and two flowing west. Volumes in sixteen subbasins were greater than 50,000 square meters and most of these were in the central Manzanos and the western facing slopes of the Sandias.

Five subbasins on the west-facing slopes of the Sandia Mountains, four of which have downstream reaches that lead into the outskirts of the City of Albuquerque, are among subbasins in the 98th percentile of integrated relative debris-flow hazard rankings. The bulk of the remaining subbasins in the 98th percentile of integrated relative debris-flow hazard rankings are located along the highest and steepest slopes of the Manzano Mountains. One of the subbasins is several miles upstream from the community of Tajique and another is several miles upstream from the community of Manzano, both on the eastern slopes of the Manzano Mountains.

This prewildfire assessment approach is valuable to resource managers because the analysis of the debris-flow threat is made before a wildfire occurs, which facilitates prewildfire management, planning, and mitigation. In northern New Mexico, widespread watershed restoration efforts are being carried out to safeguard vital watersheds against the threat of catastrophic wildfire. This study was initiated to help select ideal locations for the restoration efforts that could have the best return on investment.

First posted October 7, 2014

For additional information contact:
Director, New Mexico Water Science Center
U.S. Geological Survey
5338 Montgomery Boulevard NE
Albuquerque, New Mexico 87109–1311
http://nm.water.usgs.gov/

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Suggested citation:

Tillery, A.C., Haas, J.R., Miller, L.W., Scott, J.H., and Thompson, M.P., 2014, Potential postwildfire debris-flow hazards—A prewildfire evaluation for the Sandia and Manzano Mountains and surrounding areas, Central New Mexico: U.S. Geological Survey Scientific Investigations Report 2014–5161, 24 p. with appendix, http://dx.doi.org/10.3133/sir20145161.

ISSN 2328-031X (print)

ISSN 2328-0328 (online)



Contents

Abstract

Introduction

Methods and Approach

Modeling Results

Hazard Assessment

Integrated Relative Debris-Flow Hazard Rankings

Limitations of Hazard Assessment

Future Considerations for Prewildfire Assessments of Postwildfire Hazards

Summary

Acknowledgments

References Cited

Appendix


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