Postwildfire measurement of soil physical and hydraulic properties at selected sampling sites in the 2011 Las Conchas wildfire burn scar, Jemez Mountains, north-central New Mexico

Scientific Investigations Report 2018-5028
By: , and 

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Abstract

The generation of runoff and the resultant flash flooding can be substantially larger following wildfire than for similar rainstorms that precede wildfire disturbance. Flash flooding after the 2011 Las Conchas Fire in New Mexico provided the motivation for this investigation to assess postwildfire effects on soil-hydraulic properties (SHPs) and soil-physical properties (SPPs) as a function of remotely sensed burn severity 4 years following the wildfire. A secondary purpose of this report is to illustrate a methodology to determine SHPs that analyzes infiltrometer data by using three different analysis methods. The SPPs and SHPs are measured as a function of remotely sensed burn severity by using the difference in the Normalized Burn Ratio (dNBR) metric for seven sites. The dNBR metric was used to guide field sample collection across a full spectrum of burn severities that covered the range of Monitoring Trends in Burn Severity (MTBS) and Burned Area Reflectance Classification (BARC) thematic classes from low to high severity. The SPPs (initial and saturated soil-water content, bulk density, soil-organic matter, and soil-particle size) and SHPs (field-saturated hydraulic conductivity and sorptivity) were measured under controlled laboratory conditions for soil cores collected in the field. The SHPs were estimated by using tension infiltrometer measurements and three different data analysis methods. These measurements showed large effects of burn severity, focused in the top
1 centimeter (cm) of soil, on some SPPs (bulk density, soil organic matter, and particle sizes). The threshold of these bulk density and soil organic matter effects was between 300 and 400 dNBR, which corresponds to a MTBS thematic class between moderate and high burn severity and a BARC4 thematic class of high severity. Gravel content and the content of fines in the top 1 cm of soil had a higher threshold value between 450 and 500 dNBR. Lesser effects on SPPs were observed at depths of 1–3 cm and 3–6 cm. In contrast, SHPs showed little effect from dNBR or from MTBS/BARC4 thematic class. Measurements suggested that 4 years of elapsed time after the wildfire may be sufficient for SHP recovery in this area. These measurements also indicated that SPP differences as a function of burn severity cannot be used as reliable indicators of SHP differences as a function of burn severity.

Suggested Citation

Romero, O.C., Ebel, B.A., Martin, D.A., Buchan, K.W., and Jornigan, A.D., 2018, Postwildfire measurement of soil physical and hydraulic properties at selected sampling sites in the 2011 Las Conchas wildfire burn scar, Jemez Mountains, north-central New Mexico: U.S. Geological Survey Scientific Investigations Report 2018–5028, 35 p., https://doi.org/10.3133/sir20185028.

ISSN: 2328-0328 (online)

Study Area

Table of Contents

  • Acknowledgments
  • Abstract
  • Introduction
  • Methods and Approach
  • Field Observations of Sampling Sites and Soil-Physical and Soil-Hydraulic Properties of Las Conchas Fire Samples
  • Comparisons to Previous Studies and Implications
  • Limitations
  • Summary
  • References Cited

Additional publication details

Publication type Report
Publication Subtype USGS Numbered Series
Title Postwildfire measurement of soil physical and hydraulic properties at selected sampling sites in the 2011 Las Conchas wildfire burn scar, Jemez Mountains, north-central New Mexico
Series title Scientific Investigations Report
Series number 2018-5028
DOI 10.3133/sir20185028
Year Published 2018
Language English
Publisher U.S. Geological Survey
Publisher location Reston, VA
Contributing office(s) New Mexico Water Science Center
Description Report: viii, 34 p.; Data Release
Country United States
State New Mexico
Other Geospatial Jemez Mountains
Online Only (Y/N) Y
Additional Online Files (Y/N) Y