New Mexico Geological Society Annual Spring Meeting — Abstracts

Forest fires are well known to impact the quality of water in a watershed from hillside erosion and fire sedimentation as well as the quantity of water entering the system from decreased soil infiltration, lessened vegetation interception, and increased catchment evapotranspiration. The Gallinas Watershed in northern New Mexico was impacted by the 2022 Hermits Peak/Calf Canyon (HP/CC) Fire, the largest wildfire in New Mexico’s history (>340,000 acres). Approximately 115,542 acres burned in the Headwaters Gallinas River Watershed, 21% of which were classified by the USFS Burned Area Emergency Response team as high burn severity. As of April 8, 2023, the snow water equivalent (SWE) data from the NRCS Wesner Springs snow monitoring station at the Gallinas River’s source (Elk Mountain; 11,151 feet) stands at 17.0 in, which is trending at 142% higher than the 30-year median of 12.0 in. The above-average snowpack raises concerns for increased snowmelt in the watersheds, with heightened concern for earlier onset and higher levels of peak flows due to post-fire watershed conditions. This undergraduate study consists of monitoring in near real-time the SWE, air temperature, and soil moisture at Wesner Springs and comparing these to both historic and 2023 Gallinas River discharge with emphasis on the period during the spring snowmelt (March through May) to test what if any impact the 2022 HP/CC forest fire is having on hydrologic conditions. Historically, the hydrographs for Gallinas Creek near Montezuma, NM (USGS 08380500) show broad, diffuse, and moderate increases in discharge from March to May from snow melt in contrast to the narrow, sharp, and marked increases in discharges from June to August from monsoon rains. Review of the Gallinas River streamflow data from March 2023 to present shows a flashy spring discharge with narrow and sharp peaks at 4 to 7 times above average similar to monsoonal precipitation response rather than snowmelt response. These data suggest that the snowmelt is running off the burned hillsides rather than infiltrating the subsurface. The NRCS has calculated a forecast volume (50% exceedance probability) of 215% of the 30-year median at Gallinas Creek near Montezuma. Historically, peak discharge on the Gallinas occurs around May 15^th based on the 96-year record, but has been occurring earlier during the millennium drought. This year, with the higher SWE and post-fire conditions, monitoring in near real-time is imperative to forecast flood stages, manage fire sedimentation, and protect water supplies.