BOULDER CREEK FIRE FLUVIAL GEOMORPHOLOGY GEOCORPS POSITIONS: A LONG TERM ASSESSMENT OF CHANNEL MORPHOLOGY AND LARGE WOOD DYNAMICS IN POST-FIRE MOUNTAIN STREAMS ON THE BRIDGER-TETON NATIONAL FOREST

The GeoCorps Fluvial Geomorphology positions in 2013 are part of an assessment of changes in sedimentation, channel morphology, and large wood loading associated with a moderate-to-high severity burn. In 2000, the Boulder Creek fire burned portions of the Little Granite Creek watershed on the Bridger-Teton National Forest, near Jackson, WY. A series of monitoring reaches, established the first year post-fire, were re-surveyed to assess changes to channels within the burned area (Boulder Creek), downstream of the burned area, and within an adjacent reference watershed (Upper Little Granite Creek). There were two primary components to the survey: 1) a census of large wood and 2) an assessment of channel changes over time, including those associated with substantial input of new large wood in severely burned riparian areas. The large wood census recorded data on over 1500 individual pieces. Data collected included size, channel type, function, source, age and stability in channel. This information is used to better understand the role of large wood and its fate once it is recruited into the channel. Typical fates include burial, breakage, movement, and retention in place. To measure channel changes in the reaches, banks and centerline were re-surveyed as well as cross sections that were established every 20 meters within the reaches. Associated changes to the channel from large wood include: 1) increase in the size and number of jams; 2) coarse sediment deposition within and behind jams; 3) channel avulsions; 4) erosion of banks and terraces by re-directed flows; and 5) multiple new sources of fine sediment from bank instability.

Forest managers tasked with leading efforts to rehabilitate burned areas have lacked information on the longer-term impacts of fire on mountain streams. With the increasing risk of larger, more intense and more frequent fires on public lands, due to climate change, the results from this assessment provide managers with detailed long term information on channel disturbance and the fate of large wood post fire, both of which can contribute to chronic sedimentation. This project was conducted through the USFS, Rocky Mountain Research Station, Bridger-Teton National Forest, and Geocorps and was funded by the National Fire Plan and the USFS, Office of Geologic Resources, Hazards, and Surface Management.