Effects of catastrophic blowdown on headwater streams of the Routt National Forest, Colorado

My study focuses on the effects of a severe storm event on headwater mountain stream morphology. In 1997 the Routt Divide Blowdown felled 13,000 acres of trees in the Routt National Forest, Colorado, causing massive amounts of large wood (LW) loading in streams. A previous study (Massey, 2000) established a 1998 baseline in three streams: Sanchez Creek (control stream with 0% blowdown, no human activity, no fire), Agnes Creek (88% blowdown, no human activity, fire-affected) and South Fork Lost Dog (SFLD) Creek (92% blowdown – past logging and road construction, fire-affected). I resurveyed the streams during the summers of 2010 and 2011. I mapped channel morphology, classified and quantified the number, location, and function of LW pieces within the stream channel, and measured pebble counts. SFLD Creek had a reach-averaged increase in cross-sectional area (1998-2010) of ~1 m2 (~90%). Agnes Creek had a reach-averaged increase of ~0.1 m2 (~25%). Sanchez Creek had a reach-averaged increase of ~0.5 m2 (~45%). SFLD Creek became deeper by ~0.25 m (~65%), Agnes Creek became shallower by ~0.01 m (~3%), and Sanchez Creek became deeper by ~0.1 m (~35%). SFLD Creek was the only stream to have a coarsening trend in particle size. Comparisons of the channel margins surveyed in planview indicated changes in channel width. Agnes Creek widened by 1.5 m (~30%) whereas SFLD Creek narrowed by ~0.4 m (~20%). The map view of the control stream (Sanchez) was not surveyed in 2011 because of high snow pack. My initial hypothesis was that blowdown-related LW was a primary control on channel morphology over the 12-13 years study period. However, statistically significant differences in changes in area, width, and depth exist between SFLD and Agnes Creeks. In contrast, changes between Agnes and Sanchez Creeks were not statistically significant. This suggests other factors such as logging and road construction (as seen only in the SFLD Creek watershed) may play a larger role in channel morphology. To assess the importance of these factors on channel morphology, further studies are needed, including discharge and bank stability data, as well as recent mapping of the control stream (Sanchez).