The Mt. Vision Fire of October 1995 burned almost 13,000 acres of wilderness in Point Reyes National Seashore, about 31 miles northwest of San Francisco, CA. The 3.2 sq. mile watershed of Muddy Hollow Creek was almost entirely burned by the fire. The isolated nature of the watershed provides an excellent location to study post-fire watershed response in Northern California.

For the two years following the fire, 1996 and 1997, Collins and Ketcham (2001) documented changes to Muddy Hollow Creek and the watershed. They observed the formation of an alluvial fan and braided channel form in the lower reach. They estimated the minimum average sediment load during these two years was 2,626 tons/sq mile/year. They noted that sediment deposition during the second year after the fire was 2.7 times higher than the previous year. This was due to bed erosion and incision of the middle reach due to large amounts of woody debris falling into the river. The middle reach became entrenched due to high flows in 1996. They hypothesized that as the sediment load and flow decreased the lower reach would return to a single channel and an extensive alder forest would grow over the fan. In October 2004, we conducted the first follow-up survey since Collins and Ketcham. We surveyed three cross-sections in the middle reach of Muddy Hollow Creek and documented changes in vegetation and geomorphology from repeat ground and aerial photography in the middle and lower reaches. We did not observe significant changes in channel depth in the middle reach. We observed an increase in vegetation and alder forest growth in the lower reach of the creek as hypothesized by Collins and Ketcham. Much of the woody debris in the middle reach is still decaying, but ground cover may slow the rate of erosion seen in the first two post-fire years. Consequently, we hypothesize that less sediment will be deposited in the lower reach allowing the lower reach to form a more defined channel. Photo points and survey data that we collected can be reproduced to further analyze the post-fire response of the watershed.

Files

qt89r7b10f.pdf.txt

qt89r7b10f.pdf

Muddyhollowfigures.doc

muddyhollowcrosssections.doc