Alluvial and colluvial fans were studied to determine hydrogeomorphic disturbance type, methods of predicting disturbance type and power, and how forest operations can affect fan processes. Fifty-five fans in the southern Coast Mountains and Vancouver Island were field traversed, and watershed data collected using a geographic information system. Evidence of old debris flows (>50 years old) was observed on 41 fans; 5 showed evidence of old debris floods, and 9 showed evidence of old water floods. Only 13 fans had evidence of recent (<50 years old) debris flows, 7 had recent debris floods, and 29 had recent water floods. The best predictors of geomorphic disturbance type are the fan apex slope gradient, and the Watershed Relative Relief and Melton ratios. Thirty-nine fans had harvesting or roads, although in some cases the harvesting was minimal. Forest operations on the study fans occurred from 1957 to 2004. Forest operations caused destabilization on 15 fans, including avulsions, channel incision, bank erosion and channel widening. Zoning a fan into active, potentially active, and inactive zones is considered an important step toward effective forest management on fans. Additional information from this project can be found in Millard et al. (2006).
T.H. Millard, D.J. Wilford and M.E Oden.
Millard, Tom H., Wilford, David J.; Oden, Marian E.. 2006. Coastal fan destabilization and forest management. Forest Investment Account (FIA) - Forest Science Program. Forest Investment Account Report