Research Branch

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Managing forested watersheds for hydrogeomorphic risks on fans

Author(s) or contact(s): D.J. Wilford, M.E. Sakals, W.W. Grainger, T.H. Millard, and T.R. Giles
Source: Research Branch
Subject: Hydrology, Watershed, Watershed Management
Series: Land Management Handbook
Other details:  Published 2009. Hardcopy is available.


Fans are linked to their watersheds by hydrogeomorphic processes - floods, debris floods, and debris flows. These processes move water, sediment, and debris from the hillslopes of a watershed through channels to the fan. Fans in British Columbia are often the site of residential developments, and transportation and utility corridors, as well as high-value habitat for fish and high-productivity growing sites for forests. Collectively, these features are termed "elements-at-risk" because they may be vulnerable to watershed-generated hydrogeomorphic processes that issue onto the fan. These processes may be natural or result from land use activities, and can cause the partial or total loss of some or all of the elements on the fan.

In British Columbia, forest harvesting and road building is associated with increased hydrogeomorphic hazards. The downstream effects of these forestry activities in source areas may be far-reaching and extend beyond the scope of conventional siteoriented planning. A five-step approach is presented to assist land managers undertake risk analyses and assessments that place their proposed developments within the watershed-fan system. The five steps are: 1) identify fans and delineate watersheds; 2) identify elements-at-risk on fans; 3) investigate fan processes; 4) investigate watershed processes; and 5) analyze risks and develop plans. This scheme is applicable to forested watersheds throughout British Columbia.

Keywords: Watershed management, alluvial fans, risk analysis, forest management planning, hydrogeomorphic processes.

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Updated March 18, 2009