CGRG Bibliography of Canadian Geomorphology
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Author : Green, K.
Date : 2005.
Title : A qualitative hydro-geomorphic risk analysis for British Columbia’s Interior watersheds: A discussion paper.
Publication : Streamline. Watershed Management Bulletin
Issue : 8(2):
Page(s) : 14-20.
Abstract
Under British Columbia’s new Forest and Range Practices Act, forest management is moving towards risk analysis and professional reliance. In this new regime, forest managers must thoroughly understand potential risks to aquatic values associated with existing or proposed development. Results of a hydro-geomorphic risk analysis can guide new forest development, identify areas where more detailed assessments are required, or direct mitigative work. The results can also be used to identify aquatic values and locations in the watershed that are suitable for monitoring. The hydrologic risk analysis suggested here is ideally suited for low-order watersheds (<50 km˛) but can be adapted for use in smaller first-order watersheds (<100 ha) as well as larger landscape-level watersheds (500 km˛). In a detailed analysis, watershed processes are adjusted to reflect hillslope processes and more detailed, site-specific information is required such as likelihood of landslides, terrain and soil information, the nature of surface and subsurface runoff, slope gradient and aspect, and forest canopy characteristics. The potential for cumulative hydro-geomorphic impacts can be estimated in larger watersheds by dividing the landscape into smaller, hydrologically meaningful sub-basins and determining risk at each fan or confluence along the main stem channel. Applying this risk analysis to watersheds larger than about 50 km˛ could result in meaningless risk ratings due to the increased variability in basin response at large scales. Risks to aquatic values exist regardless of forest development. Therefore, such development should not automatically be excluded from areas of higher risk. In these cases forest managers can adapt management practices to reduce the potential hazards associated with development. Strategies to reduce the likelihood of occurrence of a hazard and thereby reduce development-related risk could include undertaking detailed drainage plans to maintain natural drainage patterns, conducting riparian assessments to ensure block boundaries do not impinge on riparian function, or adjusting the size or distribution of cutblocks to reduce the potential for increasing peak flows. As with any analysis of qualitative risk, this analysis is subject to professional experience and judgment. Therefore, all observations, interpretations, and assumptions should be appropriately documented. Eventually, with continued research initiatives directed at quantifying the effects of timber harvest and road development on watershed processes , the strength of risk analyses like the one presented here will improve. Until then, a qualitative approach to hydro-geomorphologic risk analysis is an effective tool to identify the key processes affecting aquatic values within a watershed and develop practical recommendations tominimize risks to aquatic values from forest development.
Bibliography of Canadian Geomorphology