ABSTRACT: Subsurface stormflows in the highly permeable forested watershed of southwestern British Columbia

CGRG Bibliography of Canadian Geomorphology
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Abstract

Most forested watersheds in southwestern British Columbia are characterized by steep slopes, shallow but highly permeable soils and peak flows occurring mainly in the fall-winter period in response to major rainstorms with prolonged duration of 24 hours or greater. A comparison of rainfall intensities with soil hydrologic characteristics, hydrograph analysis and field observations strongly suggest that rapid subsurface flows through macropores and/or the soil matrix play a dominant role in contributing to stormflow volumes and peaks of forested watersheds in this coastal region. Two mechanisms observed in field studies and considered to be at least partly responsible for the fast response of subsurface stormflows are (1) an effective flow delivery system associated with the expanding stream channels during a storm and (2) the rapid transmission of flow through macropores with low resistance. The contribution to stormflow volume and magnitude from the "new water" of current storms relative to that from the downslope displacement of the pre-storm "old water", i.e. antecedent watershed moisture, requires close examination locally, but as indicated by available electrical conductivity data, probably is positively related to the stormflow size. Implications of the study results are discussed with regard to peak flow estimation

Bibliography of Canadian Geomorphology