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Stream channel morphology: major fluvial disturbances in logged watersheds on the Queen Charlotte Islands

Author(s) or contact(s): R.G. Roberts
Source: Research Branch
Subject: Hydrology
Series: Land Management Report
Other details:  Published 1987. Hardcopy is available.
 

Abstract

The Fish/Forestry Interaction Program (FFIP) was initiated in 1979 to resolve management uncertainties in areas of intensive mass wastage in the Queen Charlotte Islands (Poulin 1984). This study represents one component of the project and investigates stream channels in which major deposition of fluvial sediments was observed.

Reconnaissance investigations of disturbed stream habitats early in the Fish/Forestry Interaction Program studies identified extensive, recently accumulated sediments in mid-reaches of some streams. Channel width has increased by up to 10 times, and the depositional zone is of order 1 km in length. From historical air photo and land use studies it was determined that the sediment wedges were initiated by streamside and in-stream logging practices before 1970.

A long term sediment budget was estimated for each basin to determine the relative importance of adjacent stream bank erosion (on-site land use effect) and other sediment sources - including off-site land use effects - in contributing to the sediment wedges. The most significant sediment sources in each basin were assessed in the field: minor sources were estimated from regional results. Stream banks and landslides were estimated to contribute two-thirds to three-quarters of all sediment delivered to the streams, with stream banks accounting for half or more of the sediment in three of four cases. Sediment stored in the wedges varies from all of the +1-mm input since disturbance, to possibly as little as one-quarter of the material. Long-term sediment outputs as bed load transport vary from 0 to about 10 000 m3/yr. Because far more sediment is stored in the channels than is annually transported out, the wedges will persist for a long time.

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Updated December 16, 2008