Research Branch

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Hydrologic and geomorphic considerations for silvicultural investments on the Lower Skeena River floodplain

Author(s) or contact(s): P.G. Beaudry, D.L. Hogan, and J.W. Schwab
Source: Research Branch
Subject: Hydrology
Series: FRDA Report
Other details:  Published 1990. Hardcopy is available.


This report evaluates four inter-related components essential for silvicultural planning on the lower Skeena River floodplain: biophysical information, erosion potential, flooding characteristics and environmental fate of herbicides. These components are detailed so the approach can be applied in other floodplain areas.

Detailed biophysical data of direct relevance to forest management on the Skeena River floodplain are presented. These data include: 1) the annual groundwater regime and its driving forces; 2) the stratigraphy of the alluvial deposits; 3) the physical characteristics of the soil; and 4) the climatic regime of both the air and soil.

The evaluation of floodplain stability and island longevity is based on a chronological sequence of maps. A total of five air photograph series, spanning 40 years, are used to calculate erosion and deposition rates. These rates are ranked according to a five-class system ranging from no change historically to large annual changes. Maps are presented to show: 1)historical channel shifts, and 2)floodplain and island stability. These maps are used to determine the long-term management suitability of the Skeena River. The most important factors controlling erosion are flood flows, sediment sources and specific morphological features.

The survival and growth of Sitka spruce(Picea sitchensis) are related to frequency, duration and depth of flooding. Certain topographical and morphological features of floodplains are associated with these flood characteristics and are used to identify sites that will be unfavourable for establishment and growth of Sitka spruce. The method developed uses 1:10000 scale air photographs and a five-category frequency/duration classification to identify site specific flooding potential. Ground elevation is critical in determining flood frequency, but terrain features control flood duration.

From the biophysical data and information on the nature of forestry herbicides, inferences are drawn about the probable environmental fate of herbicides on these floodplains, and recommendations are made.

FRDA Research Report 122 (2930 KB)

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Updated July 24, 2015