Pacific Northwest Research Station

Title: Multivariate geomorphic analysis of forest streams: implications for assessment of land use impacts on channel condition.

Author: Woodsmith, R.D.; Buffington, J.M.

Date: 1996

Source: Geomorphic Analysis of Forest stream Earth Surface Processes and Landforms. 21: 277-393

Description: Multivariate statistical analyses of geomorphic variables from 23 forest stream reaches in southeast Alaska result in successful discrimination between pristine streams and those disturbed by land management, specifically timber harvesting and associated road building. Results of discriminant function analysis indicate that a three-variable model discriminates 10 disturbed from 13 undisturbed reaches with 90 per cent and 92 per cent correct classification respectively. These variables are the total number of pools per reach, the ratio of mean residual pool depth to mean bankfull depth, and the ratio of critical shear stress of the median surface grain size to bankfull shear stress. The last variable can be dropped without a decrease in rate of correct classification; however, the resulting two-variable model may be less robust. Analysis of the distribution of channel units, including pool types, can also be used to discriminate disturbed from undisturbed reaches and is particularly useful for assessment of aquatic habitat condition. However, channel unit classification and inventory can be subject to considerable error and observer bias. Abundance of pool-related large woody debris is highly correlated with pool frequency and is an important factor determining channel morphology. Results of this study yield a much needed, objective, geomorphic discrimination of pristine and disturbed channel conditions, providing a reference standard for channel assessment and restoration efforts.

Keywords: fluvial geomorphology; multivariate analysis; forest streams; aquatic habitat; channel units

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Citation

Woodsmith, R.D.; Buffington, J.M.  1996.  Multivariate geomorphic analysis of forest streams: implications for assessment of land use impacts on channel condition..   Geomorphic Analysis of Forest stream Earth Surface Processes and Landforms. 21: 277-393