Instability in eight sub-basins of the Chilliwack River Valley, British Columbia, Canada: A comparison of natural and logging-related landslides
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| Authors: | Wolter, A; Ward, B; Millard, T |
| Year: | 2010 |
| Journal: | Geomorphology 120: 123-132 Article Link (DOI) |
| Title: | Instability in eight sub-basins of the Chilliwack River Valley, British Columbia, Canada: A comparison of natural and logging-related landslides |
| Abstract: | Logging causes increased landslide frequency in British Columbia. In this study, the slope, type, initiation location, aspect, rate, bedrock geology, and size of mass movements located in eight logged tributary valleys of the Chilliwack River Valley are investigated. A landslide inventory was created by digitizing landslides identified on aerial photographs dating from 1941 to 2002. This database was analysed using qualitative observations and simple statistical tests, and a comparison between natural and logging-related landslides was made. Slope tests displayed a significant difference between natural and logging-related events, indicating that, on average, logging-related landslides require lower slope gradients to initiate than natural events. Although aspect, initiation location, and landslide type did not show a significant relationship between natural and logging-related landslides, they do suggest subtle differences. Landslide rate was calculated and compared for natural and logging-related landslides. It was significantly higher for logging-related events, attaining a maximum of 31 times the natural rate in 1978 and an overall average increase of nine times the natural rate. Logging-related landslides were on average smaller than natural landslides but this nevertheless resulted in a 3.1 times increase in area affected by logging-related landslides compared to natural landslides. Geology may influence landslide frequency as well; it appears to be higher over the less resistive sedimentary rocks of the Cultus Formation and Chilliwack Group and lower in granodioritic areas. Finally, roads affected slope stability more than clearcuts in the early decades of the study, but this effect decreased over time, suggesting a correlation with improved road construction. (C) 2010 Elsevier B.V. All rights reserved. |
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