Debris flow defenses in British Columbia
A considerable amount of experience with engineering control of debris flow hazards has been gathered in British Columbia, Canada. A summary of this experience encompasses the entire spectrum of possible defensive measures. Passive measures include hazard mapping and zoning, the basic techniques of which are briefly described, and various types of warning systems that have been used with mixed success. Active defensive measures have been applied in the source areas, transportation zones, and deposition zones of debris flow-prone creek basins. The primary measures being applied at present in the source areas concentrate on controlling timber harvesting methods and encouraging reforestation. Engineered erosion control devices such as check dams and channel linings have thus far received limited use in British Columbia. In the transportation zone, design methods have been developed for training chutes and channels, deflecting dikes, diversions, adequate bridge openings and clearances, and overhead debris chutes. The most widespread designs of defensive measures relate to the deposition zone (debris fan) of mountain streams and include inexpensive “open” deposition basins, as well as more sophisticated “closed” structures incorporating a controlled discharge section and a spillway. A number of examples of completed or proposed structures are described and discussed from the point of view of design methodology.
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Debris flows and debris avalanches are among the most dangerous and destructive natural hazards that affect humans. They claim hundreds of lives and millions of dollars in property loss every year. The past two decades have produced much new scientific and engineering understanding of these occurrences and have led to new methods for mitigating the loss of life and property. These 17 papers pull together much of this recent research and present it in these categories: (1) process, (2) recognition, and (3) mitigation. Much of this work results from cooperative efforts between GSA's Engineering Geology Division and Quaternary Geology & Geomorphology Division.