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.