INNOVATION-July-August-2020

F E A T U R E

This fan portion of Sicamous Creek is a typical example of steep debris flood-prone creeks in BC. This channel has been deepened and partially armoured by riprap. However, channel sediment is likely to accumulate in the channel during extreme runoff events, which may direct bank erosion into the currently unprotected upper banks. P hoto : BGC E ngineering I nc .

during extreme runoff events. Once the largest clasts in a steep creek are in motion, further sediment entrainment on banks and channel base is easy. TOWARD AMALGAMATING SCIENCE AND ENGINEERING There are thousands of fans with urban development in BC alone, and their number is increasing as are the densities of homes and infrastructures built on them. Managing fan geohazards is difficult, and even apparently robust solutions can be failure-prone. The key challenge arises from the attempt to impose a stable engineering solution onto a naturally and episodically changing landform.

available time to clear the channel, leading to avulsions. Similarly, at fan-delta fronts, the sediment wedge extending upstream can lead to upstream avulsion no matter how deep the channel may be, especially when the receiving water level is high (like a regulated lake level in late spring, or high tides on ocean fan-deltas). Third, installed riprap is sized for a given peak flow and associated return period. But sizing guidance may fail to account for the effects of higher sediment concentration in debris floods, which facilitates the plucking of riprap from its location and starts the unraveling process common along steep creeks

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I N N O V A T I O N