INNOVATION-July-August-2020

allow for a risk-based, transparent and fair allocation of mitigation funds, as they exist in some European nations, Japan, or Hong Kong. With ever-increasing development density on fans in BC, prevention of catastrophic loss would benefit from an approach in which the numerous pros and cons of engineering measures need to be carefully evaluated in light of the natural processes that occur on active fans, and balanced with what can be achieved with available funds. Dr. Matthias Jakob, P.Geo., an adjunct professor at the Geography and Earth and Ocean Sciences Department at UBC, has been working on steep creek hazard and risk assessments in the US, Mexico, Bolivia, Peru, Chile, Argentina, Italy and Kyrgyzstan, and Canada, since 1995. He co-authored Engineers and Geoscientists

A typical engineering approach is multipronged, can be expensive, and is usually maintenance-intensive as natural fan-building processes are interrupted or disturbed in one way or another. In most cases, sediment is captured and removed from a sedimentation basin; downstream banks must be adequately protected against bank erosion. Even on relatively small fans, these steps may trigger multimillion dollar projects. However, engineered systems involving sediment capture and steep hydraulically efficient downstream channels may negatively impact fish species that require resting places, slow-flow velocities, spawning gravels, and protective covering/ shading that are generally provided by tree canopies. Learning from natural processes is advisable: alluvial fans are active depositional landforms. It may be helpful to think of fans and fan-deltas more holistically. This implies focus on natural processes and giving channels artificial confines. Riparian corridors and maintaining a natural depth-width ratio are solutions that provide a closer approximation to the natural condition than artificially deep channels that will tend to infill and create maintenance issues. Creation of fish habitat in overflow channels, behind engineered log jams or boulder steps, provides greater ecological value than a sterile boulder or concrete-armoured flume. Any human interference with fan processes will have some undesirable effects or effect chains; design solutions that reduce undesirable effects are highly valuable. Changes in BC climate, which will involve precipitation events of increased frequency amounts, as well as more wildfires and beetle-infestation related tree mortality, will place higher stresses on fans and render past observations obsolete. Therefore, prudent fan risk management accounts for the direct and indirect consequences of climate change. Catastrophic losses on fans in BC are very likely to become more frequent over time. Mitigation has, and will continue to attempt to, counter that tendency. However, funds to do so are limited and there are no long-term established funding formulas that as much space as is reasonable. Setback dikes (perhaps with bike and walking paths) apply this philosophy as opposed to squeezing a creek into

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