Predicting the Geomorphic and Aquatic Habitat Effects of Extreme Flood Events

Abstract:

High magnitude flood events can completely restructure fluvial systems and condition subsequent geomorphic and ecological regimes. The effects of such disturbances depend on factors such as existing morphology, flood magnitude and duration, and sediment supply. However, the inherent rarity of large floods makes untangling potential controls and interactions difficult. In this study, we take advantage of complete high resolution topographic and air photo data sets collected with unmanned aerial vehicle (UAV) based remote sensing to assess the reach-scale effects of catastrophic flooding that occurred in Alberta, Canada in June 2013. In particular, we combine 2D flow models with pre- and post-flood topographies to constrain the range of conditions during high flow on two rivers, and then relate these conditions to observed changes. We find that flooding on the Elbow River led to a complete channel restructuring associated with tractive forces well above thresholds for sediment transport, whereas the Kananaskis River experienced less drastic change and maintained its channel pattern. Consequently, morphodynamics are more reliably predicted using pre-flood data for the Kananaskis River. Physical changes are then related to in-stream hydraulic habitat, and implications for post-flood channel readjustment are discussed. This work provides a detailed analysis of relationships between flooding, channel morphology, and aquatic habitat in two contrasting systems, with implications for predictive capacity and stream ecosystem management.