No abstract

Abstract. Sediment routing models which simulate the coevolution of river long profile and bed grain size distributions have been used to investigate downstream fining above base level, channel response to rectification, and other disequilibrium situations at a variety of timescales. We extend one such model (SEDROUT [Hoey and Ferguson, 1994]) to deal with sand as well as gravel and test its ability to simulate aggradation and downstream fining in a well-documented Canadian river. Previous tests of this and similar models have been largely restricted to comparing observed and simulated gradients of downstream fining, but it is not obvious when to make the comparison in a timedependent model with uncertain initial state and no equilibrium except in the very long term. We discuss and apply a more rigorous set of test criteria and address issues of defining initial conditions and time to test. The model's varying sensitivity to different boundary conditions and parameters indicates key data constraints on the testability and predictive accuracy of any such model. We also consider the adequacy of one-dimensional calculations in channels with variable width and present initial results of attempts to allow for this.

Abstract:A destructive debris flood occurred between 19 and 21 June 2013 on Cougar Creek, located in Canmore, Alberta. Cougar Creek fan is likely the most densely developed alluvial fan in Canada. While no lives were lost, the event resulted in approximately $40 M of damage and closed both the Trans-Canada Highway (Highway 1) and the Canadian Pacific Railway line for a period of several days. The debris flood triggered a comprehensive hazard assessment which is the focus of this paper. Debris-flood frequencies and magnitudes are determined by combining several quantitative methods including photogrammetry, dendrochronology, radiometric dating, test pit logging, empirical relationships between rainfall volumes and sediment volumes, and landslide dam outburst flood modeling. The data analysis suggests that three distinct process types act in the watershed. The most frequent process is normal or "clearwater" floods. Less frequent but more damaging are debris floods during which excessive amounts of bedload are transported on the fan, typically associated with rapid and extensive bank erosion and channel infilling and widening. The third and most destructive process is interpreted to be landslide dam outbreak floods. This event type is estimated to occur at return periods exceeding 300 years. Using a cumulative magnitude frequency technique, the data for conventional debris floods were plotted up to the 100-300 years return period. A peak-over-threshold approach was used for landslide dam outbreak floods occurring at return periods exceeding 300 years, as not all such events were identified during test trenching. Hydrographs for 6 return period classes were approximated by using the estimated peak discharges and fitting the hydrograph shape to integrate to the debris flood volumes as determined from the frequency-magnitude relationship. The fan volume was calculated and compared with the integrated frequency-magnitude curve to check of the validity of the latter. A reasonable match was accomplished, verifying the overall relationship. The findings from this work were later used as input to a risk assessment seeking to quantify risk to loss of life and economic losses. The risk assessment then formed the basis for design of debris-flood mitigation structures.

No abstract

No abstract