Flooding in the Nechako River Basin of Canada: A random forest modeling approach to flood analysis in a regulated reservoir system

Flooding events can have significant impacts, in terms of both loss of life and property damage. Analyzing floods to understand their processes and patterns improves our ability to predict when floods will occur. Under changing climate conditions, this will become even more important. The utility of an alternative approach to conventional flood analysis was investigated in a regulated river system with a reservoir, the Nechako River Basin located in British Columbia, Canada. Using the 1955-2008 daily discharge measured on the Nechako River discharge and its major tributaries, a random forest model was constructed to evaluate the relative importance of contributing discharges to the main stem during significant flood events in the downstream community of Prince George. Discharges from the unregulated Stellako and Nautley Rivers were found to be the most important variables during a spring flood. Conversely, during a winter flood, the regulated Skins Lake Spillway and the Kemano Powerhouse discharges were found to be the most important variables in the model. During periods of no flood, the main stem Nechako River at Isle Pierre discharge was the most important. This work provides a novel source of evidence that flow regulation on the Nechako River is an important indicator of downstream winter flood conditions in Prince George, potentially exacerbating ice jams and/or causing significant property damage and economic losses.