The Tr’ondëk (Klondike River) valley has been affected by several floods in recent years. This photograph, provided by the Government of Canada, shows a high-water event caused by an ice jam in April 2003. Several distinct hydrological processes generate floods along the Klondike River and their likelihood and intensity vary from one section of the river to another.
The following graph presents annual peak water levels expressed as a function of the estimated discharge at the Klondike River Water Survey of Canada Hydrometric station during river ice breakup (red), the open water season (blue) and the freeze-up period (purple). For a given discharge, water levels in the presence of ice are higher because the ice occupies a portion of the channel and reduces average flow velocity, forcing the water level to rise. This is especially true for thick and rough ice accumulations, and this explains why, for that location, many of the highest water levels are associated with ice jams during low flow periods in Fall (e.g., 2002, 2015) and Spring (e.g., 1986, 2003, 2004, 2013).
Ice jams are more likely to occur in multichannel river segments with a floodplain (e.g., Henderson Corner, Rock Creek, Airport sector), but water levels associated with such ice jams are often not drastically high because the floodplain and secondary channels efficiently convey the flow impeded by the jam. In this case, the frequency and intensity of open water floods and ice-induced floods may be comparable.
The phenomenon of ice jamming is less frequent in a single-channel river segment of similar gradient when there is no floodplain (e.g., when a river has been modified to flow in a single channel). However, when ice jams do occur, water levels can rise quickly and get surprisingly high (as shown in the photograph above) because the water and ice is constricted to the channel.
The photo below shows that an ice jam (possibly from May 1986, provided by the Government of Yukon) was initiated in a multi-channel area of the lower Klondike River, but affected a single-channel area generating water levels 0.5 m higher than during the 2003 event (shown above).
The complexity and diversity of flooding processes in winter, combined with sediment transport and channel evolution, represent a challenge for flood risk reduction all over Canada. In the Dawson City area, research on river ice dynamics and flooding processes could help inform land use planning, infrastructure design, and flood forecasting.