Following the previous blog post about dangerous winter conditions along Chasàn Chùa (McIntyre Creek) near the YukonU Ayamdigut Campus in Whitehorse, here is a time-lapse video showing the freeze-up processes.
A camera was installed near the creek channel prior to freeze-up, and it took 3 pictures per day (one picture every 8 hours) until January. The camera also took pictures at night and no snow obstructed our setup, so the record contained no gap. A respected former colleague, Médéric Girard, built the camera setup a couple a years ago. An esteemed colleague, Tyler de Jong, prepared the montage, including the air temperature record at the Whitehorse airport.
The video shows how the anchor ice and ice dams build up (with a maximum rate of about 2 cm/h) to generate a total backwater (stage rise) varying from 1.2 to 1.6 m. Once this bankfull state (with some overbank flooding) is achieved, the combination of warmer air temperatures, the heat contained in the flow (e.g., from upstream beaver ponds), and the insulation provided by snowpack forced the melting of low elevation ice (i.e., low-lying anchor ice), eventually leaving many ice features in a free-spanning state.
Readers can imagine how this ice cover is fragile just by witnessing the way slabs collapse under their own weight as soon as the water level drops. Because this ice is not in contact with the flowing (or splashing) water, it cannot thicken and, therefore, remains weak during the whole winter.
***
The freeze-up process in the YukonU reach of Chasàn Chùa is more intense (in terms of maximum water levels) than in most other creeks presenting a similar morphology and channel size. Why? Because of a relatively high flow imposed by hydroelectric production further upstream (water from Fish Lake is diverted towards Louise (Jackson) Lake, then into the original Chasàn Chùa).
The literature confirms that altered river ice processes are common downstream of hydroelectric dams (e.g., Huokuna et al., 2017). This is the case in the large Peace River in Alberta, and it is also the case in the Äshèyi Chu (Ahishik River) near Haines Junction. In collaboration with the University of Alberta and various Yukon partners, our team is finishing a research project involving the development of models that simulate ice processes and water levels in the regulated Äshèyi Chu.
Based on observations, consequences of the modified Chasàn Chùa hydrological regime are probably similar to what is observed along the Äshèyi Chu:
- Altered channel stability (bank segments affected by the collapse of heavy ice slabs)
- Modified water quality (high suspended sediment transport rates, or turbidity, at the beginning and end of winter)
- Impact on riparian vegetation (trees falling across the channel, small bushes ripped out)
This is a reminder that, in most cases, energy production comes at an environmental cost. Fortunately, Chasàn Chùa supports many forms of life and represents a rich habitat that, many believe, should be protected against development and disruption.