This is the 5th email update sharing information about the potential flood situation for the Southern Lakes. Yellow highlight indicates where information is new from the last update. Following a conversation I had with a Tagish Lake resident this past week, I have added a graph showing Tagish Lake levels as well. I switched from the arbitrary datum used with the gauges to adjust them to elevations above mean sea level so as to make them more comparable.
* 1-May 2021 final snow bulletin is out: (https://yukon.ca/sites/yukon.ca/files/env/snow_bulletin_may_2021_final-en.pdf)
* Southern Lakes snow load = 215%
* "Water levels in the Southern Lakes are driven by a combination of snowmelt, summer precipitation and glacier melt"
* 19-March 2021, Yukon Energy (YEC) opened the locks at the Lewes River control structure (roughly 2 months early)
* The boat lock on north side of Lewes River control structure is open
* YEC has dropped elevation of Schwatka by -0.93 m to try to increase flow through Miles Canyon
* YEC continues to work with float plane users to find a solution to lower level of Schwatka for this summer
* As of 7-May 2021, Marsh Lake level began to increase again
* Currently Marsh Lake is 18 cm above average elevation for this time of year
The attached graphs shows the lake levels of Marsh and Tagish over the past 20 years based on Government of Canada hydrometric data. Peak lake levels are typically reached in August. The 2007 flood year is indicated in a purple; the 2020 year is shown in green and the average is shown in red. 2021 is shown as the dotted blue line. I have added the full-supply and low-supply levels in yellow (please note that the Gov Canada hydro data uses relative elevations, so I have now adjusted the supply levels to be actual elevations).
Looking back at 2007, through June it was apparent that the lake levels rose very quickly and that we could anticipate a flood. For 2021 and the first week of June, lake levels are currently tracking more closely to 2007 (purple line) than the 20 year average (red line). I have flagged this to the Water Resources Branch, Yukon Energy and the Emergency Measures Office.
If you know of anyone else that would like to receive this update, please let me know.