Marsh Lake levels: Update 4, 31-May 2021

This is the 4th email update sharing information about the potential flood situation for the Southern Lakes. Yellow highlight indicates where information is new from the last update. We have been getting some rain in the last weeks, but so far the lake level has been following the average fairly closely.

 *   1-May 2021 snow bulletin is now 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"
 *   This is the third and final snow bulletin
 *   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 now open
 *   YEC has dropped elevation of Schwatka by -0.93 m to try to increase flow through Miles Canyon
 *   On Wed 26-May YEC was required to raise Schwatka to full supply level for a day as part of regulatory testing; once completed they returned the lake to the -0.93 m level
 *   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 5 to 6 cm above average elevation for this time of year

The attached graph shows the lake levels 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 adjusted the supply levels to fit).