Current Water Supply Conditions and Outlook
March 31, 2015
Our current water supply and outlook is good despite the low snowpack in the Cedar and South Fork Tolt watersheds.
Last week, 2.95 inches and 3.24 inches of precipitation were recorded in our Cedar and South Fork Tolt River watersheds, respectively. With unseasonably warm temperatures and precipitation falling as rain, snowpack in our mountain watersheds is well below the long term average for this time of the year. In order to meet our normal goal of refilling our reservoirs toward the end of the spring, we are relying more than usual on rainfall than snowmelt. As part of this strategy, we maintained our reservoir water levels somewhat higher than normal in the winter while meeting multiple objectives (i.e., municipal water supply, flood management, hydropower and protecting salmon redds).
As we transition into the spring reservoir refill period the Chester Morse Reservoir and the South Fork Tolt Reservoir are close to the upper range of their target elevations for refill. Moving forward, we will manage the reservoir water levels in the upper range for refill.
Chester Morse Lake at the Overflow Dike is at elevation 1561.9 feet, about 3.0 feet higher than last week, and about 9.1 feet above its long term average (based on the years 1989 to 2005). Masonry Pool Reservoir at Masonry Dam is at elevation 1561.8 feet, about 2.9 feet higher than last week, and about 11.2 feet above its long term average. The South Fork Tolt Reservoir at the South Fork Tolt Dam is at elevation 172.5 feet, about 2.3 feet higher than last week, and about 5.0 feet above its long term average. Water releases from reservoir storage are actively being managed for water supply, fish habitat, hydropower and flood management objectives for both the Cedar and South Fork Tolt Rivers.
Water consumption for the previous seven days averaged approximately 102 mgd. That is more than the 101 mgd consumed during the same period last year, and less than the average of 115 mgd used during the same period over the years 1999-2008.
Juvenile sockeye salmon are emerging from their redds and migrating to Lake Washington on a nightly basis. Juvenile Chinook salmon have begun to emerge from their redds to migrate to the river margins to rear, although many will also move to Lake Washington for rearing. Redd surveys in the Cedar River below Landsburg indicate that steelhead and trout have not yet begun to spawn. Young coho, steelhead and trout that emerged in 2014, are rearing in the Cedar at this time.
Tolt summer-run steelhead move into the upper reaches of the South Fork Tolt River during the summer and fall where they wait to spawn during the following winter and spring. At this time, early spawning steelhead in the population have begun to construct redds. These early redds will start to produce emerging fry in late April. Adult summer steelhead will continue to spawn into the month of April. Young steelhead and coho that emerged in 2014 are currently rearing in the South Fork Tolt. Juvenile Chinook salmon in the mainstem Tolt River have begun to emerge from their redds and will be rearing in the mainstem into the month of July.
View Current Water Supply Graphs (pdf)