U.S. Army Corps of Engineers officials announce Lake Washington’s level will drop below an elevation of 20 feet and are taking steps to conserve water during this year’s dry weather through lockage efficiency.
While the lake level is presently at 20 feet, current forecasts indicate it will drop below the typical minimum elevation beginning Sept. 21, with water levels staying low until the rain returns. Based on the historical data record, the lake level is not expected to drop below 19.75 ft.
Cedar River flow into Lake Washington will increase on Sept. 23, when Seattle Public Utilities releases more water from Chester Morse Dam according to their scheduled minimum instream flow commitments. This will reduce the rate at which Lake Washington elevation lowers.
USACE typically maintains the water level between 20 and 22 feet, as measured at the Chittenden Locks. Corps officials keep winter water levels at 20 feet, and begin the annual summer refill in February, targeting a 22-foot elevation by late May to early June. The 22-feet target water elevation was accomplished in June of this year. The higher level helps meet summer water use requirements, providing water necessary for fish passage, navigation, and salinity control. Water is slowly consumed throughout the summer, until it reaches the winter level typically in early December.
Since conditions have been dry this summer, Lake Washington is lower than it typically is this time of year. The normal September precipitation in Seattle is 1.61 inches. However, through Sept. 20, Seattle has only received 0.22 inches of rain this month.
The Corps is maximizing lockage efficiency by increasing the number of recreational vessels in each locking and prioritizing use of the small locks. As lake levels change, additional measures to conserve water could be implemented.
USACE officials are recommending floating homeowners, others with floating structures and vessels moored on Lakes Washington and Union and along the Ship Canal prepare for possible lower water levels.
The record low lake level is 18.35 feet, reached in 1958. The lowest recent recorded water level below 20 feet was 19.91 feet, measured in August 2015.
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