Resource Management
8:59 am
Tue February 4, 2014

Why Is Lake Washington's Water Level So Low? Ask The Engineers

The Lake Washington Ship Canal connects the lake with Puget Sound via Lake Union. The Army Corps of Engineers controls the water level of the lake by manipulating the water flow at the Ballard Locks.
Credit Flickr Photo/Seattle Munincipal Archives

You may have noticed that water levels at Lake Washington beaches are very low.

But if you think there might be some connection with the drought that is now gripping much of the western U.S., think again.

“No, it’s not connected at all with the drought,” according to Marian Valentine, a manager with the Army Corps of Engineers.

Valentine oversees operations at the Hiram M. Chittenden Locks in Seattle’s Ballard neighborhood. The locks, along with the Lake Washington Ship Canal, were built almost a century ago to connect Lake Washington with Puget Sound.

But the locks also act as a dam between the freshwater of the lakes and the salt water of Puget Sound, which is more than 20 feet lower in elevation.

Water flows out of the lake system through a series of spillways on the locks, located at the western end of the Ship Canal.

The spillways at the Hiram M. Chittenden Locks in Ballard, Seattle.
Credit Flickr Photo/Kwong Yee Cheng

In the winter, the Corps of Engineers lets more water flow through the spillways to keep the level of the lake constant at 20 feet. In mid-February, the Corps will start closing the gates, in order to slowly raise the level of the freshwater lakes.

The gates will stay mostly closed for the next two and a half months. By May 1, the level of the lakes will be a full two feet higher than it is now.

According to Valentine, it’s “quite a bit” of extra water. In total, she calculates it would fill about 25,000 Olympic-sized swimming pools.

The Corps uses the extra water in the summer for the seasonally heavy boat traffic through the locks. Every time the large lock chamber is used, it requires about 8 million gallons of fresh water, which is then discharged into Puget Sound.

But even more water is used to help fish migration. According to Valentine, both juvenile salmon migrating to the ocean and mature salmon returning to their birthplace require a lot of extra water to help them navigate the locks.

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