Montlake Cut: The 1916 Canal That Lowered Lake Washington

The Montlake Cut is the canal dug through the Montlake Portage, the strip of land that once separated Lake Washington from Lake Union. Work on the Lake Washington Ship Canal began with it, in 1909. The canal was the last of several attempts to build a water route around the hills between Lake Washington and Seattle, to promote trade and development. Two land barriers and a difference in elevation of about 30 feet blocked the way from Lake Washington through Lake Union to Puget Sound. [1]

Major Hiram M. Chittenden of the Corps finalized the plan: a canal from Shilshole Bay on Puget Sound through Salmon Bay to Lake Union, then on to Lake Washington. A double lock at Ballard would carry boats between Puget Sound and Salmon Bay, which would be raised behind the locks to the level of Lake Union. Some had proposed a second lock between Lake Washington and Lake Union. Instead, the Corps planned to cut a canal and drain Lake Washington down to Lake Union's level, 9 feet lower than its average level. [1]

Digging the cut was hard. Earlier attempts to finish it failed because its sides kept slumping, which forced workers to build new cofferdams, drain the water out of the cut and build concrete revetments inside it. Only on the third cofferdam did the crews build up the revetment enough to stop the slumping. On August 25, 1916, the cofferdam holding Lake Union back was opened and water gushed into the cut. Three days later, the gates at the Lake Washington end were opened, and the two lakes were joined. [1]

Beginning on August 28, 1916, Lake Washington dropped 9 feet over about three months, from about 29 feet above mean lower low water at Shilshole Bay to 20 feet, the level of Lake Union. Before, its shoreline could move by as much as seven feet with the seasons. Wetlands along the shore drained. The lake fell below the channel of the Black River, at its south end in Renton, which had been its outlet. The Black River disappeared, and the ship canal became the lake's new outlet. [1]

The change ran through the whole watershed. Water now passed through Lake Washington in about two years instead of about five. The lower lake steepened the Sammamish Slough, so its current ran faster and dug a deeper channel. Far less water flowed down the Duwamish River, which reduced flooding and let farmers drain and cultivate more land. Renton had diverted the Cedar River straight into Lake Washington in 1912, and according to Renton historian Morda C. Slauson, after the lake was lowered the Black-Cedar salmon run arrived just in time to be trapped by the receding water. [1]

Not everyone gained. The Duwamish had a village on the Black River for at least 1,400 years, and tribal members lost access to the fish and plants they had long gathered there. Tribal member Joseph Moses remembered the day the water went down: 'our landing and canoes stood dry and there was no Black River at all.' [1]