Beginning on August 25, 1916, Lake Washington is lowered 8.8 feet, due to construction of the Lake Washington Ship Canal, and the Black River disappears. The ship canal is being built between Lake Washington and Puget Sound. Because of the different water levels in Lake Washington, Lake Union, Salmon Bay, and Shilshole Bay, the federal government builds a double lock at Ballard and lowers Lake Washington to the same height as Lake Union, from about 30 feet above mean lower low water (the average of each day's lowest low tide) on Shilshole Bay to 21 feet. The level of Salmon Bay is raised to 21 feet behind the locks and dam at its mouth. The lowering of Lake Washington and raising of Salmon Bay causes a number of changes to the watershed, most dramatically the drying up of the Black River, which had been Lake Washington's outlet, when the lake's water level drops below that of the river-channel entrance at its south end. As a result, the way water moves through the watershed changes drastically, with environmental and human consequences.
Reshaping the Watershed
The U.S. Army Corps of Engineers began construction of the Lake Washington Ship Canal in 1911. It was the last of several attempts to build a transportation route around the hills between Lake Washington and Seattle to promote trade and development. Two land barriers and an elevation differential of about 30 feet blocked the water route between Lake Washington via Lake Union to Puget Sound. Major Hiram M. Chittenden (1858-1917) of the Corps finalized a plan to build a canal between Shilshole Bay, on Puget Sound, and Lake Washington, passing through Salmon Bay to Lake Union, then on to Lake Washington. A double lock, at the west end of the canal at Ballard, would help boats negotiate the drop in elevation between Salmon Bay -- which would be raised behind the locks to the level of Lake Union -- and Puget Sound. Instead of a lock between Lake Washington and Lake Union, the Corps planned to cut a canal and drain Lake Washington down to the same level as Lake Union, 8.8 feet lower than its average level.
After the Montlake Cut was opened, it would take about three months for Lake Washington to drain down, resulting in radical changes in the hydrological systems of the Green-Duwamish River watershed. As a result of the lowering of the lake, a new watershed formed, a saltwater inlet became become a freshwater bay, and the way water moved through the lakes and rivers was significantly different.
The Environment Before
Before the construction of the ship canal, the drainage of the Lake Sammamish, the Sammamish River, Lake Washington, and the Black River were part of the Green-Duwamish River watershed. Lake Sammamish was fed by a number of streams that drained the surrounding land. Its outlet, the Sammamish Slough (also known as the Sammamish River), was the main source of water into Lake Washington, though that lake was also fed by creeks and springs along its perimeter. The Black River, on the lake's south end at Renton, drained Lake Washington. The Black River was joined by the Cedar River just a half mile downstream from the lake. The Black River joined with the Green River at what is now Tukwila to form the Duwamish River. Before 1906, the White River also drained into the Duwamish, but its channel shifted during a flood so that it flowed southward to become a tributary of the Puyallup River, which drained into Commencement Bay at Tacoma.
The whole Lake Sammamish, Lake Washington, and Black River system moved relatively slowly. Coastal geologist Michael Chrzastowski estimated that water stayed in Lake Washington for about five years before entering the Black River and continuing on to the sea. The slough between the two lakes was marshy, with a broad, meandering channel. The Black River crossed the slowly, but continually, rising Cedar River alluvial fan. As the fan built up over several thousand years, the level of Lake Washington also rose.
By the 1900s, the lake was about 30 feet above mean lower low water on Puget Sound at Shilshole Bay. This was its average level; seasonal changes in precipitation could cause the shoreline of the lake to vary by as much as seven feet. During exceptionally rainy periods the Black River flowed in two directions: downstream to the Duwamish and upstream, back into the lake. These fluctuation water levels created many marshy areas along the lakeshore.
When American settlers began establishing farms along the Duwamish and Black rivers, they were plagued by floods. Though the rivers' height only varied by three to four feet, it still hindered settlement and development. In an attempt to get the river moving more quickly and draining the lake more effectively, the settlers tried some dredging and debris clearing. It did speed up the river and reduce backflow from the Black back into the lake, but did not solve the problem.
The rest of the ship canal route was separate from the Green-Duwamish basin. Lake Union was fed by streams and springs along its shores and drained through a small creek known by several names -- Ross Creek, Shilshole Creek, the Outlet -- to Salmon Bay. The lake level was 21 feet above the mean lower low water at the bay. It fluctuated very little because the area of land that drained into the lake was relatively small.
Before the closing of the locks at Ballard in July 1916, Salmon Bay was a saltwater inlet of Shilshole Bay on Puget Sound. It fluctuated with the tides each day. At low tide it was a very shallow channel, about three feet deep. At the highest tides, it reached a depth of about 15 feet.
Building the Ship Canal
Work on the Lake Washington Ship Canal began in 1911. By July 1916 the locks at the western end of Salmon Bay were ready to be closed. After the locks were closed, Salmon Bay slowly rose to the level of Lake Union. Saltwater was kept, as much as possible, on the west side (the Puget Sound side) of the locks. Lake Union continued to drain along the same route, but the creek was replaced with a canal cut through the surrounding land.
Work proceeded on the strip of land, then called Montlake Portage, that separated Lake Washington and Lake Union. A canal, to be called Montlake Cut, was dug through this land. On August 25, 1916, the cofferdam holding Lake Union back from the canal was opened and water gushed into it. Within a few days, the cofferdam on the east (Lake Washington) end of the cut was opened and Lake Washington joined with Lake Union. Over the next three months, the level of Lake Washington dropped 8.8 feet. Wetlands along the shore drained and the lake dropped below the level of the Black River channel. The Lake Washington Ship Canal became the new outlet for Lake Washington.
A couple of years earlier, Renton residents had diverted the Cedar River from its channel through town that repeatedly and destructively flooded to a new channel that led to Lake Washington. According to Morda C. Slauson, a Renton historian, the spring runs of salmon arrived just in time to be trapped by the receding waters. In the 1930s, new salmon stock would be introduced via the ship canal, but the Black and Cedar river runs ended.
A New Watershed
Water moved differently through the new watershed. It passed through Lake Washington much more quickly, in about two years. The steeper gradient created by the lowered lake level on Lake Washington caused the Sammamish Slough current to move more quickly, increasing the channelization of the waterway (making a deeper channel).
At the same time, the changes drastically reduced the volume of water flowing through the Duwamish River. It reduced--but did not eliminate--flooding, and allowed farmers to drain and cultivate more land. Before long, much of the lower Duwamish would be straightened and dredged into a waterway to facilitate economic development. This, along with filling on the Seattle tidelands, led to a dramatic loss of the Duwamish estuary. Much of the industrial area of Seattle is built on top of the filled Duwamish estuary.
Benefits and Losses
Though the ship canal would bring many economic and social benefits to Seattle, its construction did have some detrimental effects. In the simplest sense, the city lost something beautiful. Clarence Dullahaut, who moved to Renton in 1903, described the Black River in an interview: "It was a pretty river, meandering along. People used to come up the Duwamish from the Sound up the Black to Lake Washington in launches" (Sato, 56).
The Duwamish tribe had a village located along the Black River for at least 1,400 years and perhaps for thousands of years and members of the tribe lived along the river. Members of area Indian tribes who had long gathered resources from those wetland areas and who relied on salmon as a foundation of their diet and as an integral part of their spiritual beliefs, lost access to those resources on Lake Washington and along the Black River. The right to fish and gather plant materials had been retained in the treaties the tribes signed with the United States, but it became difficult to exercise those rights in the much reduced environment that resulted from the hydrological changes.
There was also an emotional loss for the Duwamish. Tribal member Joseph Moses stated in an interview with David Buerge, "That was quite a day for the white people at least. The waters just went down, down, until our landing and canoes stood dry and there was no Black River at all. There were pools, of course, and the struggling fish trapped in them. People came from miles around, laughing and hollering and stuffing fish into gunny sacks" (Sato, 57). According to Morda C. Slauson, a historian in Renton, Henry Moses (1900-1969) "dragged his canoe out of the mud and said he never wanted to paddle it again" (Slauson, 5).
Like many large civil engineering projects in Seattle, the Lake Washington Ship Canal wrought enormous change to the landscape and to the lives of people who lived on the waterways affected by the project. It brought many benefits to the city, but exacted a large environmental and social price.