How to lower a lake – Seattle 1916

The other day my mom asked me a very basic question and one that I had never considered. How exactly did they lower Lake Washington during construction of the Lake Washington Ship Canal and the Hiram M. Chittenden Locks? Completed in 1916 and officially opened in 1917, this was one of the great engineering feats of Seattle history.

Map of canals and locks, from Wikipedia
Map of canals and locks, from Wikipedia

In order to keep the canal system (it consisted of two canals, or cuts, one at Montlake and one at Fremont) at the same water level, Lake Washington (LW) had to lowered down to the level of Lake Union (LU). (See map above to see how Salmon Bay connected via the Fremont canal to LU and LU connected to LW via the Montlake canal.) This necessitated about a nine foot lowering, as LW was 29 feet above sea level and LU at 20 feet. The LW number is not exactly accurate because the lake level fluctuated by as much as eight feet during the year; it was highest in winter. In addition, Salmon Bay, which historically had been a tidal inlet—filling at high tide and mostly draining out low tide—had to be raised up to the level of LU.

In regard to my mom’s question, I had long known that it “took” three months to lower LW but didn’t know the details on how they did it. Here’s a timeline of how they lowered the lake and raised the bay.

July 12, 1916 – Locks closed in order to flood Salmon Bay and raise it to the level of Fremont canal and Lake Union. “Within thirty days the greatest fresh water harbor on the Pacific seaboard will be open to ocean-going ships entering Puget Sound,” reported the Seattle Times. This was a typical response to the opening of a fresh water port in Salmon Bay.

Sluice gates in Lake Union, water going into Fremont canal, image courtesy Army Corps of Engineers
Sluice gates in Lake Union, which controlled the water going into Fremont canal and eventually into Salmon Bay. Image courtesy Army Corps of Engineers

July 30, 1916 – Steamer F.G. Reeve first boat to pass through the locks, which opened the long desired passage from Salmon Bay through the Fremont canal to Lake Union, now all at the same water level. Reeve used the smaller of the two locks.

Steamer F. G. Reeve
Steamer F. G. Reeve. From Puget Sound Marine Historical Society

August 3, 1916 – Snag steamer Swinomish, under the command of Capt. F. A. Siegal, was the first boat to pass through the larger lock, “amid handclapping, cheers and the blowing of whistles,” wrote Thomas Francis Hunt in the Seattle Times. More than 2,500 people attended the opening. Next boat through was the Orcas. Both vessels did a quick spin in Salmon Bay before returning back to the locks.

August 25, 1916 – At 2 p.m., laborers used shovels to cut an opening into the cofferdam (temporary dam built to keep water out of the way) on the east side of Portage Bay. The plan was for the water to flow out of Lake Union and fill the Montlake canal. At the east end of the canal, or the very west side of Union Bay, were sluice gates, which would control the water flowing out of Lake Washington, still nine feet higher than Lake Union. An unknown skiff piloted by an anonymous man and two bare-headed boys was the first to run the canal.

Location of cofferdam, from Seattle P-I, August 26, 1916
Location of cofferdam, from Seattle P-I, August 26, 1916
Cofferdam in Portage Bay
Cofferdam in Portage Bay, Image courtesy Army Corps of Engineers

“In exactly fifty six minutes the cut (Montlake canal) was filled to the level of Lake Union, and before the hour was up the current had ended and the eddies had ceased to foam. Logs torn from the cofferdam by the charging waters and hundreds of timbers and boards which covered the bottom of the cut floated to the surface…When the men with their shovels had broken the narrow neck of land, they sprang aside just in time to escape the inflow of water…In ten minutes the crowds on the cofferdam fled to escape being plunged into a raging torrent on the sides of the bank, which caved in in huge sections,” reported the Seattle Post-Intelligencer.

Breaching the Cofferdam, photographer is looking west toward Lake Union
Breaching the Cofferdam, photographer is looking west from south side of Montlake canal up to Lake Union, Image courtesy Army Corps of Engineers

August 28, 1916 – Sluice gates in Lake Washington opened to allow water level in the lake to drop. Level was to be reduced about one and half feet in the first week with it dropping four feet by the end of September. Lowering Lake Washington down to the level of Lake Union did not occur until October.

Sluice gates in Union Bay
Sluice gates in Union Bay, Image courtesy Army Corps of Engineers

By late October 1916 – Lake Washington and Lake Union and Salmon Bay are at the same level and boats can travel from Puget Sound to Lake Washington.

July 4, 1917 – Official opening of the locks and ship canal.

Material for for this story comes out of research I have done for my new book on Seattle – Too High and Too Steep: Reshaping Seattle’s Topography.

If you so desire, you can like my geologywriter Facebook page.


Seattle Map 6 – Lake Washington 1905

The best map showing Lake Washington before the locks and ship canal lowered the lake in 1916 is one produced by the Coast and Geodetic Survey in 1905. Based on survey work done between 1856 and 1905, it shows the topography of the lake shore and the bathymetry. Today, I’d like to focus on one section of the map, which shows the area from Rainier Beach to Wetmore Slough (today’s Genesee Park).

Lake Washington Close Up 1905

In 1870, Joseph Dunlop homesteaded 120 acres along the water at Rainier Beach. Much of it was a swamp, or slough, an excellent place, according to one time resident, A. B. Matthiesen, to lie on a beaver dam and shoot ducks. Rainier Beach High School and its playing fields now cover the lowland. The adjacent Beer Sheva Park, originally Atlantic City Park, was also underwater, and the property east of it, an island, known as Youngs’ Island until Englishman Alfred J. Pritchard bought it in 1900. You can see on the map that a footbridge leads over the slough to reach Pritchards’ eponymous isle and estate, though the island is not labeled.

When the lake dropped and the former slough became dry, or at least mostly dry land, Pritchard, like others around the lake, sought to exploit the change. He took out large advertisements in the Seattle Times with the headline “You Never Saw Such Soil!” “Everything grows in it with amazing rapidity and profusion,” touted the ads. All it took was $16 down with $16 per month payments, plus interest.

Pritchard Island 6-18-22

The next noticeable feature north of the island is the Bailey Peninsula, or what we now call Seward Park. The peninsula connected to the main land by a flat wisp of terrain. Harold Smith, who had grown up in the neighborhood in the late 1800s, told a Seattle Times writer in the 1950s that during high water, the peninsula would become an island and the “isthmus could be crossed in a canoe or rowboat.” I doubt that many would call the modern connection to the peninsula an isthmus; it is now wide enough to look like a shoulder, a result of lowering Lake Washington by nine feet.

In 1912, when the Olmsted Brothers were working on their plans for the Seattle park’s system, some locals agitated for a canal through the isthmus so that tour boats could pass through. The steamers would be a boon to “poor people [who] had no means of getting to Bailey Peninsula…without walking a great way,” noted Dawson in a report to the parks on April 5, 1912.

Almost two miles north of Seward Park at Stan Sayres Memorial Park, is another landscape changed by the lower lake level. Labeled as Wetmore Slough on the map, it extended south almost to Rainier Avenue. If you wanted to cross over the slough at the lake, you went on a wood trestle bridge at what is now Genesee Street. The slough drained and for the most part disappeared after 1916 but local residents still complained that it was a source of noxious odors and an incubator for mosquitoes. To combat these problems, the Rainier District Real Estate Association proposed in 1928 to dredge a 200-foot-wide, 2,000-foot-long canal up the old slough, and to make Columbia City into a “seaport town.” Few cottoned on to the dream, though it persisted until 1937 when construction crews began to replace the old trestle with fill excavated from the lake. Six years later the city decided to convert the area to yet another “sanitary fill,” which generated a new round of complaints, this time about dog-sized rats and odors more redolent that ever.

Material for for this story comes out of research I have done for my new book on Seattle – Too High and Too Steep: Reshaping Seattle’s Topography.

If you so desire, you can like my geologywriter Facebook page.