When the original town site of Seward was established in 1903, Lowell Creek ran down what is now Jefferson Street. (At 100 feet, Jefferson Street is the widest right-of-way in Seward.) Lowell Creek originates in the ice fields of the rugged Kenai Mountains, producing from one to three severe floods per year. Until the Diversion Tunnel was constructed in 1939, large quantities of debris – from fine silt to massive boulders – were carried down what is now Jefferson Street to the delta. The deposits amounted to some 27,000 cubic yards annually (roughly 2,700 dump truck loads). On one occasion, in 1935, the stream deposited 10,000 cubic yards in 11 hours (roughly 1,000 dump truck loads). Any property in the way of the stream’s ever-changing flood channel suffered the power of the moving water and debris.
In 1927, the Alaska Railroad Commission provided a small diversion dam and a large timber flume to carry debris down Jefferson Street and deposit it into Resurrection Bay. This flume had so deteriorated by 1937 that it was beyond repair. It was evident that a better designed flood control project was necessary.
The Lowell Creek Diversion Tunnel was constructed to replace the 1927 flume. This historic project was the U.S. Corp of Engineers first completed flood control project in Alaska, and it represents exemplary engineering for the time and place. Construction began in August 1939 and the project was completed in November 1940.
The Project consists of three parts: the Diversion Dam, the Tunnel and the Outlet.
The Diversion Dam is 400 feet long with a maximum height of 25 feet. The Tunnel, which runs through Bear Mountain, is ten feet in diameter and 2,068 feet long. It is lined with concrete, and the floor is armored with 40-pound railroad rails. The Outlet of the tunnel is located at the toe of Bear Mountain. It is an open concrete flume ten feet wide and about 109 feet long that discharges into Resurrection Bay.
Since completion of the diversion tunnel in 1940, the project has effectively controlled Lowell Creek’s regular flooding. Despite severe damage to Seward in the 1964 earthquake, the flood control project remained intact. Two years after the earthquake, during one of the heaviest run-offs on record, Lowell Creek rose to within two feet of the crest of the dam. During the more recent floods of 1986 and 1995 the creek crested within inches from the top of the dam.