Salmon Creek Dam

 

 

The site for Salmon Creek Dam project was the brainchild of Bartlett Lee Thane, a brilliant 1898 mining engineering graduate of the University of California, Berkeley. By 1912 Thane had gained control of 7 gold mines in the Juneau area including the very large but low-grade Perseverance mine which was the main orebody of what became the Alaska Gastineau Mine. These mines normally operated only during the summer months when flowing water was available.  Thane wanted to convert these operations to year-round operation and to construct a 6000 tons per day mill to treat the ore.  This would require a reliable year-round power supply.

Thane directed his chief mining engineer, Harry Wollenberg, also a brilliant University of California mining engineering graduate, to search for a suitable watershed and site for a hydroelectric dam. He found a suitable site on Salmon Creek and conducted evaluations in 1911-1912 which included precipitation and flow recording and geotechnical surveys.  He then developed a project plan and in 1912 Thane retained the consulting services of F.G. Baum and Company of San Francisco.  Baum, an electrical engineer, assigned the design work to dam design engineer, Lars Jorgenson.  Arthur Powell Davis, an early civil engineer with what is now the U.S. Bureau Reclamation and later ASCE President in 1920, also consulted with Jorgensen on the dam design.

Wollenberg then became chief construction engineer for the project initially concentrating on logistics and transportation for the work, including camps for workers, a flume and lower powerhouse for construction power and 3000 feet of inclined, steam powered tramways.

Meanwhile, Baum and Company were engaged in preliminary design and recommended that the Salmon Creek Dam be constructed as a constant angle concrete arch structure which they determined would allow for 20-25% less concrete than the conventional constant radius design.  Gastineau Mine management approved the design and construction proceeded by diverting Salmon Creek through a 6 feet diameter tunnel and the first concrete placement for the dam was made in July 1913.  Construction was complete by August 1914 and the dam was commissioned.     

Salmon Creek Dam then became the world’s first constant angle concrete arch dam constructed for a major impoundment.  It was an old concept proposed as early as 1866 but Jorgensen’s design was the first to be implemented for the concept.  The actual saving in material was 33%.  The dam served the Alaska Gastineau Mine until its closure in 1944.  The mine was the major industry in Juneau employing 900 people at peak.  The dam has since provided one third of the Juneau area water demand and over 7% of its power requirements.  

In 1931 Jorgensen reported that over 40 constant-angle concrete arch dams had been constructed all around the world up to that time.  It went on to become a major design class for narrow ‘V’ canyon sites which enabled a significant saving of materials and a much-improved factor of safety.  The project was also innovative in allowing for contraction during curing by dividing the dam into three blocks with two vertical joints.  Lars Jorgensen’s 1915 paper on the Constant Angle Arch Dam won ASCE’s Norman Medal for a technical paper that contributed to either practical or research aspects of engineering disciplines.

References:

1. ASCE Alaska Section, Historic civil Engineering Landmark Nomination of Salmon Creek Dam, 2020
2. Willis, Scott, P.E., M.ASCE, Constricting the Salmon Creek dam Hydroelectric Project, 2012, (A paper by Willis of the Alaska Light and Power Co., and a supplement to the nomination in Ref 1.)
3. Alaska Mining Hall of Fame paper, Bartlett Lee Thane, 1879 -1927, Undated (Also a supplement to the nomination in Ref 1.)

Additional References:
1. Lars Jorgensen’s 1915 paper on the Constant Angle Arch Dam