Constructed in 1916-17, with an addition in 1924, the Mountain Dell Dam is
significant in the history of U.S. technological development and in the vital
development of Salt Lake City’s water resources. The dam was designed by John S. Eastwood, considered one of American’s most important and innovative hydraulic engineers of the early 20th century. Eastwood, the man most responsible for the development and utilization of the multiple-arch dam, built the first reinforced concrete multiple-arch dam with bedrock foundations in 1908-09; and in the following years that structural form was employed throughout America, Canada, Europe, and Asia. The multiple-arch dam was selected over other design concepts for Salt Lake City’s storage reservoir in Parley’s Canyon because the bedrock there is a calcareous shale which is not waterlight and tends to decompose, requiring a structure that would not be susceptible to overturning or sliding. John Eastwood was internationally recognized as the most prolific designer of multiple-arch dams in the world, having built 17 of his dams before his death in August, 1924, at the age of 67.
The dam was added to the National Register of Historic Places (#80003930) on June 20, 1980.
Salt lake City, located in the Great Basin of the American West, is dependent
upon adequate supplies of water. As with other western regions, water
conservation and use is of vital concern. In the early years of the 1910’s
Salt Lake City found itself in a serious condition for the need of a sufficient water supply during certain seasons of the year, primarily in the late summer and mid-winter. A bond issue of 1914 resulted in a program of
improvements which included plans to build a dam in Parley’s Canyon. In the field of community planning the location of the Mountain Dell Dam was
significant because it’s location was so near the city (13 miles) that it could serve as an equalizing as well as a storage reservoir.
Three dam designs were considered, but the reinforced concrete multiple-arch dam by John S. Eastwood was chosen primarily because it was not susceptible to sliding or overturning in the bedrock of the Mountain Dell site. Eastwood’s design is important as one of the world’s first to realize the actual potential of reinforced concrete in the construction of dams and other structures which would have been difficult or impossible to build with other kinds of materials. “In the early 20th century, dam design was still dictated by principles essentially traditional in nature rather than scientific. In developing his multiple-arch dams, Eastwood employed a rigorous, scientific analysis in studying the problem of dam design and, consequently, he derived the reinforced concrete multiple-arch dam as the safest, most practical, most materially conversant and most economical design for almost all dam sites.” The material economics inherent in the design rendered the multiple-arch dam as significant in the development of the world’s water resources, and “more importantly, it demonstrated the capabilities and potential of reinforced concrete construction to engineers and industrial designers involved in all phases of structural technology.
Actual work on the dam began in 1916 by the Parrot Bros. Company. In August, 1917, the partial height of the dam was completed to 105 feet above bedrock Late in 1924 Salt Lake City decided to complete the final 40 feet of the dam, with the construction firm of Lynch Cannon Engineering being employed. Eastwood had drowned tragically in August, 1924, and as mentioned in Item 7, his design was somewhat altered by Salt Lake City engineers.
Mountain Dell Dam, when evaluated by the Historic American Engineering Record Survey in 1971, had a capacity of 1,145 million gallons, representing 65% of Salt Lake City’s water storage capacity. As with other Eastwood dams, the safety factors contended have been proven sound; and all of John Eastwood’s 17 dams, though some alterations have occurred, remain intact and functioning.