When completed in 1888 to a height of 90 feet, Sweetwater Dam was once the tallest masonry arch dam in the United States, and it led to many others of the same basic design. The original construction began in November 1886 under the direction of Frank E. Brown (civil engineer for Bear Valley Dam) with the rubble-masonry thin-arch design being 50 feet in height. Subsequently, the owner of the water system called upon civil engineer James D. Schuyler to continue and complete the project. Although the field of hydrology was very new and not fully understood at the time, Mr. Schuyler determined that the area of the watershed tributary to the dam, at about 186 square miles, justified a higher structure that would increase the reservoir capacity by five times the original design. He noted that the height change from 50 to 90 feet and the change to a gravity arch design now relied on the arch design for its "factor of safety", but felt confident with the foundation and construction methods. The volume of water expected to be stored was 18,636 acre-feet. There were subsequent modifications after the dam's original completion, with the majority completed by 1940. The major modifications were completed under the direction of Schuyler and civil engineer Hiram N. Savage.
Since its original completion, Sweetwater Dam has experienced unprecedented flood flows that overtopped the center crest three times (1895, 1909, and 1916). The 1916 flood event measured the runoff at nine times the spillway capacity with depth of flow nearly four feet over the center crest. During the 1916 flood event, damage did occur to the side spillways, but the main dam was not damaged.
In 2005, after 117 years of service, this dam was still serving its original purpose of storing water for domestic and irrigation use by the citizens of National City, Chula Vista, and Bonita. Sweetwater Dam now stands 127 feet high with a crest length of 700 feet that provides over 27,000 acre-feet of storage for local and imported (via San Diego County Water Authority) water. This is a one-year water supply for the entire service area population of nearly 177,000 people. This dam is a testament to its gravity-arch design, the construction materials and techniques of the era, and the design and construction engineers who worked on it.
Resources
- "The Construction of Sweetwater Dam", by James D. Schuyler, ASCE Transactions Vol. XIX, November 1888.
- "Development of Dam Engineering in the United States", Eric B. Kollgaard and Wallace L. Chadwick, Editors; Chapter 3, by Jan A. Veltrop, for the Unites States Committee of the International Commission on Large Dams, 1988.
