Mountain Dell Dam

August 24, 1998

Mt. Dell Dam under construction in 1916.

Mountain Dell Dam and Reservoir located approximately 5-miles east of Salt Lake City just North of I-80.  It is in the final stages of repair to bring the dam up to current State standards.

The first phase of construction of the concrete "Eastwood" multiple arch dam started in February 1916 and was completed August 6, 1917. The original construction cost was $137,000. Seven years later the dam was raised an additional 40 feet to its current height to increase the water storage to 3, 173 acre-feet at a cost of $274,000. 

The present structure is 145 feet high at its maximum section and 565 feet in top crest length.  It currently stores about 2,500 acre-feet of water used for our potable supply.  Reserved flood storage of 1,000 acre-feet is maintained above the normal storage level.

Water Supply Source

Mt. Dell is a major source of water supply to Salt Lake City’s water service area. In the years prior to the completion of Little Dell Reservoir, up stream from Mt. Dell, it provided the necessary storage of water needed to meet the municipal water demand of the City during the summer and fall months when the other canyon streams were diminishing in flow. It was the only major storage facility in Salt Lake County that was directly connected to the water distribution system and could be call upon for immediate flows into the system.  Today, it remains an important component of the City’s water supply.

Maintenance and Repairs

The structure has required on-going maintenance to keep it in good repair. Shortly after it was completed in 1926, it was repaired with a new membrane to the original 60-foot arch sections.  In 1947 a gunite application was made to the structure. Again in 1962, the up-stream face of the dam was repaired with a reinforced gunite application. Concrete repairs to arch rings were made in 1976.  In 1980, earthwork around the structure and surface repairs and sealing were completed. Additional repair work was under contract in 1987.

As the area become more concerned about the seismic considerations, in 1971, Dr. Glenn L. Enke was hired to make a comprehensive study of the dam to determine its soundness in the event of an earthquake.

Later in 1979 under the National Program Dams, the Army Corp of Engineers determined that the spillway did not meet the National Dam Safety criteria, as it would only pass 2 percent of the Probable Maximum Flood without overtopping the structure. This was addressed during the next 10 years in conjunction with the Little Dell Reservoir Project. This project was approved for construction in 1986, and completed in 1992. Little Dell Reservoir provides an additional upstream storage of 20,500 acre-foot and consequently reduces the potential flood flows into Mt. Dell Reservoir.

Mt.Dell Dam as viewed today.
In 1992, the Utah State Legislature passed legislation classifying the State’s dams and requiring certain action according to their classification.  Mt. Dell dam was classified as a High Hazard Dam. On March 26, 1993, Engineering studies were initiated to comply with the new standards.  These studies resulted in an action plan to raise the dam 5 feet to provide additional emergency overflow spillway capacity across the center of the dam and complete some additional structural repairs. This provides protection for rare extreme floods.  Construction of these improvements was done during 1997 and 1998.  Under legislation passed in 1997, the construction work is eligible for funding through the Division of Water Resources.

Operation issues

The reservoir is closed to fishing.  The last time the issue was raised was in 1949, when the Salt Lake City Commission, in response to a petition to open the reservoir to fishing, passed an resolution closing Mt. Dell to fishing to protect the Salt Lake City’s water supply from pollution.

The dam is on the Historic Society’s “National Register of Historic Places,” and has been recognized as an “American Water Works Association Landmark.”