Project Location and Description: Cherry Creek Dam, completed around 1950, was built and is currently operated by the U.S. Army Corps of Engineers (USACE) for the primary purpose of flood damage reduction. In the late 1950s, recreation replaced irrigation as a project purpose. Cherry Creek Dam is an earth-fill embankment with an outlet structure for operational water releases. The embankment is 14,300 feet long with a maximum height of 141 feet. The dam’s outlet structure is a triple barrel concrete conduit system through which water discharges into the Cherry Creek channel located a short distance downstream.
A spillway, located at the dam’s east abutment and running parallel to the alignment of the dam, is designed to minimize the likelihood of the dam overtopping in an extreme rain event. It is an open cut channel designed to transfer floodwater into the Toll Gate and Sand Creek drainage basins if the lake’s pool elevation reaches the spillway crest elevation. The spillway’s maximum flow rate is an estimated 30,000 cubic feet per second (cfs) where one cubic foot is equal to 7.5 gallons. This would cause flooding, which in some cases could be significant, in Denver, Aurora, and Commerce City.
Cherry Creek Dam is managed in combination with Chatfield and Bear Creek Dams to mitigate flood risk in the Denver area. The water control plan for Cherry Creek Dam limits releases from the outlet structure to not exceed a flow rate of 5,000 cfs at the Denver stream gage. The targeted flow past this stream gage includes reservoir releases from Cherry Creek, Chatfield and Bear Creek Dams and is imposed to prevent significant flooding in downtown Denver.
The annual benefits of flood damage reduction provided by the project are estimated to be $25 million. Recreation resources around the Cherry Creek Dam include more than 800 acres of water surrounded by nearly 4,000 acres of land. In 2013, there were an estimated 3 million visitors at Cherry Creek Dam.
Dams in General: Dams reduce, but do not completely eliminate flooding or flood damages. When runoff from a rainstorm exceeds the reservoir's storage capacity, water will be released at amounts that may cause downstream flooding. More extreme events may cause overtopping or a breach from a deficiency within the dam or its foundation. To manage these risks, USACE has a routine safety program to regularly inspect and monitor its dams and implements short and long-term remedial actions when unacceptable risks are found at any of its dams.
Cherry Creek Dam: The most significant safety concerns at Cherry Creek Dam are its location in a densely populated area that includes much of downtown Denver, and the dam’s potential for overtopping during an extremely rare rain event. Although the chances of overtopping or failure are extremely remote, the consequences, which include life loss, economic loss, and environmental damage, are what designate Cherry Creek as a high risk dam.
At Cherry Creek Dam, USACE has implemented interim risk reduction measures which are short-term measures that reduce the risk to the public while potential long-term remedial measures are pursued. One of these measures was improving the performance of gages that monitor water inflows into the dam during higher flows. This, along with improved runoff forecasting models and coordination with the National Weather Service, allows increased warning time to be provided to local emergency management agencies. Inundation mapping has also been updated for areas downstream of Cherry Creek Dam, which helps local emergency management agencies with flood evacuation efforts. Finally, to reduce seepage pressure within the dam's foundation during times when the reservoir elevation is high, additional relief wells were installed at the downstream toe of the dam.
In addition to these short-term measures, USACE is currently conducting a Dam Safety Modification Study at Cherry Creek Dam to assess long-term solutions to reduce risks associated with the dam. Additional information about the study can be found at: www.nwo.usace.army.mil/Missions/CivilWorks/Planning/PlanningProjects/CherryCreekDSMS.aspx.
What Residents Should Know: Because dams do not eliminate flood risk, downstream residents should become aware of the potential impacts to their family, home and community. They should also learn about their community’s evacuation notification plans and safe, efficient evacuation routes. The highest population at risk, due to dam failure, is immediately downstream of the dam along Cherry Creek and the South Platte River. Life loss potential also exists downstream of the spillway along Toll Gate Creek and Sand Creek. Denver, Arapahoe, and Adams Counties have the highest potential for life loss.
The mapping photo shows inundation mapping in the Denver area resulting from a dam breach due to overtopping. Inundation from a Cherry Creek Dam breach will extend downstream along the South Platte River into Nebraska.
Recommendations for Residents:
- There is risk associated with living near a dam. Know your risk.
- Managing the risk associated with living near a dam is a shared responsibility. Know your role.
- Monitor radio and TV for flood information.
- Listen for and follow instructions from local emergency management officials.
- Evaluate your need to purchase flood insurance.
- Contact your local emergency management agencies for additional information on emergency planning efforts.
Additional Information: For more information concerning Cherry Creek Dam and the release of inundation mapping, please contact the USACE Omaha District office using the information on this fact sheet. For additional information about dam safety and living with dams, please visit:
http://www.usace.army.mil/Missions/CivilWorks/DamSafetyProgram.aspx and http://www.damsafety.org/media/Documents/DownloadableDocuments/LivingWithDams_ASDSO2012.pdf