Final decision made for Cherry Creek Dam Water Control Plan Modification Study

Cherry Creek Dam looking south

Here’s the release from the Army Corps of Engineers (Katie Seefus):

In October 2015, the U.S. Army Corps of Engineers Omaha District began studying modifications to the Cherry Creek Dam Water Control Plan. A water control plan outlines predetermined regulation requirements for federally authorized project purposes.

Historically, Cherry Creek Dam has been regulated as a system with Bear Creek Dam and Chatfield Dam targeting a maximum flow of 5,000 cfs at the South Platte River at Denver, Colorado streamgage to mitigate flood risk in Denver, Colorado.

The purpose of the Cherry Creek Dam Water Control Plan Modification Study (WCPMS) was to reduce the potential risk of overtopping and failure of Cherry Creek Dam during extreme flooding events by releasing more water from the dam while limiting exposure to potential downstream damages.

The Cherry Creek Dam WCPMS analyzed the impacts due to six release alternatives and recommended an alternative that requires Cherry Creek Dam releases of 7,000 cfs if the reservoir reaches elevation 5590 feet Project Datum (PD), which is 24 feet higher than the record pool set in 1973.

Evacuating flood water from Cherry Creek Reservoir at an accelerated rate reduced the risk of overtopping and failure during an extreme rain event and resulted in minimal incremental downstream damage following single rain events that have limited rainfall downstream of the dam. Some risk of additional downstream damage is possible if releasing during subsequent storm events, however, due to the uncertainty in forecasting a thunderstorm’s intensity, duration, and location, the risk is outweighed by the need to release flood water and reduce the risk of Cherry Creek Dam’s overtopping and failure.

Public and agency meetings were held in January 2016 and again in September 2016 to collect and discuss comments from agencies and the public. All comments were resolved by December 2016 following a comment extension in November 2016. The environmental analysis resulted in a Finding of No Significant Impact (FONSI) in March 2017.

Effective April 2017, the Cherry Creek Dam, Chatfield Dam, and Bear Creek Dam water control plans were modified to reflect a 7,000 cfs release from Cherry Creek Dam if the reservoir reaches elevation 5590 feet. Releases from Chatfield Dam and Bear Creek Dam were not increased in the updated water control plans.

Background: The Cherry Creek Dam project was authorized in the 1940s for the primary purpose of mitigating flood risk to the downstream city of Denver from floods originating on Cherry Creek above Cherry Creek Dam. Cherry Creek Dam and Reservoir is located on Cherry Creek, 11.4 miles southeast of its confluence with the South Platte River in Aurora, Colo.

The final Cherry Creek Dam WCPMS report and the updated Cherry Creek Dam, Chatfield Dam, and Bear Creek Dam Water Control Plans are available below:

http://www.nwo.usace.army.mil/Missions/Water-Information/Water-Control/Cherry-Creek-WCPM/

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