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Cherry Creek Water Control Plan Modification Study

Cherry Creek Dam, completed around 1950, was built and is operated by the U.S. Army Corps of Engineers for the primary purpose of flood risk mitigation. Cherry Creek Dam is an earth-fill embankment dam 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.
Cherry Creek Dam
Cherry Creek Dam, completed around 1950, was built and is operated by the U.S. Army Corps of Engineers for the primary purpose of flood risk mitigation. Cherry Creek Dam is an earth-fill embankment dam 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.
The Cherry Creek Water Control Plan Modification Study recommends a modified release plan for Cherry Creek Reservoir during extreme precipitation events.
Cherry Creek Water Control Plan - Video Title
The Cherry Creek Water Control Plan Modification Study recommends a modified release plan for Cherry Creek Reservoir during extreme precipitation events.
The goal for the Water Control Plan Modification Study for Cherry Creek Dam is to establish a timeline for increased releases from Cherry Creek Dam in an extreme flooding event to reduce the potential for overtopping and failure as well as the overall flood extent. 
The following will be considered in the study: (1) removing the 5,000 cfs Denver maximum flow target to ensure releases can be made from Cherry Creek, (2) increasing Cherry Creek Dam releases above the 5,000 cfs limit (up to 13,300 cfs) if pool elevations reach between 5,570 feet and 5,600 feet (20-50 feet above normal pool), and (3) evaluating added impacts of Cherry Creek Dam releases to existing uncontrolled drainage flooding.
Cherry Creek Dam Water Control Plan Modification Study
The goal for the Water Control Plan Modification Study for Cherry Creek Dam is to establish a timeline for increased releases from Cherry Creek Dam in an extreme flooding event to reduce the potential for overtopping and failure as well as the overall flood extent. The following will be considered in the study: (1) removing the 5,000 cfs Denver maximum flow target to ensure releases can be made from Cherry Creek, (2) increasing Cherry Creek Dam releases above the 5,000 cfs limit (up to 13,300 cfs) if pool elevations reach between 5,570 feet and 5,600 feet (20-50 feet above normal pool), and (3) evaluating added impacts of Cherry Creek Dam releases to existing uncontrolled drainage flooding.
The proposed Cherry Creek Water Control Plan Modification addresses events in excess of the 100-year event. It is important to note that proposed modifications will not impact flood
insurance requirements. The 100-year flow for Cherry Creek at the Denver Gage is 9,700 cubic feet per second. The 100-year flow for the South Platte River at the Denver Gage is 22,300 cubic feet per second.
Cherry Creek Dam Water Control Plan Modification Study
The proposed Cherry Creek Water Control Plan Modification addresses events in excess of the 100-year event. It is important to note that proposed modifications will not impact flood insurance requirements. The 100-year flow for Cherry Creek at the Denver Gage is 9,700 cubic feet per second. The 100-year flow for the South Platte River at the Denver Gage is 22,300 cubic feet per second.
There is a significant safety concern at Cherry Creek Dam because of its location in a densely populated area that includes much of downtown Denver, and the dam’s potential for overtopping during an extreme rain event. Although the chances of overtopping or failure are very remote, the consequences, which include life loss, economic loss, and environmental damage, are what designate Cherry Creek as a high risk dam.

Under maximum conceivable flooding conditions, Cherry Creek Dam has the potential for overtopping and failure. The Water Control and Water Quality Section of the Hydrologic Engineering Branch in the USACE, Omaha District is studying potential modifications to the water control plan for Cherry Creek Dam. The goal of the study is to establish a timeline for increased releases from Cherry Creek Dam in an extreme flooding event to reduce the potential for overtopping and failure as well as the overall flood extent.

Cherry Creek Dam is managed in combination with Chatfield and Bear Creek Dams to mitigate flood risk in the Denver area. The current 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 at this stream gage includes the uncontrolled drainage flooding in Denver, Colorado, reservoir releases from Cherry Creek, Chatfield and Bear Creek Dams, and is imposed to prevent significant flooding in downtown Denver.

The following will be considered in the study: (1) removing the 5,000 cfs Denver maximum flow target to ensure releases can be made from Cherry Creek, (2) increasing Cherry Creek Dam releases above the 5,000 cfs limit (up to 13,300 cfs), and (3) evaluating added impacts of Cherry Creek Dam releases to existing uncontrolled drainage flooding.

Releasing more water from Cherry Creek Dam during extreme flooding would significantly reduce the cost of structural modifications to prevent overtopping and could prevent dam overtopping during some extreme events. Results from this study will be incorporated into the Cherry Creek Dam Safety Modification Study



Frequently Asked Questions

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A Water Control Plan (WCP) defines the timing and magnitude of releases from a US Army Corps of Engineers reservoir project. The Cherry Creek Dam WCP revolves around a 5,000 cfs maximum flow target at the South Platte River at Denver steam gage.  The maximum flow target includes releases from Cherry Creek, Chatfield, and Bear Creek Dams as well as uncontrolled drainage flooding.
When rainfall occurs in Denver north/downstream of Bear Creek, Cherry Creek and Chatfield Dams, it is not captured by the dams. Uncontrolled drainage flooding is defined by the rainfall runoff in this area.
The Cherry Creek at Denver streamgage is located on Cherry Creek at the intersection of Speer Blvd. and Champa Street.  Cherry Creek joins the South Platte River near the Pepsi Center at Confluence Park in downtown.  The South Platte River at Denver streamgage is located on the South Platte River at 19th Street.

Our goal is to reduce the potential for overtopping and failure as well as the overall flood extent by releasing water from Cherry Creek Dam during an extreme flood event. The current water control plan is sensitive to the downstream condition. A maximum flow target of 5,000 CFS at the South Platte River at Denver streamgage includes releases from Bear Creek, Chatfield and Cherry Creek Dams as well as uncontrolled drainage flooding. Modifying the plan to establish release triggers would determine when releases from Cherry Creek Dam are necessary.

A release trigger at Cherry Creek Reservoir is a pre-determined pool elevation that establishes the timing for when an increased release from Cherry Creek Dam would be necessary to reduce the potential for overtopping and failure.
The Cherry Creek Dam Water Control Plan Modification Study area extends north/downstream from Cherry Creek Dam to Henderson, Colorado.

The Probable Maximum Precipitation (PMP) is theoretically the greatest depth of precipitation for a given duration that is physically possible over a given size storm area at a particular geographic location at a certain time of the year. The Cherry Creek Dam 72 hour PMP is 24.7 inches.  The Probable Maximum Flood (PMF) is the resulting flood due to the PMP. The Cherry Creek Dam PMF peak inflow is 545,440 cfs and PMF volume is 324,336 acre-feet.

No, this study will not impact the 100-year flood plain and therefore will not impact insurance requirements.
The study will look at the flooding impacts from uncontrolled drainage to areas north/downstream of Bear Creek, Chatfield and Cherry Creek Dams and how releases from Cherry Creek Dam would add to those impacts. Impacts may include the flood extent, damage to infrastructure such as transportation, hospitals, police and fire rescue, schools, etc.

Yes. They are rare, but do happen.  The following are the top 3 storms that have occurred in the United States in 6 hours over a 10 square mile area.

  1. Port Allegheny, PA: 97% of the PMP (1942)
  2. Hale, CO: 90% of the PMP (1935)
  3. Thrall, TX: 72% of the PMP (1921)
The Corps must plan for the worst case scenario. A PMP event is the worst case scenario. Data indicates that Cherry Creek Dam would overtop and likely fail in a worst case scenario. Although the probability of a worst case scenario is low, the consequences are high. The Cherry Creek Dam Safety Modification Study (DSMS) is considering overall ways to reduce the risk of Cherry Creek Dam overtopping due to extreme rainfall, including modifications such as raising the dam and/or modifying the spillway, whereas modifying the water control plan is one option.
No. The normal operating pool elevation at Cherry Creek is 5500 feet and exists at that level to support other project purposes such as fish and wildlife and recreation.  The storage space below this level is relatively small when compared to the storage space above this level.  Analysis shows that using this space for flood control has little impact on extreme rainfall and the overtopping concern still exists.
The maximum amount of water that can physically be released from the outlet works at Cherry Creek Dam is 13,300 CFS at elevation 5644.4 feet (top of dam). The current water control plan limits how much water can be released from Cherry Creek Dam by setting a maximum target of 5,000 CFS at the Denver streamgage on the South Platte River. At this point, the South Platte River includes releases from Chatfield, Bear Creek and Cherry Creek Dams as well as uncontrolled drainage from runoff north/downstream of the dams. 

Potential changes to the Cherry Creek Dam Water Control Plan will be evaluated to ensure releases from Bear Creek and Chatfield Dams will not be impacted.

The current water control plan limits the combined releases from Chatfield, Bear Creek and Cherry Creek Dams to 5,000 CFS at the Denver Gage on the South Platte River. The 5,000 CFS limit includes the uncontrolled drainage flooding, which could be above 5,000 CFS.

If uncontrolled drainage flooding is at or above 5,000 CFS, then releases from the dams are zero under the current plan. A modified plan would allow releases from Cherry Creek Dam (if Cherry Creek pool elevations reach release triggers) but releases from Chatfield Dam and Bear Creek Dam would remain at 0 CFS.

If uncontrolled drainage is below 5,000 CFS, releases would be set from all three dams depending on flood control storage in each reservoir as in the current water control plan.  If Cherry Creek Reservoir reaches the release trigger elevation, a modified plan would allow releases from Cherry Creek Dam to be higher.
Releases from Cherry Creek Dam at the maximum rate alone cause flooding. The study will evaluate how much flooding may already be occurring from rainfall in the uncontrolled drainage area and its impacts. The next step is to add Cherry Creek Dam releases to those areas already impacted by flooding from uncontrolled drainage and determine the difference in flooded extent.

The Water Control Plan will evaluate the impacts of flooding from increased releases in an extreme rainfall event.

The Cherry Creek DSMS is considering overall ways to reduce the risk of Cherry Creek Dam overtopping due to extreme rainfall, including modifications. Vulnerable downstream areas and nonstructural alternatives to reduce flooding risks will be considered in the DSMS.
CFS stands for cubic feet per second and is a flow rate commonly used to describe water in a stream. One cubic foot is equal to 7.5 gallons.

The 100-year flow on Cherry Creek near where it joins with the South Platte River is 9,700 CFS. This was originally incorrectly reported as 4,100 CFS.

The 100-year flow on the South Platte River in downtown Denver is 22,300 CFS.

This study will not impact insurance requirements.
If Cherry Creek Reservoir rises to elevation 5610.6 feet, the spillway would begin to flow. The Cherry Creek Spillway flows over S. Chambers Road into Toll Gate Creek and then into Sand Creek. Sand Creek joins the South Platte River north of downtown Denver.

The spillway is uncontrolled, meaning if water levels are higher than the spillway elevation, it will flow through the spillway with no barrier (like the overflow drain at the top of a sink). The rate at which water flows through the spillway is determined by the reservoir pool elevation. If Cherry Creek Reservoir rises to elevation 5610.6 feet, the spillway would begin to flow.  If it rises to elevation 5647.6 feet (3 feet above the top of dam) the spillway would flow at an estimated rate of 30,000 cfs.  The non-damaging flow rate on Toll Gate Creek and Sand Creek is less than 2,000 cfs.

By modifying the plan and establishing release triggers that would determine when higher release rates from Cherry Creek Dam are needed, the potential for spillway flows, overtopping and failure, as well as the overall flood extent are reduced.

Although some water was diverted into a few canals in 2013, the Corps cannot factor canal capacity into a modified Water Control Plan due to the uncertainty of availability. The Corps will coordinate with local agencies to divert water as possible.
The Corps will collect input from the public and other agencies and determine how to address the input within the study. The next step is to determine the existing uncontrolled drainage flooding due to rainfall in downtown Denver. This step is currently underway.  The study will then determine the impact of adding Cherry Creek Dam releases (5,000 cfs up to 13,300 cfs) to the existing uncontrolled drainage flooding for the areas located north/downstream from the dam.  The study is expected to take 9-12 months at which time there will be a chance for the public and local agencies to review the study results and provide feedback.

Comment on Current Studies

Input on the proposed Cherry Creek Water Control Plan modifications may be submitted at the public meeting, emailed to kathryn.j.seefus@usace.army.mil or mailed to: U.S. Army Corps of Engineers, Omaha District; CENWO-ED-HA; ATTN: Katie Seefus; 1616 Capitol Avenue; Omaha, NE 68102-4901.
Comments must be postmarked or received by December 16, 2016.
Substantive comments on the Cherry Creek Dam Safety Modification Study may be submitted by email to amee.l.rief@usace.army.mil or mailed to: U.S. Army Corps of Engineers, Omaha District; PM-AC; ATTN: Amee Rief 1616 Capitol Avenue Omaha, NE 68102-4901.