The Chatfield Reservoir Expansion


Over the past six years and at the request of Colorado water districts, the Army Corps of Engineers considered many options to increase available water to the Denver Metro area.  Each option sought to provide an additional 8,539 acre-feet per year, and the options included a combination of non-tributary ground water and gravel pit storage, thus reallocating 20,600 acre-feet of flood water to water supply storage; a combination of reallocating 7,700 acre-feet of water supply storage and using non-tributary ground water and gravel pit storage; and even taking no action at all. The Corps considered the many stakeholders’ concerns throughout the process.

The most controversial of the options is to nearly double the capacity of the Chatfield Reservoir (the “Plan”), located approximately twenty miles southwest of Denver.  This project would result in more water for the growing Metro area but may precipitate many consequences, such as the destruction of the surrounding Chatfield State Park’s wildlife and decades-old cottonwood trees.

While the primary function of Chatfield Reservoir is flood control for the South Platte River, the Plan would utilize this existing reservoir to store more water for the growing Metro area.  Some estimates project Denver’s population will double by 2050.  The proposed Plan would inundate more than 500 acres of Chatfield State Park, increase the reservoir’s maximum storage level by twelve feet, and include fluctuating water levels of up to twenty-one feet.  The Plan is estimated to cost upward of $180 million.

Some interested parties, such as local citizens and the Audubon Society, express concern that undertaking this increase in water supply may actually result in a decrease in quality of life, as discussed below.  Proponents for the Plan on the other hand, such as the water district consortium, Trout Unlimited, The Sierra Club, The Greenway Foundation, and Western Resource Advocates, argue that the Plan is the most common-sense solution for the ever-growing issue of the Denver Metro water supply.

The Impact

The proposed changes are guaranteed to affect the Chatfield State Park’s wildlife and cottonwood trees.  The additional 20,600 acre-feet resulting from the expansion may submerge an extra ten percent of the park, resulting in the destruction of forty-five acres of cottonwoods and the habitat of approximately sixty species of birds.  The expansion would also overflow nearby fish habitats, such as those in the shallow weeds of the shore on the reservoir’s southern edge.  Expansion may also affect the endangered Preble’s meadow jumping mouse.

In addition to ecological impacts, the Plan will drastically alter the park’s surrounding recreational areas.  The proposed changes will require relocating the swimming beach and re-anchoring of the floating marina to accommodate the water level fluctuations.  The elevated water level also requires moving the popular shady picnic sites to higher, treeless locations.

Opponents state that because the water consortium owns only junior water rights, the reservoir’s water level will reach the maximum water line only during very wet seasons.  Thus, in normal or dry years, the water level will remain at the current position, with the relocated swim beach roughly 600 feet from the water’s edge.  And during wet years when the water consortiums water rights are utilized, the adjacent woodlands and riparian habitat will flood, forming mud flats.

Proponents, on the other hand, point out many benefits of the Plan.  Chatfield expansion seeks to benefit the Metro area by increasing available water, stabilizing the South Platte stream flows, and potentially supplying more locally-grown produce.  Proponents also note that water users will fully finance the expansion, as opposed to the federal or state government, and the Chatfield Reservoir expansion will benefit the Colorado economy through revenue generation.


As the Denver Metro area continues to expand, water availability is clearly a growing concern.  However, as exemplified in the controversy surrounding the Plan, many disagree as to which method is the least harmful to our quality of life, while also providing the most benefit.  This is a difficult question, and one that the Army Corps of Engineers is attempting to resolve alongside community input.  The ultimate advantages and disadvantages of the Chatfield Reservoir expansion, however, still remain unclear.