Denver Water’s Moffat Supply Project proposes to enlarge Gross Reservoir to help resolve three major supply challenges: a future water shortfall (supply), the risk of running out of water in a future drought (reliability) and a serious imbalance in Denver Water’s collection system (vulnerability).
Why Enlarge Gross Reservoir?
Supply: Denver Water has identified a shortfall in supply beginning in 2016 and growing to 34,000 acre-feet per year by 2030. Approximately 16,000 acre-feet of the shortfall is expected to be addressed through additional conservation, leaving Denver Water with an annual shortage of 18,000
acre-feet (one acre-foot is equal to 325,851 gallons of water and will supply more than two single-family households for a year).
Reliability: During the 2002 drought, Denver Water came perilously close to running out of water in the Moffat Collection System. Without water in the Moffat system, Denver Water would lose the operation of one of its three treatment plants and have difficulty meeting the needs of its customers and raw water commitments to Arvada, Westminster, Consolidated Mutual and others.
Vulnerability: Denver Water’s system is out of balance. Approximately 80 percent of its water supply relies on the unimpeded operation of Strontia Springs Reservoir. Emergencies above this reservoir threaten the operation of the entire system, as the Hayman and Buffalo Creek fires highlighted in recent years.
The project
If approved, the project would produce 18,000 acre-feet of new supply by expanding an existing reservoir rather than building a new one. The current dam height would increase from 340 feet to approximately 465 feet. The proposed project would increase Gross Reservoir from its current storage capacity of 41,811 acre-feet to approximately 114,000 acre-feet – an increase of 72,000 acre-feet. (Denver Water has determined four acre-feet of storage are needed for every one acre-foot of supply.)
Because Gross Reservoir was originally designed to be this larger size, other facilities, such as the Moffat Tunnel and South Boulder Canal, do not need to be modified and no additional water rights are needed. The additional water would be carried through the existing Moffat Tunnel from the Fraser River basin and Williams Fork River basin in Grand County, as well as from South Boulder Creek basin. Streamflow in the Fraser and Williams Fork rivers and South Boulder Creek would only be decreased by this project during wet and average years during the runoff months.
Denver Water believes enlarging Gross Reservoir would deliver the most benefits at the least cost and with similar environmental impacts compared with the other practicable alternatives.
Questions?
Denver Water is interested in your comments and will answer what questions it can at this time. Send questions to publicinformation@denverwater.org.
To be kept informed on the Moffat Collection System Project, send us your e-mail address.
Scope of Work Phases
| Phase | Process | Status |
|---|---|---|
| Phase I | NEPA Scoping | Completed |
| Phase II | Agreement on Purpose and Need, Conduct Preliminary Screen (Screen 1) | Completed |
| Phase III | Conduct Reconnaissance Screen (Screen 2) and Studies | Completed |
| Phase IV(a) | Conduct Feasibility Studies | Completed |
| Phase IV(b) | Prepare Draft EIS | Completed |
| Phase V | Prepare Final EIS | Current phase (2011) |