Frequently Asked Questions

No, conservation is critically important, but it doesn’t replace the need for this project. In 2014 our customers used less water per capita than they did in the last 40 years. Quite an accomplishment considering the Denver Metro Area population has increased by 350,000 people since 1970.

Our consumers embrace the need for water efficiency, but even when we’ve seen our customers reduce their usage by a third as they did in a previous drought year, we still run the risk of running out of water on the north end of our supply system – of which Gross Reservoir is a critical part – and this project helps offset that imbalance.

The fact is we’re vulnerable on several fronts. We are short of supply and storage capacity on the north end of our system making us vulnerable to drought. We’re also vulnerable to an infrastructure failure that could occur on the south end of our system. Consider if something like the August 2015 Animas River contamination occurred upstream on our South System; we’d be left with a limited capacity to serve the Denver Metro Area from our north system. It is not worth the risk.

It varies. Most runoff available to Denver Water during the wet winter of 2014 and spring of 2015 flowed out of state because existing Denver Water reservoirs were full and there was no place to capture and store it. Because the extra space is designed to capture and store water in average and wet years, if the Gross Reservoir Expansion Project had been completed in 2014, there would have been 72,000 acre-feet of new water storage space available by the summer of 2015 to collect and store some of that water for use during drier times.

This project requires federal permitting, which in itself is a lengthy, complex process. It was important to Denver Water that all impacts to the surrounding area and the water system were analyzed and that the most environmentally responsible and economical alternative was chosen to increase storage. In partnership with federal authorities, more than a 14 years of study has identified potential impacts and mitigation strategies. We are proud to have received federal approval from the U.S. Army Corps of Engineers in 2017 and final federal approval from the Federal Energy Regulatory Commission in 2020.

This is a great example that water projects are not a “just in time” enterprise – they must be carefully planned, undergo environmental studies, have very detailed designs, and be constructed in a safe manner to last for generations.

The primary beneficiaries of this project are the 1.5 million people Denver Water currently serves and many of the projected 8.1 million who will call Colorado home by 2050. The environment and West Slope stakeholders also benefit through two agreements related to expanding Gross Reservoir: the Colorado River Cooperative Agreement and the Mitigation and Enhancement Coordination Plan. In addition, Denver Water partnered with the Cities of Boulder and Lafayette to provide additional storage in Gross Reservoir in the form of an environmental pool that will allow water releases to South Boulder Creek to improve stream health.

Perhaps most importantly, Denver Water has made significant investments in emergency and disaster planning. Beyond supply reliability and environment safeguards, additional storage means greater water resources in times of emergency.

Preliminary design has begun and will accelerate now that the Record of Decision was handed down from the U.S. Army Corps of Engineers on July 6, 2017. Final design is expected to be complete in 2021. That will allow construction to begin in 2022 with a construction completion anticipated in 2027 and, depending on water availability, it will take approximately five years to fill the reservoir to its new capacity.

Denver Water has a responsibility to meet the needs of the 1.5 million people we serve today and future demand created by population growth. Without the project, Denver Water’s North System will remain vulnerable to catastrophic events and continue to be ill equipped to handle an increase in stress to the system. Currently, a single dry year or emergency — such as a forest fire or treatment plant shutdown — puts our water supply in jeopardy. Expanding Gross Reservoir helps us avoid running out of water in any given year and helps us put water where we need it.

As a public agency, Denver Water is entirely funded through rates, new tap fees and the sale of hydropower. No tax dollars will be directed towards Denver Water or to the Gross River Expansion Project. The City of Arvada is a partner in the project and will contribute a portion of the funding in exchange for additional water from Denver Water.

The environmental impacts of Gross Reservoir Expansion Project were all identified in the Final EIS and Denver Water has proposed mitigation and enhancements for all of these identified impacts. We have collaborated with others committed to the environmental health of our state to offset the identified environmental impacts, and are proud that in June 2016, the State of Colorado certified that our proposed approach will provide the state with a net environmental benefit to the state’s water quality.

Through the landmark Colorado River Cooperative Agreement, From Forests to Faucets program with the U.S. Forest Service and other collaborative efforts, we are taking unprecedented steps to enhance our watersheds and the communities within them.

A few examples of our commitment to watershed enhancements include:

• Agreeing with the cities of Boulder and Lafayette to provide an environmental pool in an enlarged Gross Reservoir that will be used to provide enhanced stream flows to a 17–mile stretch of South Boulder Creek below the reservoir.
• Providing water for current and future West Slope environmental and consumptive use needs.
• Protecting river flows and enhancing the aquatic environment from the headwaters of the Fraser and Blue rivers at the Continental Divide to the state line.
• Earmarking $25 million for projects on the West Slope, such as improving rivers and streams and constructing the Berthoud Pass sedimentation pond to improve water quality.
• Making available 1,000 acre-feet of water each year from Denver Water’s share of the Fraser River for environmental purposes in Grand County, at times and locations requested by Grand County. Denver Water also will release an additional 1,000 acre-feet from Williams Fork Reservoir under specified conditions at the request of Grand County.
• Partnering with Northern Water and the Colorado Parks and Wildlife to restore a portion of the Colorado River below Windy Gap Reservoir.
• Providing $16.5 million for the From Forests to Faucets partnership, to be matched by the U.S. Forest Service (total of $33 million), for forest health initiatives in our watersheds.

In our one-on-one interactions with individuals in the community and presentations to civic organizations and environmental groups, we often hear the question about whether the water temperatures at the outflow will change and what impact that might have on aquatic life downstream. Here’s how we respond:

• Environmental studies show that water temperature at the reservoir outflow is generally in the acceptable range for trout today, and will be similar in the future once the expansion is completed.
• Currently, the biggest threat to aquatic life in South Boulder Creek is lack of water, not water temperatures. As it stands today, there are times of the year when some portions of SBC run at water levels insufficient to maintain aquatic life. An expanded Gross Reservoir will include space for an Environmental Pool, which will be managed by the cities of Boulder and Lafayette. The intent of this is to enable release of water during low flow periods so SBC will have life sustaining flows year-round.
• While a Multi-Level Outlet Works (MLOW) could increase water temperatures in SBC, the Colorado Department of Public Health and Environment noted on Page 12 of its Rationale for Conditional 401 Certification that “The potential for environmental benefit from the MLOW applies to a relatively short stream reach (about 5 miles in length), and recent data suggest that the water warms noticeably over that distance.”

Ultimately, CDPHE did not include a MLOW as a permit obligation, but did require long-term monitoring of stream temperatures and aquatic life in SBC. CDPHE also recognized all the commitments Denver Water had made to enhance the environment on both sides of the divide and found the Gross Reservoir Expansion would result in a “net environmental benefit” to the state’s water quality.

All of the property being impacting by the reservoir expansion is within the FERC boundary and owned by Denver Water or the USFS. Twelve acres of private property was acquired by Denver Water in early 2020.

In collaboration with the Cities of Boulder and Lafayette, 5,000 acre-feet of water will be designated for an environmental pool for South Boulder Creek. This pool will provide water during low flow periods and will provide enhanced stream flow to a 17-mile stretch of South Boulder Creek located below the reservoir. Beyond land purchased nearby to preserve elk habitat, riparian areas, wetlands, and other unique features, property owners living near Gross Reservoir receive few direct benefits from this project.

Although we are still designing the project, at this time we anticipate that recreation along the reservoir’s north shore will continue throughout construction, but recreation in other areas, particularly near the dam and in the vicinity of the quarry, will need to be curtailed during construction for safety considerations.

Additional information on recreation during construction available here.