Dissecting Denver Water’s Mitigation Plan for the Moffat Collection System

If you follow Colorado water issues in the least, you are probably already aware of Denver Water’s proposed Moffat Collection System Project.  The proposed $250 million project will increase Gross Dam on South Boulder Creek by 125 feet, increasing Gross Reservoir by 77,000 acre-feet (AF) and tripling its capacity.

The Moffat Collection System Project addresses three major supply challenges:

  1. A future water shortfall projected to be 34,000 acre-feet by 2030
  2. Risk of running out of water in a future drought
  3. A “serious imbalance” in Denver Water’s collection system
    1. About 80% of Denver Water supplies funnel through Strontia Springs Reservoir, which could be threatened by droughts or wildfires such as the massive Hayman Fire that burned in 2002.

The project will provide 18,000 AF of additional supply for Denver Water customers and will come primarily from the Fraser River in Grand County using existing water rights.  Water will only be taken from May-July in wet years, per Denver Water’s existing rights, and no water would be taken in dry years.

It is important to note that Nearly half the amount of needed water, about 16,000 acre-feet, is expected to come from additional conservation and recycling efforts. The remainder of the shortfall will be met by expanding Gross Rese2003, Denver Water notified The Army Corps of Engineers of their intent to file a permit.  In its response, the Corps provided a draft Environmental Impact Statement (EIS) and

“determined that reductions in flow during runoff could decrease aquatic availability in the Fraser River basin and the four headwater tributaries of the Williams Fork River…the reductions in flow could also result in increasing frequency of approach or exceeding stream temperature standards at some locations.”

The Draft EIS (to which the Corps’ link is broken) also noted that temperatures in the Fraser River and Ranch Creek have already been recorded at levels exceeding the maximum standard temperature, according to data collected by the Grand County Water Information Network in 2007 and 2008.

Table compiled by author. Sourced from Denver Water mitigation plan.

One can see that most of the water will be sourced from the Fraser and Upper Williams Fork Rivers, and their tributaries.  Key mitigation goals for these rivers include $72,500 for “reestablishing a viable fishery” for two cutthroat species: the Colorado River cutthroat and the federally threatened Greenback.

How does one build a new habitat for these species? First, Denver Water will find a headwater stream in Grand County that currently doesn’t support cutties, and construct a barrier at the downstream end. Next, it will “eradicate all the trout in the stream” upstream of the barrier. Finally, it will then reintroduce “a core conservation population” of cutthroat trout. All of these steps will be funded by Denver Water and executed by the Colorado Department of Wildlife.

A second tenet of the mitigation plan for the Moffat System includes a stream temperature monitoring and reduction in diversion plan.  Under this provision, Denver Water will provide funds for a real-time temperature monitoring station on the existing Ranch Creek gaging station.  When water daily maximum temperatures rise above 70.2o F, levels between July 15 and August 31, Denver Water will forego up to 250 AF of diversions from the Fraser River Collection System.

Additionally, in a third tenet of the mitigation plan, Denver Water will provide up to $750,000 for stream habitat restoration in the Fraser, Williams Fork and their tributaries.

In total, the mitigation plan is estimated to cost over $7.2 million, and has already been approved by the Colorado Wildlife Commission, and the Colorado Water Conservation Board.  Next, the plan goes back to the Army Corps of Engineers, which is expected to release its final environmental impact study later this year.  If approved, construction could start as soon as 2015.

An angler on a very shallow Fraser River

Currently, Denver Water and other water providers divert around 65% of the native flows of the Upper Colorado River Basin to the Front Range.  If the Moffat Collection System Project and the Windy Gap Firming Project are both completed, the portion of native water diverted to the

Front Range from the Upper Colorado could reach an annual average of 85%, “pushing the Colorado and Fraser rivers…to the brink of ecological collapse,” according to a report from Trout Unlimited, Western Resource Advocates, and Colorado Environmental Coalition.

While the authors of this report include the Gross Reservoir expansion in their list of acceptable planned projects, they also cite issues yet to be resolved. A subsequent post on this blog will examine these and other issues raised by community stakeholders in response to the Denver Water project, and will also examine some proposed alternatives.


One thought on “Dissecting Denver Water’s Mitigation Plan for the Moffat Collection System

  1. lacaruana

    Great posts Parker, thank you! I am not sure how comforted I am by the current plan for “building” new habitat for the cutthroat, though – it doesn’t sound like it’s really that well thought out, and seems more like a quick fix for a problem that’s not taken very seriously by those doing the planning. I mean, really…? They just plan on eradicating trout that are already in a certain stream so they can introduce the cutthroat? Maybe it’s just because I don’t have much background on trout species and various habitats in CO, but it sounds like they would just potentially be substituting one problem for another. I am also kind of curious about what stream habitat restoration looks like without the water, and what will be considered a “dry” year, but I also understand the (increasingly) precarious situation of the Denver Water Board. ~ Lisa


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