Page is still under construction: Graphs to be added soon

On Transmountain Diversions

            “Transmountain” diversions refer to diversions across, or under, the Continental Divide that take water from the west slope and deliver it to the east slope.[1] By comparison, “transbasin” diversions divert river water from one basin to another, not necessarily across the Continental Divide.[2] The issue of transmountain diversions in Colorado is perhaps the most interesting aspect of Colorado water policy and management, as it seems to neatly divide into an “us and them” situation, which all humans innately understand. But, as a “Western Sloper,” I’ve come to think, charitably, of the dynamic more along the lines of “this is about water for our friends and neighbors on the other side of the Divide.”    For I know people who live on the Western Slope whose lives have been saved by hospitals on the Front Range and whose children have been educated at colleges on the Front Range. And I know people who live on the Front Range who relish the rivers and flyfishing on the Western Slope more than anything else. The point is, we are deeply connected as a state, we are under one state Constitution, and presumably, we all want what’s best for the entire state. But still, it’s brutal to see the entirety of a stream on the west slope pour into a grate and then through flow a tunnel to the east slope, at least from the standpoint of appreciating the sanctity of a river environment, and even when knowing that good people will use the water.  And there are many grates and tunnels in the forty-four transmountain diversion systems that send water from the Western Slope to communities along the Front Range, from Fort Collins to Pueblo.[3]

Figure 18.1 Transmountain Diversions

Transmountain Diversions in Colorado

That’s a long list, so let’s take a closer look at these transmountain diversions, starting with the one operated by Denver Water. Such a complex system may not have been foreseen when Denver was founded in 1858 as a gold mining town because water was so plentiful that it bubbled up to the surface under heavy artesian pressure. But by 1900 Front Range engineers were diverting water from the Western Slope. And today Denver Water serves more than one of every four residents in Colorado and about half of its water comes from the Western Slope.[4] The rest comes from the South Platte River basin on the east slope, where Denver Water has built five large dams starting with Antero Reservoir. "Antero," Spanish for "first," was the first dam built on the South Platte near the river's origin, 140 miles upstream from Denver.[5] Denver Water treats 290,000 acre-feet of water for delivery to 1.5 million people, using on average 139 gallons per person per day, about average for the US, according to the EPA.[6] It plans to deliver another 70,000 acre-feet to Englewood, Arvada, Golden, Westminster, Broomfield, and the area surrounding Denver International Airport in the future. That is enough water for 500,000 more people using a responsible 120 gallons per person per day.[7] Water providers need “firm yield,” water speak for dams that can deliver water upon demand, and they start feeling vulnerable when they have less than three years’ worth of deliveries stored behind dams.

Before we leave the table above, see how the Gunnison Basin as fared—less than 1,000 acre feet is diverted to the east slope each year on average. It has done a good job of holding onto its agricultural heritage as well, with nearly 50 percent of its irrigated acreage preserved by conservation easements, according to Rob Bleiberg, executive director of the Colorado West Land Trust that serves Gunnison and Mesa Counties on the west slope. Where there’s a will there’s a way.

I estimated Colorado citizens used 206 gallons per person per day in 2011, calculated by dividing 1,161,000 acre-feet delivered by 5,051,000 residents by 365 days.[8] By cutting this number in half, twice as many people can be served. I consider 120 gallons per day to be responsible water use, abbreviated as 120 gpcd, for “gallons per capita per day.” In hotter Albuquerque, people use 127 gpcd, and in far hotter Tijuana and Mexicali where the average temperature is 72oF, 22 degrees hotter than Denver’s annual average temperature, they get by with under 60 gpcd.[9] Around the world, 120 gallons a day is considered excessive. We can achieve it primarily by replacing water-hogging blue grass lawns that now use up to 30 inches of water a year with xeriscape plants that use about 12 inches a year and, less so, by using water efficient appliances and shower fixtures.

Only about 40 percent of water delivered to cities and suburbs is consumed. Outside, 95 percent of water used to irrigate lawns and trees is consumed. But indoors, only about 5 percent of water use is consumed—the rest runs down the drain and can be recycled. Water leaking from pipes, which utilities estimate is 8 percent of total municipal use, can also be reused. (The words “recycle” and “reuse” are synonymous, but water providers typically use “reuse.”) Denver Water says, “On average, Denver Water’s single-family residential customers use about 50 gallons per person per day inside the home — about 10 gallons more per day than our efficiency experts would like to see people using.”[10] Providers need to supply 22,400 acre-feet for 100,000 new residents using 200 gpcd, but only 13,400 acre-feet if they use 120 gallons a day, and only 10,300 acre-feet if they reuse 50 percent of the amount remaining after it has been used once.[11]

The Denver metropolitan area above covers about 1,800 square miles. The 202 population in the area was 2.1 million people, and that did not include 330,000 people living in Boulder county and 250,000 more living in Parker, Highlands Ranch, and Castle Rock in Douglas County. Boulder receives water from Northern Water, and Douglas County historically received water by mining the Denver Aquifer. To avoid dealing with powerful Denver Water, Englewood developed its own water supply in the 1950s by building McClellan Reservoir in Littleton.[12] Denver Water is independent, split off from the City of Denver in 1918 by Progressive Era reformers seeking to prevent crony city politicians from monopolizing water. It is supervised by a five-member board of water commissioners appointed to six-year terms by the mayor of Denver. One consequence is that while Denver city council members are lobbied heavily by the public on issues like education or traffic congestion, water matters do not receive the same scrutiny. This occurs statewide, since water boards traditionally make decisions with relatively little public oversight or input. But citizens can lobby Denver Water in the same way they can lobby Denver council members. Denver Water built reservoirs to keep pace with population growth until 1990 when the EPA rejected the proposed Two Forks Reservoir. Since 1940, the population figures below include the greater suburban area made up of seven counties, which are, in order of population, Denver, Arapahoe, Jefferson, Adams, Douglas, Boulder, and Broomfield.

Figure 18.2 Graph of Denver’s population versus water supply

The table below summarizes the larger reservoirs in Denver Water’s system.

Table 18.1 Denver’s water storage history

Denver’s Water Storage History[13]

Denver Water started negotiating with the Army Corps of Engineers in 1996 to store another 20,600 additional acre-feet in Chatfield Reservoir, located downstream of Waterton Canyon where the South Platte River exits the Rocky Mountains. The expansion, now complete, raised the reservoir’s water elevation by about twelve feet, allowing Front Range water providers to store 20,600 additional acre-feet. This flooded additional land, causing thousands of cottonwood trees to be removed in 2024 and 2025 that had drowned. New trees and shrubs will be planted along the expanded shoreline.[14] Denver Water now stores up to 28,709 acre-feet in Chatfield (up from 27,045 acre-feet), which is still only a fraction of the reservoir’s 350,653 acre-feet capacity.[15] The reservoir is purposely kept low to hold back floodwaters such as the disastrous 1965 flood that prompted its construction. 

Denver Water has two major transmountain diversions, coming from the Fraser and Blue river drainages. The two diversion systems supply 110,000 acre-feet each year on average, enough water for 825,000 residents, assuming each uses 120 gallons per day. To divert 52,390 acre-feet each year through the Moffat Tunnel, Denver Water collects water from 26 Fraser River tributaries on the north side of Berthoud Pass, capturing 60 percent of its annual flow.[16] The canal linking these diversions would be easily visible from Winter Park ski area and Highway 40 if not obscured by the forest.

This is the annual hydrograph for the 2024 water year on the Fraser River at Winter Park at USGS Gage 09024000, about a mile downstream of where Highway 40 crosses the train track exiting the Moffat Tunnel near the Winter Park ski area. Water is not actually diverted from the Fraser River at this point. Rather, a ditch upstream of the Winter Park gage that circuits the basin counter-clockwise below Berthoud Pass intercepts water from numerous tributaries before they reach the Fraser River and shunts them into the Moffatt Tunnel.

The hydrograph above shows the Fraser River peaked at 334 cfs on June 14, 2024, a flow barely enough to scrape down in a kayak. I estimate that the total acre-feet in the river flowing past Winter Park at this gage for the entire 365-day year was about 26,000 acre-feet, an average constant flow of just 36 cfs. Denver Water plans to take another 18,000 acre-feet through the Moffatt tunnel when the Gross Reservoir expansion is complete, amounting to nearly 26 cfs. This will reduce the annual average river flow here to about 10 cfs, barely enough water for a child to play in and leaving a flat line all the way across the graph except in the highest water years.

It’s a pretty minimal flow but not illegal since no minimum flow has been set for this or practically any other river in Colorado. We have rules that require us to leave water in the 15-mile reach on the Colorado River (the Programmatic Biological Opinion that mandates minimum flows to protect the four endangered fish species), the Platte River as it exits Colorado into Nebraska (again to save endangered species in Nebraska, in this case the whooping crane and piping plover), and the various compacts that obligate Colorado to deliver water to downstream states. But there’s no law that I know of that says we have to leave a certain cfs flow in the river because irreparable harm otherwise results.

Denver Water and Northern Water hired Connie Woodhouse of the University of Arizona and Jeff Lukas of NOAA in Boulder, both of whom have spoken at roundtable meetings over the years, to correlate water gage records on the Fraser and upper Colorado River with tree-ring studies going back to 1440. The correlations are high, with tree rings, which are wider in wet years, explaining about 70 percent of the variance in the water gage records we’ve been keeping since 1906.

The Fraser River gage in Winter Park was one of the gages they used in their analysis. They concluded that the 2002 Colorado River flow, the lowest flow on record, “is within the bounds of natural variability of the last three to five centuries.”[17] The climate extremes between wet and dry cycles were greater in past centuries than what we experienced in last 120 years. They also caution that the most significant impact from a warming climate “will likely be a reduction in mountain snowpack, due to increased temperatures that will influence the amount of rain compared to snow, as well as the timing and amount of runoff.”[18]

Low water years are normal, but what water managers really fear is when they occur three years in a row since water utilities typically aim to store three years’ supply. Woodhouse and Lukas define a drought as a below-median water year, and they counted six episodes where below-median runoffs occurred four years or more in a row, with one lasting 11 years, between 1440 and 1999. That would likely wreak havoc with water providers. Woodhouse and Lukas conclude, “Uncertainty is inherent in tree-ring reconstructions of streamflow [and] communicating the uncertainty in reconstructions to water resources professionals is a continuing challenge to dendrohydrologists.”[19] The water manager’s task is not easy—do they release more or less water based on current inflows, knowing that if they hold back too much they may have to spill an over-topping reservoir, or if they release too much they may not have enough in the next year.

The Colorado Airborne Snowpack Measurement (CASM) workgroup formed in 2021 with funding from the CWCB, Denver Water, the Colorado River District and roundtables to fly over the mountains and measure snowpack. They hired Airborne Snow Observatories, a public benefit corporation, to estimate how many acre-feet are in the snowpack by measuring snow depth and density, and how much light is reflected off the snowpack or absorbed by it (albedo), thereby affecting the rate of snowmelt. By comparing the LIDAR data they collect with snow depth and snow water equivalent SWE measured at Snotel sites, they have reduced the uncertainty in runoff from 40 percent to only 5 to 13 percent.[20]

They are making water managers’ jobs easier, and their estimates of extra acre-feet in 2023 permitted Denver Water to leave more water in the Fraser River all summer long.[21] But they are also confirming that snowpacks are decreasing and migrating to higher elevations. That could have big implications for the west slope, as diversions into transbasin tunnels are capturing the runoff above the diversions, and there is less snowpack remaining below the diversions to melt and flow down west slope rivers.

Once Denver Water begins diverting 18,000 more acre-feet to Gross Reservoir, the total diversion will be about 70,000 acre-feet per year, 75 percent or more of the Fraser River’s average annual flow. One problem with describing the diversion as a percent of “average flow” is that it obscures what happens in low water years. The percent goes way up in below-average years, and those are the years that diversions are even more prized by Denver water since those are the years the utility is most concerned that it will not meet its delivery requirements. .[BG1] [KR2] [22] There are years when nearly the entire flow is diverted, resulting in much higher stream temperatures, and those are likely to become more common, not less.

The Moffat Tunnel was built between 1922 and 1928 to handle train traffic between Denver and Salt Lake City. Reclamation later installed a pipeline through the reconnaissance tunnel built alongside the railroad tunnel to send Fraser River water to the Front Range. The Fraser was President Eisenhower’s favorite fishing river, but Denver Water kept purchasing and drying up ranches and kept expanding collection points in the Fraser River Valley until very little water was left in the river.[23] The Fraser flowed only four cfs in the 2002 drought, a tiny flow in what once was one of the largest headwater tributaries to the mighty Colorado River. The Fraser has received some help in recent years, as settling ponds have been built to capture hundreds of tons of sand that is used in winter road icing operations and choking the river.[24] Denver Water has also agreed to spend up to $12 million to enhance the river if Gross Reservoir is expanded, by narrowing the river channel and planting trees to shade it. It has agreed to forego taking up to 2,500 acre-feet of the proposed 18,000 acre-feet expansion if river temperatures get too high, or as needed to mimic spring flushing flows.[25] But what is really needed to improve river health is leaving more water in the stream, and just the opposite is happening—you just can’t improve river health by taking water from it.

Denver Water also owns Dillon Reservoir alongside Interstate 70 at Silverthorne. It acquired most of the land to build Dillon Reservoir at rock bottom prices during the Depression when ranchers could not afford the property taxes.[26] By then, Denver Water had already acquired most of the water rights in the Blue River valley. In 1956, Denver Water notified the remaining residents and business owners to sell and vacate by September 15, 1961. The town of Dillon began flooding in 1964 when Dillon Reservoir captured the Blue River.

Dillon Reservoir can store 254,000 acre-feet but it only diverts 58,246 acre-feet each year on average through the Roberts Tunnel.[27] It cannot send more to the Front Range because it must deliver water down the Blue River to Green Mountain Reservoir, an arrangement that chafes Denver Water to no end.

Denver Water  claims it relinquished its right to divert more water from the Western Slope when it signed the Colorado River Cooperative Agreement, or CRCA, in 2013, but it saved its numerous conditional water rights in the agreement so that it is hard to know what to make of this claim.[28] In the CRCA, seventeen Western Slope entities including the major water players in the Colorado River basin, gave up the right to ever again challenge Denver Water’s 1.6 million acre-feet of conditional water rights. These include the right to store 400,000 additional acre feet of Blue River water on the east slope and another 350,000 acre feet in a proposed reservoir north of Interstate 70 above Wolcott.[29] The proposed Wolcott reservoir, known as the “Wolcott Pumpback,” would replace the water now being released to farmers in Grand Junction from Green Mountain Reservoir. Its purpose is to allow Denver Water to send more water from Lake Dillon through the Roberts Tunnel to the South Platte River drainage.

For years Denver Water took the position that it did not need to compensate Western Slope residents when it took water from the Western Slope. The Colorado Supreme Court agreed, saying in 1961, “We find nothing in the Constitution which even intimates that waters should be retained for use in the watershed where originating. The waters here involved are the property of the public, not any segment thereof, nor are they dedicated to any geographical portion of the state.”[30] This is a sore point with Western Slope residents who believe that basin-of-origin protection is needed to protect the Western Slope environment and economy. Introducing basin-of-origin bills used to be a rite of passage for newly-elected Western Slope legislators, but Colorado has yet to enact a law that requires the Front Range to compensate the Western Slope for transmountain diversions.

When the Front Range got serious about diverting transmountain water in the 1930s, Western Slope farmers clamored for their own dams and reservoirs, known as “compensatory storage.” U.S. House Representative and Glenwood Springs native Edward Taylor, known for the Taylor Grazing Act that sought to limit overgrazing on Western lands, demanded that the Western Slope receive an acre-foot for each acre-foot diverted to the Front Range. Denver Water flatly denied the Western Slope should receive any compensatory storage at all. Northern Water was not quite as harsh, but it still claimed that delivering an acre-foot to Western Slope farmers for every acre-foot diverted to the Front Range was too much. [31]

Rep. Taylor used his authority as head of the powerful U.S. House Appropriations Committee to block funding for the Colorado-Big Thompson project, holding out for one-for-one parity. But after Taylor fell ill, Congress passed the Colorado-Big Thompson Act in 1937, authorizing annual diversions of 310,000 acre-feet to cities and farmers in northeastern Colorado. The average diversion is less than this, about 220,000 acre-feet per year, but scheduled to increase to 250,000 acre-feet annually when the Windy Gap Firming Project is complete. [32]. Congress’s agreement to build Green Mountain Reservoir allowed the Colorado-Big Thompson project to move forward. Located on the Blue River 18 miles downstream of Dillon Reservoir, Green Mountain has a water right to store 154,000 acre-feet, roughly three times the 52,000 acre-feet released each summer to farmers downstream in Grand Junction. Green Mountain Reservoir has since been a focal point of contention. Denver Water refused to relent its hardline position against Western Slope concessions, and it sued Reclamation in 1942, asserting that its right to fill Dillon Reservoir, which it had been planning for decades, was superior to Reclamation’s right to fill Green Mountain Reservoir farther down the Blue River. The Colorado Supreme Court, whose majority came from the Western Slope, disagreed and ruled in 1954 that  Reclamation’s right to fill Green Mountain Reservoir was superior to Denver Water’s right to fill Dillon Reservoir. The decision is known as the Blue River Decree.

Denver Water eventually built Williams Fork Reservoir on Williams Creek to substitute water that Denver holds back in Dillon Reservoir instead of releasing it down the Blue River to Green Mountain Reservoir. Williams Creek joins the Colorado River between Granby and Kremmling near Parshall. (Parshall is named after R.L. Parshall, a senior irrigation engineer with the Bureau of Agricultural Engineering, the federal agency that conducted an economic study for the USDA for the Colorado Big Thompson Project in 1937.)[33] Denver Water also helped pay for Wolford Mountain Reservoir north of Kremmling in return for 40 percent of the water stored there, which it also releases to satisfy Western Slope water rights. But Green Mountain Reservoir remains a key piece of infrastructure affecting the river. Denver Water holds back as much as it can in Dillon Reservoir so unless Reclamation is calling for water to fill Green Mountain Reservoir, Denver Water normally releases only 50 cfs from Dillon Reservoir. The tiny flow is not enough to float a kayak or to keep the river cool, and it is probably why the Gold Medal trout fishery has crashed in the Blue River below Dillon. Releases from Green Mountain must also satisfy a variety of downstream users, known as the “Historic User Pool,” or HUP. At least a dozen parties, including U.S. and Colorado governmental agencies and water providers from Denver to Grand Junction, hold a weekly conference call in the summer to decide when HUP releases should be made from the reservoir.[34] Releases depend on how much HUP water is stored in Green Mountain, how much runoff is projected, what the climate forecast is, how much Grand Junction irrigators are likely to demand, and expected flow levels in the 15-Mile Reach on the Colorado River. HUP water released from Green Mountain Reservoir does not directly benefit the endangered fish in the Reach, at least on paper, because it is technically diverted out of the river in Palisade, at the top of the reach. But it does at least put more wet water into the river system, which helps keep Colorado River flows below Palisade higher.

            Richard Vangytenbeek represented Colorado Trout Unlimited at Colorado River Basin Roundtable meetings starting in 2016, and he applied for several roundtable grants to improve irrigation diversion structures. Ditch structures extend across the river, typically raising the river level several feet to divert it into an irrigation ditch, but often forming an impassable fish barrier. Vangytenbeek focused on the Colorado River downstream of Glenwood Springs and his ditch structure upgrades have restored connectivity. Rainbow and other trout species now spawn in tributaries like Elk Creek near Newcastle that had been effectively cut off from the Colorado River for decades. The new irrigation structures also deliver water more efficiently to irrigated fields.

After Vangytenbeek became the environmental representative to the Colorado Basin Roundtable in 2021, he convened a group of water providers to discuss scheduling reservoir releases so they would enhance, or at least not interfere with, fish spawning. He encouraged them to gradually increase reservoir releases in steps over several days to avoid sweeping young fish fry downstream. He likewise encouraged the reservoir managers to ramp the releases back down over an extended period to avoid drying out gestating fish eggs along the banks. For years this was an afterthought, as reservoir releases were made with little regard for their impact to aquatic life. There is no law requiring reservoir operators to consider the effect that releases have on fish and the macroinvertebrate stoneflies and caddis flies they eat, but at least its’s now on their radar.

Aurora and Colorado Springs

When Aurora incorporated in 1891 east of Denver, it was only four square miles. By 2024, nearly 398,000 were living in homes that filled up 164 square miles, and it was Colorado’s third largest city after Denver and Colorado Springs.[35] The town first obtained water from a well dug by a private water company. Additional wells were dug along Sand Creek. Aurora began purchasing taps from Denver Water until the utility announced in the 1940s that it would no longer deliver water south of 6th Avenue or east of Peoria Street. Since then Aurora has obtained its own water primarily by drying up agriculture, first in the upper South Platte River basin in South Park and more recently in the Arkansas River basin.

In 1964, Aurora purchased a direct flow water right to store water in Strontia Springs Reservoir, built at the head of Waterton Canyon upstream of Chatfield Reservoir. In 1967 it partnered with Colorado Springs to build the Homestake Project near Vail. This holds back water in Homestake Reservoir on Homestake Creek, a tributary of the Eagle River, and delivers it to Spinney Mountain Reservoir in South Park. To get water to Spinney Reservoir, the Otero Pump Station near Buena Vista pumps water 565 feet up from the Arkansas River to South Park in the South Platte River basin. Half of the water is piped to Colorado Springs and the other half flows into Spinney Mountain Reservoir near Hartsel in South Park.

Aurora and Colorado Springs share the annual Homestake diversions, which yield about 25,000 acre-feet per year.[36] Homestake is one of Aurora’s two largest transmountain diversions, the other being the Busk-Ivanhoe tunnel that delivers 2,500 acre-feet each year from the Fryingpan River. Aurora and Colorado Springs hope to yield another 20,000 acre-feet from Homestake II, a project obliquely known as the “Eagle River MOU.” More recently, Aurora has been purchasing irrigation water from lower Arkansas Valley farmers in Otero and Crowley counties on the eastern plains. That water is diverted from the upper Arkansas River through the Otero Pump Station, illustrating the water concept known as “substitution”—rather than taking water lower down on the Arkansas River where farmers were using it, Aurora diverts the water 180 miles upriver at the Otero Pump Station where it is far cleaner. This also avoids transit losses—water lost to seepage as it travels down canals—which engineers calculate amounts to about 10 percent of the water diverted.

In 1973 Aurora appropriated a water right to build Spinney Mountain Reservoir, which sits on the Middle Fork of the South Platte River. Completed in 1981, the reservoir can hold nearly 55,000 acre-feet, enough water for 130,000 people using 120 gallons per day. Aurora continued purchasing irrigation water rights from South Park ranches into the 1990s, including ranches in the Tarryall Creek Basin upstream of Spinney Mountain Reservoir. Many of the water rights that formerly irrigated the South Park ranches stretching from Buena Vista to Colorado Springs along Highway 24 are now owned by Aurora.[37]

In 1986 water court approved a change of use in the Rocky Ford Canal in Otero County, the oldest diversion canal on the Arkansas River, from irrigation to domestic water. That enabled Aurora to purchase 94 percent of the canal’s ditch shares. It also acquired water rights in the Colorado Canal that formerly irrigated 57,000 acres of farmland in Crowley County (despite claims by the promoter that it would irrigate at least a million acres).[38] Today, Aurora uses about 64,000 acre-feet a year.[39] Aurora projects that it will need 73,000 acre-feet by 2030. In 2015 average daily consumption increases from 25 million gallons per day in the winter to 44 million gallons per day between April and November, a sign of how much water is consumed by outdoor landscaping in the summer. Aurora reclaims wastewater flowing into the South Platte in the Prairie Waters Project.

Colorado Springs is Colorado’s second largest city, sprawling over 195 square miles visible from Pikes Peak.[40] What you cannot see from the peak is a major river, as the city is not built alongside a river, like so many other Western mega-cities including Los Angeles, San Francisco, Phoenix, Tucson, and Las Vegas. The Colorado Springs greater metropolitan area had 768,832 residents in 2023, up 100,000 from 678,319 residents in 2013.[41] The military is among its largest employers, with Fort Carson, the Air Force Academy, US Space Command and two other military installations. The aerospace and defense industry accounts for over 40 percent of the Colorado Springs economy with over 200 space, aerospace, cybersecurity and defense companies employing 111,000 people in 2022.[42] The city of Colorado Springs receives 75 percent of its water through transmountain diversions from four river basins on the Western Slope—the Eagle, Blue, Fryingpan, and Roaring Fork river drainages, in all capturing water from thirty-six separate headwater tributaries on the Western Slope.[43]

Figure 18.3 Transmountain diversions

Transmountain diversions to Colorado Springs, Pueblo, and Aurora

from the Roaring Fork, Eagle, and Blue river basins.

Colorado Springs first tapped the Blue River when it built the Hoosier Pass Tunnel in the early 1950s.[44] Highway 9 crosses Hoosier Pass on the Continental Divide between Breckenridge on the Western Slope and South Park on the east slope. Montgomery Reservoir is about 700 feet below Hooser Pass on the Park County side, and Colorado Springs has applied to enlarge the reservoir by about 8,000 acre-feet so it can divert 4,000 more acre-feet through the Hoosier Pass Tunnel into Montgomery Reservoir and on to Colorado Springs,

Colorado Springs also receives water from Homestake Creek which flows into the Eagle River above Minturn. It now collects water from five tributaries into Homestake Reservoir before sending it through a tunnel to Turquoise Reservoir, located four miles west of Leadville.[45] Colorado University-trained engineer John P. Elliott quietly began assembling the Homestake water rights near 14,000-foot Holy Cross Peak with financial backing from Boettcher and Company in the 1940s.[46] Colorado Springs and Aurora later paid $1.4 million to Elliott in 1962 for his water and property rights to access Homestake Reservoir.[47] Elliott demonstrated that water speculation can be legal under Colorado water law, since the only beneficial use he envisioned was selling the water to cities.

Homestake Reservoir has delivered 28,000 acre-feet each year on average to Colorado Springs and Aurora since it was built in 1967. Before construction was even complete, the cities were planning to capture another 75,000 acre-feet in Homestake II. Their plan was simple—run a ditch along the hillside on the north side of Homestake Creek to capture every rivulet coursing down the hillside, 65,000 acre-feet in all. Another ditch would capture every tributary draining into the East Fork of the Eagle River, 10,000 more acre-feet, located north of Fremont Pass between Copper Mountain and Leadville. Controversial when unveiled in 1981, Homestake II led to years of lawsuits that temporarily settled in 1989 when a judge agreed that Eagle County could deny permits for the project. The fight is not over. The Colorado River District, created in 1937 to counterbalance the Colorado-Big Thompson project to protect Western Slope water supplies, has been quietly moving Homestake II forward. The project will send 20,000 acre-feet eastward to Colorado Springs and Aurora, at odds with the Colorado River District’s raison d’etre to protect Western Slope water supplies. But enough water is also being provided to a consortium of Eagle Valley water providers that the River District believes it can justify supporting the project. The Eagle County water providers would receive 10,000 acre-feet, about a third of the total, enough water for another 100,000 residents in Eagle County, the second fastest growing county in Colorado since 1980. Homestake II has been renamed the “Eagle River MOU,” for a “memorandum of understanding” related to the project. It was never discussed at a Colorado basin roundtable meeting until 2018, and it is not even mentioned in either the 2015 or 2023 Colorado Water Plans. It is referenced on page 38 of the 2022 Arkansas Basin Implementation Plan as the “Eagle River Joint-Use Project . . . a joint use water project in the Eagle River basin that minimizes environment impact.”[48]

Draining the Pan and Fork

The Fryingpan-Arkansas Project, known as “Fry-Ark,” delivers water from the Fryingpan and Roaring Fork river systems to Pueblo Reservoir for use by cities and farms in the Arkansas River basin.

While originally championed to support farming in the lower Arkansas Valley, Front Range cities have been steadily acquiring Fry-Ark water. Colorado Springs first began receiving 10,000 acre-feet of Fry-Ark water each year from Pueblo Reservoir in 1985, delivered through the Fountain Valley Conduit.[49] The Arkansas Basin Roundtable now claims that obtaining more storage is its greatest need, ostensibly to protect its dwindling agriculture. High on the roundtable’s list of IPPs (“identified projects and projects,” aka the water providers’ “wish list” for more water development) is a project referred to as the Preferred Storage Option Plan, or PSOP. It would add twelve feet of concrete to the top of Turquoise and Pueblo Reservoirs to expand their holding capacity.[50] PSOP is mentioned once in a list of acronyms in the 2015 Colorado Plan, and not mentioned at all in the 2023 Colorado Water Plan or the Arkansas Basin Implementation Plan.[51] It is never described in detail.

President Kennedy recognized the Fry-Ark Project in 1962 when he flew in to tout it, saying, “When [people] come to this state and see how vitally important [water] is, not just to this state, but to the West, to the United States, then they realize how important it is that all the people of this country support this project that belongs to all the people of this country.”

Fry-Ark’s complex diversion system captures thirteen tributaries, ten in the Fryingpan drainage and three in the Roaring Fork drainage, including Hunter Creek, which flows into the Fork in central Aspen. Reclamation claims that Fry-Ark provides water to over 720,000 people and 280,600 acres. It includes five dams and reservoirs, three power plants, and twenty-two tunnels and conduits that divert water out of a headwaters area spanning 87 square miles. The extent of Fry-Ark diversions vary widely with snowpack. For example, 98,000 acre-feet was diverted in 2010, but only 14,000 acre-feet the following year. [52] Turquoise Reservoir is only a mile from the Arkansas River, but water leaving the reservoir actually flows south in a canal a mile or so west of the river for eleven miles until it reaches the Mt. Elbert Forebay on the lower slope of Mt. Elbert, Colorado’s highest mountain. The forebay, which the rest of us would call a reservoir, generates power as it releases water down to Twin Lakes Reservoir. Water is then pumped back up from Twin Lakes into the Mt. Elbert Forebay in the middle of the night when electricity costs are low. The next day water is released back down to Twin Lakes when rates are higher, generating profit from the difference in electricity prices. The blocky concrete structure at Twin Lakes Reservoir along Highway 24 is actually a pumping station that lifts the water 1,752’ up to the Mt. Elbert Forebay. Economists call this practice “arbitrage,” and engineers call it “pumped storage.”[53] But it is not environmentally benign because the power needed to pump water uphill to the forebay has primarily come from burning coal since it was developed in 1981.

Reclamation is required to maintain bypass flows in the Fry-Ark Project to keep the mainstem of the Fryingpan from drying up. By contrast, Denver Water’s Moffat Tunnel collection system on the Fraser River tributaries lack any bypass flow requirements, which means that Denver Water could entirely dry up the tributaries. Denver Water recently agreed to allow bypass flows as a concession in return for taking 18,000 more acre-feet in the CRCA, but it diverted water into Moffatt Tunnel for nearly a century without having to release any bypass flows. Ruedi Reservoir, located nine miles above Basalt on the Fryingpan River, is part of the Fry-Ark Project and provides compensatory storage for the Western Slope. For years, water stored in Ruedi Reservoir remained unsold, but that ended in 2012 when Grand Junction and several other Western Slope providers purchased the remaining 19,500 available acre-feet.[54] Today, Ruedi Reservoir, which can hold 102,373 acre-feet when full, is also used to release water for fish in the 15-Mile Reach of the Colorado River upstream of where the Colorado and Gunnison rivers join in Grand Junction. This water is known as “10825 water” since 10,825 acre-feet must be released to enhance Colorado River flows between August and October each year.

The Roaring Fork river system, which includes Lincoln, Maroon, Castle, and Woody creeks, as well as the Fryingpan and Crystal rivers, delivers one-eighth of the Colorado River’s entire annual flow. Still, the Roaring Fork River is heavily diverted, either eastward through tunnels under the Continental Divide or westward into irrigation ditches.[55] Some sections can all but dry up in drought years.  In July 2012, only 5.7 cfs flowed down the river through Aspen, a flow barely two inches deep across the river.

The Twin Lakes Reservoir and Canal Company can divert up to 68,000 acre-feet in a single year and up to 570,000 acre-feet in a rolling 10-year period through the Twin Lakes - Independence Pass Tunnel.[56] In 2011, a wet year with above-average snowpack, 625 cfs was being sent through the Twin Lakes tunnel to the east slope but only 4 cfs was released from Grizzly Reservoir into Lincoln Creek, a tributary to the Roaring Fork. In all, 99.4 percent of the upper Roaring Fork was flowing toward the east slope! The Twin Lakes – Independence Pass Tunnel was built in the 1930s to provide water to farms in Crowley County in the lower Arkansas River valley. Colorado Springs Utilities began purchasing shares in the Twin Lakes Reservoir and Canal Company in the 1970s, and today the water provider owns 55 percent of the yield from the diversion project. Unlike the federally managed Fry-Ark Project, there are no bypass flow requirements on the Roaring Fork.

Kevin Lusk, an engineer formerly with Colorado Springs Utilities and formerly president of the Twin Lakes Reservoir and Canal Company, points out that under an intergovernmental agreement, the Twin Lakes Company leaves 3,000 acre-feet a year of water in the Roaring Fork drainage. While it helps, it amounts to only 4 cfs per day on a year-round, 24-7 basis. That’s small solace for a river as large as the Roaring Fork River. In 2011, Lusk said he was legally bound to take the maximum amount possible from the Roaring Fork. “We do have a financial responsibility as a board to our shareholders and we have some liability there for not exercising our rights," Lusk told Aspen Journalism in 2011. Rather than leaving more water in the stream, Lusk suggested we dig out the stream channel with backhoes to make it narrower. "Instead of throwing more water at the channel maybe you adjust the channel to the water that's there,” Lusk said. “Kind of live with the reality you find yourself in.”[57] That would work until the next big runoff fills the narrowed stream channel back in again. It also ignores the science that says high flows are needed to regularly tumble rocks lining the river bottom so that silt clogging them is flushed out. We could produce these flows by letting the peak snowmelt run freely for a few days or by releasing extra water from Grizzly Reservoir down Lincoln Creek and into the Roaring Fork.

Colorado Springs citizens could be the ultimate arbiters of this situation—they could lobby Colorado Springs Utility to release flushing flows and higher baseline flows to keep the upper Roaring Fork healthier. Gary Bostrom, the former chief water services officer at Colorado Springs Utilities, said at a 2014 meeting of the Arkansas Basin Roundtable that the 2015 Colorado Water Plan over-estimates municipal water conservation savings. High municipal water conservation targets (like limiting the amount of blue grass or when it could be watered or requiring water-saving fixtures) would not meet the supply gap, Bostrom said, instead claiming that low or medium conservation targets were more reasonable. Bostrom concedes that Colorado Springs Utilities received two-thirds of its water from the Colorado River through the Fry-Ark and the Independence Pass tunnel diversions. And he called on the state to develop more water from the Colorado River basin if it hopes to meet its looming supply gap. In one sense, he’s right—if you do not conserve, you need more.[58]

The Colorado-Big Thompson Project

“Notoriety has been the companion of the Colorado-Big Thompson project at every step.” So opens Roger Autobee’s history of the Colorado-Big Thompson (C-BT) project, which Reclamation considers its most productive project after the Central Valley Project in California.[59] The C-BT, according to Northern Water’s website, includes 13 reservoirs spanning 26 square miles, 35 miles of tunnels, 95 miles of canals, six hydroelectric plants, and 700 miles of transmission lines.[60] The reservoirs, six on the west slope and eight on the east slope, store over a million acre-feet. Up to 260,000 acre-feet is diverted from Grand County to the east slope every year through the Alva B. Adams Tunnel, which runs beneath Rocky Mountain National Park.[61]

Figure 18.4 Storage in the Colorado-Big Thompson Project.

Storage in the Colorado-Big Thompson Project.

The C-BTcame into being when the Public Works Administration authorized $150,000 during the Depression study its feasibility, concluding it would boost farming, employ construction workers, and provide electricity to rural areas. Grand Lake is the centerpiece of the entire project. Water is pumped 125 feet up from Granby Reservoir to Shadow Mountain Reservoir, formerly a meadow adjacent to Grand Lake before it was dammed. Shadow Mountain Reservoir and Grand Lake now form one body of water, but nutrients leaching from the meadow cause unceasing water quality problems. Grand Lake is commonly described as the headwaters of the Colorado River, the West’s most famous and iconic river, yet the water actually flows east out of Grand Lake into the Adams Tunnel before descending to Lake Estes and the eastern plains. Adams, Colorado’s US Senator who championed the project, was honored when Franklin D. Roosevelt named the tunnel after him in 1944. Despite being barely a mile wide, Grand Lake is the largest and deepest natural lake in Colorado. As much as anything, that attests to the Rockies’ old age—they have eroded so much that nearly every natural lake in Colorado was filled in long ago, transformed into either a meadow or a forest.

Weld County began eying Grand Lake as a source for water in the 1880s—it is only 13.1 miles west from Estes Park, the length of the tunnel—but the project wasn’t seriously considered until the 1930s when the WPA added it to its projects list. The United States’ thirty-year obsession with dams began in the Depression, with nearly all of the largest reservoirs in the West built between 1935 and 1965. Conservationists objected to the C-BT, raising their loudest protest since 1910 when citizens opposed damming Hetch Hetchy Valley next to Yosemite to provide drinking water to San Francisco. The Park Service opposed the Grand Lake Project because it required tunneling below Rocky Mountain National Park. Reclamation quieted the Park Service’s concerns by digging the tunnel entrances just beyond the park boundary at both ends of the tunnel. Opponents feared that Grand Lake would be ruined by fluctuating lake levels. A local woman claimed, “If God wanted crops grown (in Weld County) he would have provided the water to do it with.”[62] Interior Secretary Harold Ickes at first opposed the Grand Lake Project, which was caught between his Reclamation and Park Service departments. Proponents quietly began calling it the “Colorado-Big Thompson Project,” named for the rivers losing and receiving the water, instead of the Grand Lake Project to deflect attention from the environmental controversy.

Nearly 70 years after Grand Lake’s flow was reversed, citizens in the community of Grand Lake are still agitated because water quality in the lake remains poor. Environmental victories are temporary and always at risk of being reversed, but environmental losses are usually permanent. Shadow Mountain Reservoir used to be a meadow where my grandfather picked meadow mushrooms after summer thunderstorms. He remembered seeing the Grand Lake bottom 30 feet below, but today algae blooms often lower dissolved-oxygen levels, harming fish and clouding the water. The EPA says that Granby Reservoir, Shadow Mountain Reservoir, and Grand Lake on the west slope, and Horsetooth Reservoir and Carter Lake on the east slope, all suffer from poor water quality.[63] The problem has vexed Northern Water, which operates C-BT, for decades. One proposal is to build a tunnel to pump water from Shadow Mountain Reservoir beneath Grand Lake up into the Adams Tunnel, permitting Grand Lake to once again flow west. Stranger things have happened in the world of water projects.

            Like the Fry-Ark project, the C-BT project’s plumbing is vast and complex. Granby Reservoir is Colorado’s second largest reservoir after Blue Mesa Reservoir on the Gunnison River. Granby Reservoir can store 540,000 acre-feet, more than twice the volume of Dillon Reservoir. Granby stores water from numerous tributaries that flow into the upper Colorado River including Willow Creek, captured in Willow Creek Reservoir and then pumped 175 feet up to Granby Reservoir.[64] The power to lift this water comes from the east slope, with electricity generated from Colorado River water as it falls 2,900 feet from Lake Estes to the plains on its way to Greeley. The electricity flows back to the west slope through a power line hanging from the roof of the Adams Tunnel so it can pump water from the Colorado River up to Granby and Shadow Mountain Reservoirs.[65] The electricity generated from falling water is never enough to pump it the same distance uphill, so there is a net cost to this scheme, which has been paid by burning coal.

In the 1980s Reclamation built Windy Gap Reservoir to pump 48,000 more acre-feet 445 feet up to Granby Reservoir.[66] Today Northern Water is in the process of taking another 30,000 acre-feet from the Colorado River in the “Windy Gap firming project.” Five new reservoir sites between Granby and Loveland were analyzed to store, or “firm up,” the water, and Grand County issued the required permits in 2017. [67] The largest, Chimney Hollow Reservoir, was under construction 2024 and will store 90,000 acre-feet, three times the requested additional annual diversion from the Colorado River. Farmers in Weld, Larimer and Boulder counties along the over-appropriated South Platte River first championed the C-BT project, and they were rewarded because Northern Water’s service area is huge, covering1.5 million acres, 2,340 square miles, an area encompassing over 2 percent of all Colorado.[68]

But today, population growth is the driver. In 1949, 175,000 people lived in Northern Water’s district, but water planners expect Colorado River water will support 1.5 million people by 2050 on the eastern plains in Boulder, Longmont, Loveland, Greeley, Fort Collins and other cities. [69] Northern Water says, “While water users are much more efficient now thanks to a focus on conservation, the reality is there is no way to conserve our way to a secure water future. With a growing population and limited water supply, Northern Water must invest in creative strategies that meet future demands sustainably.” Those strategies include building Chimney Hollow Reservoir near Loveland as part of the Windy Gap Firming Project, and building Glade Park and Galeton Reservoirs as part of NISP, the Northern Integrated Supply Project.[70] It’s hard to argue with their conclusion that if we keep growing more people, we’ll have to build more dams.

Figure 18.5 Population served by C-BT Project

The amount of water diverted each year through transmountain tunnels can vary widely from snowfall, with more water often being diverted in drier years. In 2002, when water flowing down the Colorado River was the lowest in 500 years, the Adams Tunnel diverted 267,900 acre-feet, 18 percent more than its 30-year average.[71] The same was true at Dillon Reservoir where Denver diverted 131,306 acre-feet in 2002, more than twice its 58,426 acre-feet annual average diversion.[72] This is because even more water is needed during drought years when less snowmelt runs down east slope rivers. And droughts are often accompanied by hotter temperatures, so water demands increase at the very time supplies decrease, creating a double whammy for river health. In 2002, Granby Reservoir received inflow of 111,300 acre-feet, less than half of its 30-year average inflow of 252,930 acre-feet. The reduced flow was typical of all C-BT tributaries that year. Granby Reservoir started the year with 374,219 acre-feet, and ended with only 176,778 acre-feet, less than a third of its capacity.[73] If 2003 had been another low snow year, diversions to the Front Range would have been curtailed. It looked like that could happen as 2003 started, but a massive March storm dumped five feet of wet snow in the Rockies, filling reservoirs from Dillon to Granby and all along the Front Range.[74] This shows how close the system came to not working. And, it provides cover for water providers to regularly call for more and higher dams.

When the Colorado legislature first authorized water conservancy districts in 1937 to divert and store water for farming, Northern Water was one of the first to use the new law to manage C-BT water. Water conservancy districts like Northern are quasi-public entities run by private citizens who have authority to tax residents to build water infrastructure. The 1937 bill made compensatory storage mandatory, forcing diverters to compensate farmers in the basins losing water. By law, conservancy districts cannot build transmountain diversions “at the expense of the water users within the natural basin.”[75] Another consequence of the C-BT project is that some irrigation systems downstream of Granby and Windy Gap Reservoir were stranded by a depleted river. Reclamation installed pumps in the Colorado River above Kremmling in 1937 so ranchers would receive sufficient irrigation water. But the river channel has migrated nearly a quarter mile from its 1937 location because deposition patterns changed after river flows were decreased by as much as 300,000 acre-feet a year. Today, late summer river flows drop to 250 cfs and the pumps sit high and dry above the river, no longer working.

Figure 18.6 Average peak streamflow on the Colorado near Kremmling

The Colorado Basin Roundtable and the CWCB awarded $110,000 in 2014 to study the problem, and later released another $960,000 to re-work the river channel. The National Resource Conservation Service, a grant-making program run by the USDA, ponied up another $2.7 million. The funds were used to narrow the river channel, making it deeper, and anchoring large rocks in the river into “drop structures” to divert flow into the irrigation diversion pumps. Northern Water has spent millions trying to improve river conditions on this stretch, but local rancher Wendy Thompson says, “everything that’s been done in the past has gone the wrong direction.”

Figure 18.7 Diversions in the Colorado River headwaters

Diversions in the Colorado River headwaters

The earliest transmountain diversion on the Colorado River is the Grand River Ditch. The ditch captures water from 11 tributaries coming off the east slope of the Never Summer Mountains as it winds north to La Poudre Pass and the Cache La Poudre River drainage. You can make out the ditch across the Colorado River valley when descending the west side of spectacular Trail Ridge Pass in Rocky Mountain National Park. The Grand River Ditch was dug over a span of 46 years beginning in 1890 and it joined the National Register of Historic Places in 1976, the year Colorado turned 100. The ditch sends 17,462 acre-feet to Larimer County from upper Grand County each year on average.

The Grand River Ditch illustrates how simple it can be to divert water from one basin to another. By digging a ditch along a mountainside—in this case with a Japanese crew, hand tools, and black powder—each stream is successively captured along the entire length of the ditch. Note that if a tunnel anchored to the hillside was transporting the water rather than the ditch, a portion of each tributary stream could flow beneath the tunnel and keep the meadows or wetlands below from drying up. But at the time most transmountain water projects were constructed, no environmental laws required bypass flows, and we have rarely required them since. Denver Water captures Fraser River water on the north side of Berthoud Pass for delivery through the Moffat Tunnel the same way, with a continuous ditch capturing every stream above the ditch. In fact, this practice is common in Colorado. The Grand River Ditch significantly affects the meadow ecology along the North Fork of the Colorado River in Rocky Mountain National Park. The National Park Service has sued the Grand River Ditch company to increase river flows through the meadow, which it can do under its reserved rights doctrine.

Another threat recently surfaced, as the Colorado River headwaters have started dumping mud and nutrients into Shadow Mountain Reservoir. The Grand River Ditch has blown out twice in recent years, sending debris flows down to the Colorado River (it’s referred to as the North Fork of the Colorado River on some maps, but since there’s no South Fork of the Colorado, it’s fair to call it simply the headwaters or main stem of the Colorado River). The mud is now working its way into Shadow Mountain Reservoir. A citizen-group of retired water quality scientists once requested funds from the Colorado Basin Roundtable to develop a watershed plan and propose solutions to the problem, but they ran into Upper Colorado River politics, and we were told to hold off on awarding any funds until Northern Water and the citizen group settled their differences. The Colorado River has water quality issues literally from source to sea.

Today, on average, about 580,000 acre-feet is diverted from the west slope to the east slope every year.[76] The sad conclusion is that the headwater diversions from the Colorado River, arguably the most beautiful river on earth, make the upper river a shadow of its former self.

Figures

Figure 18.1 Transmountain diversions in Colorado

Figure 18.1 Denver’s population versus water supply

Figure 18.3 Transmountain diversions to Colorado Springs, Pueblo, and Aurora from the Roaring Fork, Eagle and Blue river basins

Figure 18.4 Storage in the Colorado-Big Thompson Project.

Figure 18.5 Population served by C-BT Project

Figure 18.6 Average peak streamflow on the Colorado near Kremmling

Figure 18.7 Diversions in the Colorado River headwaters

Notes

[1] Not all diversions are tunnels. The Grand Ditch, or Grand River Ditch, takes water from the Western Slope to the east slope by way of an open ditch that drops from the Never Summer Range to Joe Wright Creek, a tributary of the Cache La Poudre River above Fort Collins.

[2] One diversion actually takes water from the east slope to the west slope. That’s the Vasquez Tunnel, which takes water from Clear Creek underneath Berthoud Pass to Vasquez Creek, a tributary of the Fraser River on the west slope. Some of the water in Clear Creek originates in the Williams Fork drainage, which is the next valley to the north of I-70 as it ascends from Silverthorne to the Eisenhower Tunnel. So, water in the Williams Fork crosses to the wast slope through the Jones Pass Tunnel, then crosses back to the west slope in the Vasquez Tunnel, and then crosses back to the east slope through the Moffat Tunnel.

[3] Colorado’s 44 trans basin diversions are listed in Coleman, C., “Citizens Guide to Colorado’s Trans basin Diversions,” 2014, pg. 9, Colorado Foundation for Water Education.

[4] “Citizen’s Guide to Colorado’s Trans basin Diversions,” pg. 7.

[5] “South Platte River,” last modified Sep. 11, 2016, Wikipedia.

[6] Denver Water’s 139 gallon per day average is reported in the Denver Water System Fact Book, downloaded July 12, 2024, pgs. 11-12, https://www.denverwater.org/sites/default/files/water-supply-fact-book.pdf. The EPA says the average family uses about 320 gallons per day, about 30% of which is used outdoors over the year; EPA Water Sense, "Outdoor Water Use in the United States," downloaded July 12, 2024, https://19january2017snapshot.epa.gov/www3/watersense/pubs/outdoor.html. See also, Denver Water, “Where does your water come from, June 29, 2021, by Jay Adams, downloaded Dec. 1, 2024, https://www.denverwater.org/tap/where-does-your-water-come?size=n_21_n

[7] “AWE Charter Sponsor Profile Denver Water,” July 1, 2010, Alliance for Water Efficiency. “Colorado River Cooperative Agreement,” Section I.B.1, pg. 1, and Attachment C, available at, “Colorado River Cooperative Agreement: Path to a Secure Water Future,” Denver Water, downloaded Sep. 25, 2015.

[8] In 2011, Colorado's municipal and industrial supply was 1,161,000 acre-feet; see, SWSI 2010 Colorado Basin Report, June 2011, pgs. 5-11, 4-13. This equates to 206 gallons per person per day (206 gals x 365 days x 5,051,500 people) / 325,851 gals in an acre-foot). Of this, 53 percent was used indoors and almost all was available for reuse; 39 percent was used to water lawns and shrubs outdoors and nearly all consumed; 8 percent was lost in leaky pipes but available for reuse; and the rest, 10 percent was used in industry, most to generate electricity; see, SWSI 2010, Appendix L, page 44.

[9] Denver’s annual temperature is 50oF, Albuquerque’s is 57oF, and Mexicali’s is 72oF; U.S. Climate Data. Albuquerque, where annual rainfall is 9.5 inches, uses 127 gallons per day; US Water Alliance, One Water Spotlight: Albuquerque, New Mexico, downloaded 12-1-2024,

https://uswateralliance.org/resources/one-water-spotlight-albuquerque-new-mexico/#:~:text=Conservation%20efforts%20have%20seen%20per,potable%20ways%20to%20reuse%20it.

[10] Denver Water, “Efficient indoor water use,” February 10, 2024, downloaded July 12, 2024, https://www.denverwater.org/residential/efficiency-tip/efficient-indoor-water-use

[11] This assumes that residents use 75 gallons per day indoors, in both their residences and at commercial establishments, and that 5 percent of this is consumed; each residence has 2.53 residents, and the outdoor landscaping per residence is 4,000 square feet, of which 1,000 square feet is bluegrass receiving 30 inches of irrigation per year and the rest is xeriscaped and receives 12 inches water per year; and 95 percent of outdoor use is consumed. Together, these equate to 120 gallons per person per day. No allowance is made for outdoor irrigation at commercial or industrial businesses.

[12] Map courtesy of the 2013 Denver Water Comprehensive Annual Financial Report, pg. III-13.

[13] Denver Water Storage is from Denver Water Quality Report 2023.pdf. Population figures are from Macrotrends, Denver Metro Area Population 1950-2024, downloaded 12-1-2024, https://www.macrotrends.net/global-metrics/cities/22972/denver/population#:~:text=The%20metro%20area%20population%20of,a%201.24%25%20increase%20from%202020.

[14] Booth, M., “Why thousands of trees at Chatfield State Park are being cut down,” The Colorado Sun, Oct. 16, 2024, https://coloradosun.com/2024/10/16/chatfield-state-park-tree-removal-reservoir/

[15] Denver Water’s Chatfield storage capacity is from Denver Water Quality Report 2023, Note 13.

[16] In water year 2002, (October 1, 2001, through September 30, 2002), 131,306 acre-feet was diverted through the Roberts Tunnel from Dillon Reservoir to the east slope, over twice the average diversion of 58,426 acre-feet. See, “Description of the Big Thompson Project describing Water Year 2002,” Table 2. The average is 58,426 acre-feet; “Citizen’s Guide to Colorado’s Trans basin Diversions,” pg. 9.

[17] Woodhouse, C., Lukas, J., “Multi-Century Tree-Ring Reconstructions of Colorado Streamflow for Water Resource Planning,” Climatic Change (2006), Vol. 78, pgs. 293-315, pg. 312.

[18] Id, pg. 313.

[19] Meko, D., Woodhouse, C., “Chapter 8, Application of Streamflow Reconstruction to water Resources Management, “ Sec. 8.4.3. pg. 253.

[20] Colorado Airborne Snow Measurement Program website, downloaded December 14, 2024, https://coloradosnow.org/faqs.

[21] Jeff Deems, Airborne Snow Observatories, Inc., presentation to the Roaring Fork Collaborative, on May 23, 2024, at the Basalt Library.

[22] Best, Allen, “Less is more for the Fraser River, say parties in Moffat firming agreement,” Mar. 26, 2014, Mountain Town News.

[23] For a story describing the Fraser River’s decline, see Gilboy, C., “Obituary for a river,” June 26, 2014, Boulder Weekly, http://www.boulderweekly.com/article-13030-obituary-for-a-river.html.

[24] The Colorado Basin Roundtable helped fund this project. Berwyn, B., “Colorado: Fraser River gets a boost,” Nov. 2, 2011, Summit County Citizens Voice.

[25] Best., A., “Less is more for the Fraser River.”

[26] “Dillon Reservoir,” Wikipedia, downloaded Sep. 20, 2015.

[27] “Citizen’s Guide to Trans basin Diversions,” pg. 9.

[28] According to the Denver Water Mile High Water Talk website, the Western Slope is better off with the Moffat Project than without it. The website’s brief announcement called the CRCA “historic” and stated that the river would receive environmental benefits, but failed to mention that Denver Water was increasing its Fraser River diversion by 33 percent. Denver Water has over 1.6 million acre feet of conditional water rights available for future development, including: 161,476 af refill right in Dillon Reservoir, 350,000 af storage right in the proposed reservoir above Wolcott , 184,155 af storage right in Chatfield, and 184,345 af storage right in Gross Reservoir.

[29] The Western Slope signatories include Eagle, Grand, and Summit counties, the Colorado River District, six water providers and irrigation companies in Grand Junction, and the cities of Glenwood Springs and Rifle. “Colorado River Cooperative Agreement,” pg. 1, https://www.denverwater.org/your-water/water-supply-and-planning/environmental-planning-and-stewardship/colorado-river-cooperative-agreement

[30] Metropolitan Suburban Water Users Association v. Colorado River Water Conservation District, 148 Colo. 173, 365 P.2d 273 (1961).

[31] Conservancy districts along the Front Range are independent organizations and sometimes take opposing positions. They all want the same thing—more water for Front Range residents—but they are also competing for those limited water rights and pursue different strategies.

[32] “Colorado Big-Thompson Project,” 75th Congress 1st Session Senate Doc. No. 80. Known as “Senate Bill 80” in Colorado water circles, this document was the Congressional authorization for the C-BT project, and includes a thorough description of the diversion works on both sides of the Continental Divide, the purposes of the project, and the creation of Green Mountain Reservoir to release up to 52,000 acre-feet to protect West slope irrigators when Shoshone power plant diversions drop below 1,250 cfs (pg. 3). The annual diversion was estimated “at least” to be 310,000 acre-feet on pg. 33, but the average actual diversion from 1990-1999 was 205,718 af in footnote 3 above. The construction cost was estimated at $2 per year per af, to be repaid over 40 years by irrigators in the Northern Colorado Water Conservancy District. The report concludes on pg. 33 “That the cost of the irrigation feature of the project is within the ability of the water users to pay.”

[33] “Colorado Big-Thompson Project,” 75th Congress 1st Session Senate Doc. No. 80, pg. v.

[34] The Green Mountain Reservoir Administrative Protocol Agreement governs Green Mountain Reservoir releases; its parties include Denver Water, the Northern Colorado Water Conservancy District, the Colorado River District, Colorado Springs, the Middle Park Water Conservancy District, Climax mine, the State Engineer, the US Attorney General, the US Bureau of Reclamation, and 5 Grand Junction entities including the Ute Water Conservancy District, Grand Valley Water Users Association, Grand Valley Irrigation Company, Orchard Mesa Irrigation District, and the Palisade Irrigation District. As with most stipulated water agreements, it permits the parties to later challenge the agreement in water court , and it says that nothing in the agreement can be used as precedent is a later legal battle.

[35]  “About Aurora,” City of Aurora Colorado, downloaded 12-7-2024, https://www.auroragov.org/city_hall/about_aurora#:~:text=At%20more%20than%20164%20square,Arapahoe%2C%20Adams%20and%20Douglas%20counties.

[36] “Citizen’s Guide to Colorado’s Transbasin Diversions,” pg. 9.

[37] Aurora has dried up ten ranches along the Middle Fork of the South Platte River in South Park, which together yield 8,880 acre-feet. See “Aurora Water History,” footnote 23 above, at pg. 20.

[38] Promoter T.C. Henry envisioned building a canal that would irrigate 1 million acres on the north side of the Arkansas River. “[I]n reality irrigating 57,000 acres [was all that could be accomplished]and the canal stopped in Crowley County. This irrigation system brought a burst of growth in the population of the area, and the dry prairie flourished.” “Crowley County History,” Crowley County Genealogy and History.

[39] Aurora and Denver are the leading cities for water conservation techniques. Aurora does not have the collection sources of most major Front Range cities. It has therefore been required to seek more resourceful solutions, like conservation.

[40] “Colorado Springs,” Wikipedia. Colorado Springs was the 41st largest city in the United States in 2015. For a list of the 50 largest cities in the US, see http://www.infoplease.com/ipa/A0763098.html.

[41] Id. See the US Census data finder. The population of the Colorado Springs Metropolitan Statistical Area (MSA) was 768,832 in 2023. The MSA includes El Paso County, which has a population of 730,395, and Teller County, which has a population of 24,710. US Census Reporter.

[42] Colorado Springs Chamber & EDC, Defense & Military, Defense Development, downloaded Dec 7, 2024, https://coloradospringschamberedc.com/defense-military/defense-development/.

[43] Much of the water in Pueblo’s column actually ends up Aurora through its Rocky Ford Canal and Colorado Canal diversions, but that is not reflected in the table. “Where Does Colorado Springs Get Its Water Supply From?,” May 22, 2007, Realty Scoop.

[44] “History: Colorado Springs’ Water Collection System,” 2014 Water Tour, Colorado Springs Utilities, pg. 12, downloaded Sep. 20, 2015. Also see a story map of CSU’s water system, https://storymaps.arcgis.com/stories/27e6a3b997a74be181b9e06022f478f1, and CSU’s 2017 integrated water plan, https://www.csu.org/Documents/IWRP.pdf

[45] The six tributaries are French Creek, Fancy Creek, Missouri Creek, Sopris Creek, Homestake Creek, and the East Fork of Homestake Creek. Aurora and Colorado Springs’ “rapid rate of growth instigated Homestake Phase II, designed to divert water from Cross Creek and Fall Creek, again in the Holy Cross Wilderness, through a series of four small dams and a 13- mile underground tunnel.” See, “Phase II of Homestake Water Project, Application for approval by the Eagle County Board of County Commissioners submitted by the City of Colorado Springs and the City Of Aurora.”

[46] Best, A., “Water flowing uphill, Sep. 20, 2002, Vail Daily, https://www.vaildaily.com/news/water-flowing-uphill/.

[47] Currier, J., P.E., “Eagle River MOU and the Homestake Project, a Brief History,” Jan. 17, 2017, Colorado River District, slide 8.

[48] Smith, J., “Talks under way on landmark water project in Eagle County,” Oct. 6, 2004, Rocky Mountain News, http://knightrisser.stanford.edu/lastdrop-p5.html. The Eagle River MOU is also listed at the bottom of a spreadsheet listing 60 proposed projects in Volume 2 of the Arkansas Basin Implementation Plan, January 2022, pg. 104, as a “joint use water project in the Eagle River basin that minimizes environment (sic)”

[49] Colorado Springs also receives 28,000 acre-feet of water that formerly irrigated Crowley County through its ownership of the Colorado Canal, which receives water from Twin Lakes; “History: Colorado Springs’ Water Collection System,” 2014 Water Tour, Colorado Springs Utilities.

[50] See the Arkansas Basin Implementation Plan, Section 1, pgs. 1-1 through 1-16, 2014.

[51] PSOP is identified as the Preferred Storage Option Plan in a table of Acronyms and Abbreviations on page 4 of the 2015 Colorado Water Plan. It is listed on page 108 of Volume 2 of the Arkansas Basin 2022 Basin Implementation Plan as project number ARK-2020-0045 as “Storage Space in Basin,” with this description: “Obtain more storage space in the basin (Turquoise or Pueblo ) to store Derry 3 Water.” It is allocated a Tier 4 rating, meaning it is the lowest priority of potential projects.

[52] “Fryingpan-Arkansas Project ,” Wikipedia. Diversions are limited to 2,352,800 acre-feet every thirty-four years, or 69,200 acre-feet per year on average. Deciding how much water to divert on a yearly basis depends on availability. The potential environmental consequences are not deeply considered, nor do they have to be, according to the law.

[53] For more information about pumped storage at the Mt. Elbert Forebay, see USBR..

[54] The Ute Water Conservancy District in Grand Junction purchased 10,000 acre-feet, enough water for 75,000 new residents if they limit use to 120 gallons a day. The Colorado River District purchased 3,000 acre-feet, which some Western Slope residents believe is expanding their role as a water provider and compromising their role as a Western Slope water protector. The Basalt Water Conservancy District, Aspen, Garfield County, and other local entities purchased the remaining water. See, Colorado Basin roundtable minutes, October 22, 2012.

[55] “City of Aspen / Roaring Fork River,” Colorado Water Trust, downloaded Sep. 14, 2014.

[56] Gardner-Smith, B., “Silencing the Roaring Fork River,” July 27, 2011, Aspen Journalism, http://aspenjournalism.org/2011/07/27/silencing-the-roaring-fork-river/.

[57] Id.

[58] Comments from the Senate Bill 2014-115 hearing before the Arkansas Basin roundtable, August 21, 2014.

[59] Autobee, R., “History of the Colorado Big Thompson Project,” 1996, pg. 2, Bureau of Reclamation. https://www.usbr.gov/history/ProjectHistories/Colorado-Big-Thompson-Project.pdf

[60] Id, pg. 2.

[61] “Citizen’s Guide to Colorado’s Transbasin Diversions,” pg. 26. About 52,000 acre-feet pass through the Moffat Tunnel by Winter Park, 20,000 is diverted though the Grand Ditch to the north side of Poudre Pass, and 225,000 passes through the Alva B. Adams Tunnel in Grand Lake.

[62] Cassai, N., “Big Tom, Colorado’s Fruitful Giant,” Denver Post Empire, Dec. 1, 1968, pg. 60; Rocky Mountain News, Nov. 13, 1937, pg. 1,3.

[63] Hestmark, M., “Comments on Windy Gap Firming Project Final Environmental Impact Statement; CEQ # 20110413,” US EPA comment letter, Feb. 6, 2012.

[64] Id, pg. 17.

[65] Autobee, R., “History of the Colorado Big Thompson Project,” 1996, pg. 19, 22, Bureau of Reclamation.

[66] “Grand County Water History.” https://www.visitgrandcounty.com/places-to-go/history-museums/history-of-water/

[67] “Windy Gap Firming Project Recreation Resources Technical Report,” Figure 1, pg. 3, July 2008, US Bureau of Reclamation, http://www.co.grand.co.us/DocumentCenter/Home/View/1495.

[68] “The NCWCD covers 1.5 million acres of Colorado including almost all of Larimer, Boulder, and Weld Counties and portions of Morgan, Washington, Logan, and Sedgwick Counties,” Autobee, pg. 11..

[69] 1949 and 1990 population figures are from “History of the Colorado Big Thompson Project,” pg. 27. Population figures for 2008 through 2050 are from the South Platte Basin Implementation Plan, Table 2.1, pgs. 2-3, July 31, 2014.

[70] Northern Water, “Frequently Asked Questions about NISP,” downloaded 12-9-2024, https://www.northernwater.org/NISP/about/FAQs.

[71] “Description of the Colorado-Big Thompson Project, Bureau of Reclamation,

Summary of 2002 Operations,” pg. 5, http://www.usbr.gov/gp/aop/cbt/02cbt.pdf..

[72] Id, at Table 2, pg. 22; average Lake Dillon diversions are from “Citizen’s Guide to Colorado’s Transbasin Diversions,” pg. 9.

[73] Id, page10.

[74] Dillon Reservoir got within 6” of its crest according to Marc Wagge of Denver Water. See Berwyn, B., “Dillon Reservoir fills for the first time in four years,” June 21, 2005, Summit Daily News.

[75] CRS Section 37-45-118(1)(b)(II) provides that transmountain diversions from the Colorado River basin to the East Elope shall be subordinate to the Colorado River Compact and existing uses of water on the Western Slope. In addition, “Any [diversion] works or facilities shall be … operated in such manner that the present appropriations [and] prospective uses of water … from which water is exported will not be impaired.” The Western Slope says the italicized text protects and permits it to develop future supplies of Colorado River water for Western Slope population growth. This statute also permits Western Slope irrigators to sell their “present appropriations” to the Front Range.

[76] This map and the accompanying table are from Winchester, J., PE, “A Historical View: Transmountain Diversion Development in Colorado,” 2000, pgs. 480-481, Hydrosphere Resource Consultants. Inc.

 [BG1]Update

 [KR2]Done. Not easy.