@ColoradoClimate: Weekly Climate, Water and #Drought Assessment of the Intermountain West

Upper Colorado River Basin month to date precipitation through May 29, 2017 via the Colorado Climate Center.

Click here to read the current summary. Click here to go to the NIDIS website hosted by the Colorado Climate Center.

Asphalt core dam design for Chimney Hollow

This graphic, provided by Northern Water, depicts Chimney Hollow Reservoir, located southwest of Loveland, after it is built.

From The Loveland Reporter-Herald (Pamela Johnson):

When Chimney Hollow Reservoir is built, the dam will be one of the first in the United States with an asphalt core — a method developed in Germany in the 1960s and used widely in other countries.

The reservoir, located southwest of Loveland, will have one large and one small dam, allowing it to hold 90,000 acre-feet of water for 13 providers, including the city of Loveland.

The large dam will stand 350 feet tall — the largest built in Colorado in nearly 50 years and the tallest ever in Larimer County — and will span about 3,000 feet, or about half a mile…

The traditional type of dam used in the United States, including others in Larimer County such as Carter Lake and Horsetooth Reservoir, have an impermeable core of clay that is surrounded by rocks…

In the design of this project, engineers considered that option, but realized that there was not enough clay on site, so instead they chose an asphalt core, which is said to be safer and stronger, explained Joe Donnelly, assistant project manager with Northern Water.

An independent panel of experts reviewed the different options and agreed that was the best fit, noted Brian Werner, spokesman for Northern Water

Dams with asphalt cores are widespread in Europe, including in Norway, Austria and Germany, as well as in Canada, but there has not yet been one built in the United States.

A project in Arizona with an asphalt core dam is expected to start about the same time as Chimney Hollow, but because it is smaller (about half as tall), construction will not take as long, and it likely will be the first completed in the United States, Donnelly said.

Chimney Hollow’s two dams will become the second and third.

The largest dam at Chimney Hollow will be 1,000 feet wide at the bottom, tapering up to 30 feet wide at the top, Donnelly explained. The asphalt core, he said, will be 4 feet wide in the center of the dam.

Surrounding the core will be rock to provide the sturdiness and strength, 12 million cubic yards that will be mined on site from the land that, in about six years, will be covered with water.

#Runoff news: South Platte River running high

From The Sterling Journal-Advocate (Jeff Rice):

Higher-than-usual snowpack in the Colorado high country and a relatively wet May have irrigation reservoirs filled to the brim and ditch companies running full blast. The conditions also illustrate the need for more water storage in the South Platte River basin.

The Colorado Division of Water Resources’ May report won’t be out for another day or so, but the April report already showed reservoirs nearly brimming. A month ago the North Sterling Reservoir was at 95 percent capacity and Prewitt was at 86 percent. Jim Yahn, manager of the North Sterling Irrigation District and Prewitt Reservoir, said Tuesday both reservoirs are full…

According to the SNOTEL report, the May 30 reading showed that the snowpack contained slightly more than 10 inches of water equivalent. The peak this year was in the first week in April with about 16 inches of water. The beginning of snowmelt season had brought that down to under 10 inches in early May before a late winter blast two weeks ago boosted the snowpack some.

While the news seems good for this year – rainfall in the upper basin areas, especially in the Denver metroplex, swelled the South Platte to a little more than 3,000 cubic feet per second, while snowmelt has maintained that level – it underscores the need for additional water storage in the basin.

Frank pointed out that the South Platte River Storage Survey is under way and researchers are looking for places to put more water when it’s available, as it is this year.

“Since 2009, almost every year, we would have been able to store some water,” Frank said.

But if the high-level solution is easy, the practical aspects make it a much more complicated issue. For one thing, although on-stream storage – that is a dam across the South Platte – isn’t out of the question, it’s probably not a near-term solution.

“If we could dam the river, we probably could store 300,000 acre feet of water a year in times like this,” Frank said. “But the permitting process, with the environmental impacts and the economic considerations, are much, much longer than off-stream storage.”

And the off-stream sites that could be gravity fed already have been or are being developed, he said. That leaves pumping water out of the river “uphill” to a basin for storage. And that, Frank said, opens up another set of questions.

“Right now you probably could pump 2,000 cubic feet per second out of the river, but how often would you use that size of a pump?” he asked. “Even if you just pumped 500 cubic feet per second, you could pump 1,000 acre feet a day. The North Sterling holds 75,000 acre feet, so it would take 75 days of pumping at that rate just to fill a reservoir the size of North Sterling. This water that’s going past us, it’s not going to last 75 days. We have maybe two or three weeks.”

What makes more sense, Frank said, would be a series of pumps filling a series of smaller basins. And there’s still the question of where to locate the reservoirs.

“It’s all about location, optimization, where the demand is … it gets really complicated,” he said.

The storage study is supposed to be completed in November and will look at a variety of storage methods and will suggest a handful of sites that could be developed.

@RepDLamborn’s help with @EPA Fountain Creek lawsuit not welcome by all

Fountain Creek erosion via The Pueblo Chieftain

From The Pueblo Chieftain (Peter Roper):

Pueblo County Commission Chairman Terry Hart said Lamborn has played no role in the years of negotiations between Colorado Springs and county officials over stormwater controls, adding: “He should stay the heck out of it.”

Lamborn, from Colorado Springs, told a Denver newspaper last week that he’s spoken to new EPA Director Scott Pruitt twice about dropping the agency’s 2016 lawsuit that claims the city isn’t adequately monitoring Fountain Creek for contaminated stormwater runoff…

Lamborn argues that recent agreements between Colorado Springs and Pueblo County calling for $460 million in stormwater improvements is proof the lawsuit is unnecessary.

Hart countered that Lamborn is ignoring the importance of the lawsuit in forging a better relationship between Pueblo County and Colorado Springs Mayor John Suthers and that city’s council.

Hart said Suthers’ support for spending $460 million over 20 years is a fragile commitment between Pueblo County and the current leadership in Colorado Springs.

“The threat of that lawsuit was critically important in our reaching an intergovernmental agreement with Colorado Springs,” Hart said Tuesday. “We joined that lawsuit to protect our interests and right now, Colorado Springs is doing a good job of honoring its commitment. But the lawsuit would nail down the agreement to withstand the political winds that blow back and forth.”

The Colorado Department of Public Health and Environment also is a party to the lawsuit, as is Pueblo County.

State health officials confirmed Tuesday they joined the suit because of very real concerns that Colorado Springs continues to violate water quality standards.

“We believe that these significant violations need to be corrected in order to protect the state’s water quality,” the department said in a statement.

If Lamborn is hoping to use political clout to stop the lawsuit, Pueblo County officials are looking for help in the nation’s capital, too.

Hart said the county sent letters of concern in April to Rep. Scott Tipton, R-Colo., and the state’s two senators, Democrat Michael Bennet and Republican Cory Gardner.

Hart said the issue then was urging continued congressional support for EPA enforcement.