Fountain Creek: Detention ponds can accomplish nearly as much as a flood control dam, according to USGS

Detention pond

From The Pueblo Chieftain (Chris Woodka):

A series of detention ponds south of Colorado Springs to Pueblo could do nearly as much to reduce the impacts of a severe flood on Fountain Creek as one large dam. That’s the preliminary finding of a three-year study by the U.S. Geological Survey which will be completed later this year. The results were shared last week by David Mau, head of the Pueblo USGS office. “The report does not address water rights, transit loss or funding issues, just the hydrol­ogy and hydraulics,” Mau cautioned the Fountain Creek Watershed district board Friday.

The most effective means of reducing the impacts of a big flood for everyone along the creek would be to construct 44 detention ponds — water holding areas behind 10-foot berms that would not fall under the state’s classification of dams — up and down the creek to the confluence with the Arkansas River. It would include ponds on Monument Creek, the Upper Fountain and major tributaries. Combined, they would retain about 30,350 acre-feet of water and reduce the peak flow of a 100year flood by 59 percent, while reducing sediment by 18 percent.

Ponds would require regular maintenance.

An 85-foot tall dam 10 miles north of the confluence would provide nearly the same protection, reducing peak flows by 56 percent. It would retain far more sediment, reducing it by 62 percent, Mau said. That creates its own problems, however. About 64,000 tons of sediment — 2,500 truckloads of sand — plus trees and other debris would need to be cleared after a 100-year flood. The dam would have a permanent pool of 25,700 acre-feet and capture 25,000 acre-feet of flood water, as modeled in the study. It would also require moving railroad tracks and gas pipelines in Fountain Creek, as well as building a levee to protect Interstate 25.

Ultimately, the reservoir would help Pueblo, but would do little to protect El Paso County communities from flooding. It would cost hundreds of million dollars. Cost estimates have not been done in more than 40 years. Another option, however, would protect Pueblo almost as well, again with little benefit to El Paso County.

It would involve building just 10 detention ponds from Jimmy Camp Creek to Pueblo, and would have the potential of cutting the peak flows by 47 percent. The ponds would also trap less sediment, presumably requiring less maintenance and generating fewer complaints from downstream farmers who rely on flows of sediment. The ponds would have the effect of reducing a 1965-type flood to a less-damaging 1999-type flood. “When we get the $50 million from Colorado Springs, it may be a quicker fix,” said Richard Skorman, a Colorado Springs businessman and former councilman who is a member of the El Paso County stormwater task force. Skorman speculated that it would allow more time for the northern communities to solve internal stormwater problems while giving Pueblo and the Lower Arkansas Valley more peace of mind.

The detention areas could cost up to $1 million each, based on the demonstration project already in place on Pueblo’s North Side. But land acquisition costs could be higher, since the city of Pueblo already owned the land in the pilot project.

ABOUT THE STUDY

A study of dam sites on Fountain Creek by the U.S. Geological Survey won’t be finalized until later this year.

The $570,000 study included $300,000 funding from Colorado Springs as part of Pueblo County’s 1041 permit conditions for the Southern Delivery System.

It looked at 14 scenarios ranging from a few detention ponds on Monument Creek to a big dam on Fountain Creek itself.

Engineers used available records to assess how much the peak flow and sedimentation would be reduced as a result of projects at varying points along Fountain Creek.

Meanwhile the board is holding firm on their authority to review the Southern Delivery System’s potential impacts to Fountain Creek streamflow and water quality. Here’s a report from Chris Woodka writing for The Pueblo Chieftain:

The Southern Delivery System should still be subject to review by a district formed to protect Fountain Creek, the district’s board decided Friday. Colorado Springs Utilities plans to cross Fountain Creek with its pipeline under the SDS plan. The Fountain Creek district was given primary land-use authority in the flood plain between Fountain and Pueblo, but last month El Paso County claimed that authority for utility projects.

The board plans to tell El Paso County commissioners that the county’s newly adopted 1041 regulations do not supersede the authority of the Fountain Creek Watershed Flood Control and Greenway District under powers given to it by the state Legislature in 2009. A 1974 law, HB1041, allows counties to regulate projects with statewide impacts. “Why were we established?” board member Jane Rhodes asked in frustration.

“These tools on land use are tools we can use, and powers given to us by statutory right,” Pueblo County Commissioner Terry Hart said, adding that the nearly broke district cannot afford its own legal counsel to protect that power.

Other Fountain Creek board members agreed and directed Executive Director Larry Small to relay their concerns to El Paso County commissioners at an Aug. 6 meeting. Even Dennis Hisey, an El Paso County commissioner, was taken aback by his board’s stance. “I don’t see how it would take our right away from this board,” he said, adding that although he directed the action, he was not among those who drafted language in the 1041.

Hart said Pueblo County has interpreted its own 1041 regulations as a layer of authority, not an absolute power. “I think our position is that any design still has to be approved by the district,” Small said.

More Fountain Creek coverage here and here.

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