Study identifies plenty of potential for flood damage | AspenTimes.com

Study identifies plenty of potential for flood damage

Donna Daniels

Flooding on the Roaring Fork River could damage buildings, utilities and bridges up and down the valley, and wash out several sewage treatment facilities, as well, according to a recently completed study.

In Aspen, the Aspen Consolidated Sanitation District facility, Slaughterhouse Bridge, Aspen Art Museum and other facilities are at risk, according to the Roaring Fork and Fryingpan River Multiobjective Planning Project. The study of flood potential on the Roaring Fork and Fryingpan rivers was commissioned last year by the Colorado Water Conservation Board and funded by a $100,000 legislative appropriation engineered by Rep. Jack Taylor.

What alerted the conservation board to the need for such a study was a major flood in 1995 that washed part of Highway 82 into the Roaring Fork River near Basalt and caused extensive damage to the riverbank in that area.

The aim of the study was to evaluate areas of potential flood hazard and streambank instability along the length of the river between Aspen and Glenwood Springs, where the Roaring Fork joins the Colorado. It also recommends preventative measures to avoid the very disasters it identifies.

At risk from flooding in the upper valley, according to the study, are the Lazy Glen Trailer Park and sewer lagoons, Highway 82 from the upper Basalt bypass to Aspen Village, the Aspen Consolidated Sanitation District facility, the Slaughterhouse Bridge, the Rio Grande Trail between the Slaughterhouse and Mill Street bridges, the Aspen Art Museum, Herron Park, Rio Grande Park, and residences both upstream and downstream of the Highway 82 bridge in Aspen.

In Eagle County and the town of Basalt, Willits Lane between Aspen Junction and Hooks Bridge is at risk. Two Rivers Road, the Basalt Sanitation District wastewater treatment plant, the Emma Bridge, the Basalt Trailer Park and the upper Basalt bypass bridge all are at risk for damage from a major flood event, the study concludes.

In Carbondale, perhaps the gravest risk lies with the town’s backup water source from wells along the Roaring Fork River. Utilities and headgates along the river would be threatened, as well.

In Garfield County, utilities crossing the river are at risk, as is the Ranch at Roaring Fork subdivision east of Carbondale and its wastewater plant, the Catherine Store Bridge and major headgates to irrigation ditches along the river.

In the city of Glenwood Springs, flooding threatens one wastewater plant, the riverside trail that follows the river through the city, a raw water line that feeds into the city’s water system, the trailer park next to Veltus Park and the Seventh Avenue Bridge.

Protection possible

Channel stabilization and restoration can help protect both the riparian vegetation and man-made structures along the river.

“The key is to work with and accelerate a river’s natural tendency to achieve equilibrium and regain balance with new conditions,” the report noted. To that end, consultants BRW, a Denver engineering firm that conducted the study and prepared the report, recommend a number of mitigation measures.

Everything from low-impact revegetation to use of flood-control devices such as gabions and other concrete and rock structures could prevent flood destruction.

“Hard controls on the river should only be used when necessary to protect critical infrastructure, and hard controls should be in compliance with a regional plan to avoid pushing problems onto adjacent properties,” the report said.

Areas of channel instability – due to the natural dynamics of the river or human activity – lead to an increased danger of flood damage. The report identifies areas along the Roaring Fork River where unstable streambanks need to be monitored.

In order of priority, these include: the upper Basalt bypass bridge where extensive flood damage occurred in 1995, the Emma Bridge, the new Midland Avenue Bridge in Basalt, the Roaring Fork Club in Basalt, the Ranch at Roaring Fork, the Seventh Avenue Bridge in Glenwood Springs, Hooks Bridge in Basalt, Wingo Bridge above Basalt, Slaughterhouse Bridge in Aspen, the North Star Preserve east of Aspen, and the Westbank Bridge south of Glenwood Springs.

Such monitoring can document trends of stream cutting which could impact bridge structures in the future, according to the report.

Preservation priorities

As part of the study the consultants also identified ecologically sensitive areas worthy and in need of preservation. Among them are the upper Roaring Fork River, a 15-mile stretch from its headwaters to Aspen that includes alpine, subalpine and montane riparian vegetation systems which support a rich variety of bird species.

“The upper Roaring Fork River site supports not only significant biodiversity, but also is the longest stretch of relatively pristine riparian vegetation observed on the river,” the report notes.

Also recommended for conservation are the headwaters of Maroon and Castle creeks – about 1,000 acres of riparian vegetation communities with species of globally and state-rare plants in degraded condition.

Near El Jebel, the consultants have recommended preserving land at the Ranch at Roaring Fork. “This is one of the most intact sites and widest stretch of riparian vegetation along the lower elevations of the Roaring Fork River,” the report said. It contains the rare yellow ladies slipper orchid, and a rookery of great blue herons.

At the site of the proposed Sanders Ranch residential and commercial development, riparian communities and sightings of Colorado cutthroat trout and mountain whitefish make it worthy of conservation, the report concluded.

While there are numerous federal and state regulations in place that govern impacts to waterways and streambanks, local municipalities may need to set stronger standards to protect the river, according to the report.


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