A new Roaring Fork guide: It’s for flooding, not fishing
To build or not to build? Local governments now have a new tool to help assess development in areas that might be affected by flooding of the Roaring Fork River.
The Roaring Fork and Fryingpan Rivers Multi-Objective Planning Project is a report on river instability and other potential problems. The need for such a study was recognized after flooding in 1995. The work was completed in last month.
The report was distributed to local governments this summer. It can be used by planners and developers to decide whether building is advisable in certain areas, and whether artificial stabilization measures are needed.
Funding for the study was appropriated by the Colorado State Legislature, as a result of a bill sponsored by Rep. Jack Taylor of Steamboat Springs.
Consultant Mark Fuller, who coordinated the creation of the study for the Colorado Water Conservation Board, said the report was a huge project.
“It’s the most encyclopedic compendium of information that exists on the Roaring Fork,” Fuller said. “We found ourselves with vast amounts of data that we tried to organize in a way that’s useful.”
A river is dynamic by nature, forever shifting around within its floodplain. But as development occurs in the lower Roaring Fork Valley, the river’s movements become more and more of an issue, Fuller said, because every time development is proposed, the possibility of flooding must be considered. It wasn’t an issue in the past because only agricultural lands were affected.
Because funding for the project was quite limited, Fuller said, the group couldn’t do a lot of original research. So data was gathered from such sources as the Federal Emergency Management Agency, the Army Corps of Engineers and local county governments. Anecdotal information was also gathered from local rafting and fly fishing guides.
Much of the information contained in the report is in the form of maps of sections of the river, showing the 100-year floodplain and areas where the river channel has been unstable. One technique used in preparing the report was to compare older aerial photos of sections of the river with newer ones, observing changes in the stream bed to locate areas of chronic instability. The report will be available on CD-ROM, allowing viewing and manipulation of the maps on a computer monitor.
Keeping development out of the river’s floodplain is the best way to avoid losses. “That’s first on the list of all the recommendations here,” Fuller said.
But besides identifying areas where river instability might pose a danger, the report provides what Fuller called a “menu” of stabilization techniques for areas where roads or other infrastructure must be in the floodplain.
The most effective stabilization structures for stretches where the river is on a fairly steep gradient, Fuller said, are built by placing boulders in the stream bed to modify the flow. One kind of stabilization structure extends out and upstream from the bank in an arc, just below the surface of the water, keeping the bank from being torn away at a bend in the river.
Another type, called a drop structure, extends completely across the stream, and is intended to bring the majority of the current to the middle of the stream. This type is used to protect structures such as bridge pilings. An example can be seen just upstream of the new Midland Avenue bridge in Basalt.
The major trouble spots for instability, Fuller said, are mainly in the midvalley. One stretch that needs to be watched is from the Basalt Bypass bridge to the new Emma bridge. Another is from the Catherine bridge to Carbondale. The town of Basalt is doing a separate study on the river stretch that passes through town.
The study includes a chapter on how fish habitat and fish populations are affected by river stability; another addresses water quality. The latter notes the need to prevent materials from being washed into the river by storm water. It also addresses prevention of erosion events such as the flash flood on Seven Castles Creek last year that washed large amounts of red earth into the Fryingpan River.
Another chapter addresses the effects of trans-basin diversion, – the removal of water from the Fryingpan and Roaring Fork for use on the Front Range. Though Ruedi Dam slightly reduces the potential for flooding on the Roaring Fork, lower water levels can actually mean less healthy plant and animal life in the river, Fuller said.
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