CDOT takes precautions against Basalt flooding
February 25, 2008
Basalt ” The Colorado Department of Transportation is taking precautions to prevent flooding in Basalt in case the Roaring Fork River runs high this spring.
CDOT wants to remove an estimated 1,500 cubic yards of sand and cobble stones that have accumulated upstream from the Upper Basalt Bypass Bridge on Highway 82 in the last 20 years, Pete Mertes, resident engineer in Glenwood Springs said Friday. That is roughly the equivalent of 150 loads in dual-axle dump trucks.
The project is being undertaken “mainly to be prepared in case of high runoff,” Mertes said.
CDOT has applied with the U.S. Army Corp. of Engineers for a permit to undertake the work. CDOT wants to begin in middle to late March, Mertes said.
“They need to get it done, of course, before runoff,” said CDOT spokeswoman Nancy Shanks.
The Roaring Fork Valley, like many areas in the Colorado mountains, have received record or near-record snowfall this winter. The snowpack at the headquarters of the Roaring Fork River east of Aspen was 43 percent above average as of Friday afternoon, according to data from the U.S. Natural Resources Conservation Service.
Expectations are for higher than average runoff, although dry and warm weather in March could alter the picture.
“We’re telling people it’s too early to tell,” said Tim O’Keefe, education director for the Roaring Fork Conservancy, which tracks river issues. Typically, March bring heavy snowfall, he noted, but the month has been a dud in some recent years. Warm and dry weather could reduce the snowpack to average or below by April 1, the date typically used to forecast runoff levels.
Basalt experienced minor flooding in 1995, the last year with this high of snowpack. The foundation of Two Rivers Road on its eastern approach to town has been eaten away by the river, and a high water table swamped the Roaring Fork Mobile Home Park and Pan and Fork Mobile Home Park.
Basalt Mayor Leroy Duroux credited the transportation department for taking action in what could be a high runoff year.
“We appreciate CDOT paying attention to the problem,” he said. “It’s probably something that should be looked at every year.
Duroux said the removal of the sand and rock will ease a damming effect at the bridge that could push flood water into the Southside development.
Mertes said sand and rock has accumulated for years upstream of the upper bypass bridge. It is a process known as bed loading. To his knowledge, no dredging previously has been undertaken.
The bed loading constricts the river channel. The dredging will open up the channel and create a wider path for the water to travel. That reduces the risk of debris, like tree trunks, getting caught on the bridge girders.
Some sand and rock will be removed from under the bridge, and a small amount likely will be dredged from downstream of it, Mertes said. A track hoe and possibly a small bulldozer will be needed in the river, and a small access road will be built down to the riverbank.
CDOT still is trying to figure out what to do with 150 truckloads of material. “We’re trying to find a home for it,” Mertes said.
The bridge’s role in Basalt’s flooding potential has raised questions in the past. The bridge was built in the late 1980s when Highway 82 was routed outside of downtown Basalt.
In 2000, a consultant hired by the town said the bridge, which has two piers in the river, speeds the accumulation of bed loading. Rick McLaughlin of McLaughlin Water Engineers in Denver warned the Basalt Town Council eight years ago this month that the bridge and other factors made the river’s behavior during flooding unpredictable through a 2.7-mile stretch through Basalt.