Flood repair comes to an end
More than two years after the devastating 1997 New Year’s Flood, repairs on the Carson River are finally coming to an end.
Mark Twyeffort, project engineer for the Natural Resources Conservation Service, who has been facilitating much of the work during the last two years, said the final large project – the Lutheran Bridge to Highway 88 stretch of the East Fork of the Carson River – is nearly complete.
“We’re getting ready to finish the job there,” he said. “I’d estimate we’re about 80 percent done. Probably within the next three weeks they’ll have the major construction finished.”
Construction on the project has been in progress off and on since January, with heavy equipment unable to work during bad weather or high water, according to Dan Kaffer, NRCS western area coordinator.
“We’re progressing, and just hoping to get it done before the spring runoff,” Kaffer said.
Twyeffort said this final major river project has been one of the most difficult to coordinate.
“In terms of trying to accomplish a lot of different objectives, this has been a positive project,” he said. “We had to consider many factors, such as irrigation ditches, infrastructure, channel capacity, and we had about 10 to 12 landowners on that stretch of the river and they all had different interests and concerns.”
n Applying new technology. Utilizing some of the newer engineering technologies, Twyeffort said many people may be looking at the end results and wondering if it will “hold water.”
“We had technical input from several individuals and designers on the curves in that stretch of the river,” he said. “The end design incorporated some new geomorphological principals and bioengineering components.”
While the directives on the river project were never to provide flood control to a 100-year-flood, Twyeffort said three basic elements coordinate to make the river flow where the engineers want, Twyeffort said.
“First, we make a low flow channel, making the bed better able to carry the flows and enhance sediment transport,” he said.
The second engineering feature, relatively new in its implementation in the Carson Valley, is the installation of “stream barbs,” or fingers of rock and dirt that jut out from the outside curves, providing boundaries to control the undesired “lateral migration,” Twyeffort explained.
As the river turns, these barbs catch water, funneling it into the chambers inbetween and the sediment drops to the bottom of the chamber.
This way, property is less likely to be completely washed away downstream and instead of the river channel moving little by little toward the outside bend, it actually builds up, preventing the lateral movement.
“We’re always looking at the geometry, and trying to stabilize the lateral migration, though,” Twyeffort said. “Here, the river wants to move to the north, so we try to develop boundaries for the it based on land use and infrastructure factors.”
The third piece of the river repair puzzle is three-foot thick layer of riprap, or large rocks, placed on the river bank as protection for higher flows and to preserve the curvature from larger flows, he said. Areas with riprap also receive willow plantings, he said.
n Making it even better. These geomorphological features, combined with a variety of plantings, serve to “tell the river where to go,” Twyeffort said. Reseeding of native plants will take place this fall, when the time is more conducive to plant success, and some larger cottonwood trees will be planted sooner.
“The cottonwoods are planted in open spaces to provide more stability for the river and flood plane,” he said. “Plus, we want to establish a green corridor for wildlife. Once things settle down, we hope to see not only restoration, but enhancement, of the river before the damage.”
Rock structure placement is designed to complement fish habitat, providing future scour holes, he said, adding to the eventual improvement of the entire site.
n Cooperative funding. The Carson River repair projects have been largely funded – 75 percent – by federal sources in response to the 1997 flood, with the remaining 25 percent the responsibility of the sponsor, which in this case is Douglas County.
Of that 25 percent, the county sought several funding sources, and asked land owners on each project to assist by providing at least “in kind” contributions such as provide cuttings from their existing trees or whatever they’re capable of, according to Pam Jenkins, emergency management assistant.
“Many of these landowners have existing willows on their property, and we’ve asked them to provide slips for planting,” she said. “The landowners do have some responsibility, and most have been very gracious.”
Twyeffort said engineers and consultants wanted to coordinate the vegetation planting and river uses with landowners’ operations ranging from farming and ranching to small home properties.
“We needed a balance there,” he said. “Of the 10 to 12 landowners, their concerns are all different, plus we want to keep the river away from the town. These things all had to be worked into the overall plan.”
Twyeffort said each project he has been involved with has been different.
“We did do something similar to this in Dayton, but it had a different setting and concerns,” he said.
n Cost overrun. The initial winning bid (out of 13 contract bids) of $541,000 by Casazza Trucking Co., who did the repairs, did not include the additional material that had to be imported for the project due to the shortage on site, bringing the final cost for the project to $650,000, according to Maggie Libel, NRCS contract specialist.
“They initially estimated that there were 84,000 cubic yards of excavation material available on site, but when they got into the project, there was less,” she said. “The contractor provided the extra fill, which accounts for the higher cost.”
Libel said a total of 20,000 tons of rock was used on the project. She and Twyeffort, who both work out of the Reno NRCS office, said the completion of this last large river repair will signal an end to what has been a challenge on many levels.
“This was a complicated project,” Libel said. “We’ll celebrate when this one is over.”