Post-Flood Restoration Creates a More Resilient Big Thompson River
Clean-up and repairs along the Big Thompson River west of Loveland, Colo., have been ongoing since torrential floods from heavy rains in fall 2013 caused widespread damage to property and landscapes.
Nine deaths were attributed to the flooding, which necessitated a massive air evacuation by Colorado National Guard troops. State officials estimated that nearly 2,000 homes were damaged, bridges washed away and riparian areas destroyed, resulting in an estimated $2 billion in damages.
Soon after the event, a group of property owners, local government officials and recreational users working with the Natural Resources Conservation Service and the Colorado Water Conservation Board formed the Big Thompson Watershed Coalition (BTWC).
The nonprofit raised money and coordinated projects aimed at the long-term sustainability of the area that stretches roughly from the Olympus Dam outside Estes Park to the Big Thompson’s confluence with the South Platte River.
Soon after the flooding, work got underway to stabilize the foundations of riverside homes and cabins, as well as repair compromised sections of Highway 34, which runs adjacent to the Big Thompson. But plans for longer-term restoration efforts have taken more time to develop and fund, according to Shayna Jones, watershed coordinator for the BTWC.
“In 2015 the coalition spearheaded a Big Thompson River Restoration Master Plan,” Jones says. “The master plan looked at several criteria, post-flood, and developed rankings for different areas, including flood risk, geomorphic instability risk, potential for riparian habitat improvement and the potential for aquatic habitat improvement.”
Two areas with highest priority in the master plan were the Cedar Cove and Jasper Lake reaches of the river. The engineering firm Stantec, working from its office in Fort Collins, was retained to develop conceptual designs for nearly six miles of the river, including the Cedar Cove and Jasper Lake sections.
Restoration of a nearly 2,700-ft stretch of the Big Thompson known as Jasper Lake got underway in early spring, before heavy flows from runoff started.
Randy Walsh, project manager and restoration ecologist for Stantec, says the Jasper Lake and Cedar Cove areas sustained extensive damage, partly due to their geography.
“These were areas where the river comes out of a canyon, and it has picked up energy and sediment. This is where the canyon opens up, and there is a lower gradient, and you get a lot of material dumped and lots of erosion,” says Walsh.
“The emergency repairs basically put the river back in its channel, but in a trench with steep sides. Part of our design was to reconnect it with the floodplain. Our goal was to restore proper channel geometry as well as improve the hydrologic and biologic function of the river system,” he says.
“We want to restore the function of the river and, to the greatest degree possible, create a system that is more sustainable and will have greater resilience in future flood events,” he adds.
RMC Consultants of Wheat Ridge worked on the $800,000 project using a small, specialized team that included geologists and biologists, says Claude Murray, senior project manager for the firm.
“Part of the work was to give the channel more capacity and create a more natural, meandering shape and get more of the natural elements back in place,” says Murray.
Jones notes that the team also worked with the Colorado Dept. of Transportation to use material from road restructuring projects in the canyon. “CDOT was generating material we were able to utilize. Some of the larger rocks we needed came from work they were doing along Highway 34,” Jones says.
Murray says the team also used native materials to help stabilize the riverbanks and create a better wildlife habitat. “We used trees with root balls that had been washed downstream in the flood and brought them back to the site and buried them in in the banks,” he says. “They provide a natural bank stabilization and add complexity.”
In addition to the reclaimed trees, Murray says his team placed nearly 3,000 “willow stakes” (willow tree starts) along the edge of the river channel.
“The stakes were cut from other trees in the area. They are about five ft long, and when you bury them in the banks, in a few months they will start to root again and sprout,” he adds.
Murray says his team brought in nearly 820 cu yd of topsoil to cover areas on either side of the river where floods had carried it away.
“We worked that and fertilizer into about eight inches of existing soil,” he says.
“There were areas where we put down a fast-growing, riparian material and a mix of seeds on a biodegradable core-mat. We put in pine-tree starts and choke cherries and other native plants. It was all covered with a wood-strand mulch to hold the moisture and protect the seeds,” Murray says.
Walsh says material was placed in the river channel to create ripple structures, “J-hooks” and deeper pools for fish habitat.
“It was all done with native materials that came from the area,” he says.
His team completed the work and had their equipment out of the river before water levels began to rise with the spring runoff in May.
“During the runoff, things stayed stabilized. We went back a few times during the summer, and things were starting to grow,” he says. “We’ll be going back in the fall with more seeds and about 1,000 more plants and get those in place.”
Walsh says that a similar but larger project involving channel realignment and replanting of riparian areas began farther west from Jasper Lake in the Cedar Cove area. That restoration, budgeted for $2 million, started in July. The project will continue into late fall.
Walsh notes that working with a variety of stakeholders was one of the more complex aspects of the project. “There are people who live along the river or who have vacation homes there that have been in the same family for generations. There are people that fish the river and people concerned with the watershed,” he says.
“They are very engaged and very concerned and want the resource restored because it is so important to them. They are really the caretakers of the river. It has been an extremely valuable experience for us. I think the Jasper Lake section has been a success, not only from a technical standpoint, but from a social engagement aspect as well.”
Before the Jasper Lake and Cedar Cove projects, Jones says the coalition completed two restoration projects farther east in the Sylvan Dale area and near the Loveland Water Treatment Plant, with 12 more in planning phases.