Intense runoff from spring snow and rain overtopped a new dam at the Colorado River bypass project at Windy Gap Reservoir in Grand County, causing damage that can’t be fully assessed until waters recede this summer.
Contractors had not finished placing riprap on the south side of the dam’s berm, though the work had been completed on the north side, according to Northern Water, the project manager. Runoff in the Colorado River leading up to Windy Gap nearly tripled over three days in early May, to 2,200 cubic feet per second, said Northern Water spokesperson Jeff Stahla.
“That was certainly more than we anticipated,” Stahla said. “We knew that we were up for a strong runoff this year.” Area water officials estimate nearby Lake Granby will fill in the coming days and need to employ the dam spillway, Stahla said, as another example of high runoff in Grand County.
“We knew that that was coming, and it still surprised us just with how quick it got there,” he said.
The damage will increase the cost of the multimillion-dollar project, but should not delay its “substantial completion” in 2024, Northern Water said. It’s not yet clear, Stahla said, whether partners will have to put more money into construction as a result of the flooding.
“The project included a contingency fund that will be accessed for any additional work,” Stahla said. “If project work goes above the contingency, we will meet with stakeholders to discuss next steps.”
State dam inspection officials said they did not have safety concerns about Wind Gap Reservoir’s existing dam or the new structures, and they have been in touch with Northern Water about the flooding.
Longtime critics of multiple diversion dams on the Colorado River below its headwaters in the mountains north of Granby said the Windy Gap damage was predictable, and could be repeated.
“One of my big concerns is that with climate impacts, there wouldn’t be enough water in the bypass to keep the fish alive. Similarly, climate impacts may cause more severe flooding which could wipe out the bypass,” said Gary Wockner of the nonprofit Save the Colorado. His nonprofit and other groups settled a case against Windy Gap and gave the proceeds to the Grand Foundation for river mitigation in the area.
“Rivers are alive — perhaps more so now than ever in a climate-changed world — and they do what they want,” Wockner said.
The enormous increase in channel flow would have made it hard to avoid construction damage, Northern Water said.
“Windy Gap Reservoir is tiny — 445 acre-feet — it’s not a storage reservoir but a place where water can be backed up for pumping,” Stahla said. “A flow of 2,000 cubic feet per second will mean 4,000 acre-feet goes by in 24 hours — 10 times the capacity of the reservoir. We are hopeful that as the water recedes it will show that damage was limited to the small area in the photo.”
There will be some additional cost to repair the berm, which will be covered under the contingencies built into the construction budget.
Wildlife advocates who negotiated the reservoir bypass for the river in recent years said they are not overly concerned with the flood damage. That includes questions from anglers about reservoir problems with whirling disease, which has devastated some Colorado trout populations, and whether the flooding might have pushed whirling disease downstream on the Colorado River.
“Windy Gap spills every year, so we’re not sure that things are that different this year,” said Mely Whiting, legal counsel for Trout Unlimited, one of the partners in the bypass agreement. Contractors tested the entire area for worms that carry the disease and “removed soils where detected, placing them higher up, out of the flood plain,” Whiting said.
The flooding “did not impact the downstream fishery,” said Travis Duncan, a spokesperson for the Colorado Parks and Wildlife division. “There aren’t concerns with high flows or an active breach causing whirling disease issues downstream of Windy Gap. Overall, this year’s high flows in the river will flush out fine sediments which will reduce whirling disease habitat in the river,” Duncan said.
The partners have been reassured about the project schedule after the flooding, Whiting said.
“To work on the berm, the site has to be pumped and that won’t happen until flows recede a bit,” she said. “I think contractors are looking at an end of July time frame right now, which gives us a short construction season. Still, I’m told we expect the berm to be fixed, the concrete wall within the berm built, and riprap installed this year,” she wrote, in an email.
“In the meanwhile, the contractors are building the lower portion of the connectivity channel itself,” Whiting said.
The wildlife advocates also try to keep the flooding in perspective.
“These high flows have certainly been a challenge, but they are oh so good for the river!” Whiting said.
The $27 million project to rebuild a Colorado River channel around Windy Gap is meant to correct damage to fisheries and other wildlife caused by the reservoir slowing the river and warming up the water past safe levels. Stopping the flow also allowed disease-tainted sludge to build up. After years of negotiations among Northern Water and multiple nonprofit groups and private and corporate donors, a host of dignitaries launched construction last summer.