Attempting to separate Chatfield Reservoir and Chatfield State Park is a bit like splitting conjoined twins. There is significant risk, potential reward and inevitable growing pain. Yet that’s essentially what the proposed Chatfield Reservoir Storage Reallocation does. The plan to double water storage in the reservoir from its current recreational pool size will significantly alter the identity of the popular park that relies upon it.
The comment period on the project’s Final Environmental Impact Study closed at the beginning of September, and if the recommended alternative for reallocation is approved, neither Chatfield will ever be the same.
“It’s going to change the way the park operates if it goes through,” Chatfield State Park manager Scott Roush said. “The way we operate now, we know the water that Denver has is going to be there when we fill the reservoir back up in the spring. With this new plan, the reservoir is expected to fill up maybe three out of every 10 years. That makes it hard on the recreational side.”
Constructed on the South Platte just south of Denver in 1975, Chatfield Reservoir was built for both flood control and recreation. The 1,423-acre reservoir and encompassing 3,768 acres of land are owned by the U.S. Army Corps of Engineers and leased to Colorado Parks and Wildlife in 25-year cycles currently running through 2028. The park originally opened in 1979, the same year the state arranged an agreement with Denver Water granting storage rights in the reservoir with the understanding that, in general, it would be operated to allow for 20,000 acre-feet of storage (5,427-foot elevation) every summer for recreational purposes. From Memorial Day to Labor Day, Chatfield typically fluctuates no more than 5 feet. According to Roush, 2013 marked the first summer since 1979 that the pool dipped below the baseline elevation of 5,423 feet.
“That’s a pretty good track record,” Roush said. “We’re trying to maintain the water in the reservoir at a reasonable level for recreation like we’ve been able to do in the past. Visitors that come to Chatfield, that’s what they’re used to.”
Consensus holds that will no longer be the case should the reallocation proposal preferred by the Corps of Engineers be approved by federal and state officials as soon as January 2014. That plan to allow up to 20,600 additional acre-feet of storage for a conglomeration of municipal, industrial and agricultural water providers would raise the reservoir 12 vertical feet.
But the Corps’ own analysis recognizes that the junior water rights of the reallocation mean filling the pool to the new operating elevation of 5,444 feet will be inconsistent at best. And the absence of an operating agreement akin to the 1979 contract leaves park managers to deal with potentially frequent water fluctuations of 17 feet or more, affecting recreational users in a number of ways.
Filling the reservoir to the new level will flood 587 additional acres. Roads, parking lots, beaches, bike paths, trails, boat ramps, picnic shelters, fishing ponds and dog parks will be inundated. Restrooms and other buildings will be relocated to more than 600 horizontal feet above the low water line. Many relocated facilities will be constructed within the 10-year floodplain in order to provide reasonable access to the reservoir.
In a recent report to the state Parks and Wildlife Commission, Roush cited an increase in boating hazards along the reservoir’s shallow southern edge, shoreline mudflats exposed in dry years, loss of existing wetlands and new weed proliferation because of more frequent and greater water level fluctuations. Increased bank erosion is anticipated along with the loss of 0.7 upstream miles of the South Platte and wildlife habitat as up to 285 acres of trees will be removed.
Increased water fluctuation may disrupt spawning and recruitment of the lake’s wild smallmouth bass, CPW senior aquatic biologist Ken Kehmeier said. Similarly vacillating water levels are associated with elevated mercury levels in walleye at other reservoirs. Kehmeier says the proposal is likely to result in an additional 70 “zero flow” days per year in the South Platte below the Chatfield dam.
“We’ve been in discussion with the participants for the last year to try to put together a plan that would, if not mitigate, then minimize impacts. The toughest ones, obviously, have been park infrastructure and taking care of the park itself. And then the downstream issues,” Kehmeier said. “Because they’re such junior rights, there’s going to be a lot of years that they’re not going to have any water to release.”
Officials estimate a three-year construction period to restore services and implement proposed environmental mitigation in the park that annually attracts more than 1.5 million visitors and generates $2.2 million for the economically strapped state park division.
Not everyone believes the park’s current natural aesthetic can be re-established, however. “The quality of the recreational experience will be vastly different,” said Gene Reetz, a retired EPA employee and volunteer with SaveChatfield.org. “A lot of people think it will be just like it is now, only with higher water level. But most of the time it won’t be like that. It would be pretty devastating, not just to recreation, but to wildlife as well.”
Project proponents such as Rick McCloud with Centennial Water and Sanitation District maintain that even a changed Chatfield will remain a superb recreation and wildlife area. Others are skeptical. “I’m concerned as a manager about how successful the mitigation will be,” Roush said. “Is it going to be successful enough to maintain what you have today?”