By T.R. Witcher
Dam conversions on Iowa rivers are replacing safety hazards with whitewater-style recreational amenities.
Low-head dams such as this one in Manchester, Iowa, are being phased out across the state due to safety concerns. Recreation Engineering and Planning
February 17, 2015—Dams have been part of the development of Iowa since the middle of the 19
century, first to help power grist, woolen, and saw mills, later to generate hydroelectric power. Many of Iowa's dams are low-head dams, which do not block a river's flow entirely—water and watercraft can still flow across them. In fact, a 2010 state inventory found that of 245 structures on major rivers, 177 were low-head dams.
But these simple-looking dams are deceptively unsafe. More than 160 people have died in dam-related incidents in Iowa since 1900. Forty-six lives have been lost just since 1990, including two since January. Victims have died during a variety of water activities, including swimming, fishing, tubing, kayaking, canoeing, and jet skiing.
In 2008, the Iowa Department of Natural Resources (DNR) established a low-head dam public hazard program to try to mitigate the dangers those kinds of dams pose. In 2010, the DNR released a dam mitigation plan that inventoried the dams and provided design templates for improving their safety.
The report found that the dam infrastructure is "failing rapidly," which can "cause downstream flooding and excessive sediment releases, and may elevate downstream turbidity for months or years." In the three years before the report was issued, there were at least 10 structural failures, a combination of aging dams, powerful storms, and flooding.
Fine-particle sediment can accumulate upstream, creating poor wildlife habitat and recreation conditions, while downstream a high degree of scour and sediment disequilibrium "create bank erosion and streambed downcutting," the report notes. Fish passage has been an issue, too, with some species unable to leap upstream.
John Wenck, the water trails coordinator for the DNR, responded in writing to questions posed by
online. "The initial drive to do something about dams in Iowa was the increasing number of drownings that were occurring at low-head dams," he noted. "With increasing river use, naturally there were increasing deaths. But when we began to understand the additional negative impacts of dams, such as impeding fish passage, contributing to the poor ecology of the river, decreasing the population of mussels, flooding, et cetera, it was apparent that a mitigation program was necessary."
A hydraulic jump, associated foam pile, and surfing wave can now be found within the Maquoketa River. Water levels will increase significantly during the spring and summer. Recreation Engineering and Planning
Still, safety has been the key driver. The danger comes when boats or other water craft slide over the tops of these low-head dams; it feels like going over a water slide, says Gary Lacy, the chief executive officer of Boulder-based Recreation Engineering and Planning (REP), whose company has designed several dam conversion projects in Iowa. "To the untrained eye, it looks like fun. They're not that loud. So you go over them and you get trapped at the base of the dam. They call them drowning machines. There's no current to push you out. You just rotate until you drown, at the base of the dam."
According to the Iowa Whitewater Coalitio's website, "when water flows over the top of a dam and hits the water below, it creates a backwash or boil that re-circulates surface water back against the dam." Anything floating in that zone gets trapped and churned around. "A life vest will not help you and even the strongest swimmers will drown in these currents. Typical low-head dams also have concrete side walls that prevent escape at the sides of the dam."
Now communities across Iowa are in the midst of replacing these antiquated dams with recreational amenities that make the rivers safer and more attractive. "Dealing with the safety issue is opening up all these other opportunities for recreational use," says Teva Dawson, a senior planner with the Des Moines Area Metropolitan Planning Organization. "There are some communities that are seeing a huge interest from a tourist perspective. There's a cascading benefit in terms of economic development, and not just recreation."
According to the state's Department of Natural Resources, eight dam mitigation projects have been completed, and 20 more are on the way. Some have resulted in recreational amenities though others have not. In the last two years the state has awarded $500,000 in grants to help communities replace their dams.
Charles City’s redevelopment of the Cedar River includes several types of drops to match users’ experience levels. Recreation Engineering and Planning
One major project under way now is in Manchester, a small community of just fewer than 6,000 in eastern Iowa, located between Dubuque, Waterloo, and Cedar Rapids. Planners began brainstorming ways to improve the community in 2008 and examined the Maquoketa River, which runs through the center of town. Inspired by Charles City, another community that was planning to replace its own dam with a whitewater park, Manchester leaders turned toward the river itself and opted to do the same.
The conversion involves taking down most of the 182 ft wide dam that spans the Maquoketa—at between 2/3 and ¾ of its height—and building three new drops upstream as well as two drops downstream, for a total of six structures. Combined with beautification efforts at the riverbanks, the dam conversion will create a whitewater park about 900 ft long.
Lacy's company has already completed a significant dam modification project Charles City. He says that each dam project is unique—solutions depend on the size of the river, its flow rate, and the type of dam, as well as on the size of the hydraulic drop. But there are a number of similarities in dam modification projects.
Dams, of course, are straight lines—which helps create the uniform hydraulics at the base of dams that you can't get free of. Part of the solution to make the dams safer is to break the hydraulic drop of a larger low-head dam into smaller pieces: essentially one dam becomes a series of smaller dams, perhaps a few upstream and few downstream. Each of the drops is a maximum of say 2 ft, although 14 to 18 in. is more ideal.
But people can still drown at the base of a drop of less than 2 ft. So the next step is to curve the dam into an arch shape and constrict it toward the center. In cross section, the dam dishes—water is deeper in the center and shallower at edges—which also forces movement to the center. "Even if you want to swim and stay in you're going to get pushed out," Lacy explains.
From there, REP creates whitewater features that allow people to use the river more safely. "Some are waves, some are holes, some are foam piles," he says. (The latter are recirculating currents that form as a result of a hydraulic jump. The turbulence of the water creates an illusion of foam.) "You get in with a canoe, freestyle kayak, or stand-up board, and you can surf for hours on it. It's incredibly popular. People love doing it."
It looks dangerous, Lacy says, but the second people fall in, the geometry of the modified dams pushes them clear of the dams' base. "Everything is a jet of water that pushes a body or boat away from construction," he explains. People are "never trapped, they're always pushed out to a recovery pool."
The drops are configured to create attractive whitewater features. Pools between drops are made with natural stone instead of concrete. Curves rather than straight lines are the norm. The idea is to make these new river structures not only safe, but as natural-looking natural as possible.
The design of the whitewater features depends on a variety of factors: the dam dimensions, size of the river, width of the opening and exit, the slope, and the face of the drop. "You just juggle with all those parameters," Lacy says. "It's not an exact science."
To allay the concerns of local fishermen, Manchester city manager Tim Bick says that each of the five dams will have a 5 ft wide passage for fish, alongside the 20 ft wide whitewater drops. Construction began in November 2014 and is scheduled to be complete the first of June. The $1.8-million project was funded by a combination of grants, city funds, and private donations.
The state capital, Des Moines, may be getting in on the act as well. Des Moines is beginning a process of developing a regional water trails plan, which will include discussion of two "highly dangerous" dams, as Dawson puts, in the heart of downtown. The first phase, an existing conditions report, should be complete within nine months. The second phase will engage the community about the vision for uses and experiences in and around the public waterways, including places for paddling, for instance, or bird watching. The next step will be a draft plan, which is expected to be complete by spring 2016. A final plan will be adopted that fall.
Despite ample parks along Iowa's rivers, there has never been much in the way of coordinated riverside planning. "This whole planning process is hoping to galvanize a shared vision for our rivers beyond the fact that they flood and have poor water quality," Dawson says. The aim, he says, is to help Iowans "re-remember we're a river town, and turn back to the rivers."