Dam Removal to Restore Rivers in Minnesota
by Chris LenhartDams are being removed increasingly across the country as a means of restoring rivers. This has often been done purely from an economic and safety perspective, to get rid of aging pieces of infrastructure. However, the ecological benefits of improved fish passage and restored stream flow conditions drive many project as well. Dams have been placed across virtually every major river in the U.S., except just a few, altering river ecosystems in a multitude of ways. Dams alter hydrologic and sediment transport pathways while blocking movement of fish and other aquatic organisms such as mussels. They have been recognized as one of the major threats to the preservation of aquatic biodiversity in the U.S. (Richter et al. 1997).
Yet dams play a crucial role in water management, providing benefits such as flood control, river navigation, water supply and hydropower. (Though no dam provides all these functions, for example the Ford Dam in the Twin Cities serves no significant flood control function, but provides hydropower and commercial shipping.) Balancing costs and benefits, is difficult. Additionally there are often misperceptions concerning the role and function of dams, sometimes making dam removal decisions more complicated than necessary.
Dam removal in Minnesota
In many cases, the ecological benefits of improved water quality (in shallow, eutrophic water impoundments), restored hydrologic and sediment transport regimes as well as fish passage make dam removal a clear choice. For example, approximately 100 dams have been removed in Wisconsin since 1990 alone. In most of these cases, the dams had become aging, dilapidated safety hazards that would have costs significantly more to repair than to remove. Ecologically the projects benefited aspects of water quality, fish habitat and fish passage. Minnesota has not removed nearly as many dams as Wisconsin or some of the northeastern states, such as Maine, but there have been at least 10 removals. Some of the major ones are described below.
In recent years the Minnesota DNR has removed several dams in the Red River basin, primarily to improve fish passage and water quality. Two of the more successful dam removal projects in Minnesota were at Banning State Park on the Kettle River and along the Cannon River near Welsh, MN. The Kettle River dam removal enabled whitewater boater access to one of the most-used kayak runs in the state and allowed fish passage to the upper river that had been blocked by the dam. The Cannon River improved water quality in the reservoir area, opened up fish passage (and canoe passage) on this state wild and scenic river at a cost significantly lower than repair would have cost. More recently a dam was removed from the Lac Qui Parle River in western Minnesota, allowing enhanced fish passage and restoration using natural channel design principles. These dams no longer served any practical functional purpose by the time they were removed.
Dam removal issues
One of the major issues arising in dam removal projects, is whether to remove or repair aging dams that have become dysfunctional, safety hazards, and/or detrimental to the stream environment. Dam removal has been chosen in many cases, simply because winning because it's cheaper than repair, with the added ecological benefits. Aside from socioeconomic issues, there are many important issues regarding biologic and physical properties that are changed by dam removal. Changes to hydrology and sediment transport are key issues as well as improved habitat conditions. Dam removal will generally always improve fish passage, as dams serve as barriers to fish movement (and other aquatic organisms, such as mussels). Hydrologic characteristics of in-stream flow and velocity are generally restored to pre-dam conditions. However, dams often trap large quantities of sediment, and this issue needs to be addressed when planning for removal (or maintaining an existing reservoir). These issues are well-summarized in a report called, "Dam Removal: Science and Decision Making" by the Heinz Center (Heinz Center 2002).
Studies of dam removal in Minnesota
There are at least two major dam removal studies currently in progress or proposed in Minnesota. The first proposal is the proposed study of removing the Ford Dam in Minneapolis/St. Paul to restore the Mississippi River gorge. The proposal put forth to the Minnesota legislature in 2004, suggested looking at a range of activities ranging from no change to modification of the existing lock and dam and shipping channel to removal and complete ecological restoration. This project is described in more detail in the Dean Rebuffoni article.
The second is the Rapidan Dam on the Blue Earth River, near Mankato, Minnesota. This dam no longer serves its original function and is almost completely filled in with sediment. Right now the US Army Corps of Engineers has proposed a feasibility study to "… assess the potential for a Corps of Engineers project to remove or alter the Rapidan Dam to allow fish passage and restore the Blue Earth River to a more natural condition. The study would also look at other options, including rehabilitating the dam for continued hydroelectric power generation."
Additionally, the Minnesota DNR studies and implements river restoration and fish passage improvement opportunities at aging dams and situations where the opportunity arises.
Conclusion
Dam removal is an excellent tool for restoring river ecosystems altered by dams. While not appropriate in many circumstances, the number of aging dams in the eastern U.S. is growing rapidly to the point that hundreds more will be removed in the upcoming decades. In Minnesota, dam removal (or alteration for improved fish habitat, in-stream flow and water quality conditions) should be pursued when applicable situations arise. The Mississippi River Gorge, one of Minnesota's outstanding natural features has been submerged through damming and would be a 'crown jewel' of river restoration projects in the state if it were carried out. At this point, the Sierra Club is recommending a study to examine all of the options in more detail, ranging from no action, to partial modification of the existing system to comprehensive ecological restoration.
References:
The Heinz Center 2002. Dam removal: Science and Decision Making. Washington D.C.: The H. John Heinz Center for Science, Economics and the Environment.
Richter et al. 1997. Threats to Freshwater Fauna. Conservation Biology 11 (5): 1081-1093.
Contacts:
Craig Regalia — MN DNR
Luther Aadland — MN DNR
Chris Lenhart — Sierra Club
Dean Rebuffoni — Sierra Club