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=**__Advantages and Disadvantages of Dams and Dam Removal__**=

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Effects of Dams on Water Temperature and the Surrounding Ecosystem
As the reservoir behind the dam builds up, the water at the surface of this newly formed water body will heat up quickly. The sun’s energy is able to increase the surface temperature so rapidly because of increases water surface area and a slower flow velocity 1. This warmer water remains at the top of the reservoir, while the cool, denser water sinks and settles at the bottom. The separation of the two layers is known as temperature stratification, and does not allow for oxygen from the surface to mix with the water deeper down. This change results in very low dissolved oxygen levels at the bottom of the reservoir 1. This stratification can cause an alteration in the habitat and species diversity in the river below the dam in one of two ways. If the dam pulls the water from the surface of the reservoir, then the river below the dam will be significantly warmer. This results in a decrease in some species of coldwater fish (such as salmon and trout) that are now no longer able to thrive in or migrate through that section of the river 1. However, if the dam pulls water from the lower layer of the reservoir (as is common in large hydroelectric dams) then water temperatures downstream of the dam will dramatically decrease. This water contains reduced amounts of oxygen, so when it disperses into the downstream ecosystem, it results in semi-anaerobic conditions 1. This change reduces the diversity of species that are able to persist in that water body. If a dam was removed, the temperature of the resulting river would eventually return to its natural level. For example, after the removal of the Salling Dam along the AuSable River in Michigan, it is expected that the river’s temperature in that area will drop around 3° Celsius within a few years, thus returning it close to its natural pre-dam state 1. [Mary Bammer]

Resources
1 Bednarek, A.T. 2001. Undamming Rivers: A Review of the Ecological Impacts of Dam Removal. Environmental Management. 27(6):803-814.

**Negative Consequences of Dam Removal: Invasive Species** One of the most critical arguments against dam removal is the threat and spread of invasive species. Dams act as a barrier by blocking invasive species from waters upstream. A prime example of this is the sea lamprey in the Great Lakes region. Sea Lamprey need to use river systems to spawn and lay their eggs. Since sea lamprey cannot jump, large or low-head dams can prohibit them from going completely upstream to spawn1. This keeps the population from growing more rapidly as it decreases the amount of available habitat for them. By acting as a barrier, managers can focus their population control methods, such as chemical treatments, to a smaller area. Moreover, large amounts of money do not have to be spent treating an entire river system. Another issue is that when a dam is removed, waterways become fully reconnected again. This is particularly dangerous because an invasive species can run rampant through greater areas of a country or countries, affecting multiple ecosystems. This can be seen through the current Asian carp situation in the United States. Even though Asian carp were introduced in the south to clean aquaculture areas, they have entered rivers and have been able to travel almost all the way up to the Great Lakes. Certain dams like the Gavins Point Dam, just below the Missouri River have been able to stop the Asian carp from migrating further2. Yet the spread of the Asian Carp is still continuing elsewhere. By removing more dams, invasive species are given more opportunities to spread and cause more damage to important ecosystems.

Resources
1. RAHEL, F. J., BIERWAGEN, B. and TANIGUCHI, Y. (2008), Managing Aquatic Species of Conservation Concern in the Face of Climate Change and Invasive Species. Conservation Biology, 22: 551–561. 2. http://www.fws.gov/greatplainsfishandwildlife/AsianCarpStudy.html

[Chris Gomon]

While most people are well informed on the ways in which dams can be harmful to the environment, most people seem to overlook the positive impacts that a dam can have on the body of water and the surrounding land. A dam can create a warm water fishery that was not previously available in the area.1 There are many fish that simply cannot live and reproduce in the cold water environment of a free flowing river. When a dam is created, you get a deeper, warmer, slower moving body of water which is very similar to a lake. Now this can give you a dual fishery; the warm water reservoir and the cold water fishery downstream from the dam. This will make the area more appealing to a wider range of sportsman. Not only can a dam create favorable habitat for fish, many birds and animals will also benefit from the lake it ceates. A dam will back up the water and in many areas that it floods, it will create shallow flats where aquatic plants will be become abundant. These plants are a main food source for many different birds and animals. Many of the shallow marsh like areas on the reservoir will also be prefect nesting places for many birds.1 [Kyle Maki] 1G. Ledec, J.D. Quintero. November 2003. Good Dams and Bad Dams: Environmental Criteria for Site Selection of Hydroelectric Projects.
 * Positive Habitat Changes From Dams **
 * Resources**

Positive Effects of Dam Removal on Invasive Species
The removal of a dam can decimate the previously inhabitance of invasive species and push toward the revival of native fish species. When a dam is put in place, over time it can force a large backup of water, creating a slow moving, stagnant lake. The newly developed environment may be suitable for tourism, but is a prime niche for the undesirable common carp. Carp will make a large dent in harming lake structure as well as fish populations by uprooting and disturbing aquatic vegetation. In dealing with the Woolen Mills Dam in Wisconsin, the common carp put direct pressure on ﻿the smallmouth bass populations, resulting in an unfishable and healthless ecosystem. In efforts to restore a once plentiful fishery, a removal of the dam was proposed and eventually acted on. As expected, the removal of the dam eliminated the slow moving lake and decimated the common carp populations, allowing for the smallmouth bass species to rise again 1. Although we have seen a positive effect of a single dam removal, not all dams will follow this success as other highly researched aspects need to be put into play. With the removal of some dams, invasive species will be put to extinction. [Jacob Schauer]

Resources 1. Stanley, Emily H., and Martin W. Doyle. "Trading Off: The Ecological Effects of Dam Removal." Frontiers in Ecology and the Environment 1.1 (2003): 15-22.

Economic Costs of Dam Removal
One highly debated consequence of dam removal is the economic cost of removing the dam. Removal costs come from not only from the physical deconstruction and disposal of the dam but also from the loss and replacement of renewable power sources (if removing a hydroelectric dams) and property value losses; leading to property reimbursement costs. Some costs of dam removal are covered by grants and trust funds, but much of the economic burden is placed upon the taxpayers. A CDM study of the economic costs of the four Klamath River hydroelectric dams finds that the estimated total cost of removing the dams to be anywhere from $466 million to $1 billion dollars1. Along with reservoir restoration, costing between $35 and $53 million, the physical removal of the dams (costing only $95 million) is less costly than the socioeconomic costs of dam removal. The costs of dealing with the effects of sedimentation, which affects tribes and local fisheries, watershed, and recreational group, could range anywhere from $170 to 350 million. Property value damages from dam removal and the costs or property reimbursements are estimated between $13 and $27 million. More than twice as costly as property value loss, the decommission design and studies of the dams themselves cost the taxpayer nearly $34 to $67 million. A rough estimate of the Kalamath River hydroelectric dam removal project is estimated at $836.5 million for its suggested target of dam removal in 2020. [Pamela Snyder] Resources: 1 Boerger, P. 2009. Klamath dam removal costs, liabilities studied. http://www.mtshastanews.com/news/x1699595587/Klamath-dam-removal-costs-liabilities-studied.

=Positive Habitat Changes from Dam Removal= Dams can negatively impact the natural river habitat in many areas. This especially includes the impact of dams on aquatic biota and sediment transportation. While in the short term for small dam removal sediment can build up in the river, in the long term the sediment usually dissipates. The amount of time sediment takes to clear from downstream depends on factors such as the length of time sediment has been accumulating, the velocity of the river, the gradient of the riverbed, and the techniques of removal. However in some cases such as the removal of the Grangeville and Lewiston dams on the Clearwater River in Idaho, the silt and sediment moved downstream within one week even though the reservoir of the Lewiston Dam had been completely filled with sediment (1). Sediment flow is important in rivers because it provides habitat for fish and aqautic biota. Dams create a flow of sediment depleted water downstream of the dam, which means the soil downstream is nutrient depleted (1). Certain aquatic plant species that thrive in river habitats because of the constant oxygen and nutrient flow suffer with dams in place. Therefore, removing dams could allow these plant species to return to dominance in their natural environment (1). [Brian Cari]



**Resources:** 1. Bednarek, Angela. 2001. Undamming Rivers: A Review of the Ecological Impacts of Dam Removal. Environmental Management. 27(6):803-814. = __Eco-Friendly Dams__ =

Due to some of the positive effects of dams in that they provide clean energy, jobs, and economic benefit, it might be more productive to keep dams while also making sure that the wildlife who use the habitat in and surrounding the dam can have a better quality of life, and higher reproductive rates, while also giving nature friendly people a piece of mind. Here are some compromises that can be put into place: Many fisheries have been decimated due to the fishes' inability to spawn upriver of a dam. Those people whose livelihoods depend on fish and the recreational fishermen want something to be done about dams due to their affect on fish spawning. One solution to this problem could be to install fish ladders, like the one at the Berrien Springs Dam on the St. Joseph River in Berrien County, MI. These fish ladders, or fishways, consist of a series of ascending pools that are reached by swimming against a stream of water until they're beyond the dam¹. There are several different types of fish ladders. The one built on the St. Joseph River is known as a Pool-Weir fishway, and is one of the oldest designs. Fish move up the dam by jumping a series of cement steps, resting in pools on each step until they make it past the dam. Other designs include the Vertical Slot Fishway, which does not require fish to jump, the Denil Fishway, which acts as a ramp for fish to ascend, the Steeppass Fishway, which simulates rapids at varying speeds for multiple fish species to navigate effectively, and the Natural Bypass ². The Natural Bypass fishway consists of building a natural stream or river around the dam for fish to use as a detour. It requires extra land and more effort, but is the most natural for fish to navigate. Another, simpler way to benefit fish reproduction would be to put gravel on the bottom of the river downstream of a dam. Since many fish species spawn on gravel beds, having gravel downstream of the dam should help their numbers increase while still allowing the dam to remain. The positve benefits of dams should not be overlooked, and these are some ways where both fishermen and those who value the dam can be pacified. 

Another action that can be done to improve both the habitat upstream and downstream of a dam is dredging. By dredging the sediment that builds up on the upstream side of the dam it removes harmful toxins that accumulate and improves the dissolved oxygen content. The dredged portion of the river would be deeper, and would decrease water temperatures, which might benefit cold water fish species. The dissolved oxygen content increase would benefit fish, other wildlife, and plants that live downstream of the dam as well. By implementing some of these procedures the benefit to fish, other wildlife, and economic benefit to humans that inhabit the area would be great. [Stephanie Honeycutt] 1. Edmonds, Molly. 2010. What are Fish Ladders? []. 2. Michigan DNRE. 2010. What is a Fish Ladder? []
 * Resources:**

** Positive Affects of Dam Removal on River Sediment ** Dam removal positively affects the flow of sediment through the river system. When a dam is built it alters the natural flow of water as well as the flow of sediment. In the dams reservoir sediment accumulates and slowly piles up along the face of the dam and the bottom of the reservoir. This can be detrimental to the health of the river because without this sediment the river will erode away the riverbanks as well as the bed. Without this eroded bed and bank sediment being replaced the river can lose valuable aquatic habitat for both animals and vegetation (1). When a dam is removed the accumulated sediment will slowly be washed down the river by the current. When this sediment is washed down stream the river will slowly return to its natural gradient and slope. Once these habitats are destroyed by the lack of sediment it is not certain that they can be recovered but there is a good chance they will re-occur. The entire process of the river returning back to its natural slope and gradient may take up to 30 years. While it may be costly to remove a dam the positive effects it has on the health of the river and the rivers habitat are worth it (2). [Alex Barnes]

__** Resources **__ 1.) http://landscape.ced.berkeley.edu/~kondolf/topics/releases/releases.html

2.) Dr. Burroughs guest lecture