Any American today has most likely seen a dam in their lifetime. People do not notice the effects many of these structures have today. Imagine the Hoover Dam, an enormous concrete structure blocking the Colorado River to make hydroelectric power. Imagine that same river without the dam. The river is raging and full of life, there are fish jumping everywhere and even the surrounding river basin is more beautiful due to the increase in water.  Many people may not be informed of the dangers dams pose; but one of the major recent environmental issues in the United States today is dam removal. It is all over the news, especially on the West Coast. There has been ample research linking environmental hazards to dams. The issue really boils down to three main factors: environmental concerns, economics and safety. What are the major environmental risks taken by leaving a dam up (or taking one down)? And, because these are going to be government funded projects, Is it worth our tax money to demolish these structures? Last what is the safest way to remove dams, or are the existing dams posing a safety risk? The large majority of the dams in the United states are outdated and provide no service, these, and others 

When most people think of dams they think of the Hoover Dam, and subsequently hydroelectric power. However, dams have two main functions. The first is storing water for changes in river flow or height. The second is the raise the water level upstream in order to divert water to a canal, or to a turbine to produce hydroelectric power. Hydroelectric power accounts for nearly a fifth of the world's electricity (McCully).  Flood control is an important role dams play and is the primary reason for many of the dams in the United States. These control the water level and save many lives in places that are prone to disastrous flooding (Chouinard). There are two main types of dams, most of the dams we see today have separate reservoirs to store water and help to regulate the rate of flow downstream. However, the older style that is still around today are the run-of-river dams. These dams create only one small reservoir called a head pond. These are unable to control flooding and are much more prone to destruction by natural causes, which could be devastating not only the the people close the that river, but also to the river's ecosystem and surrounding habitat (McCully).

Historically, dams have played an important role not only in the United States but in the rest of the world as well. Dams can be seen in history as early as Mesopotamia. The Romans were the first to use dams widely. Some Roman dams still stand today, including one in Spain that is 46 meters high. Romans also were among the first to use waterwheels to grind corn, one of the earliest forms of hydroelectric power. In the 19th century Great Britain was the first to rapidly build dams; mainly as water storage to support its expanding cities. By 1900, Britain had almost as many dams as the rest of the world combined. Shortly after the United States started dam construction, which was largely used for irrigation and expansion into the western states. The Hoover Dam was one of the largest from this period. It's 730 feet tall and was built with 60 million tons of concrete. The largest was the Grand Coulee Dam in Washington state. These two dams were the two largest sources of electricity to the United States in 1945 and played a pivotal role in weapon production during World War II (McCully).

Over time, these once distinguished works of engineering cause several environmental impacts. One such impact is the degradation of water quality. Organic materials get caught up behind the dam. Over time they decompose; a process which consumes oxygen. When these organics build up and are not allowed to spread out down stream, the oxygen they consume can kill many species who require high oxygen content in their water. In rare cases, this can trigger an algal bloom. An algal bloom is when algae becomes the dominant biomass in a body of water, making that area uninhabitable due to the lack of oxygen (Davenport). Another way that dams degrade their water quality is through temperature. The colder the water is in a river, the more dense it is, and therefore, the more oxygen it can contain. When dams are built they reduce the flow of rivers. This slowing causes the water to be under direct sunlight for longer, warming the water (Poff 716). This warming of the water and buildup of organic materials can harm or even kill entire species in that specific area. In 2011, there was a large algal bloom that started in the western basin of Lake Erie that grew to consume almost a third of the entire lake (Michalak 6449). This killed many fish and there was a great decline in the number of fish caught for consumption following. The large eutrophication also decreased biodiversity and habitat quality.

Another environmental concern regarding dams is sediment buildup. Dams alter the normal flow of sediment downstream which modifies biochemical cycles and the dynamics of aquatic habitats. Sedimentation does not just hurt the ecosystem and organisms, it also impairs dam functionality. The buildup of sediment reduces reservoir storage capacity. This can happen at different rates depending on the speed of river flow and the types of rocks and minerals that are found in the river. The Matilija Dam in Southern California had such high sedimentation rates that its reservoir capacity was down by 50 percent over the course of about 50 years (Poff 662). This buildup of sediment can cause potential problems if a dam like the Matilija is to be removed. The rush of all this sediment downstream at once could be fatal to many of the organisms living in or around the river. This can be seen first hand during the removal of the Old Conduit Dam along the White Salmon River in Washington State (NationalGeographic).

The last environmental threat by dams is to salmon. This is seen a lot more in the Pacific Northwest of the United States. Dams prevent the travel of salmon up and down stream, making it more difficult, or impossible in many cases, for salmon to swim upstream to their spawn points to lay eggs. These adults already have a good chance of dying swimming upstream without two or more dams to travel through in both directions. Since most of the west was dammed up some 50 years ago, the salmon population has gone down by roughly 85 percent  (Davenport).  These salmon have been a big part of life on the west and help sustain many people. Elmer Crow, one of the elders of the Nez Perce tribe along the snake river in Oregon and Washington describes his first experience seeing the salmon run as a child, saying: 

"My father took me outside my tent, it was still dark, he said 'listen' it sounded like a thousand people with an ore beating on the water. It was salmon swimming upstream" (DamNation).

The salmon are probably the biggest issue involved with dams. There are many endangered species of salmon today, and this is entirely due to human interference with their habitats and rivers. Before the great Elwha dam was removed in 2014, it blocked off the Snake River from Olympic National Park. It had no fish ladder, or any way for fish to travel above and below the dam. This alone made that dam constitutionally unlawful according to the Endangered Species Act. During this time, the Salmon would swim up to the dam and bump their heads against the bottom of the dam. Their instinct was so great, their tie to their spawn points so strong that many would kill themselves trying to swim through (DamNation).

The question that most people in the United States are asking today is: Is destruction of these dams worth it? Removal of the larger dams built by the United States in the 1940s will cost money, money that will come from the taxpayers. What many people overlook is that these dams are costing a lot of tax money as it is. These massive structures are holding back tons and tons of water, the most powerful erosional factor in the United States. The upkeep alone to keep these dams running properly and safely is quite expensive in many cases. Another cost concern is the opportunity cost of the electricity many of these dams provide. But with the ever emerging sustainable energy craze, hydroelectricity only provides about 7% of the United States' power (Lieb). One of the worst disasters in U.S. history happened in 1889 when the South Fork Dam in Pennsylvania failed and killed over 2200 people (DamNation). It is amazing that this is still considered a "natural disaster," but really there is nothing natural about a man-made dam that failed and decimated an entire town. So yes, dam removal projects are quite costly, some costing hundreds of millions of dollars. However, these are one time fees, as opposed to the cost of these dams over time. Many of which do not produce enough the relative amount of electricity they once did. Our country has a limited supply of money and surely will not be undertaking the removal of all dams in one year. So which dams should be removed first? There has been a proposed system of prioritizing which dams should be removed and in what order. This system is based on economics and environmental factors. The fact that there is not as much information on dam removal makes destruction of dams quite the undertaking. The system of Prioritizing dams will not only make the most effective use of tax dollars, but will allow the government and scientific community to gather more information regarding the risks associated with dam removal, and the restoration of the river ecosystem after the removal of the dam is complete (Environmental, 462). 

Although there is not an extensive amount of dam removal data there is certainly enough to see the positive long term effects the destruction of dams has on the local environment. One of the earliest studies done on dam removal and the environmental effects was done in 1987 at the Woolen Mills Dam of the Milwaukee River. They saw an initial decrease in water quality, habitat quality, and biomass. By 1993 all three categories were higher than before the dam was destroyed (Kanehl, 396). In 2014, the largest dam removal to date was completed in Washington State. The removal of the Elwha Dam was an extremely controversial concept during the late 1900s and early 2000s. 

Thirty years ago, when I was in law school in the Pacific Northwest, removing the dams from the Elwha River was seen as a crazy, wild-eyed idea," says Bob Irvin, President and CEO of the conservation group American Rivers. "Now dam removal is an accepted way to restore a river. It's become a mainstream idea." (Nijhuis)

It took nearly two decades for actual demolition to begin. But just three years after the removal was complete salmon are migrating past the former dam sites, and trees and shrubs are sprouting in the drained reservoir beds surround the river (Nijhuis). The popularity of this issue has increased tenfold as well. The number of removals has doubled the last 3 decades (Poff 666). In February 2016 plans were made to remove four dams along the Klamath River in Oregon. This plan bypasses congress and allows the state governments of Oregon and California to remove four aging dams without congressional approval. This project will cost nearly 250 million dollars and could take anywhere between 3-8 years (Mapes).

Dams should be removed if we want to see healthier river systems and higher habitat quality. Dams should be prioritized and removed over time, to gain a better understanding of the hazards destroying these could cause. We know that dams are bad what needs to be established now is the safest, most cost efficient way to remove them. People do not realize that most dams are not like the Hoover Dam, or Elwha, or Klamath. Most dams are no larger than 2 meters high. There are over a million dams 0-2 meters high (Poff 663). These provide no hydroelectric power; they are idly catching sediment and organic materials. These are the dams that need to be removed sooner. They are small, relatively easy to remove, and have serious negative effects on the environment surrounding them. As the removal of dams becomes a bigger and bigger issue here in the United States, the information behind the removals and how to minimize cost and maximize effectiveness is an important subject to discuss. Time will tell what the government is willing to do about this issue affecting a large part of our rivers. One thing is for sure, these archaic structures need to be taken out.

