A Guide to the Advantages and Disadvantages of Dams
Building a large dam in most areas is a huge undertaking (often in more ways than one) -- and the numerous advantages and disadvantages of dams should always be considered beforehand in a detailed cost benefit analysis. In this article we take a brief look at the benefits that dams can provide and as well as the potential harmful issues they can cause too -- but before we do, I believe it is best to firstly give a brief overview and definition as to exactly what a 'dam' actually is and what a 'dam' does.
There are numerous definitions for dams, as they have a wide range of given purposes and functions, but the Collins World English Dictionary gives a rather good and broad concept of a dam -- 'a barrier of concrete, earth, etc, built across a river to create a body of water for a hydroelectric power station, domestic water supply etc.' 
The Advantages of Dams - Pros
Hydro Electric Power
It's pretty hard to ignore the main benefit that larger dams provide; a way to produce essentually 'green' (clean) electricity. This is usually the main draw for the building of dams in the first place and the influx of power for a town to use and sell can cause cities to grow and thrive.
Tourism and Camping
Dams are a great draw for tourists and provide an attractive place for families to go camping and fishing etc. This can improve the local economy of an area by attracting travellers who will often spend money at the nearby businesses, and will hence provide more jobs for locas as more labour is needed to keep the tourists 'happy' -- with Hotels etc.
Still Water for Animals
Some species of animal actually require still water in order to survive. As such, a dam can provide a way for these species to thrive in an area where they otherwise might not have. However, you will see later in this article that dams also cause problems for other such species.
Clean Drinking Water for Nearby Cities and Towns
Dams can provide a very good source of water for towns and cities in the area. This water can be used for drinking or industry and can take advantage of an otherwise unusable water source.
Flooding and Water Management
They can also be specifically designed to help ease and solve flooding problems within a settled area, and through the dam -- the water can be controlled to provide a form of irrigation for agricultural land and even source of transportation for goods.
The Disadvantages of Dams - Cons
Expensive and Difficulties in Becoming Profitable
The larger dams are incredibly expensive to build and, as such, they can take many years to pay for themselves and become profitable. Most dams are estimated to operate for at least two to three decades, if not more, to become profitable and this is a cost that is usually taken on by the government and the taxpayers. This debt can be a large burden on the government for a long time and can influence fiscal polices for the life of the debt -- not to mention the potential unforessen maintenance costs.
Disruption to Natural Environment and Water Ecology During Construction
Building a dam requires diverting water temporarily and it also means a lot of digging and construction on the dam site. While this construction is only temporary, it can have long lasting effects on the environment -- and potentially harm or worse still destroy local ecosystems.
Geological Disruption and Earthquakes
The Hoover dam is the perfect example of the geological disruption that can be caused by larger dams. The weight of the Hoover dam has actually resulted in the compression of the earth in that area. This has had follow on effects such as minor earthquakes and tremors in the area around the dam. This effect could potentially become more serious over time.
Danger of Dam Breaches
Dams being built today are much more stable than dams built in the past but many older dams have problems with breaches or even collapses. Because of the large volumes of water behind these dams this can cause catastrophes for nearby people and wildlife.
Disruption of Fish Ecology
Most dams can cause complete death of migratory fish in the area since they are no longer able to head up stream to breed or feed. Some dam designs allow for this migration to continue somewhat normally but these are usually more expensive and complex to build. The disruption to the salmon breeding cycles in areas with many dams is the largest known impact of this though many other species are negatively impacted as well.
Impacted by Drought
In times of heavy drought dams will stop functioning properly and some can even lose their structural integrity. If local cities rely on the dam for their power then droughts can be devastating with both power and water becoming scarce. This means that most dam-powered towns and cities must have access to an alternative power source, which can potentially negate the positive effects of the dam in the first place.
Affects on Water Quality and Flow
Low oxygen levels in dam water are the result of the hydroelectric production process. The disruption of the natural flow of water can have impacts on the turbidity of water as well, which can seriously harm aquatic life.
Summary -- Are Dams a Good Idea?
Overall, the disadvantages of dams are being found to outweigh the benefits as more and more problems present themselves overtime. Initially, hydroelectric power was seen as a very 'green' alternative to other power sources and dams were said to have many positive effects for nearby townships and cities. However, the issues with building large dams is becoming more apparent and hydroelectric power and damming of lakes and rivers is becoming a less common practice. But, on the whole, it is a case by case scenario, where every opportunity has its own unique pros and cons (cost benefits analysis) to consider as to whether to build a dam or not.
If you have any comments or questions specifically regarding the advantages and disadvantages of dams then please make them in the comments section below.