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Roger Weller, geology instructor

wellerr@cochise.edu


Dams
by Johnathon Brittain
Physical Geology
Fall 2009

                                        Dams: A Helpful Hindrance
 

                A dam is a testament to the ingenuity of the human race. It is a structure that prevents or regulates the flow of a body of water, forever changing the area in which it is constructed. Dams provide a myriad of beneficial effects, ranging from harnessing their power for the generation of electricity, to creating jobs and tourist attractions, allowing local businesses to sell products such as boats. The lakes resulting from dams can bring in tourists to an area, for fun, for fishing, or in some cases just to see a large body of water. However, with everything positive that a damn brings with it, there are plenty of arguments on why they shouldn’t be brought into an area. They can have a devastating impact on the flora and fauna on both sides of the dam. The landscape will be radically changed on both sides, private property with rich history risks being buried under hundreds of feet of water. Dams also bring the added risk of breakage, resulting in a disastrous flood rushing downstream. So while they’re an amazing feat, they aren’t perfect.
 


 

                Dams come in many shapes and sizes, methods of construction, and can vary slightly in purpose. At the most basic level a dam is, “… a barrier built across a water course to hold back or control the water flow. (Hassam)” There are three main categories of purpose involved in the construction of a dam, this includes storage, diversion, and overflow. A storage dam is designed with the intent to store water, or create a surplus to draw on later. A diversion dam is utilized to divert water for the purposes of irrigation, or any other purpose the water might be needed for. And overflow dam is designed to be overtopped at some point, not meaning to be a permanent solution at any point.
 

                Dams are also made from a variety of materials, be it man made or not. Dams can be constructed economically when they are earthfill structures. Earthfill means that they take advantage of materials in the surrounding area in the construction of the dam, saving on bringing in materials from other areas as they take use of what is nearby, forming rolled-earth or earthen dams. Possibly the most iconic dam to most people is the arch dam. The arch dam retains stability due primarily to its arched shape, taking advantage, usually, of relatively narrow canyons. The canyon bows into the body of water as opposed to away from it to maintain support.



 

                Now that these dams are built, there is an unavoidable impact on the surrounding area. Rivers usually carry debris downstream, depositing it evenly as it flows are now dammed up, and this debris has nowhere to go. This however, is one of the smaller problems we face with the construction of a dam. The entire environment on each side of the damn is going to change drastically. Areas that weren’t submerged prior to construction will now be below massive amounts of water, causing a loss in plant life and animal habitat. One of the most readily apparent effects on wildlife due to the construction of a dam can be seen in fish. Fish don’t live in one place, they travel both up and down stream at various times in their life cycle, this is something that many dams, not all, can impede or make impossible. With this disruption, the reproductive cycle can be interrupted causing a change in numbers of a particular fish in any given area. In addition to this blockage, oxygen levels are changed on the falling side of the dam, this will often cause that area to remain essentially uninhabitable to fish due to nitrogen content, or just reduced oxygen.

 

                Another potential problem involved in the construction of a dam is the potential loss of land that was previously or currently inhabited by humans. The area in North Carolina that my family comes from was in serious danger of experiencing this in earlier in the 20th century. The Tennessee Valley Authority wanted to construct a dam near Mills River that would have put hundreds of acres of rich historical areas underwater. While we may view new dams as catalysts for job creation, tourism and the like, you have to consider that an area’s history is about to be submerged. And while it may not have a direct impact on you, an indifferent eye towards this sort of thing is a bad direction to lean. Damming has displaced a potential 40-80 million people according to the World Commission on Dams Report. This is a staggering number of lives that are impacted, possibly not even benefiting much from the construction of the dam. 
 


 

                Unfortunately, dams, like many things can be viewed as both a blessing and a curse. While they can occur entirely due nature, or in a smaller scale as a result of animal activity, they can also be massive in scale and constructed by man for many reasons. Such an incredible undertaking is never without effects on both sides of the scales, as much as they benefit humans, they’re a potential detriment to the ecological stability of any given area. While they remain a handy tool for taking advantage of the energy found in nature, dams are something to be regarded with respect, and caution should be used in the construction of such environment shifting undertakings.    

 

Image Sources     

http://oh.water.usgs.gov/wse/dams.gif

http://msnbcmedia4.msn.com/j/msnbc/Components/Photo_StoryLevel/080303/080303-dams-hmed10a.hmedium.jpg

http://www.melrosemn.org/tour/HistoricPhotos/500x333DamBreakApril1922.jpg

http://www.markmallett.com/blog/wp-images/Dam_Break.jpg

http://www.chase-1.com/gdam1a.jpg

Information Sources

http://www.dam-research.org/

http://internationalrivers.org/en/way-forward/world-commission-dams/world-commission-dams-framework-brief-introduction

http://en.structurae.de/structures/stype/index.cfm?id=3

http://www.wisegeek.com/why-are-dams-potentially-harmful-to-fish.htm