Floods

Several rivers have been set aside as "wild rivers" on which dams cannot be built. Give at least four arguments against building dams on rivers. Give at least four arguments in favor of building dams.

Building dams is an issue politically, social/cultural, economically, and biological/ecological. There are many positive and negative responses to building or not building dams. In my opinion, the pros weigh out the cons.
Dams are beneficial to the development and overall well being of a river. Dams can store water directly from a river and during a drought period the dam will be able to continuously supply water. Dams also help control river floods when excessive rainfall occurs. Dams are generally inexpensive after completion with very little breakdowns and maintenance issues. Dams are also easy to shut down if necessary; they are a renewable energy source, and a great method to producing power. (2004, Dams).
Even though dams are inexpensive to maintain after completion, they are costly to build. Dams can be very fragile structures and may end up being damaged or completely destroyed during or after a massive flood. Sometimes dams will interfere with the natural seasonal changes which may cause ecosystems to be destroyed. Sediment may also build-up behind the dam instead of traveling through the stream, fish population can decrease because their path is blocked, and erosion to the channel may increase. (2002, Siddall).

How is the recurrence interval for a flood determined? How may new data affect the flood-frequency curve?
Floods have recurrence intervals, which means the time between each flood. The recurrence interval is determined by calculating the annual peak discharge, adding 1 to the number of years of record, and then dividing the rank. The algebraic expression used is R=recurrence interval, N=number of years of record, and M=rank. A flood recurrence interval may be classified as a "100-year-flood" which means a few different facts. The flood may occur every 100 years, it has a 1% chance of occurring any year, and can occur even twice during 100 years.

The flood-frequency curve is a beneficial tool used to estimate how often a flood may occur. The flood-frequency curve is based on plotting the discharge at annual peaks against the recurrence intervals. The flood-frequency calculations can be impacted greatly by adding different data. Catastrophic floods added to the list will change the outcome of data because they rarely occur. Our textbook gives an example of data and graphs for the flood-frequency curve. The curve is steeper when data from 1997 was included. The data increased the 100-year-flood from 73,000 cfs to 82,000 cfs. This jump was all because of the one additional year of data added. Further data entered will also change the outcome.

References
Dams. (2004). Pros and Cons. Revolution of Core Knowledge: Water Project (ROCK). Retrieved March 8, 2007 from http://drake.marin.k12.ca.us/stuwork/rockwater
Siddall, S. (2002). Large Dams in the Western United States: Biological/Ecological. Kenyon College. Retrieved March 8, 2007 from http://phi.kenyon.edu/Projects/Dams/index.html