In 2011 the event focused on the role of fresh water: rivers, streams, lakes and aquifers in the Earth System.
A good place to start is the University of Wisconsin-Stevens Point, which has a good online textbook:
The Encyclopedia of Earth (www.eoearth.org) also has some useful information. Look particularly at the articles on
The US Geological Survey also has a number of useful sites:
Connor and Costa (http://pubs.usgs.gov/circ/2003/circ1245/pdf/circ1245.pdf) has a good discussion of floods in the US, where and why they occur.
http://pubs.usgs.gov/gip/106/ talks about the 100 year flood.