There is a really good paper about the flood here. Unfortunately it is a PDF file and not so easy to navigate (the best thing would be to download the file and view it with a PDF viewer - like Adobe Acrobat - or print it out). This paper is the transcript of a lecture with slides given by Christopher Clarkson in 2003. Clarkson was in Florence in 1966 and worked on rescuing books at The Biblioteca Nazionale Centrale Firenze first hand. This is probably one of the best source materials on the web for the Florence flood and a very compelling read.