The rises and falls of the water level at the Iffley Lock downsteam monitoring station closely mirror the rises and falls of the water level on the Abingdon Road in Oxford.
However, the Environment Agency's own website only gives the current water level and a graph for the previous five days - better than the two days it used to be, but still lacking in history. This page was set up to save information from the monitoring station, to make it easier to see at a glance if Oxford is likely to go underwater.
New: 8th February 2014 - The page now includes data from Hinksey Stream (Cold Harbour), Osney Lock downstream, Kings Mill downstream, New Botley and Minns Estate monitoring stations. Graphs of Osney and Kings Mill are at the bottom of the page; data from all stations can be downloaded as csv files.
These rough-and-ready rules of thumb are based on ad-hoc comparisons of what the river and surrounding areas look like with what the graph looks like at various times from Nov 2012 - Jan 2014. They should not be taken as "fact".
This graph starts on 1st December 2015. The station is polled every 20 minutes and the graph will automatically refresh.
This graph starts on 1st December 2013.
A flood alert for for the River Thames and tributaries in the Oxford Area was issued on 23rd December 2013, and a flood warning on 4th January 2014. Another flood warning was issued on 1st February 2014.
Look at or download the data files used to plot the graphs: 01/12/15 to date, 01/12/13 to 09/02/16, 26/12/12 - 26/12/13
Consult these websites if you want an expert opinion
This graph covers the year from boxing day 2012-2013. The data starts too late to include levels from the flooding during November 2012. (Note that this graph overlaps with the current graph above during December 2013.)
Download Hinksey Stream - Cold Harbour data
Download Bullstake Stream - New Botley data
Download Seacourt Stream - Minns Estate data
Disclaimer: I am not an expert, just someone who screen-scraped the data on the EA's website.