Thames flood and navigation conditions

The aims of these pages are to help you if you live near the Thames, to give you some idea of potential for flooding from the river in the next few days. You can see whether flows and levels are rising or falling and how fast, and how much rain there has been recently. This should help you judge whether there is more to come from upstream or whether it's past the worst.

The main levels display has four sections:

  1. a recent (two week) history of flows
  2. the corresponding water levels at a particular point (currently Bourne End but this will be extended shortly)
  3. recent rainfall in four places in the Thames valley;
  4. Total rainfall in the last 7 days, this and last month, and as a percentage of the monthly average for the four places.

The first is coloured according to the navigation state of the river: blue for normal, amber for an increasing stream, red for a strong stream (navigation not advised) and yellow for a decreasing stream. The second shows red when the level is above what the EA considers the "normal maximum" and amber when it is above one third of the way from the normal minimum to normal maximum. This is a somewhat arbitrary cutoff but indicates when riverside paths start to flood. The rainfall graph has different colours for the four places.

The Map of Warnings shows the navigation status on the whole river. If you scroll in and click on the map it will show the different locks and if you click on the "river levels" link it will show the levels at that place on the river. Flow information isn't available everywhere.

If you want to consult levels at a different place to Bourne End regularly, saving a link when on that page will do the trick (it adds a reminder such as "?base=49" to indicate the place).

The information comes from different places.

  1. Flow information comes from the Environment Agency using their API and is sampled daily from 7 places along the river and also from the Jubilee River which forms a bypass to Maidenhead and Windsor. These are not evenly spaced as one of their main uses is to monitor water extraction from the river. In particular there is no gauge between Boulters Lock in Maidenhead and Shiplake Lock in Reading. So the flow at Bourne End is established by adding the Maidenhead to the Jubilee River readings.
  2. Levels are now taken from the Flood Information Service web pages which record levels upstream and downstream of all the locks. These levels are used by the lock keepers to adjust the flow in the river by means of sluices and so the level above a weir can actually drop (usually temporarily) when the flow is increasing. The sensors sometimes fail as did those on Cookham Lock before Christmas 2019 for a few days. In this case it's not possible to show any data.
  3. Rainfall information comes from the WeatherOnline website. This now uses the 24 hour reading taken at 6am so that it includes last night's rain. The records are mainly from airfields and rather more reliable than the Wunderground (amateur) readings that were used previously. The runoff can take at least four days to reach the lower parts of the river or longer if the ground is dry.
  4. The navigational state of the river is taken from EA River Conditions website.

All these values are stored in a database so that it is possible to look at previous dates using the arrows at the top of the screen.