Q: What is the main factor that affects the height of a tide?
A: It's the phase of the moon that has the biggest effect. High tides are highest around the dates of full moon and new moon, with full moon tides generally being rather bigger than new moon tides. The peak actually happens about 2 days after full moon or new moon. Low tides are lowest at these times too.

Q: I checked the tide time in the newspaper and it was very different to the time on this site. Why?
A: Times in the press are usually given for London Bridge, and are often in GMT, even in summer. This site shows the predicted time for each location, and uses local clock times.

Q: Why is the tide height in my newspaper (or another website) different to the one on this site?
A: There are two possible reasons. There are at least three organisations which publish tide height predictions, the Port of London Authority (whose figures I use), the UK Hydrographic Office (part of the Admiralty), and the Proudman Laboratory. Predicting tides is not an exact science, and there are minor differences in predicted heights (and also times) in the tables from these three sources. If the height shown elsewhere is a lot lower than mine, it could be that they are using a local chart datum such as Kew Bridge instead of that for London Bridge.

Q: I thought we had the Thames Barrier to protect us. Why do we still get flooded roads?
A: The Thames Barrier does indeed protect us, and is closed whenever there is a risk of the river getting higher than the flood defences. In most areas, the flood defence is the river wall or bank. But in some places, building a flood defence wall would alter the historic character of the riverside scene, so the flood defence is set back from the river.

Q: I know that 7.3 metres is a very high tide, but how can I tell if it will flood my road?
A: Good question! The predicted tide heights on this site are the heights relative to the chart datum at London Bridge. They are roughly the depth of the water at London Bridge above the lowest possible river level there. Matching those heights to actual situations on the ground further upstream is tricky.

As a rule of thumb, the Embankment road at Putney is liable to flood on a tide of 7 metres or more at London Bridge. Similarly, I reckon that the level of the pavement by Fuller's brewery at the corner of Chiswick Mall and Chiswick Lane South is just covered by a 6.9 metre tide at London Bridge. But the further upstream you go, the effect of the fluvial flow (fresh water from the upper Thames) increases, so these rules of thumb are only a guide. Remember that the weather will also have an effect. Actual tide heights in real time relative to the local chart datums are available on the Thames NOW page (scroll down to Raw Data).

I would like to be able to show the tide height as an altitude above sea level, which can then be compared with known land heights. But that needs more research, so don't hold your breath!  At last, AOD heights are now being introduced for 2020. Click on AOD on the menu.

Q: How can I find out if the Thames Barrier has been closed?
A: Just click on Thames NOW on the left-hand menu! Although the Environment Agency don't give this information in real time, it's possible to detect a closure from the tide heights at Charlton and Silvertown, respectively upstream and downstream of the barrier.