Guide To Tides
Why do tides matter?
At high water on a spring tide there really isn't a lot of beach at Teignmouth; there is some by the pier but the beach at Eastcliff doesn't start to appear until about two hours after high water.
Conversely with a neap tide there is a beach available at high water even at Eastcliff.
The Spratt Sands between the pier and the harbour channel makes an awfully tempting walk at low water springs when a vast expanse is exposed but the tide rises quickly and it is all too easy to be cut off. If you must explore take a boat or board with you or learn to read the tide tables.
If you want to know what the tide will be doing when you visit, read on...
Understanding Tide Tables
The times and heights of tides can be found from the noticeboard outside our Lookout, on the internet or in a set of tide tables that you can buy from shops around Teignmouth.
Entries for a few days of the Teigmmouth Approaches tide table are shown here but you won't find the column headed "range" on a normal set of tables; this is something you would have to calculate for yourself.
For simplicity we have highlighted the high and low tides.
Note: Published tide tables invariably give times in UTC (GMT in old money); in the summer you must add one hour to the times shown.
Several points are immediately obvious from the table:
- the times of the tides advance each day. High water on day one is at 07:09, two days later high water is at 08:17 and a week later high water occurs at 11:12.
- the heights of tide at high and low water change progressively from day to day. The biggest high water shown here is 5.1m and the smallest is just 3.3m. Similarly the heights of low water vary from 0.3m to 2.1m.
- the range (the difference in height between high and low water) also changes each day from 4.8m on the morning of Friday 23rd to just 1.3m early on Saturday 31st.
- The biggest tides are known as spring tides whilst the smallest tides are known as neaps.
- spring tides occur approximately every 15 days - the times of tides on Thursday 22nd are very much the same as those 15 days later on Friday 6th September. Both are spring tides although the height of tide on 6th September is considerably less than the height on 22nd August. The 22nd August was an exceptionally large tide.
- High Water at spring tides occurs around 08:00 or 09:00 BST morning and evening whereas high water neaps occurs between 14:00 and 15:00 BST.
How fast does the tide rise and fall?
The technical answer is that the tide follows a bell curve and there are different curves for different ports, the one for Teignmouth being based on Plymouth Devonport, but the quick approximation is the rule of twelfths, which states that either side of high water the tide will rise or fall:-
- 1/12th of the difference between high and low water in the first hour
- 2/12ths (1/6th) in the second hour
- 3/12ths (1/4) in the third hour
- 3/12ths (1/4) in the fourth hour
- 2/12ths (1/6th) in the fith hour
- 1/12th in the sixth hour
For example, if the height of high water is 5.1 and the height of low water is 0.3 then the difference, range, is 4.8m thus in the first hour after high water the tide will rise/fall 1/12th of 4.8 or 0.4 metres. In the second hour it will rise/fall a further 0.8 metres and so on.
A few more facts for the curious
- Tidal heights are measured above chart datum which is not the same as ordnance datum. Chart datum is the lowest astronomically predictable tide and at Teignmouth is 2.65m below the ordnance datum.
- Tides can be affected by both wind and barometric pressure. A large high pressure system or a deep low can lower or raise heights respectively by as much as 30cm.
For a detailed explanation of tides see en.wikipedia.org/wiki/Tide or
Practical explanations for boaters