If you are a coastal footpath walker, a sailor, a fisherman or a beach-goer in Pembrokeshire you need to understand tides!
You should certainly have a set of tide tables to hand (and note whether, during the summer, they use GMT or BST) but understanding the sequence of changing tides and the advance and retreat of tide heights over a 28 day period (the moon cycle) is handy to know.
SO HOW DO TIDES WORK?
There are high tides and low tides, and the time between high and low tide is just over 6 hours. Every day there are (usually) two high tide and two low tides. However because of the “just over 6 hours” on some days there are only 2 low and one high, or two high and one low.
The difference between high tide and low tide (the tidal range), here in Pembrokeshire, ranges from 7.5 metres to about 3 metres. Those days when the tidal range is at its highest are called “spring tides” or “springs”. These will occur a couple of days after new moon and full moon. Those days when the tidal range is at its lowest are called “neap tides” or “neaps”. These will occur a couple of days after half-moon.
At spring tides the high tide will be about 7 metres and low tide about 0.5 metres. At neap tides the high tide will be about 5.5 metres and the low tide about 2 meters.
At a high spring tide (say, over 7 metres) many of Pembrokeshire’s best beaches are more-or-less under water, maybe with just a fringe of pebbles at the top. At high neap tides however (5.5 metres or so), there is often a little bit of beach showing. All beaches are best at low water, whether springs or neaps.
Each day the tide times move on by just less than an hour (12 hours over 14 days) but the advance in tide times is not regular. At springs they advance quite slowly – perhaps 45 minutes per day or less, whilst at neaps they advance about an hour.
TIDAL RANGE VARIATION
The tidal ranges vary through the year. The biggest ranges are often around the March and October equinoxes, so if you want to service a drying mooring these are the dates to look out for. At these times, during a low spring tide, parts of beaches are exposed which are not normally exposed and those keen on “pêche a pieds” will be out there trying to grab a few razor clams. It is also a very good time for rock pooling. The tidal height at these times will often be only a little over 0m, which is as low as it usually goes. (But see below!)
Because of the way the tidal cycle works, the highest spring tides are always at roughly the same time of day. In the particular case of Pembrokeshire these tides occur at about 7:00 am in the morning. This means that low tide is about 1:00 pm, perfect for beach goers. During neap tides the high tides are about 2:00pm – not so good.
There are other factors to bear in mind when looking at tide heights. If the weather is stormy (low pressure) and there is a brisk south-westerly blowing into Milford Haven, then tidal heights (both low and high tide) can be much higher than predicted. It is as times like these when the flood gates such as those at Dale are put in place. In contrast, in periods of high pressure, the tide heights can be much lower than predicted and a low tide can go below 0m.
And one last note – coastal footpath walkers have tidal crossings to navigate at The Gann and at Sandy Haven. The general recommendation is that these should be crossed within 2 hours of low water. However, life is not that simple – at some neap high tides, the Gann crossing never covers at all and at springs in winter after heavy rainfall and low pressure, it sometimes never uncovers! The high-tide route at Sandy Haven is very long and tedious and should definitely be avoided. The Gann high-tide route is shorter but you miss a vary interesting paart of the path.
So in summary, many of the activities which take place in Pembrokeshire are dependant on a good knowledge of the tides. A set of tide tables is useful, or access to a Tide Times website such as www.ntslf.org or www.mhpa.co.uk/search-tide-times/ And if you want to see what the tide is doing now, the Port of Milford Haven web page www.mhpa.co.uk/tide-heights/ will tell you.
And do not despair if on the first day of you holidays you find the tide times are inconvenient for the beach – by the end of the week they will be fine!
SOME MORE NOTES FOR WATER BASED ACTIVITIES
Of course, the tides are of key importance to sailors and fishermen. They need to take note of the depth of water available for mooring and anchoring. The Dale Pontoon dries at 1.5m which means it dries out at many low tides, and the Dale Slipway dries out at virtually all low waters (2m).
And of course any waterborne craft needs to make allowance for the tidal streams which can be very strong at springs. These tidal streams are strong at the entrance to Milford Haven, and notoriously strong through Jack Sound. Not only is it slow progress trying got make headway against the tide, It can be very uncomfortable, especially when the wind is in the opposite direction.
In the case of Jack Sound, it is virtually impossible (and certainly inadvisable) unless you have a motorboat with big engines and you have a strong constitution! It is worth noting that the tidal streams through Jack Sound change direction 2 -3 hours after high or low water (it varies with tide direction and springs/neaps – you need a tidal stream diagram to be on the safe side).
Incidentally, the most unpleasant part of Jack Sound is not the sound itself, once you have identified the various rocks and hazards, but the tidal race on the exit from the sound. Going north to south on a favourable stream against a SW breeze can be most uncomfortable.
The tidal flows around the islands and in and out of Milford Haven can be quite difficult to understand. The flood tide (rising) sweeps up the Irish Sea and flows into Milford Haven. But at high tide in Milford Haven the tide is still flooding up the Irish Sea. You really need a decent set of tidal stream charts, or careful perusal of the tidal diamonds on paper charts (I have no idea how this all works with electronic navigation!) to make sure you are not going to battle the tides and to work out how to best use them to your advantage.