12. Tidal Information

Tidal Information for Walkers of the Anglesey Coastal Path

With the exception of those few walkers who will see Anglesey's wonderful coastal path as a pure physical challenge, the majority will take their pleasure from walking the well-signed pathway at their own leisurely pace. For variety and interest therefore, some may wish to deviate down onto the alternative beach-walk sections, where they exist. Others may use the coastal path as a means of gaining access to Anglesey's many splendid beaches and so, with these alternatives in mind, some knowledge of the tides will be appropriate from the points of view of safety, avoiding disappointment or even a long wait!

There are a number of web-sites that give tidal predictions. A good site for free predictions is Admiralty ‘EasyTide’ for the day and 6 days ahead. Links to tide times at the closest port for each tidal stretch are also provided on the Path Maps page (03). However, walkers may prefer to carry the pocket-sized booklet “Liverpool & Irish Sea Tide Table” published by Laver. Based upon the times and heights of the tides at Liverpool, these tables also give time differences for High Water at ten locations around Anglesey. BUT REMEMBER to add one hour to the predictions for British Summer Time. Also, very low atmospheric pressure and/or a prolonged southerly gale will raise tide levels around Anglesey above predictions, whereas a northerly gale and/or high pressure will depress tide levels.

Stretches with no alternative inland routes and not passable at High Water

Section 1 Alaw estuary area near the bridge can be flooded at high water

Section 6 Lleiniog Google map (green arrow)

Section 8 Afon Braint Google map (green arrow)

Section 10 Porth Lleidiog, Aberffraw (only impassable on Spring tides) Google map (green arrow)

Section 11 Four Mile Bridge estuary

Alternative Tidal routes

In general, these shoreline routes or beach walks are not available at High Water (Spring Tides)

Section 1 Gorad Beach. Valley

Porth Trwyn to Church Bay (Porth Swtan)

Section 2 Cemlyn lagoon causeway (may not be passable on very high tides)

Section 4 Traeth Dulas

Section 5 Traeth Bychan

Benllech Sands to Red Wharf Bay (do not cross on the Flood tide)

Red Wharf Bay (will be a wet walk at high tide)

Section 7 St Mary's to Pwllfanogl

Section 8 Porthamel to Llanidan

Tal-y-foel shore

Section 9 Traeth Llanddwyn to Llanddwyn Island (on Spring tides, may be marooned)

Malltraeth sands

Traeth Mawr, Aberffraw

Section 10 Porth Nobla to Rhosneigr (Traeth Llydan)

Section 11 Cymyran

Access to Beaches

In general, the following beaches are completely covered around High Water (Spring Tides)

• Traeth Penrhos
• Trwyn Du.
• Cemaes Bay
• Traeth Lligwy.
• Beaumaris
• Traeth Llanddwyn
• Traeth Mawr, Aberffraw
• Porth Cwyfan
• Porth Trecastell
• Silver Bay
• Borthwen , Rhoscolyn
• Porth Dafarch

Detailed Understanding (article by Terry Beggs)

Other Tide Levels

Published predictions give only the times and heights of HIGH WATER and LOW WATER.

For accurate intermediate times and heights, it is necessary to consult the full Admiralty Tide Tables, volume 1; definitely NOT designed for walkers!

However, there is a simple, albeit approximate, way to work out intermediate heights of tide using the following:

Rule of Thumb; just memorise the sequence: 1. 2. 3. 3. 2. 1. ( Total 12).

LOW WATER HIGH WATER

Suppose the predictions gave: 0815 0.0 m 1415 9.0 m

This tide rises over a 6 hour period through a range of 9 metres.

At 0815, the height of tide is 0.00 m

At 0915, .. .. .. .. .. 9/12 . (1) = 0.75 m

At 1015, .. .. .. .. .. 9/12 . (1+2) = 2.25 m

At 1115, .. .. .. .. .. 9/12 . (1+2+3) = 4.50 m

At 1215, .. .. .. .. .. 9/12 . (1+2+3+3) = 6.75 m

At 1315, .. .. .. .. .. 9/12 . (1+2+3+3+2) = 8.25 m

At 1415, .. .. .. .. .. 9/12 . (1+2+3+3+2+1) = 9.00 m

The method still works for less convenient predictions although paper and pencil may be required!

Further Understanding

The gravitational attraction of the Moon is the main force responsible for generating the Earth’s tides. This force varies inversely as the square of the distance from the Moon. The Moon therefore draws the ‘near side’ waters away from the solid Earth, creating a slight bulge in the ocean on that side of the Earth and, at the same time, it pulls the solid Earth away from the ‘far side’ waters, creating a second slight bulge in the ocean on the other side of the Earth.

The Earth takes 24 hours 50 minutes to rotate once relative to the Moon, causing the two diametrically opposite bulges to move westwards as small progressive waves of very long wavelength, thereby creating our twice daily tide cycles. Disrupted somewhat by landmasses, the two waves are diverted into the oceans of the world and, as they reach the shallows, they grow considerably in height due to friction with the sea bed, giving rise to observed tides of 10 metres in some places.

The Sun is the other main player in our tidal system, behaving in a similar manner to the Moon except that, because of the vast distance to the Sun, the tide-raising force and therefore the progressive waves generated are less than half those due to the Moon. The other difference is that the Earth takes just 24 hours to rotate relative to the Sun and so the tide-raising forces of the Moon and Sun are sometimes in phase (Spring Tides) and sometimes out of phase (Neap Tides). Spring tides occur every 14 days, when Earth, Moon and Sun lie in the same meridian plane; neap tides also occur every 14 days, when Moon and Sun form a right-angle when viewed from Earth.

Terry Beggs