Reading Tide Tables Before a Seaside Walk

Why the Tide Belongs in Your Plan

Most of us check the weather forecast before pulling on our boots, then set off without a second thought for the sea. That works fine on a hill. It does not work on a beach, a tidal causeway or a headland path with a rocky cove at the bottom. Around the UK coastline, the sea rises and falls twice a day, and in some places it moves faster than you can walk. The good news is that tides are the most predictable thing in the outdoors. A five-minute look at a tide table before you leave the house removes almost all the risk.

What a Tide Table Actually Tells You

A tide table lists, for each day, the times and heights of high and low water. You will usually see four entries a day: two highs and two lows, roughly six hours apart, with the whole cycle running about 12 hours and 25 minutes. So if today's high water is at 10am, tomorrow's is about 10.25am.

The heights matter as much as the times. They are given in metres above chart datum, the lowest astronomical tide used as a baseline by mapmakers and mariners. A high water of 5.6 metres means a lot more beach disappears than one of 4.2 metres. A low water of 0.4 metres means you might walk out to a wreck or a causeway that is under water for most of the month.

Two things trip people up:

• Standard ports and secondary ports. Tables are published for big reference ports, and nearby spots need a local adjustment added or subtracted. A harbour ten miles along the coast can differ by half an hour or more.
• Clock changes. Many tables are printed in GMT, so add an hour in British Summer Time. Getting this wrong puts you on the sand at exactly the wrong moment.

Springs, Neaps and the Rule of Twelfths

Twice a month, around the full and new moon, the sun and moon pull together and we get spring tides — bigger ranges, lower lows and higher highs. Between them come neap tides, when the range shrinks noticeably. A beach that is safely walkable at neaps can be a foot deep at springs.

The tide never rises at a steady rate. It moves slowest at high and low water and fastest in the middle two hours, and the old rule of twelfths captures this neatly. Over roughly six hours of rising tide, the water gains one twelfth of its total range in the first hour, two in the second, three in the third, three in the fourth, two in the fifth and one in the sixth. In other words, if the range is six metres, half of that six metres arrives in just two hours. That is why a beach can look generous when you set off and alarmingly narrow when you turn round.

The Places That Catch People Out

Any flat sand or mud between the tideline and the dunes is a candidate, but some settings deserve extra respect:

• Long estuaries and bays with wide, shallow sand, where the incoming water spreads fast across flat ground rather than rising up a wall.
• Headlands with a low-tide route round the base, where the alternative is a long climb back over the top.
• Tidal causeways and stepping-stone crossings to islands, which are only passable for a window either side of low water.
• Beaches backed by cliffs, where there is no easy exit if the water reaches the rocks and the path out is behind you.
• River mouths, where fresh water meets the sea and the flood can arrive quicker than the table suggests.

Building the Tide Into Your Day

Once you know the times, the planning becomes straightforward. Pick a walk that suits the tide rather than hoping the tide suits the walk.

• Walk the low-tide section on a falling tide, so the water is still retreating as you go and you have hours of margin on the way back.
• Allow two hours either side of low water for anything involving exposed sand, causeways or rocky shorelines, and add more if the ground is soft or the route is slow.
• Identify your escape route on the map before you set out — a slipway, a set of steps, a path up through the cliffs. If there is only one, do not go past it.
• Keep the high water time in mind as a hard turnaround, not a suggestion. Set an alarm on your phone if it helps.
• Tell someone your route and expected return, and carry a charged phone in a dry bag.

If you are unsure, the local harbour office, coastguard station or a harbourmaster's noticeboard will have the corrected figures for that stretch of coast, and staff are usually glad to be asked.

Reading the Sea on the Day

Tables are a forecast, not a guarantee. Wind pushes water: a strong onshore breeze can bring the flood in early and higher, while a stiff offshore wind holds it back. Low pressure adds height, high pressure takes it away. Watch for the classic warning signs — waves breaking where there were none twenty minutes ago, water creeping round the seaward side of rocks you walked past, gulls and waders shifting inland. If the sea is behind you and the ground ahead is flat and low, turn round now rather than later. The coast is at its best when you have given the tide the respect it has earned.