Reading tide tables for safe rockpooling with children

Why the tide table matters more than the bucket

Rockpooling with children is one of the great free pleasures of a British seaside childhood. But the difference between a magical hour of crab-spotting and a frightening scramble up a slippery gully is usually decided before you leave the house, by a small table of numbers. Tide tables are not just for sailors. They tell you when the water will be at its lowest, how low it will actually go, and how quickly it will come back. Read them properly and you can plan a rockpooling trip that is genuinely safe rather than merely lucky.

Most tide tables are free: harbour noticeboards, local tourist information, the coastguard's safety advice, and printed booklets sold in seaside shops all carry them. What matters is that you look at the right location, the right date, and the right time zone.

Understanding high water, low water and heights

A tide table for a given port lists two high waters and two low waters for most days. Each has a time and a height in metres above chart datum, the standard baseline used around the UK coast. Times are normally given in GMT or BST, and getting that wrong by an hour is a genuine hazard, so check which one the table uses.

The height is the part families often skip, and it is the most useful number on the page. A low water of 0.2 metres exposes a huge, generous stretch of pool-studded reef. A low water of 1.6 metres barely uncovers the same ground, leaving you peering at shallow pools at the top of the shore. Before you promise anyone starfish, look for a low tide under about 1.0 metre, and preferably well under it.

• Note the time of low water, and work backwards from it.
• Note the height, and be realistic about what will be exposed.
• Check whether low water falls in daylight and whether it clashes with lunch, naps or the drive home.
• Note the time of the following high water, because that is your deadline.

Spring tides, neap tides and what the moon is doing

Twice a month, around the new moon and the full moon, the sun and moon line up and their pull combines. The result is a spring tide: a bigger range between high and low water, a lower low, and more of the shore revealed. This is what you want for rockpooling, because the best pools sit lowest on the shore and only appear on the biggest tides.

Spring tides also bring the fastest-moving water. The same volume of sea has further to travel, so it comes in more briskly. Neap tides, roughly a week after each spring, have a smaller range, so less shore is exposed and the water moves more gently. A neap low tide in a rocky cove may be barely worth the trip; a spring low can be spectacular, provided you respect the speed of the return.

The rule of twelfths, and why the sea sneaks up on you

Tides do not rise at a steady rate. In the first hour after low water, the sea rises roughly one twelfth of the total range. In the second hour, two twelfths; the third hour, three twelfths; the fourth, three again; then two, then one. In other words, the water creeps in almost imperceptibly at first and then accelerates through the middle hours of the flood.

This is why families get caught out. You arrive at low water, the tide seems barely to move for half an hour, and you relax. Two hours later the same channel you skipped across is knee-deep and rising fast. As a practical rule, plan to leave the lowest ground about two hours after low water, and be back on the upper shore well before the mid-point of the flood. Set a phone alarm at the start of the trip rather than trusting your sense of time, and tell the children what the alarm means.

Local hazards that never appear on the chart

The tide table is the foundation, not the whole picture. Weather and local geography change everything.

• Onshore wind and swell push water up the beach and raise the effective tide level, sometimes by a considerable margin. A brisk onshore breeze on an exposed coast can make a modest tide feel like a big one.
• Gullies, channels and sandbars cut off routes you used on the way out. On a rising tide, always return by the same path and keep an escape route in mind.
• Cliff-backed coves and headlands can trap a family with no way up. Look behind you before you commit to a pool.
• Seaweed-covered rock is brutally slippery. Wellies are a poor choice for rockpooling: they have no grip and fill with water if you go in.
• Estuary mud and soft sand near river mouths can be deeper than it looks.

A simple routine before you set off

Check the tide table for your exact beach, not a town twenty miles away, and confirm the time zone. Pick a day with a low water under about 1.0 metre, ideally during a spring tide, and aim to arrive as the tide is falling rather than rising. Check the wind direction and any swell forecast; if it is onshore and brisk, save the trip for another day. Tell someone where you are going, take a charged phone in a dry bag, and accept that many coves have no signal at all.

Dress children in firm-soled, grippy shoes, with layers and a waterproof. Give little ones a hand at all times near the water's edge, and never turn your back on the sea. Keep the visiting gentle: look under stones and put them back, leave anemones attached, and return anything you have borrowed to its pool. Then, when the alarm sounds, go — the same tide that revealed the shore will just as cheerfully take it back.