Start With the Tide Table, Not the Weather Forecast

On the coast, the forecast is a comfort and the tide table is a plan. Before you choose a route, find the tide times for the nearest standard port, then apply the local correction for the stretch you actually intend to walk. Published tables are accurate at the port itself, but a headland, a long estuary or a shallow bay can shift the timing by half an hour or more. A harbour noticeboard, a local tackle shop or a quick word with the coastguard station will tell you what the tables cannot.

Write down three things before you leave the house: the time of low water, the time of high water and the height of that day's tide. A 0.6 metre low water and a 1.3 metre low water look identical on the beach but behave very differently on a causeway, and a spring tide at the wrong moment can turn a comfortable crossing into a wade.

• Springs (around new and full moon) push further up the beach and come in faster.
• Neaps are gentler, but a strong onshore wind and low pressure can add 30–60 cm and bring the water in early.
• Wind against tide makes short, steep chop that soaks you and slows everybody down.

Understand How Fast the Water Actually Comes In

The tide does not rise at a steady rate. In the hours either side of low water very little happens, and it is tempting to think you have all the time in the world. Then the middle of the flood arrives and the sea moves faster than most people can walk across soft ground.

The old rule of twelfths is worth remembering: in each of the six hours of a rising tide the water gains roughly 1/12, 2/12, 3/12, 3/12, 2/12 and 1/12 of its total height. The hours in the middle are the dangerous ones. Sand that was ankle deep at 10am can be waist deep by noon, and a channel that was a trickle becomes a fast, cold barrier you cannot cross.

Add terrain to that. On firm, flat sand most walkers manage 4 km/h. On shingle, soft mud or wet rock expect 2 km/h or less. Estuary mud is slower still and can grip a boot hard enough to pull you off balance, which is why the great tidal flats are best treated as out-and-back walks from a firm edge rather than crossings.

Read the Map for Causeways, Not Just Paths

For coastal walking, use a detailed 1:25,000 map rather than a road atlas or a phone screenshot. At that scale you can see whether a path crosses a tidal causeway, whether a beach is shown as sand or mud, and whether the line of a route ends on dry land at both sides or dead-ends on a spit that vanishes at high water.

Look specifically for the words and symbols that matter: tidal causeway, island at high water, footpath across sands, ford, permissive path. Well-known crossings such as Holy Island, Burgh Island, St Michael's Mount, Sully Island and the Worms Head causeway all have safe windows on most days, but each has its own timings and its own local quirks, and none of them should be attempted on a rising tide.

Mark the crossing on the map, mark your planned turn-round point, and mark any high ground you could reach in a hurry. Fold the map so the relevant section faces out and keep it accessible rather than buried in a rucksack.

Plan Escape Routes Before You Need Them

On the outward leg, look back. Note the dunes, sea walls, rocky shoulders, slipways and sets of steps you pass. These are your exits if the tide runs ahead of schedule, and they are far easier to spot while the beach is still open than when the water is lapping at the sandbank behind you.

If you are cut off, resist the urge to swim or wade a channel. Head for the highest available ground, stay together, and call 999 and ask for the coastguard. Give a clear position — a grid reference, the name of the bay, or a description of the nearest landmark. A whistle, six blasts in short bursts, carries further than a voice.

Pace, Kit and the Little Habits That Save Time

Build slack into the day. Use the slower of your group's pace, add 25–30 per cent for the return leg, and then add another half hour. Carry a paper map and compass, a head torch, water, a spare warm layer, a charged phone in a waterproof pouch and footwear with grip and ankle support. Tell somebody where you are going and when you expect to be back, and text them when you turn round.

Set an alarm on your watch for the turn-round time, not just the crossing time, and trust it over your own sense of how long you have been walking. Dogs are wonderful coastal companions but they tire more quietly than people do, and a tired dog on a rising tide is a serious problem.

Local Knowledge and Final Checks

Before you set off, ask yourself one blunt question: if the water arrived an hour early, where would I go? If you cannot answer it, choose a different route. Pick a half-tide walk rather than a full crossing for your first attempt on any new stretch, keep an eye on the weather and the wind direction through the day, and be willing to turn back early. The coast will still be there next week — and the people who walk it most are the ones who are most careful about it.