Why the tide table comes first

An estuary at low water can look like a wide, inviting pavement of sand and mud. It is one of Britain’s great coastal pleasures: the light, the wading birds, the sense of walking on the sea floor. But an estuary is not a beach. It is a working waterway with a tide that can return faster than you can walk. Before you plan a route across exposed sandbanks, learn to read a tide table. It is the single most useful safety skill for estuary exploring, and it costs nothing but a few minutes.

Tide tables are predictions, not promises. They tell you when high and low water are expected at a reference port, and how high the water should be. Local conditions, wind, air pressure and river flow can all shift the timing and height. Treat the table as your baseline, then add local knowledge and a generous margin for error.

The three numbers that matter: time, height and range

Most tables list four columns for each day: the time of high water, its height, the time of low water, and its height. Heights are usually given in metres above chart datum, a low-water benchmark. Times are normally in GMT or BST, so check which one applies. If you are using a secondary port, you may need to apply a time difference and a height correction.

The difference between high and low water is the range. A small range means gentle movement; a large range means the sea has more work to do, and it often does it quickly. On an estuary sandbank, the range tells you how much sand will be exposed and how fast the channels will fill.

• High water time is your deadline, not your starting gun.
• Low water time is the best window for a crossing, but not the whole window.
• Range shows how much water will move between the two.
• Time zone matters: an hour’s error can put you on the sand as the flood begins.

Spring and neap tides: the fortnightly rhythm

Around the new and full moon, the sun and moon pull together and the tide range grows. These are spring tides. They give the highest high waters and the lowest low waters, exposing the widest sandbanks. They are wonderful for exploring, but they are also the most unforgiving. The flood can travel across flat sand faster than a brisk walk, and the return route may be cut off earlier than you expect.

Around the quarter moons, the range shrinks. These are neap tides, with higher low waters and lower high waters. Neaps are generally gentler, but they can still catch you out. A neap low water may not expose the bank you hoped to cross, and a neap high water may still cover a causeway. Always read the actual heights, not just the label on the calendar.

Local hazards: mud, channels and the speed of the flood

Estuaries are dynamic. Channels migrate after storms, sandbanks shift, and soft mud can look firm until you step on it. The incoming tide does not always arrive as a neat line. In some estuaries it creeps up gullies and creeks first, cutting off your route from behind. In a few, it arrives as a low wall of water or a tidal bore. Either way, the water can be deeper and faster than it appears.

Other hazards are less obvious. Cold water can sap your strength quickly. Fog can erase landmarks. A strong onshore wind can raise the water level and push the flood in earlier. Heavy rain upstream can increase river flow and change the shape of the sand. Never assume the route you walked last month is the route you will walk today.

• Soft mud and quicksand patches, especially near channel edges.
• Deep gullies that fill before the main tide reaches you.
• Fast-moving water in channels, even at mid-tide.
• Cut-off points behind you as creeks and creeks fill.
• Poor phone signal, slippery rocks and sudden fog.

Planning a safe low-water walk

Start with the official tide table for your chosen day and port. Identify the low water time and height, then work backwards. Aim to be back on firm ground at least two hours before the next high water. On spring tides, with an onshore wind, or after heavy rain, make that three hours. The safest window is usually a short one, not the whole period between high waters.

Check the weather forecast for wind direction and strength, rain, and visibility. Look at a large-scale map and identify high ground, escape routes and obvious channels. If you are new to the estuary, go with a local guide or an experienced group. Tell someone your route, your expected return time, and what to do if you are not back. Carry a charged phone in a waterproof pouch, a whistle, a torch, warm layers and water.

• Read the table for the correct date, time zone and local corrections.
• Note the range: spring or neap, and how fast the water will move.
• Plan to turn back well before the flood, not as it starts.
• Watch for changes in water colour, ripples and bird behaviour.
• Avoid crossing channels; follow the firmest, highest ground.

When to turn back — and what to do if caught

The moment you see water where there was none, or hear the first trickle in a gully, treat it as a signal to leave. Do not run for the far shore. Head for the nearest safe high ground or the bank you came from. If you are cut off, stay calm, stay visible and call 999 and ask for the coastguard. Give your location using landmarks, grid references if you have them, and a clear description of what you are wearing.

Do not try to wade or swim a deep channel. Estuary currents are strong, the water is cold, and the bottom is often soft. If you must move, keep to the highest ground and wait for help. A little patience on a sandbank is far better than a struggle in a flooding channel. With a tide table, a plan and a healthy respect for the sea, estuary exploring can be one of the most rewarding ways to spend a day on the British coast.