Reading a tide table before a low-tide walk

A tide table lists the predicted times and heights of high and low water for a specific place, and a low-tide walk is planned around the low. To use one, find the station nearest your beach, note the time and height of the low, and plan to be on the shore for roughly an hour either side of it. Then work backward from the return: the tide can cover flat sand faster than most walkers expect, so the turn-around point needs a margin.

The details matter because a table can be read in several ways. Times may be shown in local time or in UTC, the height may be in feet or meters, and the table may be for a station that is far from your beach.

Finding the right table and station

Use tide predictions from a national or regional agency, or from a reputable tide service that cites one. In the United States, the National Oceanic and Atmospheric Administration publishes official predictions free of charge online. Tide tables are organized by station, and the station may be a harbor or port several miles from your beach. Many tables include corrections for nearby beaches, so you can adjust the time and height if your beach is not the reference point.

Before you rely on a table, check three things: the time zone and whether daylight saving time is included, the units used for height, and the datum, which is the reference level that heights are measured from. US predictions are given in feet relative to mean lower low water (MLLW), which is the average of the lower of the two daily lows over a long period. A negative number means the water is that far below that average. Because the lowest tides often fall below it, the best tide-pool lows often appear as negative numbers, such as -1.0 ft. A more negative low exposes more rock, so a -1.5 ft low opens more ground than a -0.5 ft low. Read the table once for the date you plan to walk, then read it again on the morning of the walk.

Understanding the cycle of the tide

Many US coasts have two highs and two lows a day, but on mixed-tide coasts the two lows can differ a lot in height. The Pacific coast of the United States is a common example of mixed tides, and parts of the Gulf of Mexico get only one high and one low each day. Because of this, pick the lower of the day's two lows from the table when you plan a walk, and check how many lows the day actually has.

A tidal day runs about 24 hours and 50 minutes, so the low tide arrives roughly 50 minutes later each day. If the lowest water on Saturday is at mid-morning, the lowest water on Sunday will be about 50 minutes later. This shift is why a walk that worked well one weekend may need a different start time the next.

The size of the low also changes over the month. Spring tides, which come near the new and full moons, produce the lowest lows and the widest range between high and low water, and they expose the most rock and pool area. Neap tides, which come about a week later, bring smaller ranges and shallower lows. For tide pool and rock walks, a low spring tide usually gives the most to see. The table lists the height, so you can compare it with the lows you have seen before.

Weather can move the water away from the prediction. Strong onshore winds and low atmospheric pressure tend to push water higher than predicted, while offshore winds can hold it lower. A forecast with a stiff breeze blowing toward the shore is a reason to leave earlier and to be more cautious about how far out you go.

Setting a turn-around time with margin

Plan to arrive about an hour before the low, so you have time to reach the most interesting area while the water is still dropping. Once the low has passed, the water begins to flood back in, and the time you have to explore shrinks quickly. A useful habit is to calculate the total walking time from the start, out to the farthest point, and back again, then add a margin of at least thirty minutes.

Set your turn-around time earlier still for routes where the return follows a channel, a gully or a flat stretch of sand, because these fill first. Pick a walk that has an escape route up to dry land, such as a cliff path, a set of steps or a beach access road. Note where the water would cut you off, and do not walk past those points as the tide rises. Walkers caught by a rising tide often misjudge how quickly the sea covers low ground. If the water does cut you off, do not try to wade or swim across a channel. Move to the highest safe ground you can reach and call 911.

Preparing the plan on the day

Before you leave, check the tide times again, along with the weather and the wind direction. Tell someone where you are going and when you expect to return, and carry a charged phone and a watch, since a tide app will not help if the battery dies. Wear shoes with good grip, and take a warm layer, because the wind on a rock shelf or a flat beach can feel much colder than the forecast suggests.

Avoid soft mud and sandbanks in estuaries, which can trap walkers even when the water is some distance away. Follow posted signs about cliffs, and stay clear of the base of a cliff that is being undercut by waves. If the plan changes, shorten the walk rather than pushing on to see one more pool. A low-tide walk is most rewarding when you have time to look around, and it stays that way only when you turn back before the water does.