Working with Tides

Living near the California Coast affords me ample opportunities for photographing the seashore, and an important part of learning to photograph in and around coastal areas is learning a little bit about tides. Low tides often allow fascinating tidepool opportunities, and (at least in the coastal areas near here) often bring a lot of interesting geology out of the water.

The rise and fall of the ocean along the shore is affected by three factors, the gravitational influence of the sun, of the moon, and the shape of the shoreline and sea floor. Historically, tidal prediction was a difficult problem, even today, tides at a given location are not so much computed from first principles as they are modeled in part based on records of past tide levels. Fortunately, you don’t have to get into the tidal prediction business yourself, many tidal prediction resources exist.

It is helpful to build up a bit of intuition about tides. In any given day, the tide will cycle up and down, often by seemingly unpredictable amounts, twice. So the basic pace of rhythm of tides is measured in hours. How much tides vary at a particular location varies both over the lunar month and over the year. In each month, the greatest tidal variation happens at about the time of the full moon or the new moon, as such, I plan a lot of my longer coastal trips to conincide with the full moon, both for the full moon itself and for it providing a greater range of tides to photograph in. There’s also variation through the year, the lowest low and highest high tides are those nearest early January and early July (earth’s perihelion and aphelion, but don’t worry, that won’t be on the quiz!). In short, I find that the full moons, particularly near the beginning and middle of the year offer some of the best times for coastal photography.

Today, detailed tide predictions are not hard to find. Many web sites provide tidal information, such as the NOAA Tides and Currents page, which covers the United States, it’s not hard to find other sites for many locations. These web pages work well if you plan ahead or have an internet connection where you’re going to be photographing.

Another great resource for tidal predictions is the annual Tidelog graphic almanac from Pacific Publishers. By providing tide information for different areas in a week-at-a-glance graphic format, as well as sunrise/sunset, moonrise/moonset and phase information, it’s remarkably easy to pick great times for coastal photographic trips by flipping through pages and scanning for deep tides quickly.

With the growing popularity of smart phones there are a handful of tide prediction applications available as well. For Palm OS-based devices, TideTool is my favorite choice, as it offers graphic tidal predictions and works just as well offline (that is, when your phone doesn’t have a signal.) Tide App for Apple’s iPhone platform is also a good choice but doesn’t (yet) offer offline prediction. I haven’t used cTide for PocketPC devices, but it has been recommended to me and also offers offline prediction.

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