Tides and Dive Planning

The sun and moon's constant push and pull on the sea creates a rhythmic heartbeat that affects the ocean in profound ways. If an astute diver understands these powerful forces, he or she can use that understanding to their advantage in their dive planning. Tidal forces can affect dive planning in several different scenarios, or combinations thereof. Let's take a look at each of these, beginning with the least critical and finishing with the most important.

CURRENTS

Powerful oceanic currents are primarily a result of the winds and the turning of the earth. Tides can, however, affect these currents. During times of large tide swings between high and low tide, normal oceanic currents are accentuated, but not dramatically. Dive sites that are known for strong currents and rapidly shifting currents should perhaps be avoided during these times.

DEPTH

This is also generally not a critical factor in dive planning on the west coast with regards to tides. Tidal swings in California are rarely more than nine feet (except in enclosed bays), and this is the extreme. Even so, if you'll be diving on a deep dive site where bottom time and depth planning is critical, you may want to take tides into consideration.

MARINE LIFE

Much of shoreline marine life is deeply in tune with tidal rhythms. Although it varies from species to species, a high or outgoing tide seems to be the time of highest activity. It is during these times that shallower waters, and the food that lies within, are more accessible. The outflowing tide takes some of this food and casts it offshore. The level of activity will vary from site to site.

VISIBILITY

High tide is the best time for visibility. It is rather simple actually. Generally, clearer water lies farther from shore. High tide pushes that clearer water closer to shore. The difference may not be dramatic, but enough to make a beach dive doable or a bust.

BEACH DIVING

If you are beach diving, some beach dive sites are better dived at low tide and others at high tide. Familiarity with the site is a must. Varying water levels can necessitate climbing over sharp shallow reefs. Most beach dive sites are best approached at high tide.

BAY DIVING

And finally scenario four generally does not affect California divers, but where influential it has a radical impact on safety. Dives made within enclosed bays or in or near the inlets or outlets of bays must be planned carefully to coincide with what is known as "slack tide." Currents running through bays or the bay's mouth can be quite dramatic during tidal movements, sometimes exceeding five knots. Divers can be swept out to sea or into boating lanes. Slack tide are those times of peak low or high tides (again, high tide is usually best for visibility in bays). Morro Bay is a good example. Several good dives lie within the calm bay but dives must be planned around the tides. If a dive is planned in a bay, or in the mouth of a bay, enter the water about 20 minutes before peak high tide. Peak high tide is when water will be moving the least. With a dive of 30 to 40 minutes, you will be out before the current picks up as the tide goes out.

BASIC TIDE MECHANICS

There are two high tides and two low tides per day, one each moderate, the others more dramatic. Peak tide times and levels change by location and day, advancing about 30 minutes each day. The gravitational pull of the sun and moon are what cause the tides, with the moon being most pronounced due to its close proximity to earth. When the sun and moon are aligned, such as during full or new moon phases, tidal changes are the most dramatic. This is known as a "spring tide" (having nothing, however, to do with the season). When the sun and moon pull against each other, the tides are less dramatic. This is known as "neap tide."

USING TIDE TABLES

Tide tables are an excellent resource for dive planning, with the best being the kind that show tides in a curve graph. With this kind of graph you can estimate water movement. The less water movement (a smoother curve, one with less dramatic peaks and valleys) and diving at high tide, gives the best visibility.

Published tide tables are for one specific location. Because tide times and levels vary by location, make sure your tide tables also have a table to correct for specific location. These tables will give how much time to add or subtract for the specific location of interest.

Should you plan your dives around the tides? With bay diving, it is a must, but in most cases, there is no need. For maximum enjoyment on your dive, however, it is a factor to consider.

Dale Sheckler is Publisher of California Diving News, co-author of the book Southern California's Best Beach Dives and Producer of SCUBA Show 2000, June 3 & 4 at the Long Beach Convention Center.