Looking at Life's Ups & Downs

By Robin Battley

We all know life has its ups and downs. From a diver's perspective, that includes examining area tides and currents before jumping in over your head, so to speak. Oh sure, you regularly dive at sites where you believe neither tide nor current are a major factor, right? In your "x" years (fill in the appropriate number) of diving experience, you've neither checked a tide table nor considered prevailing weather conditions, and all your dives have all been greator mostly? Well, consider the following questions. Have you ever arrived at a dive site and discovered the visibility to be substantially reduced for no apparent reason? Have you ever jumped off the dive boat to discover a mysterious surface current you never encountered before? These situations can be predicted if you take a little time to study tides and currents.

Tides are the periodic rise and fall of all waters, although most evident in the oceans, caused by the gravitational attraction of the moon and to a lesser extent, the sun. Every lunar day most shores experience two highs and two lows called semi-diurnal tides. How do you find the extent of such changes in water levels? The most common resource for salt water enthusiasts is the annual Canadian Tide and Current Tables. These volumes provide predicted times and heights for the tides as well as predicted times for slack water and maximum velocities for currents. Fresh water fans can check the "Recent and Forecast Water Level Data" distributed in monthly bulletins by the Canadian Hydrographic Service for each of the Great Lakes. Another source of information gaining popularity is the increasing number of computer programs accessible through the Internet offering calculations for water levels and currents. When using these, remember that the accuracy of tide and current predictions is only as good as the quality and quantity of tidal constants used to compute them. Every effort should have been made to use constants derived from the longest and most consistent period of observation and record. Sample calculations derived from the computer program should be compared to reputable published sources before entrusting yourself to those numbers.

Whether using government publications or Internet calculations, a number of other factors can cause significant changes in the water environment around you. Be observant of strong or prolonged winds in your area, abrupt changes in barometric pressure, or even prolonged periods or high or low pressure. Any one of thesemeteorological effects can cause fluctuations in water levels or the speed and direction of a current. Your continued practice of "reading the water" will alert you to the existence of any of the above factors that cannot be forecast.

Another important complement to this reference material is a local chart. As a diver, you will have invaluable information available for planning your next dive including entry and exit points, depth, bottom composition, types of underwater features to expect (drop-offs, pinnacles, rocks), direction and strength of currents, and boating traffic patterns to name a few. Combined with your local water level information, you will have a comprehensive dive plan knowing where and when to dive. Don't be surprised if you start enjoying your dives more. You may encounter better visibility by selecting your days and times more carefully. The increased relaxation of knowing what to expect at even a new site may result in prolonged bottom times. And the confidence provided by some background information may encourage you and your buddy to explore new dive sites instead of always returning to the same old place.

And remember, the "same old place" is not always the same from day to day as a result of changing weather and water levels. Here's an example. Whytecliff Park, a local BC diver training site will experience an extreme range of almost 16 feet on July 2nd this year. It's a Sunday on the long weekend in the middle of the summer, and I would expect many divers in the area that day. How many of them will be prepared for the silty conditions and surface currents caused by an incoming tide of an extra 2.5 feet every hour all through the afternoon? Do I have a crystal ball? No, just a copy of the local Canadian Tide and Current Tables and a familiarity with the dive site. It's a wonderful dive site with lots of marine life to offer the new and the experienced diver alike but it is certainly not my choice on Sunday afternoon, July 2nd. Another time will suit much better.