When establishing diving safety, think about the hydrographics and related conditions of the dive site. A number of complex and interrelated conditions can exist in most dive areas. They include wind, waves, current and the hydrography of the area.
Boundaries of adjoining ocean water masses that have different characteristics often produce turbulence. This includes down-currents, upwellings and agitated surface conditions. Generally, the differences in ocean conditions are noticeable. Surface turbulence may appear in the form of small eddies a foot or two in diameter with swirling bubbles extending deeper than the extent of visibility. Discolored water is another noticeable characteristic of upwelling water.
When ocean current flows up and across a shallow reef area and into deep water on the seaward side, a venturi-like effect develops, leaving a narrow buffer zone adjacent to the wall itself that is reasonably undisturbed. When diving from a boat, it is easy to miss the undisturbed area and start a dive in an area of strong down-currents.
The circulation of ocean waters is derived partly from the speed and direction of the wind (as influenced by the Coriolis effect) and partly from convective activity. Surface currents with which divers are concerned are primarily wind-driven.
Temperature and density contrasts between adjoining water masses account mostly for both horizontal and vertical subsurface currents. Water mass boundaries usually develop eddies that vary in size from one to several miles across. Strong down-currents are associated with these upwellings.
Still another characteristic of the atmosphere/ocean relationship is that when the wind blows parallel, or nearly parallel, to a coastline, water is driven away from the coast, occasionally for a considerable distance. When this occurs, subsurface water wells up to replace it. The warmer, out-flowing water subducts into clear water as strong down-currents.
Warm, clear waters are two of the reasons for the popularity of many dive sites, and even small changes in the temperatures of these waters will have a great deal to do with horizontal and vertical circulation. In such a case, changes in circulation patterns should be plainly evident. The upwelling water may have a dirty appearance with poor visibility underwater. The surface will likely be turbulent or agitated with a distinct color line appearing between the two masses of water. At the juncture of the out-going warm current and the upwelling cold water, there may be increased turbulence, even to the point of small breakers. Any change in the appearance of surface water should be a warning to divers that underwater conditions may not be normal. Safety considerations should be made accordingly.
Back to Alaska’s Wreck
In the November 1999 issue of Skin Diver, Cross Talk asked for more information on this popular wreck. John Lachelt of Juneau, Alaska, wrote, “This is a particularly interesting wreck in this area, and one that is a great diving adventure provided a diver is [properly] outfitted and enjoys diving in 40°F water. She and her sister ship Princess Marguerite were luxury liners built in Scotland in 1925. They both had 290 berths and 136 staterooms, and carried 1,500 passengers and 30 automobiles. Both vessels were used as troop ships during World War II. The Marguerite was torpedoed and sunk by the Germans in August 1942.
Continuing his report, Lachelt wrote, “The Kathleen sailed a total of 250,000 wartime miles without being touched by enemy forces, and she was returned to passenger service in 1947. In 1951, she was struck amid ships by the steamer Prince Rupert, causing $250,000 in damage. She was again refurbished and placed back in service. On her last trip of the season in 1952, at about 0300, she ran aground on Lena Point. About 10 hours later (1:30 pm), the tide had raised her vertically in the water, and she capsized onto the port side and sank in about 140 feet of water. Depth to the bow is only about 35 feet.”
Dive shop owner Lachelt warns, “There are some tricks to diving the Kathleen. A knowledgeable local divemaster or instructor can make the difference between a successful, comfortable dive and a disaster in the making. Normally this wreck is recommended for advanced divers. Occasionally conditions permit more novice divers to enjoy one of the finest wreck dives anywhere.”
Even though the wreck is basically intact, the Canadian Pacific Railway, owners of the Kathleen, chose not to salvage her. Their decision was primarily due to almost constant adverse weather, not because of depth.