HAZARDOUS MARINE ENVIRONMENT
A Review From Sharky's Dive
HAZARDOUS MARINE ENVIRONMENTS
With over 70% of the earth's surface covered with water, either the Ocean
or the large and small fresh water lakes, Our planet is truly a divers paradise.
When diving in either fresh water or in the Seas of the world, there are
some environmental hazards common to both , and unique to each. The marine environment has
many variations which include different types of bottoms, currents, plants and animal
life. The cautious diver is advised to talk to the local people who are familiar with the
diving area and find out what to expect.
OCEAN CURRENTS:
The ever changing conditions like currents, tides, temperature, and
pollution can also be a problem to the sport diver. Interactions between the atmosphere
and an aquatic environment are very complex. Oceans and large lake circulation's is
primarily dependent on two factors wind and uneven heating of the earth's surface. These
rivers in the sea may be known as currents, streams or drifts. Wind driven circulation,
however, is stronger than convection circulation.
As waves move toward the shoreline at an angle, a "alongshore"
current flowing parallel to the beach develops. Depending on the environmental conditions,
alongshore currents vary in speed, but rarely do they exceed one knot. Alongshore currents
are most common along straight beaches. The speed of the current increases with the height
of the breakers, decreasing wave period, increasing angle of the breakers to the beach,
and increasing beach slopes. Sediment from the beach is transported down current and
reduce visibility.
If swimming in a alongshore current, swim towards the shore, perpendicular
to the current attempt to swim up current.
Rip Currents are the result of water flowing rapidly away from shore. They
are easily distinguished by "dirty water" and a fast movement flowing seaward.
The water within the rip area appears "dirty" because it is laden with sediment
picked up from the shore. Current "head" is the area of reduced current
velocity.
Rip currents may from in a number of ways, but primarily because of the
presence of a longshore current. When alongshore currents become strong enough to overcome
the incoming waves, a sediment trough will form beneath the immediate area and allow the
current to move seaward.
In a cove, along shore currents may diverge to form a rip current.
Alongshore currents sometimes encounter irregularities in the bottom topography close to
shore, like sand bars of reefs.
TIDAL CURRENTS"
Tides are the daily vertical rise and fall of water. Tides are created by
the moon and sun both pulling on the large mass of water which covers our earth. The diver
should pay close attention to the tides in order to use them to his advantage.
The changes in water temperature cause a condition known as thermoclines
which are layers of water having different temperatures. These thermoclines can occur to
the surface or deep in the water. They also have a great affect on the visibility. Hear in
Florida the temperature differential can be as much as 20 degrees.
By studying a tide curve of a lunar month you can see that there are
periodic variations in the "tidal range," the difference between successive high
and low tides. Maximum tidal ranges are called "spring tides,"
Times of minimal tidal range are "neap tides." Both occur at
approximately two week intervals. Spring tides occur during times of new and full moon.
During neap tides, the sun and the moon are not aligned and tend to cancel one another,
producing the lowest of all tidal situations.
"Tidal currents" are horizontal water movements associated with
the periodic rise and fall of water during tidal changes. Not every seacoast has tidal
currents.
Bays or estuaries that have openings amplify the effects of tidal flooding
and ebbing by concentrating the tidal energy through narrow openings. Deep channels
between two shallow reefs or islands, such as those found in certain parts of the
Caribbean, may also concentrate tidal currents.
Where tidal flow is restricted to channels open to the sea, as in some
rivers of straits, the currents reversal with the rise and fall of the tide.
SLACK WATER, or periods of no tidal currents, can be experienced between
each reversal of the tide.
Periods of slack water are appropriate for safe diving activities.
Rivers pose unique water movement problems. As the channel narrows or
widens, the current increases or decreases respectively.
The current will be greater on the outside of the bend in a river than on
the inside of the bend.
Water flow follows bottom contours in rivers and can create whirlpools,
downward flowing currents, and reverse currents in holes.
These currents can carry a diver suddenly to unexpected depths or in a
direction opposite to that desired.
Being carried along in swift water also presents the hazard of hitting
rocks and other obstacles. Attempting to stop in a strong current by grabbing onto some
object can result in the loss of the mask or other equipment.
Maintaining buddy contact is difficult. Al sorts of trash and debris are
found on river bottoms and pose entanglement problems which are compounded by water
movement.
OTHER HAZARDOUS
Caves, cracks and crevices are common to both fresh and salt water diving
environments. A diver should always be careful not to enter into one of these areas that
may be too small to maneuver in, and become trapped. These areas are also ideal hiding
places and homes for many forms of marine life. Caves, cracks and crevices are often
unstable, and just the water disturbance may cause the surrounding rock formations to
shift and possibly trap the diver.
WRECK-DIVING PROCEDURES
Whether in fresh or salt water, diving on shipwrecks has certain safety
and procedural considerations in addition to those of normal diving. It is not the purpose
of this subsection to teach proper wreck-diving techniques, but rather to discuss the
different conditions shipwrecks may be found in, potential hazards associated with wreck
diving, the special requirements for penetrating a shipwreck and the importance of wreck-
diving training.
SHIPWRECK CONDITION;
The condition of a sunken ship affects the techniques used in diving on it
and is largely a result of its location and the effects of aquatic life. As mentioned
previously, salt water deteriorates a shipwreck faster than fresh water, so whether the
wreck lies in fresh or salt water is a key factor in its condition. Depth also plays a
part because in shallow water, wave action tears against the wreck. breaking it up faster,
whereas in deeper water, wave action has less effect. Another reason depth is a factor is
that winter ice floes break up wrecks that lie in shallow water.
Aquatic life also tales its toll on sunken ships, particularly on those
made of wood. In fresh water or colder water, there are fewer such organisms, and wreck
may generally be expected to last longer in that regard.
POTENTIAL HAZARDS:
Wreck diving is generally not a dangerous activity. There are some
hazards, however depending in part on the condition of the wreck.
SHARP EDGES/ROUGH SURFACES:
Probably the most common hazards around a wreck are jagged metal edges
(often rusted) and glass. Marine life growing on the surface of a wreck can also be
abrasive.
ENTANGLEMENT:
Sunken ships tend to attract a great number of fish, which in turn tend to
attract a great number of commercial and recreational fishermen. Over the years, a wreck
can accumulate old fish nets, monofilament (fishing) line and anchor ropes.
DEPTH AND CURRENTS
Although deep water and strong currents can be a factor in other types of
diving, they are particularly common in diving on larger, offshore shipwrecks.
Planning helps to minimize these hazards. Wreck divers typically wear
protective gloves and clothing to prevent injury, and they carry knives in case of
entanglement. Proper dive planning takes onto account possible currents and consideration
for the depth of the water.
DEEP-DIVING PROCEDURES:
When divers venture into the deeper water, they expose themselves to some
potential hazards not found, or not as immediate, on shallow dives. By recognizing these
potentials, and by using proper equipment, planning and techniques, the qualified diver
may safely descend to deeper depths.
FRESH WATER MARINE LIFE HAZARDS:
The diver will not find near the number of hazardous marine life in fresh
water as in salt water.
Fresh water diving in Florida poses several challenges for the diver. When
diving in a man made lakes and rock pits, there is usually a very heavy layer of sediment
on the bottom, when stirred up by the diver it will severely impair the divers visibility.
In natural lakes and springs and canals the weed coverings keep the sediments down but
pose a hazard of their own. In the tropical regions we have the water Hyacinth which grow
in clumps and floats on the surface, this makes it difficult for a diver to reach the
surface in heavy constrictions. The Hydrilla is another fresh water marine plant which is
common is shallower rock pits. They can reach the surface from depths of eighteen to
twenty five feet. Becoming entangled in this plant life is a real hazard to any diver. The
best advise is to avoid these heavily overgrown areas, but if a diver dose become
entangled he should REMAIN CALM, and carefully untangle himself and return to the surface.
As long as the buddy system is always adhered to, This situation should be
no great problem, as the buddy will assist in freeing the entangled diver. Alligators,
Kaymans and Crocodiles,
Diver should be cautious and alert when diving in fresh water known to
have alligators or crocodiles. Leave the water if individuals are sighted.
The most common hazard to fresh water diving are poisonous snakes. Many
varieties are found around the shores of lakes or canals, some like the water moccasin are
able to bite underwater. The best prevention is to avoid these creatures.
Other less serious hazards are the Gar Fish, which can grow up to 100
pounds or more. Gar fish are known to be aggressive bitters. There are also about 100
species of catfish which can sting with a venomous stiff spine located at the dorsal fin.
There are some species of fresh water turtles that are known for biting.
They strike by extending their neck to bite and scratch the victim. The soft shell turtle
may also give a diver or swimmer a bad bite.
ALL the above mentioned turtles should be avoided while fresh water
diving.
The only other fresh water marine life hazard may be the common muskrat.
It will only attach defensively. The bit may not be a severe one, but the chance that they
have rabies is very high. If bitten by muskrat you should capture it and keep it for
examination to see if it has rabies.
There is one key thing to remember when the diver faces any hazardous
situation that is to REMAIN CALM, this applies to any and all the hazards covered in this
report. Only a calm rational diver will be able to survive a hazardous situation, and keep
it from turning it into a lethal situation. Follow all the rules and laws that are taught
to divers in there very basic courses of diving, never dive alone, plan your dive, and
remain calm in any challenging situation.
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