Diving in Silty and Sensitive Environments
Some of the most awesome diving spots in the world have a bit of a dual personality when it comes to good viz – a bit of a natural Jeckle & Hyde, if you will.
We rave about 20 to 30m viz days on Aliwal Shoal or at Sodwana, and many of us associate fresh water diving with poor viz and not much to see.
Yet to those who have answered to the beckoning allure of underwater caves, a different world opens up. A world not often disturbed by light and the life that thrives by day. Without daylight, green algae don’t survive there, and the water is often so gin-clear that you can see as far as your torch illuminates the walls and passages around you.
Yet despite the mind blowing clarity of the water, cave divers know that disturbing the sediment on the floor, walls and even ceilings of these beautiful caverns can foul up visibility in an instant.
Diving in quarries can benefit by learning some simple techniques that cave and wreck divers have developed to deal with silt.
Option 1 is simply to not foul it up in the first place.
New divers often find it takes practice to descend and not hit the bottom before stabilising buoyancy. Descending in a horizontal position slows down the rate of descent, and in less than perfect viz allows one to see the bottom sooner than when going feet first. Tapping air into the BC via the power inflator as one descends helps keep the descent under control (of course, not being too heavily weighted in the first place really helps). New divers should practice this directly over a 5m grid to get their timing and judgement right before trying a direct descent over the silty bottom.
If you must descend feet first (e.g. ear problems, or course requirements) make sure that you don't kick your fins as you approach the bottom. Use your BC and breathing only. You will cloud the water far more by fanning the bottom with your fins than by simply touching down on it. If you do hit the bottom, don't move your fins at all. Simply inflate your BC enough to rise off the bottom a meter or so, then gently move your fins to get your body horizontal in the water, and adjust your buoyancy so that you don't ascend too far.
a) Kicking strokes: commonly new divers are taught only one kick – the flutter kick, with its broad up and down movements that push water in a vertical plane almost as much as backwards. This may be fine in mid water, or over a sandy bottom, but in a silty environment, it is the number one destroyer of viz.
b) An anti silting kick such as a frog kick or modified frog kick is perfect for not disturbing the silt. The frog kick works because, if done correctly, it scoops water back and slightly upwards, away from the silty floor. Skilled divers can swim as close as 15cm from a muddy floor without disturbing it at all. Andrew Georgitsis has a very good demo video clip of the frog kick on his web site http://www.breakthrudiving.com . From his main page, click on the Learning Centre button, then select Frog Kick under the Video Skills section. (You need Apple Quicktime to view it, and the download takes a while). You will notice that a lot of the control and thrust of this agile kick comes from the ankles.
c) Trim in the water: this is the angle one’s body lies at in the water – whether stationery or swimming. Swimming perfectly horizontally creates the least drag, uses less air, and makes one least tired. Stop swimming and see if you stay perfectly level, or if you start to rise or sink. If you don’t stay put, correct your buoyancy and then see whether your feet rise or sink without finning at all. Many people find their feet sink, because they carry most weight on their weight belts rather than distributing it evenly around their centre of lift (BC & wetsuit). Ironically, the more weight added to the weight belt, the more the BC needs to compensate for it, and the more the diver tends to hang legs down in the water.
d) Getting the right distribution of weight and lift is important to maintaining a comfortable horizontal trim in the water – especially if you want to be able to frog kick correctly.
e) Positioning of the feet while swimming: An efficient way of finning is to keep the feet slightly up, in the slipstream of the tank, without letting the knees drop below the horizontal plane of the chest. If the knees drop down, they create drag, and can disturb the silt if you are close enough to it. Keeping the feet up and horizontal helps them stay a respectable distance from the silty floor, even if your chest nearly touches the floor
f) With a little practice, it is easy to do 360° turns while remaining completely horizontal, simply by using a modification of the frog kick, called a helicopter turn.
g) When it’s time to ascend, don’t drop your feet to begin swimming up. That will immediately stir up the silt if you are anywhere near the bottom. Simply breathe in deeply to begin ascending in a horizontal position, and then dribble air gradually from your BC to keep control of your rate of ascent.
h) Note: frog kicking and control is easiest with flat bladed fins, like jetfins. If you have split fins or buckling blades like the Mares Volo, you may find frog kicking more difficult than most. An alternative is the modified flutter kick. Keeping body horizontal, keep the knees bent & fins up. Now the "downward" stroke of straightening the leg forces water backwards and not directly at the floor.
Option 2 is to handle the cloudy water as safely as possible
a) Find out how deep the water is, and where you will be diving.
b) Discuss with your buddy and team in detail what the dive plan will be, and especially what to do if you get separated.
c) Discuss and agree on touch signals in case you can’t see hand signals at all.
d) Take compass bearings for exits and targets before you descend, and note them on a slate if they are even slightly complex.
e) Stay particularly close to your buddy, even getting into touch contact before you enter a silt cloud. Proceed with caution, in case the cause of the cloud is still kicking wildly somewhere inside it.
f) Take a good dive light that can be used to signal through the “fog”, first checking that it is working properly before you descend. If you go through a really bad patch of cloudy water (left by other less skilled divers, of course) and lose sight of your buddy who is only a metre or 2 away, finding each other’s torch beams can be a lot easier than no lights at all. Remember that black neoprene doesn't stand out too well in poor viz conditions.
g) Reading your compass in a heavy silt blackout may be possible by torch light, when it is impossible otherwise. Remember that it can get very dark in just a few metres of water if the viz is only 15cm (think Emmarentia dam at 3m).
h) Keep a close eye on your depth and pressure gauges. In silty water it is easy to become disorientated, go deeper, and use more gas than you realise – particularly if you are feeling uneasy.
Option 3 go sky diving instead - 40m+ viz isn't unheard of up there ;-)