Coping with downcurrents
Ever got caught in a downcurrent? If so, you’ll know what a heart-pounding situation it can be for even the most assured of divers
You are on a one-hour dive with a healthy visibility of 10m on the Longships, a collection of rocks just off the tip of the Cornish coast. The current has been predictably strong. You are at 10m and turn to your buddy to signal to ascend.
But before you have even had time to give the thumbs-up, you are being pushed violently downwards. Your bubbles enclose you before disappearing below you. You fill your BC with air and fin as hard as possible, but the water continues to carry you further down. The depth gauge reads 20m, then 30m and 40m.
Then, suddenly, everything stops. What may have only lasted a minute seemed like forever. Thankfully, your buddy is right there with you. Your heart pounds as you both dump your air and make a slow ascent back to the surface with the remaining reserve of air in your cylinder.
Being forced to ride with a strong downcurrent is a humbling experience for even the most experienced of divers. This incident described above happened to DIVE’s Charles Hood 12 years ago. It was an isolated event; he has dived the Longships many times since without incident. However, it’s a reminder that no matter how many dives we have or how strong we are, there’s no arguing with the ocean if it decides to hit us with a powerful rush of water and force us metres below where we plan to be. And for those who enjoy the thrills of fast drifts and the marine life to be seen in nutrient-rich waters, downcurrents and even upcurrents are threats we may have to face at some point.
Downcurrents in current-rich areas can occur unexpectedly at any given time. The cause of downcurrents has never been entirely understood, although they generally happen when a strong current runs across a flat bottom to a sharp vertical reef drop-off, forcing it downwards. Other explanations are converging horizontal currents – water cannot be compressed, so is forced down. This is more common where topography of the sea bed or reef forces the flow of water to converge. In the North Atlantic, downcurrents might be caused by convection – where the water becomes dense as it cools and sinks into extremely deep water. Other causes include wind and wave power.
Thankfully, downcurrents generally remain localised, which means there is better chance of escape. Some downcurrents will require little more than a few fin kicks and a small blast of air in the BC for you to break free; however, the stronger down-blasts take a lot more effort.
There is no hard and fast rule on how to deal with a downcurrent, as it depends entirely on how strong it is, how much time you have to react and your depth. Here we look at some of the most common downcurrent escape plans.
1 Be prepared
Watch out for any signs of shifts in current direction and be on the lookout for a downcurrent. In the UK, kelp is often a good indicator. Also, monitor the direction of your bubbles. Another strong indicator of current direction or strength is reef fish. Generally, small fish will all be facing up-current, unless it is so strong they are forced to take shelter. In a downcurrent, however, fish may be finning up and down and frantically in circles. If the downcurrent is particularly strong, you may even see larger fish being swept downwards.
Avoid using nitrox if you know you are at risk of being hit by a strong downcurrent. Oxygen toxicity, caused by exceeding maximum nitrox operating depths, can take its toll quickly.
2 To dump or not to dump air?
Well, there is a school of thought that says adding air to the BC creates a greater area for the current to push down on and should be avoided. Nevertheless, having no air in the BC will make you extremely negatively buoyant when being pushed to greater depths. It’s best to inflate the BC to give you a greater lift, but be sure to dump the air quickly once you have made your way out of the current.
3 Move away
One option is to fin from the reef, where the strength of the downcurrent dissipates. However, you may become stuck in the blue and will have to surface without any reference. Keep an eye on the depth gauge and gain control over your ascent rate as you may become disorientated. Always deploy a delayed surface marker buoy (DSMB) when it is safe to do so.
4 Take shelter
Get close to the reef and tuck yourself behind a ledge. If you are not in any particular danger, stick close to the wall and ascend or wait. You can also try moving along the wall in one direction or another to escape.
5 Climb up the reef
Obviously, you don’t want to damage the reef by climbing all over it, but this may be your only option. Try to grab areas where there is little or
no coral cover.
6 Go with the flow
When it’s too strong to fight, you may just have to go with it and allow it to spit you out at the end.
Be prepared to dump air from your BC as soon as your descent slows.
7 Ditch the belt
This is definitely the last resort when there is no other way of escaping in very deep water. Such occasions are extremely rare and there is a high risk of decompression illness and associated problems caused by a rapid ascent.
Up and away
I had a serious wake-up call during a dive off the Similan Islands in Thailand when I was blasted by an extremely cold upcurrent. I was finning slowly on a reef ledge at 35m when a hazy, light-green channel of water hit me.
It was as if I had been shot by a fire hose at full force. My buddy was a few metres ahead of me and I could see him tucking himself behind a ledge. As soon as I saw the current coming, I grabbed hold of a boulder and fought to dump my air and breathe out. The lower half of my body was forced violently upwards and my regulator and mask shuddered.
The temperature shifts in the current of about 6°C created a haze for about 30 seconds before the upflow ceased. Luckily, I had been warned in the briefing about the ‘green monster’ and saw it coming before I was forced on a fast ascent from 35m.
Dealing with upcurrents follows the same principles as downcurrents, just in reverse. The danger to avoid in this situation is an extremely fast ascent. I found the trick was to keep my body as streamlined as possible, while dumping air and holding on tight until it passed.