Waterfalls & Downdrafts - Incident

[TVPB 0]

For those contemplating waterfall jumps, here are some considerations that need to be accounted for.

Waterfalls are a fluid mass that moves relative to / through a mass of air (another fluid).

Whilst the water is moving down under the force of gravity, the air mass must be displaced somwhere. This has a number of affects. Firstly, a component of the displaced air mass is taken down with the waterfall. That is one of the reasons why you see lots of bubbles under the waterfall. The volume and speed of the water/air fall, coupled with friction, forces air adjacent to the water to be literally sucked down as well. In laymans terms, this creates a downdraft adjacent to the waterfall that increases in speed and intensity as you get lower (until the water reaches terminal velocity of course - the water then spreads around a bit more and falls at the same rate and begins to have less affect) - i.e. the bottom of a 250m waterfall with a large volume of water is probably more dangerous than the bottom of a 1000m waterfall with the equivalent volume.

Another thing that happens is that from the centre of the waterfall, to an area several tens of metres away that is not affected by the waterfall, there are changing air flow patterns.

The centre of the waterfall is straight down. Given its higher density than the air surrounding it, it falls with great speed. Immediately adjacent to the waterfall you will still have strong downdraft and some water molecules floating around as they are not subjected as much to the falling mass. Here is where it gets interesting. We are about to transition from down to no movement. It is almost like a wind shear but it is complicated with eddies and turbulence from the downdraft and waterfall. i.e this is where the air flow becomes less predictable to the naked untrained eye (reasonably predictable to anyone familiar with chaos theory). Basically, you will get a combination of downdrafts, sidedrafts, updrafts, etc. As you move further out, the affects becomes less in terms of force but the motion probably occurs in greater distances. What I mean by this is that radius of the eddies next to the waterfall are smaller but more noticeable than further out.

Finally, you are in clear air.

Hence, if you BASE jump next to a waterfall, the following things will probably happen:

If you throw a p/c in the downdraft right next to the waterfall, it may well keep falling with you and never create enough drag to pull your canopy out. IF you either fly into or freefall into the waterfall, you have minimal chance of landing an inflated canopy (this problem is greater for high volume/flow rate falls). These results will be fairly predictable.

If you deploy or fly a few metres out, you will have less predictability. You might get sucked down, you might open quickly, you might? ? ? ? ?

etc.

This stuff should be particularly noted when deploying at low altitudes immediately adjacent to a high volume waterfall, where the water is still reasonable contained as one mass.

This stuff was posted for people to learn from and think.

If you have different ideas, I'd be happy to hear them.

Stay Safe
Have Fun
Good Luck

Tom

p.s. apparently the bloke in question will be OK once he recovers. Get well soon. Wish I was there.

Stay Safe - Have Fun - Good Luck

The above could be crap, thought provoking, useful, or . . But not personal. You decide.