Hydraulic Currents

God forbid any one of you should ever need this info, but just in case you do, here it is.

A hydraulic current (also known as a souse hole, a ledge hole, pour-over, keeper, or reversal) develops where water flows over a dam, waterfall, or ledge with enough volume and force to create a backwave that returns, on the surface, to the obstruction over which the water just flowed. These recirculating currents plunge water to the bottom of the river with such force that it sets up a cylindrical wave that returns to the surface and turns back toward the drop that caused it. Depending upon the height of the drop and the volume of water that is plunging over it, a hydraulic current can be very strong and can, in fact, be a "keeper" that grabs swimmers and boats, then refuses to let them go.  It is much like the motion of a washing machine, but instead of being spun sideways the victim will be forced to the bottom of the river repeatedly.  Because of this, it is often referred to as getting "Maytagged".  In addtion to the current, another hazard is created by the curling back of the wave.  As the wave curls in on itself, it forces air bubbles into the water which decreases its buoyancy by one-third.  Even if the victim is wearing a personal flotation device (PFD), they will have a hard time staying afloat due to reduced buoyancy and literally being forced to the bottom of the river.

This particular image best captures the nature of Double Suck.  It has a ledge with a pretty immediate souse hole and then some feet away is another souse hole, thus the name Double.  The second of the souse holes is the stronger one in this particular instance and was the one in which I became stuck.

How to Self-Escape a Hydraulic Current :
1. Swim to the side and catch an eddy (a calm spot behind a rock) which will release you from the pull of the current.
2.  Ball up and follow the current to the bottom of the river at which point you should sprawl out and allow the strong current at the bottom to flush you out.  There is inherent risk in this techinique because you could become entrapped in tree limbs or other objects on the bottom.  Also, I assume to fully reach the bottom you would have to remove your PFD.  And lastly, there is no guarantee it would work and you have no idea how far down the riverbed is.

You can of course be rescued by rope, as was the case for me, or by holding on to some other object, like an oar or tree branch, and being pulled from the water.  If you are being rescued by rope it is important to grab it over your shoulder and float on your back.  If you are reeled in face down your body will act as a lure and sink down as you are being pulled.

And that is everything you never wanted to know about hydraulic currents.