Robert Redford's movie "A River Runs Through It" and Meryl Streep's acting in "River Wild" both graphically show the power of Western rivers. Several decades ago, a big, strong Brigham Young University football player died at the Murdock Division Dam at the mouth of Provo Canyon. Many people wondered how such a thing could happen. One factor in his death was a phenomenon known as hydraulics.
Hydraulics, also known as holes, reversals, rollers, suck holes and pour-overs, are the most common hazards in rivers. A hydraulic is created when water flows over an obstacle, causing a depression that produces a relative vacuum within which the downstream water recirculates. River runners should be well-acquainted with this situation. Rafts and kayaks can be turned upside down by the force of a hydralic, and if the reversal currents are strong enough, crafts and people can become trapped in the recirculated flow. It can be either artificial, like a low-head dam (such as the Murdock Division Dam) or natural, like a rock drop-off or shelf.Beginners often misjudge the force of hydraulics. It is not the height of the drop that generates the recirculating power but rather the shape and angle of the obstruction.
Another hazard is entrapment. Undercut rocks are boulders or ledges that have been eroded just beneath the water surface. They can be difficult to recognize and pose significant risks for entrapment and drowning.
The potential for entrapment can also occur when swimmers attempt to stand up and walk in swift-moving currents. A foot can become wedged in an undercut rock or between rocks beneath the surface, causing the victim to fall face down into the river. With the foot entrapped, the victim cannot regain an upright or even face-up position. People have drowned in 3 feet of water because of entrapment.
Self-rescue
River rescue literature has long advocated several self-rescue theories for hydraulics. One is to swim toward the hole and let the water drive you to the bottom, where you should stay as long as possible, hopefully surfacing past the area. However, a danger with this technique is potential entrapment in the debris that has been pushed into the hole; rescuers should be especially wary at low-head dams.
Another technique is to swim to the side of the hydraulic, which can be difficult depending on the force of the current. The best option is to use as much floatation as possible - an extra personal floatation device (PFD), an inflatable boat, inner tube or some other object - until help arrives. Be aware that even for the properly equipped swift-water rescuer in helmet, wet suit and PFD, being trapped in a hydraulic is disorienting and exhausting.
Victim rescue
The victim in a hydraulic immediately needs additional floatation. This can be accomplished in several ways. First, immediately throw an extra PFD, life ring or some other floatation to the victim. Next, tossing a line is the most common method of providing quick rescue to people trapped in hydraulics. You can also combine the two: tying the floating to the line provides instant floatation to the victim and a way for rescuers to quickly pull out the victim in one step. Your toss must be accurate. Your accuracy may save the victim's life and save you from having to put a rescuer in the water. A low-tech but effective technique is to use a simple inner tube with towlines held by rescuers on each shore who work the line up toward the hydraulic.
Rafting, canoeing and kayaking have become the third largest outdoor recreation industry in the United States. Those riding the rivers in the intermountain west should receive training and have the right equipment. They should always approach hydraulics or potential hydraulics with great caution. Their lives depend on it.