Rafting News

Jul 26 2014

Preventing submerged hydraulic jumps became an important study at Brigham Young University after a couple drowned when their kayak capsized. Only 20 feet from where they fell into the water, the couple became trapped in a dangerous current. In fact, this deadly current was a mere small drop, less than three feet high.

This tiny little pool of water developed a deadly current where the water on the surface was smooth, but underneath it was moving upstream. This type of unforeseen current is known as a “hydraulic” or “roller.” What this current essentially does is trap someone under water, depriving him/her of oxygen enough to cause drowning.

This type of hydraulic jump is a phenomenon that occurs when shallow, supercritical water meets and combines with moving, subcritical water. The shallow, yet turbulent current transitions are what define this as a hydraulic jump.

Large basins often have a stilling area that is installed, which helps dramatically control and confine the harmful nature of the hydraulic jumps. Low-head, shallow structures often do not have stilling basins, which causes them to be not controlled, causing high energy to churn at dangerous velocities beneath the surface.

This study shows that as water plunges downhill towards the bottom of a channel, the momentum caused by the air produces a strong current. Once this current reaches the surface of the water, it can double back and create a second current – one that goes upstream – which essentially creates a deadly whirlpool of inescapable energy.

While there are many ways to prevent deadly hydraulic jumps from developing, these solutions have serious drawbacks, such as cost, energy dissipation, safety, sediment deposition, headwater depth effects, ice passage, etc.

Scientists tested a promising solution that can literally transfer and apply to any submerged hydraulic jump. In fact, this design was used to help juvenile salmon pass downstream. By using a simple plunging nappe, the downward velocity force is eliminated, thereby preventing air from entering the water and sucking people under. This type of manmade addition can also decrease swift downstream currents, helping ensure more safe passage of swimmers, kayakers and rafting enthusiasts.

This study is a primary reason why outdoor adventurists need to seriously consider hiring whitewater rafting guides that are experienced and know the subtle differences between churning and slow-driven rapids. Always embark on adventures using a buddy system, as this can help save your life if you should encounter such a deadly situation.