Tailwater effect on waves

Tailwater is the water body immediately downstream of the wave. The elevation of the tailwater has a huge and predictable impact on wave formation. Controlling the elevation of tailwater relative to the wave is required for reliably making good river waves.

This article is part of Surf Anywhere sharing wave building knowledge to make river wave building easier and to improve wave quality. An overview of the research is at SurfAnywhere.ca/wave-research.

This excellent video by Dominik Puckert shows how wave formation changes as tailwater goes from low to high.

Low tailwater making B-jump

At low tailwater levels, a B-jump forms which is not good for surfing.

Ideal tailwater making max wave

At ideal tailwater levels, a max wave forms and is the best shape for surfing.

High tailwater making A-jump

When the tailwater is too high, an “A-jump” forms which is not good for surfing.

Deadly tailwater elevations

If the tailwater continues to rise, the kicker no longer influences the wave shape and a deadly retentive hydraulic forms called a submerged hydraulic jump. These types of features kill people every year and must be prevented at recreation river wave locations. A deadly hydraulic can also form on ramps if the tailwater is too far below the kickers.

This video by Practical Engineering provides a great explanation of retentive hydraulics or keepers.

Tailwater changes on a ramp the multi adjustable kicker system

These videos show how tailwater changes affect waves on a ramp with kickers in different positions. If the tailwater moves too far above or below the kickers a deadly hydraulic will form. The design of the river waves and surrounding area must control the tailwater levels and wave formation to prevent dangerous features.

Surf Anywhere recommendation

Ensure your wave design has strong control of tailwater elevation relative to kicker elevation. The control can be on the:

1. tailwater elevation or
2. kicker elevation or
3. both.