Ramp angles for waves

The ramp or slope upstream of the wave generates the water velocity needed to create a river wave. The angle of the ramp has a big impact on the footprint and the volume of the ramp. Higher footprint and volume can cause big increases in cost because more work and material are required.

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.

A water velocity of at least 3 m/s to 4 m/s is required to generate a surf wave with high performance river waves having over 4.5 m/s water velocity. A drop of 1m can generate over 4 m/s of water velocity. A range of ramp angles from at 6 degrees to 32 degrees are proven to create good waves. The angle of the water surface will always be steeper than the angle for the ramp structure.

Modelling of ramp angles that make waves

These images show different angles producing waves. The wave is smaller with a flatter ramp because the ramp has a fixed length. For a fixed length ramp, a flatter ramp means less drop and less water velocity. Less water velocity means a weaker and smaller wave. Flatter ramps can produce large waves but the ramp needs to be significantly longer to generate the necessary water velocity.

Ramp angle and water surface angle comparison

The model image below shows that a very steep ramp can form a wave. The image also shows how the water surface angle is steeper than the ramp angle because the water is shallower when it is moving faster. Steeper ramps may need transitions to make the distance between ramp and wave wide enough for all surf maneuvers. This is a screen shot from Dominik Puckert’s research video.

Water surface angles of existing river waves

The angles below are for the water surface not the ramp. The physical ramp angles are less than the water surface angles because the water gets shallower as it accelerates down the ramp. The water at the top of the ramp is deeper than the water at the bottom of the ramp which makes the water surface angle steeper than the physical ramp angle. For example, the Bend water surface angle below is 9 degrees while the physical ramp angle is 6 degrees.

Impacts of ramp angles

These are some of the impacts of using steep or flat ramps for river waves.

CharacteristicSteep RampFlat Ramp
Material required to build. Less material.More material.
Change in water direction to form a wave.Larger change in water direction.Smaller change in water direction.
Distance between water on ramp and surface of wave.Smaller distance. Distance can be increased with a transition between ramp and wave location.Larger distance.

Diagram of how ramp angle affects ramp length and profile area

Low angle ramps are a lot bigger than steep ramps.

Angle
(degrees)
Ramp length (m)Ramp profile area (m2)Ramp profile area compared
with 40 degree angle ramp
401.20.61x
202.71.372.3x
69.54.757.9x

Footprint and volume changes for a 5m wide ramp

Angle
(degrees)
Foot print for 5m
wide wave (m2)
Increase in footprint
for flatter ramp (m2)
Ramp volume for 5m
wide wave (m3)
Increase in volume for
flatter ramp (m3)
406.00.03.00.0
2013.57.56.93.9
647.541.523.820.8

Footprint and volume changes for a 10m wide ramp

Angle
(degrees)
Foot print for 10m
wide wave (m2)
Increase in footprint
for flatter ramp (m2)
Ramp volume for 10m
wide wave (m3)
Increase in volume for
flatter ramp (m3)
4012.00.06.00.0
2027.015.013.77.7
695.083.047.541.5

Surf Anywhere recommendation

Build a fixed ramp and choose the angle to minimize complexity and cost. The ramp is the largest and heaviest part of wave structure which makes it the most expensive to move. Make other components adjustable to control wave quality. Some situations may require an adjustable ramp such as needing the ramp to flatten for environmental reasons or to protect the wave structure from flood and ice.