Effects of channel walls on waves
Full channel walls allow for a higher wave and a cleaner wave. The walls allow the tailwater to be higher which allows for the wave to be higher. As the walls lower, water enters the wave from the side making the wave break at lower tailwater levels. Only the part of the wall below the water level matters for wave formation.
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.
Effect of channel walls on ramp wave
Removing the wall from one side of the wave causes the open side to flood and break that half of the wave. The maximum tail water level is only slightly reduced because one side of the channel has a wall and the tailwater cannot easily access that side of the wave.
Effect of channel walls on flat bottom wave
Moving the kickers outside of the channel allows water to flood in from the side creating turbulence on the sides of the wave. The maximum tailwater level before breaking the wave is reduced which means the wave is shorter.