"Creating one good surfing wave in an artificial pool is not a problem for wave engineers," says coastal engineer, Erik Van Ettinger. The hard part, he says, is the "trajectory control" -- which means generating one good wave without producing a lot of secondary waves. Remember your pebble and your bucket: when the stone hits the water it creates more than one ripple. In the ocean, each ripple is actually a rideable wave. In the confines of a pool, secondary waves are not strong enough to be ridden and only distort the first. The small space creates another problem: wave reflection. "You need to find a way to dampen the energy of each wave so that it doesn't reflect off the walls and cause a big mess," says Van Ettinger. In his home country of the Netherlands, Van Ettinger created a functioning artificial surfing reef at Scheveningen Beach in 2010. He is currently designing his own wave pool.