The scientists studied how groups of waves behave in the surf zone. They used experiments with cnoidal waves on a flat beach. They found that the breaking of waves is influenced by how grouped they are. Inside the surf zone, the wave groups change, affecting the long wave motion. The long wave is forced at the group frequency and creates a standing wave. A model based on conservation equations and dispersion relation accurately predicted wave behavior in the shoaling region but not in the surf zone.