In fluid dynamics, wave setup is the change in mean water level due to the presence of waves. This setup is primarily present in and near the coastal surf zone. Besides a spatial variation in the (mean) wave setup, also a variation in time may be present – known as surf beat – causing infragravity wave radiation.
Mathematically, wave setup can be modelled through the spatial (and temporal) variations in radiation stress (Longuet-Higgins & Stewart 1962). These variations are due to the changes in wave height by shoaling and breaking.