Angle of incidence
From MarineSpecies Traits Wiki
The angle between the wave propagation direction and the normal to the coastline or the angle between the wave front and the coastline. The deep water angle of incidence is denoted α0 ; the wave incidence angle at the depth contour where waves start breaking is denoted αb. 
- Mangor, Karsten. 2004. “Shoreline Management Guidelines”. DHI Water and Environment, 294pp.