The balance between the material deposited on, and eroded from, a beach; see Davidson-Arnott and Van Heyningen (2003) Sedimentol. 50, 6. During winter, waves tend to be destructive, and gradients steepen, but, with summer conditions, waves become constructive, and gradients slacken; a sequence detailed in Engels and Roberts (2005) J. Sed. Res. 75, 6. See Martinez and Psuty (2004) Ecol. Studs 171 on foredunes and beach budgets.