Beach Fill Calculator
The equilibrium beach profile is given by h = A x ^(2/3); that is, the depth is given by a profile parameter A (which depends on the grain size of the sand) times the distance offshore x raised to the 2/3 power. For the original beach, the profile parameter is A_N, and for the filled beach (denoted in the figure above by the magenta), the parameter is A_F.
With this applet, it is pretty easy to see that the coarser the fill material, the steeper the beach profile and the less sand is required to create a beach of a given width. Not that if the sand is too fine (compared with the native material), most of the sand will eventually be deposited offshore near the depth of closure.
Comments: Robert A. Dalrymple
Center for Applied Coastal Research
University of Delaware, Newark DE 19716