It may be anticipated that if various properties of the beach are 
measured at a number of points on the beach, the measurements should show 
an areal pattern that reflects the processes taking place. Some beach 
properties, such as average grain size, sand firmness, and others, show 
fairly strong gradients between the plunge point and the berm, and a less 
marked but still systematic gradient on the backshore, with a transition 
to the hinterland dunes. 
Figure 4 is a schematic map of beach firmness constructed by measuring 
the sand penetrability at a number of points, and drawing contours through 
the resulting field of numbers. The softest part of the beach is commonly 
along the berm crest, and firmness increases rapidly across the foreshore 
toward the water edge. On aggrading beaches a reversal in firmness may 
occur near the water line, though the situation shown in Figure 4 is not 
uncommon on sand beaches along the western shore of Lake Michigan. On 
the backshore the pattern of contours becomes less regular, though some 
zonation may be preserved. The dry, relatively fine wind-blown sand may 
show a decrease in firmness in the transition zone between backshore and 
dunes. 
A BEACH PROCESS-RESPONSE MODEL 
Consideration of Figure 2, 3, and 4 furnishes a basis for constructing 
a conceptual process-response model of a natural beach. Figure 5 shows 
this model schematically, with the process elements on the left, and an 
arrow pointing to the response elements on the right. 
The process elements include three major items. The first is the 
energy factor, expressed in terms of wave height, period, and angle of 
approach; by tidal range and related features; by the velocity and direc- 
tion of the shore current; and by the velocity and direction of winds that 
operate on the backshore. The material factor on the process side includes 
all natural materials - pebbles, sand, silt, shells, etc. - which initially 
are present in the beach area and are available for movement or shifting 
about by the energy factors. The last element on the process side is the 
overall geometry of the shoreline. This represents the "boundary conditions" 
in which the beach processes operate. Thus, the distribution of wave energy | 
along the shore is related to the form of the shoreline and to the nearshore 
bottom slope, which influence the pattern of wave refraction. 
The response elements in the model include two main items as shown on 
the right-hand side of Figure 5. The first is the geometry of the beach 
deposit, which includes foreshore slope and width, height of berm, and 
width of backshore. In a three-dimensional sense, the geometric element 
also includes the volume and shape of the beach deposit as a whole. 
The properties of the beach materials on the response side of the 
model are controlled by the kinds of material originally available at the 
