Artificially nourished and constructed beaches are used extensively 
at present to restore required conditions suitable for recreational areas 
(Figure 14). The installation of this type of structure involves replacing 
a beach using the criteria derived from the natural beach. That is, the 
grain size of the material and its gradation; beach slopes (both foreshore 
and backshore); and elevation of berm are adhered to as strictly as possible. 
In the event that a different beach material, such as sand of different 
grain size, need be used, the reconstructed beach will possess different 
characteristics even when nourishment is supplied at a rate equal to past 
natural losses. This type of constructed beach, however, behaves as did 
the natural beach with respect to adjacent shores and is normally bene- 
ficial to the downdrift shores. 
BEHAVIOR OF SYSTEMS OF STRUCTURES 
Structures used singly or in systems have a marked effect on the land 
forms in the immediate and contiguous areas through accretion and erosion. 
Groin fields are designed to build and hold a beach usually of appreciable 
size. Numerous factors must be considered in design, namely, the magnitude 
and direction of littoral drift and the resultant direction and magnitude 
of natural forces in the area. In an area of abundant littoral drift, or 
where natural sand supply approaches the capacity of littoral forces to 
transport it, a system of groins can be designed to increase the dimen- 
sions of the natural beaches (Figure 11). In constructing a groin field, 
construction should proceed updrift. In other words, the downdrift groin 
should be constructed first so that the adjacent updrift embayments can 
be filling as construction proceeds updrift. Occasionally extended periods 
of time are required between the construction of each groin to achieve the 
best results. If the groins are built to a low profile, with top at the 
elevation of the natural beach, the littoral material passes over their 
tops, nourishing the entire system. The process continues until all groins 
are full. An undesirable feature of this procedure may be, that while the 
groins are filling, the beach downdrift from the groin system may be 
eroded, Almost without exception, groin systems are now filled artifici- 
ally to allow immediate movement of the littoral material through the 
groin field, 
For beaches in areas of little or no drift (or relatively little 
natural supply of beach sand), two or more high groins in combination with 
beach fill can be used to accomplish this same purpose. In this type of 
arrangement, the high groins are used at the downdrift ends of the com- 
parmented areas to form pockets or bayheads that restrain the material 
from being moved out of the area by the littoral forces. Since there was 
little or no natural drift in such an area to start with, accelerated 
erosion of the downdrift shore should not be induced in important degree. 
In locations where a field of low groins is installed adjacent to the 
end of a littoral compartment with appreciable natural drift, terminating 
32 
