Table 4. Summary of beach area changes south of Holland Harbor. 
Measured area Lake level Lake level Area Net area Rate 
(N.Y. datum) difference | correction 
(1,000 ft?) (ft) (£t) (1,000 ft?) | (1,000 ft?) | (1,000 £t2/yr) 
Breakwater to 1,200 feet south 
on 12.1 for a length from 1,200 feet to 3,600 feet south of the breakwater. 
The values shown in Table 4 can be added for a representative length of shore- 
line of 3,600 feet to yield the result that an accretion rate as high as 48,500 
Square feet per year in the period 1856 to 1871 decreased to a rate of about 
6,000 square feet per year from 1871 to 1906, then increased again to 20,500 
square feet per year following construction of the breakwater extensions after 
1906, and finally showed an average erosion rate of 8,000 square feet per year 
from 1933 to 1945. This last value corresponds to an erosion rate of 0.75 foot 
per year as determined from analysis of the aerial photos. However, it should 
be emphasized that the recently observed erosion rates reflect two effects: 
(a) The length of shoreline near the harbor has been protected by rubble and 
groins, and (b) the unprotected shoreline farther south is backed by dunes with 
an average height of about 120 feet with peaks more than 200 feet above the 
lake level. 
The rate of accretion at times on the south side may seem somewhat surpris- 
ing, but it must be recalled that the littoral drift often reverses (see Fig. 
22) and in some years may be completely reversed. The variable direction of 
littoral drift is also evidenced by the two surveys in Figure 12, which shows 
the harbor entrance shoal from the south side as being apparently larger than 
that from the north in 1973. 
Using the approximation of 1 cubic yard of sediment per square foot of beach 
the 1950-73 observed average erosion rate for about 9,000 feet south of Holland 
Harbor is 0.75 cubic yard per year per foot of shoreline, plus the bluff contri- 
bution of 0.75 x 120/27 = 3.33 cubic yards per year per foot for a total loss 
rate for unprotected shoreline of 4.08 cubic yards per year per foot of shore- 
line. When compared with the erosion rates observed for the shoreline about 1 
mile or more north of Holland Harbor of 3.18 cubic yards per year per foot, the 
difference of 0.9 cubic yard per year per foot of 22 percent can be attributed 
to the navigation structure. The effect is very small and should not be ex- 
pected to be readily apparent. The rate of loss of 0.9 cubic yard per year per 
foot of bluff material would correspond to a shoreline erosion rate of less than 
0.2 foot per year for a bluff height of 120 feet. 
56 
