this source if the lagoon is less than 5 miles wide. Where the lagoon 

 is wider (especially 10 miles or greater) flooding from the lagoon side by 

 wind setup should be investigated before large dune construction projects 

 are undertaken. 



4.622 Reservoir of Beach Sand . During storms, erosion of the beach occurs 

 and the shoreline recedes. If the storm is severe, waves attack and erode 

 the foredunes and supply sand to the beach; in later erosion stages, sand 

 is supplied to the back of the island by overwash. (Godfrey, 1972.) 



Volumes of sand eroded from beaches during storms have been estimated 

 in recent beach investigations. Everts (1973) reported on two storms dur- 

 ing February 1972 which affected Jones Beach, New York. The first storm 

 eroded an average of 27,000 cubic yards per mile above mean sea level for 

 the 9-mile study area; the second storm (2 weeks later) eroded an average 

 of 35,000 cubic yards of sand per mile above mean sea level at the same 

 site. Losses at individual profiles ranged up to 120,000 cubic yards per 

 mile. Davis (1972) reported a beach erosion rate on Mustang Island, Texas, 

 following Hurricane Fern (September 1971), of 12.3 cubic yards per linear 

 foot of beach for a 1,500-foot stretch of beach (about 65,000 cubic yards 

 per mile of beach). On Lake Michigan in July 1969, a storm eroded an aver- 

 age of 3.6 cubic yards per linear foot of beach (about 29,000 cubic yards 

 per mile) from an 800-foot beach near Stevensville, Michigan. (Fox, 1970.) 

 Because much of the eroded sand is usually returned to the beach by wave 

 action soon after the storm, these volumes are probably representative of 

 temporary storm losses. 



Volumes equivalent to those eroded during storms have been trapped 

 and stored in foredunes adjacent to the beach. Foredunes constructed 

 along Padre Island, Texas, and Core Banks, North Carolina, (Section 6.43 

 and 6.447) contain from 30,000 to 80,000 cubic yards of sand per mile of 

 beach. Assuming the present rate of entrapment of sand continues for the 

 next 3 years at these sites, sand volumes ranging from 50,000 to 160,000 

 cubic yards per mile of beach will be available to nourish eroding beaches 

 during a major storm. Sand volumes trapped during a 30-year period by 

 European beachgrass at Clatsop Spit, Oregon, averaged about 800,000 cubic 

 yards per mile of beach. Tlius, within a few years, foredunes can trap and 

 store a volume of sand equivalent to the volumes eroded from beaches dur- 

 ing storms of moderate intensity. 



4.623 Long-Term Effects . Dolan, (1972-73) advances the concept that a 

 massive, unbroken foredune line restricts the landward edge of the surf 

 zone during storms causing narrower beaches and thus increased turbulence 

 in the surf zone. The increased turbulence causes higher sand grain attri- 

 tion and winnowing rates and leads to accelerated losses of fine sand, an 

 erosive process that may be detrimental to the long-range stability of bar- 

 rier islands. However, as discussed in Section 4.521, the effects of sedi- 

 ment size are usually of secondary importance in littoral transport pro- 

 cesses - processes which are important in barrier island stability. In 

 addition, geographical location is probably more important in determining 

 beach sand size than dune effects, since both fine and coarse sand beaches 



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