Section V. SUMMARY 



The entrance to Chesapeake Bay study area lies between Cape Charles 

 and Cape Henry encompassing shallow portions of lower Chesapeake Bay and 

 the adjacent Atlantic Continental Shelf. 



Wide expanses of sandy to silty bottom in less than 35 feet of 

 water characterize the entrance. These shallow flats are cut by deeper 

 channels reaching -40 to -90 feet MLW; locally, linear shoals and de- 

 pressions create depths of -50 feet to less than -10 feet. 



Borings in the Bay Entrance show that it is underlain by Miocene, 

 Pleistocene and Holocene sediments. Seismic reflection records showing 

 bedding in sediments to -300 feet MLW indicate that the deeper strata 

 underlying the Entrance area are more or less mutually parallel and dip 

 gently toward the east and southeast. Most of these strata are thought 

 to be Miocene. Shallower subbottom strata in Chesapeake Bay Entrance 

 are complexly bedded; internal bedding surfaces, channels and discon- 

 tinuous sediment lenses are characteristic. 



Large channels, now filled and buried, cut under the Entrance area 

 in an easterly and southeasterly direction. These channels are be- 

 lieved to be Pleistocene Channels of major streams now tributaries to 

 Chesapeake Bay. 



The dominant sediment in the Bay Entrance is a fine to very fine 

 gray sand which covers much of the northern two thirds of the area. 

 Silt occupies Lynnhaven Bay and covers much of the channel floor. 

 Coarse, gravelly sand is exposed locally in Thimble Shoals Channel and 

 occurs in patches elsewhere. 



Sand suitable for nourishment of ocean beaches within reasonable 

 hauling distance of the Bay Entrance occurs only in the coarse sand and 

 gravelly sand exposure in Thimble Shoals Channel. It is estimated that 

 19.4 X 10^ cubic yards of this sand can be obtained either in exposure 

 or under less than 5 feet of overburden. 



It is estimated that 1.8 x 10^ cubic yards of the fine gray sand 

 has accumulated in the Bay Entrance. This sand is considered to be 

 Holocene age and derived primarily from sources on the adjacent Atlantic 

 Shelf or littoral rather than from Bayward sources. The coarse gravelly 

 sand of Thimble Shoals Channel is believed to be a relict fluvial de- 

 posit of Pleistocene age or earlier. The silty sediments of the channels 

 and in Lynnhaven bay are judged to be of Holocene age. 



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