residual which is presumably due to other 

 forces and changes dramatically from year 

 to year. Dominant among these other 

 forces and responsible for the secondary 

 maximum in spring and the following 

 secondary minimun in mid-summer is the 

 seasonally changing, dominant wind regime 

 over the Gulf of Mexico (Chew 1962),. 

 Maximum east and southeast winds in 

 spring and fall result in an onshore 

 transport of water. During winter and 

 summer westerly winds (southwest in 

 summer, northwest in winter) strengthen 

 the Mexican Current and draw a return flow 

 of water from the estuaries (Baumann 

 1980). 



Superimposed on the seasonal water 

 level change is a diurnal tide averaging 



Airplane Lake 



7 krti (fom GuH 



' ' ' ' 



October 1972 



Figure 11. 

 marshes: a) 

 daily. 



Water level trends in delta 

 long term; b) seasonal; c) 



about 30 cm at the coast. Because of the 

 broad, shallow expanse of the coastal 

 estuaries, the tides attenuate in an inland 

 direction. Figure lie shows how the 

 normal tide range decreases from salt to 

 freshwater marshes. In this example 



tides are still perceptible 50 km inland 

 fran the tidal passes because of the 

 extremely slight slope of the land. 



It would be misleading to infer that 

 water levels slavishly follow predictable 

 daily and seasonal cycles. In reality 

 they are modified strongly by stochastic 

 meteorologic events which set up or set 

 down water in the bays and marshes. The 

 effect is clearly shown in Figure lie, 

 where gradually decreasing water levels 

 associated with a "cold front" began on 12 

 October. Then the water levels suddenly 

 rose on 19-22 October when the wind came 

 around to the south. Typically, "cold 

 fronts" moving across the coast lower 

 water levels dramatically. "Warm fronts" 

 with winds from the southern quadrant set 

 up water in the estuaries. The magnitude 

 of these wind effects is often 40-50 cm, 

 which when combined with astronomic tides 

 can result in water level shifts of over a 

 meter within 12 hours. 



Table 3. Average coastal submergence on 

 the U.S. east and gulf coasts (Bruun 1973 

 compiled by Hicks). 



Location 



Record yr 



Rate 



Eastport, Maine 

 Portsmouth, N.H. 

 Woods Hole, Mass. 

 Newport , R. I. 

 New London, Conn. 

 New York, N.Y. 

 Sandy Hook, N.J. 

 Baltimore, Md. 

 Washington, D.C. 

 Portsmouth, Va. 

 Charleston, S.C. 

 Fort Pul aski , Ga. 

 May port, Fla. 

 Miami Beach, Fla. 

 Pensacola, Fla. 

 Eugene Island, La, 

 Galveston, Tex. 



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