(2) at this pointy constructing a diffraction diagram carrying successive 

 crests 3 or ii wave lengths shorewsrdj and (3) with the wave crest and wave 

 direction indicated by the last shoreward wave crest determined from the 

 diffraction diagram, constructing a new refraction diagram to the breaker 

 line. A typical refraction-diffraction diagram is shown on Figure 33. 



CHANGES IN InfATER LEVEL 



55 o Tides o - There are usually two high and two low waters in a tidal 

 or lunar day. Tides follow the moon more closely than 'Ji-hey'' do the sun. 

 As the lunar day is about 50 minutes longer than the solar day^ the tides 

 occur later each day. Because of the varying effects of the sun and moon^ 

 a diurnal inequality in tides occurs in which, at certain plaeesj there 

 may be a difference of only a few tenths of a foot between one high water 

 and the succeeding low water of a day but a marked difference in hei^t 

 between the other high water and its succeeding low water. Along the 

 Atantic coast the two tides each day are of nearly the same height. On 

 the Gulf coast the tides are very low but in some instances have a pronoanced 

 diurnal inequality. Pacific coast tides compare in height with those on 

 the Atlantic coast but have a decided diurnal inequality (see Figure 5 

 Appendix A) . 



56, Pertinent data concerning tidal ranges along the sea coasts of 

 the United States are given in the following tables. Spring ranges are 

 shown for areas having approximately equal daily tides and diurnal ran'ges 

 are shown for areas having a pronounced inequality. Detailed data con- 

 cerning tidal ranges are given in Tide Tables, U, S, Department of Commerce, 

 Coast and Geodetic Survey, 



Table 3 - Tidal Ranges - Atlantic Coast 













Coastal Area 



Approximate 



Reference Station 



From 



To 



-;i-Tidal Ranges (i 



Eastport, Maine 



Calais 



V/. Quoddy Head 



18-22 



Eastportj Maine 



¥, Quoddy Head 



Englishman Bay 



lii-l8 



Portland J Maine 



Englishman Bay 



Belfast, Maine 



11 -111 



Portland, Maine 



Belfast 



Rockportj Mass, 



8-11 



Boston, Mass. 



Rockport., Mass. 



Province town 



10-11 



Boston^ Mass. 



Province town 



Chatham 



5-10 



Boston^ Mass, 



Chathajn 



Cuttyhunk Island 



2^k 



Boston & New London 



Cuttyhunk Isd. 



Connecticut River 



3-6 



Bridgeport ck Willets Pt 



Connecticut R. 



Truman Beach 



U-8 



Wew London &. Sandy Hook 



Truman Beach 



Hempstead Bay 



1-3 



Sandy Hook & iMew ^ork 



Hempstead Bay 



Cape May 



ii-6 





Delaware 



Bay 



5~? 



Sandy Hook 



Rehoboth 



Smith island 



U-5 



Hampton Roads - 



Cape Henry 



South Santee 



3-5 



Charleston 





River 





Charleston 



So Santee R, 



N. Edisto River 



5-7 



Charleston-Savannah 



N. Edisto R. 



Nassau 



7-9 



River Entrance 





Sound 





Mayport 



Nassau Sound. 



Daytona Beach 



h-6 



Miami k Key West 



Daytona Beach 



Tarpon ^ellj Keys 



1-3 



■"fSpring range 



i;0 



