0.70 



0.60 

 „ 0.50 

 ^ 0.40 

 t 0.30 



o 



g 0.20 



a> 



'^ 0.10 



o 



::: 



'£ -0.10 

 -^ -0.20 



o 



ID 



2 -0.30 



>s 



= -0.40 



o 



-0.50 



-0.60 



-0.70 



Jan. Feb. Mor. Apr. May June July Aug. Sept. Oct. Nov. Dec. 



Figure 3. Long-term monthly mean water level variability. 



of monthly mean values of the tidal range and the water level from the long- 

 term average. Good agreement exists among the three stations, indicating 

 relatively uniform long-term behavior of the gulf tides throughout the study 

 area. Figure 3 also includes the mean levels at Galveston due solely to 

 astronomical forces, which were predicted using a computer program developed 

 at CERC (Dr. D.L. Harris, Oceanographer , personal communication, 1978). 



Maximum monthly ranges occur at the summer and winter solstices (June and 

 December) when the sun's gravitational vector is more nearly parallel to the 

 Earth's in subtropical and higher latitudes (Fig. 2). Minimum ranges occur at 

 the equinoxes (September and March) when the sun's gravitational vector is 

 smallest. The tidal range fluctuations shown in Figure 2 include the effects 

 of winds. 



The seasonal cycle in tidal range is not in phase with a similar cycle 

 in water level, which results primarily from astronomical forces, modified 



1 1 1 1 1 II 



1 1 



1 1 



Long-Term Mean Water Level 







( ft above N6VD ) 



/"^x. 





Golveston Pleasure Pier 0.35 



A' 



^> 



Freeport Horbor -0.02 



>> 



Sabine Pass 0.75 





4 





/ 



'\\ 



/■i^.X 



1 / 





#-OvV\ 



A 



A- 





J 



- 1 "A/ 





N _ 



// 







- -.— y/ 





- 



.^■' 







Galveston Pleasure Pier (1958-1978) 





Freeport Harbor (1955-1975) 





Sobine Pass (1960-1975) 







Predicted Astronomicol Variation for G 



alveston 



Ctionnel Primary Station 

 1 1 1 1 1 1 1 



1 1 



1 1 



14 



