somewhat by meteorological and steric effects. Maximum water levels occur in 

 September when onshore winds combine with warmest (least dense) water. A 

 secondary maximum associated with onshore winds and astronomical forces occurs 

 in May. Minimum levels occur in February, when the water is coldest (most 

 dense) and astronomical influences produce a near-minimum level, and in July. 



Figure 4 illustrates the variability in diurnal tide level and range for a 

 representative year (1974), using data from a number of NOS and SWG gages 

 throughout the study area. Note the typical pattern of tide level variation 

 at stations from Freeport to Sabine Pass, although deviations from the mean 

 are much larger than the long-term data in Figure 3. Figure 5 shows greater 

 scatter in the range variation, probably due to meteorological effects. 



3. Annual Variability in Tidal Range and Level. 



In analyzing the data, it became apparent that another type of variabil- 

 ity, the difference between mean annual ranges and levels and their long-term 

 means, could be important. Available data from 1955 to 1975 for three NOS 

 gulf coast tide stations are plotted in Figures 6 and 7. The NOS Galveston 

 channel gage records, which began in 1909, provide perspective to the trends 

 shown at the three stations in Figures 6 and 7. Plots of the historical 

 variation in level and range at this site are shown in Figures 8 and 9. 

 Figures 6 and 8 illustrate a recent rapid increase in mean annual water levels 

 at all stations; the average rate of rise was rather gradual between 1955 and 

 1970, then increased drastically between 1970 and 1975. The last time such a 

 rapid increase occurred was in 1940. Most of the recent rise may be due to 

 increased subsidence, since the pattern of relative water level rise, which 

 had been similar for the three stations between 1960 and 1970, shows consider- 

 ably different trends in the last 5 years of record (Fig. 6). Marmer (1951) 

 analyzed long-term records from a number of gulf coast stations and found the 

 average rate of rise was not constant throughout the gulf. He assumed this 

 difference was due to localized subsidence. The importance of mean water 

 elevation changes to beach and inlet stability cannot be neglected and is 

 discussed later in this report. 



The historical record of annual mean diurnal tidal range at Galveston 

 (Fig. 9) clearly shows the 19-year-cycle characteristic of ocean tides. This 

 results from interference of shorter period astronomical tide components; 

 therefore, the pattern also holds for Freeport Harbor and Galveston Pleasure 

 Pier, where the mean annual diurnal range varied as much as 0.34 foot between 

 1955 and 1975 (Fig. 7). The Sabine Pass range variation did not follow this 

 pattern, perhaps due to the effects of freshwater flow on the midpass water 

 levels. The predicted values shown in Figure 7 result from the computer 

 program developed at CERC (Dr. D.L. Harris). 



III. HYDRAULICS AND STABILITY OF SPECIFIC INLETS 



1. Brazos River-Freeport Harbor Entrance . 



a. Historical Review. Freeport Harbor (the old Brazos River Estuary) is 

 the southernmost entrance studied (Fig. 10). Before the existence of Freeport 

 Harbor, the Brazos River was a major sediment contributor to this area of 

 the Texas coast; the harbor is under consideration as a site for a deep-draft 

 port. Construction activities in this area have been extensive and varied, 

 and interesting effects of such activities on the littoral regime have 

 developed. 



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