1933 Shoreline 



2,000 4,000(1 



Figure 20. San Luis Pass, 1933 (after USC&GS chart H5488). 



some discrepancy between the longitudes on the first two surveys and the 1933 

 survey. If permanent interior reference points are used, the longitude lines 

 of the early surveys are 1,460 feet (more than 0.4°) west of their counter- 

 parts on the 1933 survey. The 1867 survey is also questionable in other 

 respects; the survey shows that the west end of Galveston Island had extended 

 westward more than 2,000 feet in only 14 years. These surveys and numerous 

 aerial photos were used to determine the historical variation in inlet cross- 

 sectional area, minimum width, and hydraulic radius (Fig. 21). Widths 

 obtained from the photos are approximately from mean high water (MHW) to MHW 

 and are accurate to at least 10 percent. Cross-sectional profiles of the 

 minimum-width cross section are shown in Figure 22. 



The deepest part of San Luis Pass has historically been the southwest side 

 of the inlet, very close to San Luis and Follett's Islands. Through at least 

 1867, San Luis Island and Follett's Island were separated by a wide and rela- 

 tively deep channel known as Cold Pass which, with another channel on the 

 north side of San Luis Island, supplied gulf water to Christmas Bay and adja- 

 cent areas. By 1933 (Fig. 20), Follett's Island extended across Cold Pass and 

 connected with San Luis Island. By 1938 (Fig. 23) , a wide platform with a 

 high berm along the outer edge had developed gulfward of San Luis Island. 

 Between 1938 and 1952 (Fig. 24) the width drastically decreased due to west- 

 ward growth of Galveston Island. Unfortunately, no photos were available 

 which revealed the possible causes of this event. Major hurricanes in the 

 early 1940's and weather patterns associated with a drought in the late 1940's 

 and early 1950' s may have contributed. 



31 



