A period of inlet widening began between 1952 and 1954. Figure 25 shows 

 parts of the ebb tidal delta. Continued widening between 1954 and 1956 coin- 

 cided with slight accretion on the southwest shoulder and minor rotation of 

 the shoal adjacent to it. Figures 26 and 27 provide a comparison of the 

 entire extent of the ebb tidal delta in 1957 and the posthurricane condition 

 in 1961. During this 4-year period, the end of Cold Pass was overtopped and a 

 large hurricane washover, with a similar breach on the east side, developed. 

 A large bulge formed on the southwest shoulder; gulf ward of the bulge the ebb 

 tidal delta had moved about 1,700 feet southwest. These major changes were 

 undoubtedly due to hurricanes. A hurricane in 1959 passed directly over the 

 pass, and in 1961 Carla struck, the coast at Pass Cavallo, producing unusually 

 large waves and strong currents at San Luis Pass. Unfortunately, no photos 

 were available between 1957 and 1961 to indicate the extent of these changes. 



The 1962 photo (Fig. 28) shows continued change in the location and shape 

 of the ebb tidal delta, but the southwest beach remained relatively constant. 

 The first available cross section since 1933 showed an increase of about 4,000 

 square feet in the minimum area, with a shallower thalweg located about 500 

 feet east and a deeper east side (Fig. 22). Between 1962 and 1965 (Fig. 29) 

 the southwest shoreline bulge remained exactly in line with the end of the ebb 

 tidal delta, but both had moved away from the pass, and the inlet width had 

 increased to more than 4,000 feet. On the northeast side, a thin spit con- 

 necting Galveston Island with the higher remnants of the island was exposed in 

 1962 (Fig. 23). Since 1965, the inlet width has remained almost constant at 

 slightly more than 4,000 feet; the cross-sectional area apparently remained 

 constant between 1962 and 1976. Beaches within 5,000 feet southwest of the 

 pass have accreted, while those within 10,000 feet northeast have eroded, 

 accentuating the downdrift offset typical of many Texas inlets. 



b. Sediment Volume Changes . 



(1) Ebb Tidal Delta . The 1853 and 1933 surveys provided enough data 

 to quantitatively define the ebb tidal delta, and three methods were used to 

 calculate sediment volume changes. The first method was that' of Dean and 

 Walton (1973), where the ebb tidal delta was delineated by the points at which 

 shore-parallel bottom contours are first distorted by the influence of the 

 inlet. These contours were then drawn shore-parallel across the inlet loca- 

 tion to their counterparts on the opposite side. Grids were superimposed on 

 these contours and the actual survey, and differences between the artificial 

 and actual depths at each grid point were calculated. An average depth dif- 

 ference from the four corners of each grid square was calculated, and this 

 difference was multiplied by the grid square area to arrive at a volume. The 

 volumes were then summed over the entire ebb tidal delta to yield the total 

 volume of sediment in the delta. Each side of the squares used in this analy- 

 sis was 625 feet long. 



The ebb tidal delta volume in 1853 was 4,815,000 cubic yards over an area 

 of 8.67 X 10^ square feet. By 1933 the volume had increased to 6,070,000 

 cubic yards over an area of 7.3 x 10 square feet. Between 1853 and 1933 

 relative sea level rose 1.4 feet or 0.0175 foot per year (Hicks, 1972), which 

 over an area of 7.3 x 10 square feet amounts to a volumetric increase of 

 3,790,000 cubic yards. Therefore, the total volume change on the ebb tidal 

 delta between 1853 and 1933 was 5,050,000 cubic yards, with an annual accre- 

 tion rate of 63,000 cubic yards per year. An area decrease of 1.37 x 10 

 square feet off the tip of Follett's Island also occurred during this period. 



34 



