directed currents toward the north end of Galveston Island (U.S. Army Engineer 

 District, Galveston, 1942). By 1965, the channel had once again reached a 

 50-f oot-maximum depth, though this point was westward of its 1933 position, 

 causing a steep-sided channel adjacent to the south jetty. Increases in 

 cross-sectional area and hydraulic radius between 1933 and 1965 (Fig. 42) may 

 have been due to natural expansions of the profile or from the dredging to 

 increased project depths. 



(2) Changes to Adjacent Beaches and Offshore Zones . The effect of 

 jetty construction on Galveston entrance is illustrated in the Galveston 

 Island shorelines from 1851 to 1*^^75 (Figs. 43 and 45), and maps of bathymetric 

 changes between survey dates (Figs. 46 to 50). The effect of a relative sea 

 level rise of 0.02 foot per year during this century was included in all 

 volumetric calculations (see Fig. 8). 



(a) Changes Between 1851 and 1889 . Between 1851 and 1867, the 

 northern end of Galveston Island receded greatly (Fig. 43); a storm in October 

 1867 cut a 1 ,000-f oot-wide channel 2 feet deep across the northern end of the 

 island (U.S. Army Corps of Engineers, 1868). Construction of the submerged 

 jetty in 1880 caused local accretion at the tip of the island (compare the 

 1867 and 1884 shorelines in Fig. 43). More extensive deposition occurred 

 between 1884 and 1889, corresponding to construction of the shoreward part of 

 the south jetty between 1887 and 1889. Figure 46 shows the bathymetric 

 changes which occurred between 1867 and 1888. About 3.5 million cubic yards 

 of sand accumulated in the fillet on the tip of Galveston Island, at an aver- 

 age rate of about 166,000 cubic yards per year. However, most of this accumu- 

 lation may have occurred between 1884 and 1888, when the impermeable jetty 

 probably prohibited sand movement around the tip. Extensive offshore deposi- 

 tion occurred on the north side, and nearshore deposition on the south side of 

 the entrance; about twice as much was deposited on the north as on the 

 south. The northern deposition was due to natural processes, since the south 

 jetty had not been extended seaward in 1888 and north jetty construction did 

 not start until 1893. An extensive zone of minor erosion existed in the 

 offshore area on the south side. 



(b) Changes Between 1888 and 1908 . The north tip of Galveston 

 Island accreted rapidly in response to jetty construction (Fig. 45). Compar- 

 ing Figures 46 and 47 shows that about 14.7 million cubic yards of sand accu- 

 mulated in the south fillet between 1888 and 1908. However, Figure 47 also 

 shows a large offshore erosion zone with a deposition zone landward extending 

 to the fillet. The volume deposited between 1867 and 1908 was about the same 

 as the volume eroded (i.e., about 15 million cubic yards). 



Between 1888 and 1908, south side erosion totaled 15.5 million cubic 

 yards, nearshore deposition was 5.8 million cubic yards, and 14.7 million 

 cubic yards accumulated in the fillet. Thus, total south side deposition 

 following jetty construction was 20.5 million cubic yards and the net change 

 was +5 million cubic yards or about 250,000 cubic yards per year. It is 

 concluded that much of the material which comprised the fillet actually came 

 from adjustment of the ebb tidal delta to jetty construction. With jetty 

 construction, the erosion zone, which had previously experienced considerable 

 tidal current action, was subjected only to waves and wave-induced currents. 

 These tended to drive the material landward into the fillet and perhaps also 

 through the jetty. 



53 



