On the northeast side, deposition between 1888 and 1908 was about 8.6 

 million cubic yards, a rate of 430,000 cubic yards per year. How much of this 

 occurred as a result of the north jetty is difficult to determine. The area 

 had accreted rapidly (1,060,000 cubic yards per year) before jetty construc- 

 tion. The 1908 shoreline showed little change from the 1867 condition. 



(c) Changes Between 1908 and 1933 . The shoreline of Galveston 

 Island continued to grow seaward during this period (Fig. 45). Next to both 

 the north and south jetties, a similar pattern of offshore erosion and near- 

 shore accretion occurred (Fig. 48). One million cubic yards accreted south of 

 the jetty, at an average rate of about 40,000 cubic yards per year. However, 

 extensive deposition occurred just north of the jetty, and much of this 

 material may have come through or over the jetty. Some of the material could 

 also have come from scour of the entrance channel. On the northeast side, net 

 deposition was 10.8 million cubic yards, an annual rate of 430,000 cubic yards 

 per year. The shape of the deposition area shown in Figure 48 indicates that 

 the north jetty may have been impermeable, trapping most of the westward- 

 moving longshore transport. If this was the case, and the area of deposition 

 extended eastward beyond the limits of the available data, then the minimum 

 westward transport rate was 500,000 cubic yards per year between 1908 and 

 1933. 



(d) Changes Between 1933 and 1965 . Figure 49 shows the 1965 

 shoreline intercepting the south jetty about 2,300 feet seaward of the 1933 

 intercept. However, offshore changes south of the jetty were relatively 

 minor, and it is concluded that the adjustment of the ebb tidal delta to a 

 wave-dominated environment had been completed by 1933. On the north side, 

 however, deposition continued between 1933 and 1965 (at a rate of at least 

 420,000 cubic yards per year), and minor erosion occurred along the seaward 

 section of the jetty. 



(e) Changes Between 1965 and 1975 . The shorelines on either 

 side of the pass changed little between 1965 and 1975 (Fig. 45). In the 

 offshore zone south of the south jetty, erosion totaled about 1 million cubic 

 yards between 1968 and 1975 (Fig. 50); on the north side the erosion was about 

 six times greater. Much of this was concentrated in a region just north of 

 the gulf end of the jetty. 



(f) Summary of Changes Between 1867 and 1975 . Bathymetric and 

 shoreline changes were previously examined at 20- to 25-year intervals. 

 Morton (1977) analyzed changes at many Texas inlets and found those for 

 Galveston between 1867 and 1974 (Fig. 51) to be similar to those at Sabine, 

 Brazos-Santiago, and Freeport, i.e., a downdrift tripartite pattern of off- 

 shore deposition, nearshore erosion, fillet and beach accretion, and an up- 

 drift pattern of widespread accretion. This analysis revealed that these 

 patterns were established shortly after the completion of the jetty construc- 

 tion, and that later adjustments were relatively minor compared to those 

 occurring in the first 10 to 15 years. Estimates of westward longshore sedi- 

 ment transport rates based on postconstruction accumulation are between 

 420,000 and 500,000 cubic yards. Calculations of eastward rates were compli- 

 cated by landward migration of the ebb tidal delta but averaged 170,000 cubic 

 yards per year, for about a 2.5:1 westward-to-eastward ratio. 



(g) Changes in Entrance Channel. Shoaling and scour patterns 

 for the entrance channel between 1890 and 1940-41 were provided by U.S. Army 



57 



