Air photo analysis of the impact of Hurricane Alicia on Galveston Island.

The advent of Hurricane Alicia at Galveston Island in August 1983 brought not only widely reported structural damage but significant, less-publicized shoreline erosion as well. The purpose of this study was to quantify the erosional impact of Alicia and to determine whether that impact was a departure from, or merely a continuation of, the ongoing pattern of mid- to long-term shoreline movement on the island. The study compared aerial photography taken shortly after Alicia's passage with similat photographic sequences taken in 1979, 1977, 1967 and 1952 as well as a number of individual photos from 1970 and 1980. Measurements were made on each set of photos between fixed landmarks and the seaward edge of the line of natural vegetation to determine how far and in which direction that line had moved between photographic dates. Vegetation-line position provides a better index of erosion or accretion than the actual shoreline because it is not subject to anomalous diurnal or seasonal movement which might confuse the results. The vegetation line also has an important legal significance in Texas. Structural damage from Alicia, which seems to have been a major hurricane but not an extreme one like Carla, Celia or Allen, was concentrated along the beachfront and on the southwestern half of the island. Erosion from 1979 to 1983, most of which was due to Alicia, was fairly uniform: close to 100 feet over most of West Beach except for a short stretch near the southwest tip of the island where it exceeded 200 feet. Shoreline change at West Beach was more erratic during the 1952-1967 and 1967-1979 periods: 1952-1967 saw mostly moderate erosion except for some accretion at the southwest tip; from 1967 to 1979 there was modest accretion over most of West Beach but rapid erosion at the southwest tip. The vegetated bluffs along undeveloped beaches withstand erosional events better than developed beachfronts. Bulkheading does not appear to significantly inhibit erosion resulting from direct hits by major storms such as Hurricane Alicia. The Texas Open Beaches Act defines the public beach as the area between the vegetation line and the low water line, stipulating that no structures are allowed in that zone. Scores of beachfront homes which were behind the vegetation line prior to Alicia ended up either parially or wholly on this public access area in the storm's wake. This initiated legal proceedings which have apparently not yet been fully resolved. It is quite unlikely that the West Beach vegetation line will move seaward significantly over the years to come. The sand source which had provided some nourishment to that area in the past has apparently been depleted. Even East Beach, which has steadily accreted since the 1890's when the Galveston jetties were built, is showing signs of an erosional future. Considering the implications of the Texas Open Beaches Act and the probability of continued long-term erosion along West Beach, purchase of a beachfront home in that area is a chancy proposition at best. We suggest that any new waterfront structure be set back sufficiently far from the vegetation line to accommodate at least thirty years of projected erosion for the particular stretch of beach on which it is to be built.