From Bureau of Economic Geology, The
University of Texas at Austin (www.beg.utexas.edu).
NOAA Coastal Services Center, Shoreline Change Conference II, Charleston, SC, May 3, 2006
Texas Shoreline Change Analysis and Communicating
Multiple shorelines along the Texas Gulf of Mexico coast dating from 1930 through 2000 were analyzed for change. The purpose of the analysis is to predict future change; therefore, shorelines prior to 1930 were not used because engineering activities altered the sand budget beginning in the early 1900's. The Shoreline Change and Projection (SCAP) computer program determined shoreline change statistics along shore-normal transects spaced every 50 m alongshore and made future projections of shoreline positions on the basis of the linear regression rate. In 1930, some shoreline segments were still adjusting to new sand budgets. A qualitative evaluation of the alongshore trend of the standard error of shoreline positions at each transect and knowledge of engineering works guided the elimination of 1930's and 1950's shorelines from the analysis for some segments.
Of the 585-km Gulf shoreline, 30% is stable (change < 0.61 m/yr), 8% is advancing, and 62% is retreating at an average rate of 2.6 m/yr. Linear regressions for stable shoreline transects generally do not pass the F Test at the 95% confidence level. Retreating or advancing shoreline segments near river mouths and tidal inlets also typically do not pass the F Test. This means that there is a range in our certainty, which should be conveyed to coastal managers and the public, in how the shoreline will change in the future. Maps showing color-coded shoreline change rates with background haloes sized according to the statistical confidence interval, maps showing future shorelines projected using upper and lower bounds of the confidence intervals of shoreline change rates, and maps showing the maximum envelope of historical shoreline position are proving useful for conveying the nature of shoreline change.