Historical Shoreline Change Through 2007, Texas Gulf Coast: Rates, Contributing Causes, and Holocene Context
Jeffrey G. Paine, Sojan Mathew, and Tiffany Caudle
Bureau of Economic Geology, Jackson School of Geosciences, University of Texas at Austin, University Station, Box X, Austin, Texas 78713, U.S.A.
Long-term historical rates of Gulf shoreline change along the Texas coast have been determined through 2007 (the latest imagery that predates Hurricane Ike) from a series of shoreline positions that includes those depicted on 1800s charts and mapped from aerial photographs, ground GPS surveys, and airborne lidar surveys. Net rates measured at 11,731 sites spaced at 164 ft (50 m) along the 332 mi (535 km) of Texas Gulf shoreline average 4.1 ft/yr (1.2 m/yr) of retreat, significantly lower than late Pleistocene to early-Holocene retreat rates of 8 to 181 ft/yr (2.4 to 55 m/yr) and similar to mid- to late Holocene rates estimated using past sea-level positions and shelf bathymetric contours as a shoreline proxy. Net shoreline retreat occurred along 84 percent of the Texas Gulf shoreline, resulting in an estimated land loss of 13,890 ac (5621 ha) since 1930 at an average rate of 180 ac/yr (73 ha/yr). Rates of change are more recessional on the upper Texas coast (-5.3 ft/yr [-1.6 m/yr] east of the Colorado River) than they are on the central and lower coast (-3.3 ft/yr [-1.0 m/yr] from the Colorado River to the Rio Grande). Rates are slightly lower than those reported through 2000, possibly reflecting lower major storm incidence and decreased relative sea-level rise rates.
Areas undergoing significant net retreat include: (1) the muddy marshes on the upper Texas coast between High Island and Sabine Pass; (2) segments on the sandy barrier-island shoreline on Galveston Island; (3) the combined fluvial/deltaic headland constructed by the Brazos and Colorado rivers; (4) sandy, headland-flanking Matagorda Peninsula west of the Colorado River; and (5) San José Island, a sandy barrier island on the central Texas coast; and (6) the northern end and much of the southern half of Padre Island, a sandy barrier island on the lower coast. Significant net shoreline advance occurred (1) adjacent to the jetties that protect dredged channels at Sabine Pass, Bolivar Roads, and Aransas Pass; (2) near tidal inlets at the western ends of Galveston Island and Matagorda Peninsula; (3) near the mouth of the Brazos River; (4) along most of Matagorda Island; and (5) on central Padre Island.
Shoreline change rates were calculated for the latest coast-wide aerial photography that predates Hurricane Ike, which struck the upper Texas coast in September 2008 and significantly altered beach and dune morphology and shoreline position. Pre-Ike photography was chosen to avoid emphasizing the nearly instantaneous effects of Ike, recognizing that significant aspects of the recovery process can continue for two or more years after a major storm. The next update of long-term shoreline change rates will be based on shoreline positions extracted from coast-wide airborne lidar data acquired in 2012.
AAPG Search and Discovery Article #90158©2012 GCAGS and GC-SEPM 6nd Annual Convention, Austin, Texas, 21-24 October 2012