Texas Gulf Shoreline Change Rates through 2007

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Long-term rates of Gulf shoreline change along the Texas coast have been calculated through 2007 from a series of shoreline positions that includes those depicted on 19th-century topographic charts (in selected areas), aerial photographs from 1930 to 2007, ground GPS surveys, and airborne Lidar surveys. Net rates of long-term change measured at 11,731 sites spaced at 50 m along the 535 km (332 mi) of Texas shoreline fronting the Gulf of Mexico average 1.24 m/yr of retreat, identical to the average rate of change calculated using linear regression analysis.

Net shoreline retreat occurred along 84 percent of the Texas Gulf shoreline, resulting in an estimated net land loss of 5,621 ha (13,890 ac) since 1930 at an average rate of 73 ha/yr (180 ac/yr). Average rates of change are more recessional on the upper Texas coast (-1.6 m/yr east of the Colorado River) than they are on the central and lower coast (-1.0 m/yr from the Colorado River to the Rio Grande).

Notable areas undergoing extensive and significant net shoreline retreat include the muddy marshes on the upper Texas coast between High Island and Sabine Pass, the sandy barrier-island shoreline on Galveston Island west of the seawall, the low, fluvial/deltaic headland constructed by the Brazos and Colorado rivers, the sandy, headland-flanking Matagorda Peninsula west of the Colorado River, San Jose Island (a sandy, central Texas coast barrier island), and the northern end and much of the southern half of Padre Island, a sandy barrier island on the lower Texas coast.

Significant net shoreline advance occurred adjacent to the long jetties that protect dredged channels at Sabine Pass, Bolivar Roads, and Aransas Pass, near tidal inlets at the western ends of Galveston Island and Matagorda Peninsula, near the mouth of the Brazos River, along most of Matagorda Island, and on the central part of 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 shorelines extracted from coast-wide airborne Lidar data scheduled to be acquired in spring 2012.


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