Paper No. 196-9
Presentation Time: 10:30 AM
HISTORICAL TO RECENT TEXAS GULF SHORELINE MOVEMENT AND ITS POSTGLACIAL CONTEXT
Long-term Gulf shoreline movement along the Texas coast has been determined from a series of shoreline positions that includes those depicted on aerial photographs from the 1930’s to 2007, GPS surveys, and airborne lidar surveys in 2000 and 2012. Net rates of shoreline movement measured at 11,749 sites along the 585 km of Texas shoreline fronting the Gulf of Mexico average 1.26 m/yr of retreat. Net retreat occurred along 80 percent of the shoreline, resulting in an estimated net land loss of 5,907 ha since 1930. Areas undergoing significant retreat include: (1) the muddy upper Texas coast marshes; (2) segments on the sandy barrier-island shorelines on Galveston Island, San José Island, and parts of Padre Island; and (3) the Brazos/Colorado fluvial and deltaic headland and the flanking Matagorda Peninsula. Net shoreline advance occurred adjacent to jetties, near tidal inlets, near the Brazos River, along Matagorda Island, and on central Padre Island. Shoreline change rates were determined for shorter periods to assess change in rates over time. Net shoreline movement rates measured from the 1950’s to 2012 average 1.47 m/yr of retreat. Rates measured for the most recent period (2000 to 2012) are lower (retreat at 1.18 m/yr) than those calculated for longer periods. Long-term rates estimated from historical shoreline positions are lower than late Pleistocene to early Holocene rates that range from 3 to 55 m/yr estimated from bathymetric contour shoreline proxies and past sea-level positions, but are similar to mid- to late Holocene retreat rates of 0.1 to 1.7 m/yr. A statistical relationship between postglacial relative sea-level rise rates and retreat rates calculated from the shoreline proxy suggests that each mm/yr of sea-level rise translates to 0.8 to 1.8 m/yr of shoreline retreat. This empirical relationship can be used to estimate future shoreline retreat rates under sea-level rise scenarios similar to those observed during postglacial sea-level rise.