CSG
 
Beach and Dune Analysis Using Chiroptera Imaging System, South Padre and Brazos Islands, Texas Gulf Coast
 
Project Summary
Researchers from the Bureau of Economic Geology (BEG) acquired lidar data and color infrared (CIR) aerial imagery of South Padre Island and Brazos Island, Texas (Mansfield Channel to Rio Grande) on February 4 and 5, 2013. The data collected has been used to (1) evaluate position and change rates of the shoreline, position of the vegetation line, and dune-crest elevations; (2) map geomorphic units; and (3) provide beach and dune system volume analysis. Data were collected using the BEG's new airborne system (Chiroptera), which collects topographic lidar data, shallow bathymetric lidar data, and high-resolution natural color/color infrared imagery. Topographic data and CIR images were collected for a 500-m swath (three passes) of South Padre Island and Brazos Island (71 km length) landward of the shoreline. Bathymetric data were collected from the shoreline 1000 m seaward. This project is intended to establish the depth-penetration and water-clarity limitations of Chiroptera on the open Gulf of Mexico coast.
topobathy

Figure 1.
Merged topographic and bathymetric lidar digital elevation model (DEM) of South Padre Island and nearshore environment adjacent to north jetty at Brazos Santigo Pass (Isla Blanca County Park).

 


Change Rate Analysis
On average, long-term shoreline change trends are erosional for South Padre Island and Brazos Island. The average rate of shoreline retreat between 1937 and 2013 was 2.2 m/yr (7.2 ft/yr) (Fig. 2). The Gulf shoreline between Mansfield Channel and the Rio Grande is retreating at 84% of the monitoring sites. Areas of advancing shorelines are concentrated adjacent to the jetties at Mansfield Channel and Brazos Santiago Pass. Maximum long-term retreat is found at the mouth of the Rio Grande and in the central portion of South Padre Island. Rates decreased over the last decade (2000 to 2013) to 1.1 m/yr of retreat (76 percent of sites retreating). The trend changed between 2010 and 2013 with 64 percent of monitoring sites advancing at an average distance of 4.9 m.

longterm

Figure 2.
Long-term net shoreline change between 1937 and 2013 from Mansfield Pass to the Rio Grande. Change calculated from shoreline positions determined from aerial photography and airborne lidar surveys. Positive values indicate shoreline advance; negative values indicate shoreline retreat.

 

Changerates

Figure 3.
Net shoreline change rates at southern end of South Padre Island: A) long-term, 1937–2013; B) decadal scale, 2000–2013; and C) short-term, 2010–2013. Change calculated from shoreline positions determined from aerial photography and airborne lidar surveys. Positive values indicate shoreline advance; negative values indicate shoreline retreat.
 
click for interactive map of South Padre IslandFigure 4. Interactive map showing shoreline, potential vegetation line, back-dune boundary, dune-crest elevations, geomorphic unit locations, and shoreline change rates along South Padre Island and Brazos Island.
 
 

Data Download

2013 GIS files

Presentation


 
 

 

Sponsors and Collaborators
This project was supported by grant no. 13-030-000-6895 from the General Land Office of Texas to the Bureau of Economic Geology, The University of Texas at Austin. The project was funded under a Coastal Management Program (Cycle 17) grant made available to the State of Texas by the U.S. Department of Commerce, National Oceanic and Atmospheric Administration pursuant to the Federal Coastal Zone Management Act of 1972. Additional funds from the State of Texas were provided through the State of Texas Advanced Oil and Gas Resource Recovery (STARR) program.
ION Geophysical
NOAA
STARR

 

 

 

 

 

 

 

 

 


 

 

 

 

 

 

 

 
BEG