|2007 GSA Denver Annual Meeting (28–31 October 2007)|
|Paper No. 33-9|
|Presentation Time: 4:10 PM-4:30 PM|
SEVERE BEACH EROSION AT SURFSIDE, TEXAS CAUSED BY ENGINEERING MODIFICATIONS TO THE COAST AND RIVERS
WATSON, Richard L., P.O. Box 1040, Port Aransas, TX 78373-1040, Richard@TexasCoastGeology.com|
Surfside Village, Texas, a small beachfront community of stilt homes, on the south end of Follets Island, is suffering severe and accelerating shoreline retreat. Several rows of homes have been lost and more are now below the vegetation line on the beach. The Brazos River flowed into the Gulf of Mexico at Surfside, until it was diverted 11 km in the down drift direction in 1929. In the 80 years since the Brazos river was diverted to the south, the old Brazos delta has completely eroded away and no longer serves as a nearshore source for sand.
Construction of long jetties and a deep ship channel just downdrift of Surfside precludes sand transport in either direction across the harbor entrance. In addition, sand moving southwest along the beach at Surfside is carried out along the east jetty and deposited in the channel, where it is forever lost to the Surfside beach.
The U.S. Army Corps of Engineers and the Bureau of Economic Geology of the University of Texas at Austin maintain that the lack of an updrift fillet of sand and the recently accelerated erosion at Surfside beach may be due to wave amplification by the recently extended east jetty. Since the jetty was extended in 1992 and the channel was deepened to 14 m, the amount of sediment dredged annually from the outer bar channel has nearly doubled.
Extraction of large amounts of ground water for Freeport industries has caused subsidence of the land surface at Surfside, resulting in at least 0.3 meters of relative sea level rise by 1978. Extrapolation of the rate of subsidence suggests the total is now at least 0.6 meters at Surfside, resulting in additional shoreline retreat.
Finally, distant updrift sand losses further contribute to the Surfside sand shortage. At least 8.5 million cubic meters of sand has been lost inward through Rollover Pass since it was built in 1956 and more than 23 million cubic meters of sand have been caught and permanently stored east of the jetties at Bolivar Roads. This is a combined total of 5 million dump trucks of sand lost to the downdrift beaches.
River diversion, reduced river sand output due to dams and reservoirs, jetty construction, maintenance of a deep channel, land subsidence due to water extraction, and impoundment of updrift sand sources, all are present at Surfside. There is no other location on the Texas coast which is subject to such a complete collection of man-made causes of beach erosion.
2007 GSA Denver Annual Meeting (28–31 October 2007)
General Information for this Meeting
|Presentation Handout (.pps format, 4997.0 kb)|
|Session No. 33|
Identifying America’s Most Vulnerable Oceanfront Communities: A Geological Perspective
Colorado Convention Center: 708/710/712
1:30 PM-5:30 PM, Sunday, 28 October 2007
Geological Society of America Abstracts with Programs, Vol. 39, No. 6, p. 96
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