The beach environment dominates

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1 Beaches of the Texas Gulf Coast By Richard A. Davis, Jr. ABSTRACT The Texas coast is home to some of the best beaches in the world. The microtidal and low-energy, wave-dominated environment lends itself to relatively stable to prograding conditions. Only the eastern portion of the Bolivar Peninsula and Galveston Island plus the Brazos/San Bernard delta area experience chronic erosion. Most of the barrier island coast is essentially pristine because of the absence of vehicular access and preservation as government-held land. Hurricanes have had a major impact on the coast both in populated and uninhabited areas. Beach nourishment has been conducted in the Galveston and South Padre areas with mixed results. Overall, the Texas beaches are in good shape and are likely to remain so in the future. The beach environment dominates the Gulf Coast of Texas from one end to the other. Except for two short distances in the northeast portion, all are attached to wave-dominated barrier islands (Figure 1). This coast is microtidal and wind-dominated (Morton 1994). The prevailing wind is from the southeast with intense northerly wind associated with the passage of cold fronts in the winter. Spring tidal range is about 0.9 m plus or minus about 0.1 m. QUATERNARY GEOLOGY During the Quaternary Period of about 2.5 million years, there have been changes in sea level along this coast that exceeded 100 meters during multiple excursions and incursions of the shoreline. Coastal plain environments have migrated with the shoreline during these cycles. As sea level was lowered, the fluvial systems extended out across what is now the continental shelf. The Trinity, Brazos, Colorado, and other of the current rivers of the Texas coastal plain had ancestral versions that were active during low sea level stages (Anderson and Fillon 2004). Extensive work by the group from Rice University under the direction of John Anderson has provided maps of the sedimentary environments (e.g. Figure 2) in multiple publications. These fluvial systems included extensive flood plains dominated by mud, numerous linear channel sand bodies, and deltas that contain a combination of mud and sand (Anderson 2007). The shoreline moved back and forth across this wide, low relief coastal complex reworking the sediments during transgression and depositing sediments as the sea level lowered and the strand line moved Gulfward. The most recent transgression began about 18,000 years ago as glacial melting began. The initial rate of sea level rise was rapid; averaging about a centimeter per year. About 7,000 years ago it slowed to only about 2 millimeters per year. Shortly thereafter, barrier islands began to form and the geomorphology of the coast as we see it began to form. Various researchers have cored these barriers and find that they range in age from about 5,000-6,000 years. Padre Island (Fisk 1959) on the south and Galveston Island (Bernard et al. 1970) near the north end of the Texas coast began about 5,000 years ago; Mustang Island (Simms et al. 2006) and Matagorda Island (Wilkinson 1975) near the middle are about the same age. The sediment available to form these islands came from a combination of reworking the older deposits on the shelf as sea level rose and some from the rivers that drain the Texas coastal plain. The barriers as we now see them have been in place for about 3,000 years with considerable modification due to storms. COASTAL PROCESSES Weather is a major factor in the beach environment on the Texas coast. Except for a few months during the summer, there is a significant and persistent wind from the southeast. This wind direction produces longshore currents and therefore sediment transport from north to south along most of the coast to about the middle of Padre Island (Figure 1). From the southern border of Texas to this area in Padre Island the prevailing longshore ADDITIONAL KEYWORDS: Beach nourishment, Bolivar Peninsula, Galveston, Padre Island, San Bernard delta, Brazos delta. Manuscript submitted 16 May 2013, accepted 30 June currents are from south to north resulting in a convergence of longshore sediment transport (Davis 1978). During the winter months, the passage of cold fronts produces strong offshore wind that results in minimal longshore currents and sediment transport. About 10 or 12 of these pass the coast in a given year. The most important event-related processes are associated with tropical storms and hurricanes. Although the season lasts from June through November, the majority of these storms occur in August and September. The warm water temperatures in the Gulf of Mexico in the summer cause strengthening of the storms as they move to the Texas coast. Several major hurricanes have impacted this coast during the past hundred plus years (Table 1). By far the most devastating hurricane on the Texas coast was at Galveston in 1900 where 8,000 people died and the city was destroyed. This storm led to the raising of the city by about 2 meters and construction of the famous Galveston Seawall. The most recent hurricane to hit this area was Hurricane Ike in Although only a Category 2 storm at landfall, it was large and moved rather slowly thus causing tremendous damage (Carlisle 2009). Although the Texas coast is wavedominated there are also tides, both lunar and wind generated. The lunar tides here are similar to those throughout the Gulf of Mexico. They are microtidal, generally on the low end of that category, with spring values less than a meter. In addition, lunar tides are mixed, i.e. in part of the lunar month they are semi-diurnal and during part of the month they are diurnal. The low magnitude of the tidal range Shore & Beach Vol. 81, No. 3 Summer 2013 Page 31

2 Figure 1. Index map of the Texas coast showing the major geomorphic features (modified from Morton 1994). creates little intertidal zone on the beach and causes little tidal-influenced beach change. The wind can cause as much change in sea level on this coast as the lunar tides, in both directions depending on whether it is onshore or offshore. The latter is limited to the passage of cold fronts in the winter. Hurricanes and tropical storms cause meters of storm surge that have a tremendous effect on the beaches; typically in a negative manner. It is not uncommon for a single storm to remove all of the dry beach and cause washover fans or channels through the dunes. TEXAS BEACHES There is a good deal of commonality among the beaches of Texas regardless of where you are on the coast. At most locations, the backshore is about a meter above mean sea level with a foreshore that tends to be gently sloping. All of the beaches are terrigenous sand with a fairly complex composition of minerals and rock fragments (Bullard 1942). Grain size of these terrigenous sands is fine to very fine sand and is typically well sorted. There is a variable shell component that ranges from sand size to gravel including whole shells. The variation is both in time and space. The following discussion will consider the nature of the geomorphology and sediments of the beaches in each section. Mainland beaches There is no barrier island from the border with Louisiana at Sabine Pass for about 35 km to the southwest where the Bolivar Peninsula begins (Figure 1). This region has been subjected to considerable erosion over the past few decades, to the extent that the state highway is washed out from the High Island area to the east. The combination of eroding beaches and the absence of new sediment while relative sea level is rising rather rapidly makes for poor beach environments. Sea level is rising about 6-8 mm per year in this area (Davis 2012). The largest reach of mainland beaches is associated with the deltaic complexes of the Brazos and San Bernard rivers, both of which empty directly into the Gulf of Mexico. The coastal section is about 40 km wide. The Brazos, the largest of the two rivers, naturally emptied into the Gulf at the city of Freeport, a major port for the petrochemical industry. In order to stabilize the port entrance and eliminate the mobility of the Brazos delta, the mouth of the river was relocated west of the city in 1929 by the U.S. Army Corps of Engineers. These mainland beaches tend to have sand veneers over muddy marsh deposits that can be exposed in the surf after storms. At one location, Sargent Beach (a small vacation village) has lost multiple streets of property and shows the situation quite well (Figure 3). Hurricane Carla in 1961 (Table 1) was especially damaging to this coast. The continual retreat of the shoreline caused the Corps of Engineers to construct a low seawall made of large granite blocks (Figure 4). Although many people thought that this structure was to protect the residences, it was really to halt erosion that was projected to eventually reach the Intracoastal Waterway, a major commercial thoroughfare along this coast. This structure has been quite successful in stopping the erosion and is now essentially buried by beach sand so it presents no visual expression. Barrier island beaches Northeast The northeasternmost reach of barrier beaches extends from the Bolivar Peninsula to near Freeport and includes both Galveston Island and Follets Island. These are classic wave-dominated barrier islands with a range of beach qualities; some progradational and some erosional. The problems of erosion mentioned in the section of the eastern mainland beaches continue across the Bolivar Peninsula. Coastal communities here have experienced hurricanes that have devastated their beaches; the most recent being Hurricane Ike in 2008 (Table 1). A low concrete wall has been placed just Gulfward of the coastal highway in order to try to keep sand from being washed onto the road (Figure 5). Galveston Island presents considerable unusual conditions for Texas beaches. It is separated from Bolivar Peninsula by the ship channel that goes to the Ports of Galveston and Houston. Page 32 Shore & Beach Vol. 81, No. 3 Summer 2013

3 Although downdrift regionally, there has been tremendous accumulation at the end of Galveston Island; more than a kilometer in a century (Figure 6). This situation changes in only a short distance where there is no dry beach in front of the seawall (Figure 7). Although the Galveston seawall has withstood a century of storms, there has been difficulty maintaining a beach. A large nourishment project was completed in 1995, more than 5.75 km (3.6 mi) long with about 560,000 m 3 (750,000 yd 3 ) of sand. Unfortunately, it did not perform well and most of the sand was lost in a few of years. Small-scale nourishment projects were completed over the next few years, and then in 2008 Hurricane Ike devastated the island. There have been multiple protection and nourishment projects since then, with most of the activity directed toward the west portion of the island, downcoast of the seawall. The west portion of Galveston Island is low and quite susceptible to erosion. Hurricane Ike was particular destructive to this part of the island. Longard tubes have been used to protect the extensive development and the beach has been nourished multiple times. These efforts have not been especially successful, but they continue. There are some efforts to design and apply for a permit for a socalled Ike Dike that would essentially surround the island. Follets Island (Figure 1) is relatively undeveloped on its eastern portion but becomes developed as one approaches Freeport. The beach on this island is wide and driveable (Figure 8) with small dunes landward. It is popular for fishing and general beach recreation. Small recent nourishment and protection projects have been carried out on the west end during Barrier island beaches Central Beginning just west of the San Bernard River mouth, the remainder of the Texas coast is barrier islands (Figure 1) with generally well-developed beaches. Most of this coast is undeveloped and has limited or no vehicular access. It consists of Matagorda Peninsula and Island, San Jose Island, and Mustang Island. Only the latter has significant development in the form of the town of Port Aransas. One stretch of about a kilometer on Matagorda Peninsula is the mouth of the Colorado River (Figure 1) that now emp- Figure 2. Map of the drainage system of the Texas coast as it appeared during a low stage of sea level during glacial advance (modified from Berryhill 1978). Table 1. Major hurricanes on the Texas coast. Date and name Category Landfall area 1900 No name 4 Galveston 1915 No name 4 Galveston 1916 No name 4 Corpus Christi 1919 No name 4 Corpus Christi 1961 Carla 4 Port Lavaca 1970 Celia 3 Corpus Christi 1980 Allen 3 Brownsville 1983 Alicia 3 Galveston 1999 Bret 3 Padre Island 2008 Dolly 3 South Padre Island 2008 Ike 2 Galveston Shore & Beach Vol. 81, No. 3 Summer 2013 Page 33

4 Figure 3. Oblique aerial photo of the Sargent Beach area during the early 1980s showing a thin veneer of beach sand overlying muddy marsh deposits as this shoreline was transgressing. Figure 4. Photographs of the Sargent Beach protection structure: a) (above)shortly after completion of the structure in 1998, and b) (right) its present buried condition in Figure 5. Low concrete wall on the Bolivar Peninsula designed to keep sand from being washed on to the highway. ties directly into the Gulf. This is a recent development in that the Colorado delta has prograded across Matagorda Bay in less than a century to become part of the open Gulf Coast (Figure 1). The two undeveloped barrier islands of Matagorda and San Jose are a government preserve and a private ranch, respectively. These two islands display well the pristine nature of barrier island beaches. The dunes are experiencing some erosion and blowover (Figure 9a) and there is a range in the width of dry beach. In some locations it is nearly absent (Figure 9b). The only indication of human activity is the widespread and abundant trash on the beach, most of which is plastic. This is a major problem on the Texas coast and between the plastic and the fishing line, the turtles and birds have major hazards with which to cope on a continual basis. Mustang Island is partly densely developed, partly sparsely developed, and partly undeveloped. Port Aransas is a community that is a primary tourist destination on this coast. Its beaches are maintained including raking on a regular basis and holding the Gulf boundary of the foredune location back of its natural position (Figure 10). Other than that, the beach is wide and natural except that it is also a maintained county road. The more natural and major part of the island has multiple historical natural tidal inlets that have been closed for decades plus a manmade pass that has been closed about as long. One of the natural passes, Packery Channel, has recently been dredged and structured. Over all, Mustang Island has excellent beaches that attract a large number of visitors throughout the year. Barrier island beaches South Padre Island is the longest barrier island in North America and one of the longest in the world. It is continuous except for Mansfield Channel, a dredged, stabilized, and maintained tidal inlet about two-thirds of the distance from the north end of the island (Figure 1). This island is home to one of the oldest and most extensive National Seashore parks in the country. The northern few kilometers of the island have development and are visited by many tourists, but fewer go to the National Seashore. Although one can drive the beach throughout the entire island, much of it is for four-wheel drive vehicles. As such, only a few fisherman Page 34 Shore & Beach Vol. 81, No. 3 Summer 2013

5 and tourists venture there. The beaches are generally wide and prograding with abundant coppice mounds fronting the foredunes (Figure 11). This part of Padre Island hosts the highest density of turtle nests in Texas. Only the Kemps Ridley species nests here and all nests are collected and incubated, then the hatchlings are released. Moving past mile post 15 on the Padre Island National Seashore beach one comes to the area called Little Shell, characterized by shell gravel that is broken fragments. These beaches are in excess of 50% shell debris. After a few more miles the shell beach changes to Big Shell, the section of beach that has mostly whole shells making up the beach (Figure 12). These areas are also the zone of the beach where longshore currents and sediment transport converge (Davis 1978). Most of Padre Island south of Mansfield Pass (Figure 1) is four-wheel drive only and is natural with wide beaches. Dune scarps from Hurricane Dolly (2008) are still prevalent (Figure 13). The only indication of human activity is the presence of large, cylindrical hay bales to help stabilize dunes and enhance their growth. The southern few kilometers of the island are the site of the community of South Padre Island, a major tourist attraction (Figure 14). This is a growing community with beach erosion problems that have been addressed by multiple nourishment projects. Problems still exist but the local management team is working hard to keep the beach in good shape. CONCLUSIONS Texas has great beaches! Most are fronting barrier islands and few are suffering chronic erosion. Wave energy is modest except during extreme events and tidal range is low in the microtidal range. Except in the Galveston area, human modification is minor with few seawalls or similar structures. Nourishment projects have been conducted at each of the three areas of development but the project in the central area was at a single time and was quite small. Overall, Texas beaches are doing well with the possible exception of the west end of Galveston Island. REFERENCES Anderson, J.B., The Formation and Future of the Upper Texas Coast. College Station, Texas A&M Press, 163 p. Anderson, J.B., and R.H. Fillon, (eds) Late Quaternary Stratigraphic Evolution of the Figure 6. Galveston seawall near the jetty at the Houston ship channel showing the tremendous accumulation of sediment since the wall was constructed in the early 1900s. Figure 7. Present condition of the Galveston seawall and the adjacent beach that is essentially absent. Figure 8. Wide and natural beach on Follets Island as it appeared in Shore & Beach Vol. 81, No. 3 Summer 2013 Page 35

6 Figure 9. San Jose Island is a privately owned barrier island that is a cattle ranch with a) (right) natural beach and scarped dunes, and b) (below) dunes that are presently somewhat active showing a blowover appearance. Figure 10. Photo of beach that is maintained as a parking lot and where the foredune border with the beach is kept at a landward position in order to keep the parking lot and the road on the active beach. Figure 11. The foredune, coppice mounds, beach, and surf zone of a typical Padre Island beach location. Figure 12. The foreshore and surf zone at Big Shell on Padre Island. Complete shells comprise most of the beach sediment here. Page 36 Shore & Beach Vol. 81, No. 3 Summer 2013

7 Northern Gulf of Mexico Margin. Tulsa, SEPM, Special Publ. 79, 311 p. Bernard, H.A., C.F. Major, B.S. Parrott, and R.J. LeBlanc Recent sediments of southeast Texas: A field guide to the Brazos alluvial and deltaic plains and the Galveston barrier island complex. Austin. University of Texas, Bureau of Econ. Geol. Guidebook 11, 132 p. Berryhill, H.L., South Texas continental shelf and continental slope: Late Pleistocene/ Holocene evolution and sea-floor stability. U.S. Geological Survey open-file report, Bullard, F.M., Source of beach and river sands on Gulf Coast of Texas. Geological Society of America Bulletin, 53, Carlisle, B., After Ike: Aerial Views from the No-Fly Zone. College Station, Texas A&M University Press, 127 p. Davis, R.A., Beach sedimentology of Mustang and Padre Islands: a time-series approach. J. of Geology, 86, Davis, R.A., Sea-Level Change in the Gulf of Mexico. College Station, Texas A&M Press, 172 p. Fisk, H.N., Padre Island and the Laguna Madre flats, coastal South Texas. Proc 2nd Coastal Geography Conf., Baton Rouge, Louisiana State Univ., Morton, R.A., Texas Barriers. In Davis, R.A., Holocene Barrier Island Systems, Heidelberg, Springer-Verlag, Inc, Simms, A. R., J. B. Anderson, and M. Blum Barrier-island aggradation via inlet migration: Mustang Island, Texas. Sedimentary Geology, 187, Wilkinson, B.H., Matagorda Island, Texas: The Evolution of a Gulf Coast Barrier Complex. Geological Society of America Bulletin, 86, Figure 13. Relict dune scarps on the southern portion of Padre Island that remain from Hurricane Dolly in Figure 14. The South Padre Island community, the second largest coastal community on the Texas coast. Photo: J. Reeves-Wilson. Shore & Beach Vol. 81, No. 3 Summer 2013 Page 37