The Formation and Future of the Upper Texas Coast: A Geologist Answers Questions about Sand, Storms, and Living by the Sea

Introduction

Introduction Ask any coastal geologist whether natural forces, particularly sea level rise, or humans are having the greatest impact on the world’s coasts, and they will probably say that humans are winning the race. Factor in our contributions to global warming and coastal subsidence, or sinking of the land surface, and we, by far, are the greatest threat to coasts. Nowhere on Earth does the impact of humans and natural forces pose a greater threat to coasts than in Louisiana and Texas. This book deals with the part of the Texas coast between Sabine Pass and the Brazos River. This part of our coast is the most populated and the most threatened by coastal subsidence and overdevelopment. As a result, it has been more greatly affected than any other part of the Texas coast. Those of us who have visited the beach for more than a decade, a time interval that now seems short to me, need little convincing that our shoreline is in a state of change. A seawall stands as a fortress between the city of Galveston and the advancing shoreline. Long-term shoreline retreat along the upper Texas coast has occurred at rates between 3 and 15 feet per year. The beach that exists seaward of the seawall is artificial, nourished by sands pumped from offshore during the mid-1990s. County Road 87 between Galveston and Sabine Pass has been overtaken by the advancing shoreline, and all along the coast the advancing shore is consuming houses. Phase one of the Galveston Seawall, constructed between 1903 and 1922 after the “Great Storm” of 1900, has been called the mightiest seawall on any barrier island in the world. It now stands as the last line of defense against the advancing shoreline. Other changes taking place within our coastal system are not as obvious but pose an equal threat to our coasts. The shorelines of area bays are eroding at alarming rates, averaging just over 2 feet per year, but in places exceeding 10 feet per year (Bureau of Economic Geology Web site, http://www.beg.utexas.edu/coastal/coasta101.htm; see also chapter 5). xii I N T R O D U C T I O N Phase one of the Galveston Seawall was constructed between 1903 and 1922, after the Great Storm of 1900, and has been called the mightiest seawall on any barrier island in the world. West of the Galveston Seawall the shoreline continues to advance landward as sea level rises. The remains of the foundation for a VHF antenna that once stood behind the dune line is a reminder of this ongoing process. I N T R O D U C T I O N xiii The eastern shoreline of Galveston Bay has become a virtually continuous line of concrete riprap that helps slow the erosion of the shore. The wetlands that once lined the eastern shore are gone. This photograph of County Road 87 was taken in 1977. The highway , which once connected High Island and Sabine Pass, was overtaken by the advancing shoreline and was closed a few years after this photo was taken. Today County Road 3005 on Follets Island faces a similar fate. xiv I N T R O D U C T I O N In addition, thousands of acres of wetlands have been submerged by subsidence in the past fifty years. Humans have contributed to coastal and bay erosion and wetlands loss by damming rivers, increasing rates of land subsidence with groundwater withdrawal and oil and gas extraction, and developing land without allowing for the natural migration of coastal environments . The construction of ship channels and the Texas City Dike has altered the natural circulation within bays. This in turn has altered the salinity of the bays and affected their inhabitants. The laws that are intended to protect the coast are, for various reasons, not working. The changes that have occurred along the upper Texas coast may well be minimal compared to those changes that will occur this century as our climate continues to change and the rate of relative sea level rise increases . Chapter 1 of this book explains some of the basic geological processes that occur daily and control those changes that we currently observe along our coast. Chapter 2 focuses on the long-term evolution of our coast, a perspective that allows us to predict future changes and to gauge human impact relative...