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Governments Plan for Development of Land Vulnerable to Rising Sea Level: Texas
Summary of Report by Texas Sea Grant
Sea level is rising 3-4 millimeters per year (12 to 16 inches per century) along the Texas coast. Beaches are eroding, which requires the removal of homes along the Gulf of Mexico after major storms. Marshes are converting to open water, and low-lying farms, forests, and residential yards are gradually converting to marsh. Water levels in roadside ditches rise and fall with the tides in some low-lying areas. All of these effects would become more commonplace if rising global temperatures cause the rate of sea level rise to accelerate. The Intergovernmental Panel on Climate Change, for example, estimates that by the end of the next century, sea level is likely to be rising 0 to 8 mm/yr (3 inches per decade) more rapidly than today (excluding the possible impacts of increased ice discharges from the Greenland and Antarctic ice sheets).
Rising sea level erodes beaches, drowns wetlands, submerges low-lying lands, exacerbates coastal flooding, and increases the salinity of estuaries and aquifers. Coastal communities must ultimately choose between one of three general responses:
---Armor the shore with seawalls, dikes, revetments, bulkheads, and other structures. This approach preserves existing land uses, but wetlands and beaches are squeezed between the development and the rising sea.
---Elevate the land and perhaps the wetlands and beaches as well. This approach can preserve both the natural shores and existing land uses, but often costs more than shoreline armoring.
---Retreat by allowing the wetlands and beaches to take over land that is dry today. This approach can preserve natural shores, but existing land uses are lost.
Each of these approaches are being pursued somewhere in Texas. Bulkheads are common along many estuarine shores. The federal and state governments have placed sand onto the eroding recreational beaches in Galveston. In the aftermath of the Hurricane of 1900, the city of Galveston rebuilt about 5 feet higher than before, and protected with a large seawall along the Gulf. Homes are regularly given up to retreating shores.
The Texas Open Beaches Act ensures that most of the developed Gulf Coast will retain beaches, by prohibiting shoreline armoring and requiring the removal of structures that interfere with the beach. In some cases, those structures may be protected with beach nourishment. Nevertheless, there is no explicit plan regarding which estuarine shores will be armored, and even along the Gulf it is not always clear whether beach nourishment or continued shore erosion should be expected. Environmental planners do not know whether to assume that the coastal wetlands will be lost or simply migrate inland. Those who plan coastal infrastructure do not know whether to assume that a given area will be submerged by rising waters or protected from the sea. And even in developed low lands that will presumably be protected, public works departments do not know whether to assume that the land surfaces will gradually be elevated or that the area will be protected with a dike.
This report develops maps that distinguish shores that are likely to be protected from the sea from those areas that are likely to be submerged, assuming current coastal policies, development trends, and shore protection practices. Our purpose is primarily to promote the dialogue by which society decides where to hold back the sea and where to yield the right of way to the inland migration of wetlands and beaches. A key step in evaluating whether new policies are needed is to evaluate what would happen under current policies. The maps in this report represent neither a recommendation nor an unconditional forecast of what will happen, but simply the likelihood that shores would be protected if current trends continue.
We followed the general approach of the EPA sea level rise planning project as documented in the in the Environmental Research Letters study by Titus et al., as well as various EPA reports. We obtained available land use, planning, and conservation data, and consulted with local officials. However, because most counties in Texas do not have land use planning authority, we supplemented that approach by speaking with key demographers, major landowners, and other key observers of development trends in the various coastal counties.
By "shore protection" we mean activities that prevent dry land from converting to either wetland or water. Activities that protect coastal wetlands from eroding or being submerged were outside the scope of this study. This study does not analyze the timing of possible shore protection; it simply examines whether land would be protected once it became threatened. Nor do we analyze whether shore protection is likely to be a transitional response or sustained indefinitely.
The sea level rise planning maps divide the dry land close to sea level into four categories of shore protection:
--Shore protection almost certain (brown);
--Shore protection likely (red);
--Shore protection unlikely (blue); and
--No shore protection, i.e., protection is prohibited by existing policies (light green).
For reasons related to data quality, our study area includes lands within about 20 8 feet (6 meters) above the tides. (We did not project the fates of secured federal installations but depicted them in red so that they stand out.)
One can also view these maps as representing three shore protection scenarios. For example, in an "enhanced wetland migration" scenario, only the areas depicted in brown would be protected; but in an "enhanced shore protection" scenario, only the areas depicted in light green would be submerged. Thus the prospects for shore protection are best understood in the areas shown in brown and light green, while those shown in red and blue are most amenable to coastal planning. "Expected shore protection" is an intermediate scenario in which the areas depicted in brown and red are protected, while those shown in blue and light green are submerged.
This site provides county-by-county summaries of the statewide study directed by John Jacob of Texas Sea Grant, which we divide into four coastal regions: Golden Triangle, the Greater Houston area, Coastal Bend, and Laguna Madre.
Governments Plan for Development of Most Land Vulnerable to Rising Sea (PDF, 7 pp., 1.3 MB, was originally published in Environmental Research Letters , Issue 3, Volume 4 (2009).