Here in landlocked Austin, Texas, we don’t hear too much about the Texas Gulf Coast, at least not until a major storm wallops homes and businesses. It’s perhaps more than a little ironic, then, that some of the people with the best perspective on the coast—what it was like in the past, how it’s changing, what threats it faces—are at The University of Texas at Austin, a good 3 or 4 hours’ drive from the nearest point on the coast.

For more than 3 decades, scientists at the Bureau of Economic Geology, a research unit in the University’s Jackson School of Geosciences, have tracked Texas’ changing coastal environment.

Bureau Director Scott Tinker sees coastal geology as a key issue for Texas, noting that “As global coastlines adapt to ongoing changes in climate and human development, the Bureau’s role in mapping and understanding coastal processes in Texas—land use, land cover, subsidence and beyond—is vital”.

From the 1970’s through the 1990’s, Bureau coastal scientists studied historical Gulf and bay shoreline changes using topographic charts published in the late 1800’s and sequences of aerial photographs dating to the late 1920’s and early 1930’s. Results of these studies, disseminated to the public through numerous Bureau publications, established the Bureau as the prime provider of data and scientific analysis on the changing Texas coast. After major storms such as Hurricane Alicia, which struck the Houston and Galveston area in 1983, field and remote-sensing investigations at the Bureau were integrated to analyze the effects of tropical storms and the prospects for recovery.

In the 1970’s, the Bureau produced the landmark Environmental Geologic Atlas of the Texas Coastal Zone, which for the first time mapped in great detail the state’s entire coastal zone.

“It really made a name for the Bureau at that time,” says Tom Tremblay, a specialist in wetland mapping at the Bureau.

In 2000, owing to its historical strength in this research, the Bureau signed an agreement with Texas’ General Land Office (GLO) to supply coastal information for policy making. Bureau scientists use instruments on aircraft to map coastal topography, shorelines, plant and animal communities, wetlands, dunes, and beaches. They also enlist hundreds of high school students each year to make direct observations on the ground at a few targeted, long-term sites. The information they gather and interpret helps inform sensible policies for protecting people and the natural environment. The process is never ending because the coast itself is constantly evolving.

Below are four snapshots of the Bureau’s recent and ongoing work along the coast.

Photographic Memory

For the past decade or so, scientists studying the coastal environment have had access to airborne lidar instruments and other techniques to measure topography. By taking a set of measurements before and after a storm event, for example, they can accurately determine where and how sand has moved around in the system. But what about long-term change? What if you wanted to study how the coast has evolved over several decades? No lidar or other remote-sensing data exist that far back.

Sojan Mathew is a postdoctoral researcher at the Bureau who is refining an old-fashioned technique called photogrammetry to do a bit of time traveling. Photogrammetry, which is almost as old as photography itself, was how topo maps, such as those produced by the U.S. Geological Survey, were originally produced. Overlapping photos were taken from airplanes, and then rooms full of people and equipment were used to extract topographic information. It was expensive and labor intensive.

“Advances in electronics, optical physics, and computational power have helped us recreate this in a desktop environment,” says Mathew.

He says the technique can be used to (1) quantify how the shoreline, dunes, and other features evolve; (2) measure topographic changes; and (3) evaluate volumetric changes (how much sand is gained or lost), all of which result from breaking waves, longshore currents, land subsidence, and sea-level rise, as well as dynamic processes associated with severe storms.

Before coming to the Bureau, Dr. Mathew was a doctoral student at the University of Guelph in Canada. At the time, only a handful of studies had been done using this updated, digital photogrammetry technique to generate digital terrain models of beach dune systems. For his Ph.D. project, Mathew used historical photos of Prince Edward Island in northeastern Canada dating back to the 1930’s. A storm a few years earlier had washed much of the island away. Using a sediment-budget approach, he was able to reconstruct the stages and duration of recovery processes over 7 decades and better explain how the island rebuilt a continuous line of tall foredunes with stable vegetation.

Mathew is now using the technique to reconstruct the evolution of the Texas coastal environment going back to the 1930’s. He’s learning what factors control beach-dune evolution and how fast these features recover from storm events. His work also has immediate practical benefits. His data could be used by GLO to help set construction setback lines, which limit where development can occur. The data are useful for wildlife managers, geologists, and wetlands conservationists. Mathew is also helping to monitor recovery of the beach-dune system in the wake of last year’s Hurricane Ike, as well as updating long-term, short-term, and event-based shoreline change rates along the Texas Gulf coast.

Sneakers on the Ground

Hurricane Ike pounded Galveston Island and several Caribbean islands last September, causing over 100 deaths and billions of dollars in damage, including millions to The University of Texas at Austin’s Medical Branch. It also destroyed a state park to which Tiffany Caudle used to take students as part of the Bureau’s High School Coastal Monitoring Program.

“We’re just taking a hiatus this year,” she says. “We would like to remain in the same locations because of our history of monitoring from those sites. Also, we need to keep the safety of students as our first priority, and right now our monitoring sites do not have safe accessibility.”

So instead, at least this spring, she’ll meet with students from Ball High School (“Home of the Golden Tors,” as in “tornadoes”) in their classroom. She’ll take students from the other five schools to sites on Mustang Island, South Padre Island, and Matagorda Peninsula.

Caudle takes students to the same coastal sites three times a year, every year. At each site, they measure the vertical profile of the beach using basic surveying equipment: Emery rods, a metric tape, and a hand level. By starting at the same Global Positioning System (GPS)-surveyed datum stake and following the same path to the shore each time, they insure that the profile overlaps with previous profiles at that site. They also map the vegetation line and shoreline by walking along the edges of these features with differential GPS units. The data are then loaded into Geographic Information System software for display as interactive digital maps.

The data they collect allow scientists to track changes to beaches, dunes, and vegetation following storm events such as Ike.

Because measurements are taken in the fall, winter, and spring (students are on break in the summer), scientists can also study seasonal patterns that shape a beach. Such patterns might go unnoticed if the observations were taken less frequently.

Caudle came to the Bureau in 2000 and became principal investigator of the monitoring program, which had started in 1997 with the goal of offering students who live on the coast an inquiry-based learning experience.

“It’s amazing how much the kids who live in the coastal environment don’t know about the coast,” says Caudle. She says it’s barely covered in the typical Texas high school curriculum.

Students learn good note taking, observation skills, and the importance of precise measurements in science. They make a connection with the concepts in a fresh way because they are out in the real world, getting their hands dirty, working on a real science project.

“The data are important to their communities,” says Caudle.

“Also,” she adds, “the students typically enjoy having a field trip to the beach.”

Out of Sight

Jeff Vincent, a recent postdoctoral researcher at the Bureau, used a technology called hyperspectral imaging to map different vegetation types in a nature reserve near Port Aransas, Texas. In this technique, a sensor on an orbiting satellite or airplane detects light bouncing off Earth’s surface in dozens or even hundreds of colors, or frequencies. The frequencies span the light spectrum, including those too high (ultraviolet) or too low (infrared) for the human eye to see. Different types of vegetation reflect light in distinct signatures that can be teased out of the hyperspectral data. Even when two different plants look to be the same color to the human eye, this technique can tell them apart.
 
Vincent’s maps will serve as a baseline for comparison with future maps to help track changes in the Mission–Aransas National Estuarine Research Reserve.

One of the reserve’s star residents is the endangered whooping crane, one of the rarest birds in North America, with a total population of only a few hundred. The only self-sustaining migrating flock breeds in Canada and overwinters in the reserve. Vincent says black mangroves, which are not native to the area, have been moving in and altering the habitats that the cranes prefer. There is evidence that as global temperatures rise, tropical plants such as mangroves are moving increasingly northward into such subtropical areas. Some experts are concerned about the impacts this change will have on the cranes.

Many parts of the reserve are hard to cover on foot because of mud, dense vegetation, snakes, and alligators. A mapping technique that combines the relatively fast, large-scale view of an aerial survey with the precision of targeted ground surveys is indispensible for this kind of work.

Declining Tidal Flats

Texas is losing its tidal flats—those open, muddy flatlands between the sea and dry land that are periodically inundated with fresh water and saltwater. They look barren but are actually biologically rich habitats for crabs, shorebirds, and a host of other less glamorous creatures (yet critical in terms of ecosystem services), such as worms and algae.

“Tidal flats are a component of the larger wetland ecosystem,” says Tom Tremblay. “The tidal flat is the habitat for many species that live and feed in the intertidal zone. These species are part of the food web that includes economically important resources such as fish and culturally important resources like the whooping crane.”

The flats are also the interface for nutrient cycling into bays and lagoons.

“Tidal flats are an important part of estuaries or wetlands,” says Tremblay. “If you lose a component of that system, then the system doesn’t work.”

In this era of rising global temperatures and sea levels, tidal flats also play a vital role as release valves for marshes. As sea level rises, they are the most likely places for marshes to move. Tremblay warns that if there were no flats, marshes would be restricted and eventually die off.

Tremblay first became aware of the decline in tidal flats a few years ago when he was conducting a barrier-island wetland “status and trends” study. He says it became clear that tidal-flat loss was common along much of the Texas barrier system.

“The loss of flats was not a surprise, but the magnitude of the loss in certain places was alarming,” he says.

He says no one knows for sure why they’re disappearing, but a possible answer is that flats have a longer response time to a rise in sea level. They already experience occasional saltwater flooding, so they might not respond to more frequent flooding very quickly. On the other hand, marshes are stimulated to grow by more frequent flooding. So marshes move in pretty quickly.

“If sea level reaches a critical height, flats may begin to spread,” he says.

Having completed the barrier-island work, Tremblay is now in the middle of a 5-year status and trends study of coastal wetlands on the Texas mainland. He uses aerial photographs to create high-resolution maps of wetland locations and compares these with earlier maps going back half a century to see how they’ve changed. The maps will also serve as useful snapshots for researchers years from now.

In addition to the decline in tidal flats, Tremblay has noticed a north-south trend in overall wetland change. The upper Texas coast is losing wetlands, while the lower Texas coast is gaining them. In the upper region, near Houston, the loss stems from a combination of rising global sea levels and subsidence of the land caused by removal of groundwater, oil, and gas. The rate of subsidence has slowed from a peak in the 1970’s. On the lower Texas coast, subsidence occurs at a much lower rate, and as sea level rises, new wetlands develop farther up on land to replace those that are lost to the sea. The drier, warmer climate also affects the types of plants that can grow there and enhances the formation of tidal flats.

Although the decline of tidal flats has impacts, the loss of entire wetlands could have enormous consequences. They provide protection from damaging storm surges, support shrimp and other large fisheries, provide recreational opportunities, and support rare plant and animal communities. To remain healthy, wetlands have to evolve along with a physical environment that is constantly evolving.

“On Galveston Island and elsewhere along the coast, there is a lot of development,” says Tremblay. “If you develop an area, you may preclude the movement of wetlands into that area. And if they can’t move somewhere, they could become drowned.”