by Christopher Dow
You might think that the Antarctic and the Texas Gulf Coast are about as different as possible while still sharing the same planet, but for John Anderson, the W. Maurice Ewing Chair in Oceanography and professor of earth science at Rice University, the two are inextricably linked. Anderson’s love of the Gulf Coast goes back to his childhood, and even after he began research on the Antarctic that focused on ice sheets and their decay and contribution to sea level-rise, he maintained his interest in the Texas coastline. The one-year anniversary of Hurricane Ike was an opportune time to talk to Anderson about what is happening to the Texas coast and to get his prognosis for the future.
CD: What makes the Texas coast a good subject for study?
JA: The Texas Gulf Coast is a beautiful natural laboratory for understanding how coasts evolve and how they respond to sea level change and hurricanes because it has a fairly low gradient, and it doesn’t have the huge subsidence rate that Louisiana does.
CD: How do you determine the effects of sea level rise, and what are you finding?
JA: We study drill cores and other data from a wide range of estuaries—from Mobile Bay all the way to Corpus Christi Bay—to see how they developed and responded to changing conditions over the last 10,000 years. The information we gather allows us to estimate future response. These bays have changed dramatically during that time, and they continue to change. It’s predicted that, by the end of this century, sea level rise will be about five millimeters per year, or half a meter in a century. It’s well known that the bays of the Gulf Coast are much more sensitive to sea level rise than is the coast. Coastal erosion gets a lot of attention because people have houses on the beach, but the bays are really the most threatened.
JA: In some places, sediments coming down rivers help balance out rising water levels, but that’s rarely the case in Texas. Our bays have a very low gradient, and Galveston Bay, in particular, is very shallow. Around here, a sea level rise of five millimeters per year can result in one to one-and-a-half meters of coastal retreat, and that amount starts to exceed the capacity of the bays to keep up. The effect is widespread flooding, changes of the bay margins and, at times, complete disappearances of deltas. Changes like these in the past occurred at a time when the ice sheets, particularly in Antarctica, were still experiencing some episodic retreat, but there’s little question that humans are responsible for the accelerated rise we’ve seen over the past fifty years.
CD: Why aren’t people more concerned?
JA: Saying that the sea level will rise half a meter doesn’t mean a thing to most people—certainly not to policymakers. You have to put it into context using maps that show how much area gets submerged. Sometimes it rings a bell and makes them think, but the reality is, maps like those show best-case scenarios. Coastal systems don’t just sit there while sea level rises and slowly inundates the landscape. When coasts are in perturbed modes and along comes a hurricane like Ike, the system can respond radically. We get what might be ten years of normal erosion in a single day. And in bays, we see dramatic changes, as well. We know that Sabine Lake once had a large bay head delta, much like Galveston Bay has, and it disappeared sometime during the last couple of centuries, probably in response to a large hurricane.
CD: When you look at our area, many of the chemical plants along the Houston Ship Channel could be endangered by that kind of sea level rise, which is certainly an economic consideration for policymakers.
JA: Absolutely. Some of the best storm surge models come from NASA’s Johnson Space Center in Clear Lake. You might wonder why, but they’re in a pretty vulnerable place, and it got a lot more vulnerable in the 1970s because of all the subsidence. They lost half their elevation, and the area is extremely prone to storm surge.
CD: What effect did Hurricane Ike have on the Texas coast?
JA: The dunes that once lined the coast of Bolivar Peninsula are another thing that puts things into context. They were 1,500 to 2,000 years old, and Ike destroyed them overnight. And it’s not the fi rst time such a thing has happened. Everything south of the highway on Bolivar is only six hundred years old. What that tells us is that the peninsula was decapitated around six hundred years ago, and it’s taken all this time to reform.
People say, “The beach will recover,” and, yes, the beach does recover, but it doesn’t recover where it was. It recovers where it is now, and the dunes would recover, except there are houses sitting where dunes would develop. The same is happening on Galveston, where some fairly prominent dune ridges now are gone, replaced by miles and miles of real estate. That’s the end of those dunes.
CD: The U.S. Geological Survey reports an elevation loss of between three and ten feet on Bolivar, leaving an average elevation of only three feet. That might make it vulnerable to even a strong tropical storm, much less a hurricane.
JA: Elevation is a big thing. I’ve heard people who aren’t very knowledgeable about these things say that those little beach ridges you see in aerial photographs can’t possibly offer any protection from storm waves. On any given day at the beach, you see fairly large waves breaking over sandbars that are less than a meter high. That’s a daily reminder that it doesn’t take a lot of elevation to disrupt wave energy. When sea level goes up during a storm surge, and those waves move across the barrier islands, this ridge-and-swell topography is a very effective way of dampening that energy and causing those waves to break and lose their energy. Yet, on the west end of Galveston, developers are allowed to go in and level the landscape. I don’t understand the rationale.
People who are rebuilding there and on Bolivar face an even greater threat because there’s not much left to protect them. We know from Hurricane Alicia, and now from Ike, that no matter what we do, houses that are built in the first two rows from the beach are going to get wiped out. People might pile sand under endangered houses, but once that beach profile is cut down, they can pile all the sand they want, and it’s not going to last. It’s just going to wash away during the next storm. Unfortunately, people’s memory spans on storms only last about a year. I hate to see people rebuilding right back in spots where house were destroyed a year ago.
CD: Hurricane Ike caused considerable erosion around Rollover Pass on Bolivar. Because of the pass, Bolivar is now, in effect, an island rather than a peninsula. Would another hurricane like Ike make Bolivar an island in fact?
JA: Follett’s Island, which is just west of Galveston Island, was once part of Galveston Island. It became a separate island when a storm breached Galveston sometime within the last 2,000 years—more than likely, within the last several centuries. This is a natural progression of barrier island evolution. They tend to get longer and narrower, and along comes a big hurricane and just slices off the end, and there’s a new barrier. So, yes, the day will come when Bolivar will be breached.
Right now, Galveston is in a sort of quasi-equilibrium. It actually underwent a phase of growth for several thousand years, and now it’s starting to retreat. It’s actually shrinking—eroding on both the gulf and bay sides. Follett’s Island is retreating three times faster than Galveston on its gulf side, but if you look at the bay side, you see that it’s actually growing on its landward side. It’s shifted into what’s called the rollover stage, where hurricanes take sand off the beach and pile it onto the back side of the island. Follett’s will continue to migrate landward at a rate of about ten to twelve feet per year until it reaches some geological feature, such as the big fault line that runs along the north shore of West Bay and East Bay. If we allow the shoreline to do its natural thing, the waves will eat an escarpment there, pile up the sand and form the next barrier shoreline. The system could step to that location pretty quickly if we have three or four Ikes in a matter of twenty years.
CD: Recently, there has been publicity about a plan to extend the Galveston seawall to the west end of Galveston Island and all the way up Bolivar Peninsula. The plan includes huge retractable dikes across Bolivar Roads and San Luis Pass to limit storm surge. What would be the effects on the coast here if such a seawall were built?
JA: Chris Hight, an associate professor in the School of Architecture here at Rice, and I have a project funded through the Shell Center for Sustainability called Sustainable Strategy for Galveston Island. When the Ike Dike idea was raised, our response was: After the 1900 storm, they put that seawall in there, and that set the stage for the way Galveston was going to be for the next hundred years. Then along comes Ike, and now they’re going to completely entomb the island.
Despite all the hype around the Ike Dike, I’ve yet to see a serious storm surge model to determine if it’s even going to work. It’s ironic that a lot of supporters for the Ike Dike are people who have property on the west end on the beach. I think they envision this thing out at the water’s edge protecting their private property. If you’re going to spend $3 billion on a feature for which the justification is to prevent storm surge in the Houston Ship Channel, the last place you’re going to want to put it is on the beach. If they did, the reality is that the beach is going to continue to erode, and in a predictable number of years, the water will be right up to the seawall just like it is now along the west end of the present seawall. End of beach.
If they do build an Ike Dike, it’s going to have to be far enough inland that it won’t have to be maintained every year as we do the seawall. It probably will be along the highway rather than the beach, or maybe on the other side of the island at the Intercoastal Waterway.
Another consideration is the effect it will have on the wetlands. San Luis Pass, which is one of the top natural preserves on the Texas coast for birding and wildlife of all sorts, is probably going to be devastated because there’s no way to put a lock across San Luis Pass without destroying the integrity of the tidal inlet. And the geometry of that inlet controls the exchange of water between the gulf and West Bay. At the very minimum, I’d like to see some studies done.What are the most important issues facing the communities along the Upper Texas Coast? Are there any practical solutions to these?
Public education is the main issue. We’re living in a state of denial, and we keep making the same mistakes over and over. We can’t continue to rebuild right back where we did before the last hurricane. That ignorance of coastal processes goes to a fairly high level in state government. Texas spends millions of dollars each year dumping truck loads of sand on beaches, and the sand doesn’t last a year. We could use that money on a sand nourishment project that would really do some good. We’re convinced that we can engineer our way out of the problem with an Ike Dike, or other such project, when we actually need to accept the fact that this coastline is changing and that it’s going to change even faster in the next several decades.
The project Chris and I are working on is to develop a fifty- to one-hundred-year plan for how Galveston Island might fortify itself and, more important, how it might change the way it does things. The current trend is that developers come in and buy a big tract of land on the west end, then level the terrain and chew up wetlands. Chris and I have been trying to change the culture of the island to get people to want to move to high-rise condos on the east end. The Strand is there, there’s already a seawall and there’s a natural beach.
Beyond that, we need to think about coastal sustainability—not just sustainable development but sustainable preservation of the coast. To accomplish that, we may need to just let go. Look at Galveston Island State Park. It’s doing quite well and has a nice beach. It may be that we ought to just back off and live with the changes.
Reprinted from Rice Magazine, #4, 2009.