Sand dune proposal digs up questions
Feasibility and impact on environment, wildlife are challenges to Gulf plan
Nearly a decade before the “Ike Dike” became accepted jargon for coastal residents of southeast Texas, there were geotubes.
Installed on the beaches of Galveston and Bolivar Peninsula in 2001, geotubes — nicknamed “sand socks” — were sediment-filled oval sleeves made of a special fabric, anchored to an apron placed in a trench along the dune line.
Their intent was to provide an artificial dune structure to guard coastal residents from floodwaters. The installation cost $5.4 million, a relative pittance for a flood mitigation measure.
The geotubes were damaged by various storms, and Hurricane Ike delivered the death blow in 2008. The Category 2 hurricane brought 100-mph winds and a 17-foot storm surge from the Gulf of Mexico, leveling the dune lines on Bolivar and Galveston and leaving the exposed geotubes prone on the sand like beached whales.
Ike showed, said Rice University professor emeritus John Anderson, that “one storm could defeat all our progress.”
Having learned this lesson the hard way, the Army Corps of Engineers has proposed 14foot-high natural sand dunes in the latest version of its up-to
$32 billion plan for protecting the Houston-Galveston region from storm surge. The plan calls for dunes and flood gates running from High Island to San Luis Pass, as well as ecosystem restoration farther south.
The dunes are seen as the latest innovation designed for Texas to engineer its way out of an existential crisis: a coastline gradually vanishing and increasingly vulnerable to massive storm surges and sea level rise.
The Corps believes the natural dunes will endure longer than the geotubes, which were a Band-Aid of sorts quickly tested after construction and now considered a costly failure.
The shift to natural sand dunes has been largely embraced by experts as the most practical and politically expedient next step for storm surge mitigation, even with the project’s hefty price tag. But questions have been raised about their cost, as well as how much protection they can provide to coastal communities in the event of a powerful tropical storm.
The dunes proposal follows a vocal backlash from Galveston and Bolivar residents to an original proposal to construct levees that would run parallel to FM 3005 on Galveston Island and Texas 87 on Bolivar Peninsula but behind the dune line. This plan for the harder barrier would have left thousands of homes adjacent to the beach exposed to flooding and likely required extensive eminent domain buyouts.
“We’re talking about a dune system that runs along the existing dune line,” Kelly Burks-Copes, the Corps’ project manager, said of the current plan. “Basically, it’s just one solid continuous line, with beach access still afforded, with drive-overs and walk-overs, in compliance with the Open Beaches Act.”
While bolstering the coast’s natural barriers would be less disruptive to coastal property owners, dunes present challenges of their own. The Corps acknowledges they will not protect coastal residents from every storm and will not be as strong as a levee. The proposed dunes also won’t be anchored, and some experts believe they would benefit from a hardened clay core.
Sand, a global commodity, is in abundant supply, but far enough from the Texas coast that dredging the necessary volume to build the dunes will be costly. Annual beach nourishment will be required, further stretching state and federal resources. The Corps will also have to contend with the constant threat of tropical storms and hurricanes that can lay waste to even the most robust dune systems.
“We have a fairly good understanding of how large a dune or a nourishment or a maintenance plan should be to withstand certain storm design conditions,” said Jens Figlus, a professor of ocean engineering at Texas A&M Galveston. “But what is really hard is to look 30, 40, 50 or even 100 years into the future and say, ‘What will that dune look like at that point?’ ”
Massive dredging
The sand dune field is among a series of revisions the Corps has made recently to the draft coastal barrier alignment released last year. The plan is similar but more ambitious than the “Ike Dike” proposed by Texas A&M researchers after Ike devastated the Texas Gulf Coast.
The current proposal includes a gate across the mouth of Galveston Bay to protect the Houston Ship Channel, which is less restrictive that what was originally proposed. It would provide for one-way boat traffic in both directions and not limit water flow as much — something environmentalists had called for. The plan still doesn’t include the mid-bay gate that Rice University researchers say is needed to protect the Port of Houston and the sprawling industrial and petrochemical facilities along the bay.
The Corps would establish roughly 44 miles of sand dunes from High Island southwest to the tip of Bolivar Peninsula, and then farther down the coast from the end of the Galveston seawall to San Luis Pass.
Dunes were already a part of the Corps’ original plan but at a smaller scale, 10 feet above sea level versus the 14 feet proposed now. The dunes are intended to be multipurpose — reduce shoreline erosion losses, absorb surge during storms, and provide habitat for turtles and birds. The dune field model is intended to provide multiple lines of defense against storm surge — one dune at the edge of the beach to provide additional sand to absorb surge and wave energy, while increasing nesting habitat for sea turtles and birds.
The idea is to replenish the existing beaches on Bolivar Peninsula and Galveston Island, extending the shoreline farther seaward, while building the dune line high enough to provide a bulwark against an Ike-level surge or worse.
“It would effectively double the width of the dunes, with the beachfront being the same because they have to keep the same slope,” said Azure Bevington, a coastal ecologist and High Island resident who has participated in meetings with the Corps to discuss the proposal. “It allows natural sand to move between those dunes and build up more complex dune fields.”
Building a dune system of that magnitude will require a colossal dredging operation that would dwarf the Corps’ maintenance dredging of relatively small waterways such as the Houston and Corpus Christi ship channels. In fact, it would be one of the largest dunebuilding projects in the Corps’ history.
Journalist Vince Beiser, author of the book “The World in a Grain: The Story of Sand and How it Transformed Civilization,” recently spent time on the Ellis Island, a 433-foot long hopper dredge, the largest of its kind in the country, as it rebuilt Ship Island, a barrier island off the Gulf Coast of Mississippi. Beiser said the Corps will have to be precise on where to draw its dredge material, given the quality of sand needed to build dunes.
“You can’t just drop a suction pipe in the bottom of the Gulf, you’ve got to find somewhere where there is the right kind of sand and where you can pull it up without really harming the environment,” Beiser said.
The Corps estimates 40 to 50 million cubic yards of sand over 50 years would be needed to maintain the proposed dune systems. To supply the necessary material, the Corps is targeting two sand banks in the Gulf: Sabine Bank, 17 miles south of the mouth of Sabine Pass; and Heald Bank, 27 miles offshore from Galveston.
Anderson, the former Rice professor and author of the book, “The Formation and Future of the Upper Texas Coast,” is skeptical that Sabine and Heald Bank have enough sand volume to sustain the Corps proposal.
Sabine and Heald Bank “will nowhere near fit the bill,” Anderson said. “If you look at the rough area of these banks, there’s only about 2 or 3 feet of sand in those banks.”
The Colorado River Delta Complex could be a more plentiful source of sand, Anderson says, but is farther offshore, south of Matagorda Bay.
The state might eventually have to purchase its own dredge ship to manage the regular nourishment that a dune system requires, Anderson added. The Corps says the shift to a dune model will likely not change the original cost estimate for the coastal barrier system — somewhere between $23 billion and $32 billion — but that does not factor in annual maintenance costs.
Sustaining the dune structure will likely require costly annual beach nourishment, particularly as major storms continue to batter the coastline.
“What we’re analyzing is (dune) performance in the face of one or multiple storms and the cost of renourishment,” said BurksCopes, the project manager.
Push for hybrid dunes
The dunes could also mitigate the continued erosion of the Texas coastline due to sea level rise and the dwindling conveyor belt of sediment moving from coastal tributaries. The Bureau of Economic Geology, which monitors shoreline changes along the Texas coast, estimates that parts of Galveston and Bolivar have lost 5 to 8 feet of shoreline over the last 80 years.
“If you do add sand or width (to) the beach or a dune to the coastline, it buys you some time, it does not eliminate the (erosion) process,” Figlus said. “Instead of eroding the porch of your house, it’s eroding the dune or the beach that you just put there as replenishment.”
The erosion problem has led to a push for a hybrid dune system — essentially a sand dune with a fortified core made of a clay composite. A hard structure underpinning the dunes could reduce the cost of replenishing sand on the beaches.
Bill Merrell, a professor at Texas A&M University at Galveston who developed the Ike Dike concept nearly a decade ago, hopes to raise funds to build a model fortified dune on Galveston’s West End to demonstrate its effectiveness to the public.
Fortified dunes “provide less of a footprint, it can be much smaller in width, and we can get protection up to the point of a hard core, put sand over it (and) they look totally natural,” Merrell said.
Merrell said the dune height that the Corps has proposed is insufficient to guard against an Ike-level storm surge, and said the fortified dune he envisions would rise as high as 17 feet. He cited a thesis recently published by Luis Rodriguez Galvez, a student at Delft University of Technology in the Netherlands, that argues for dunes as high as 23 feet to protect Galveston and Bolivar.
The Corps “is not providing enough protection, I’ve told them that dozens of times,” Merrell said.
A Corps spokeswoman said there is interest in Merrell’s demonstration but that further study is needed on the maintenance requirements for the fortified dunes, as well as the impacts on wildlife, erosion and sediment processes.
Environmentalists say a dune could contribute to habitat loss for endangered species, such as the Kemp’s Ridley sea turtle.
Joanie Steinhaus, the Gulf program director of the Turtle Island Restoration Network, said fortified dunes built on Follets Island, across San Luis Pass from Galveston, were unable to maintain enough sand and vegetation for the turtles to nest at the foot of the dunes, leaving what is now a mostly bare seawall.
“We’ve had instances of turtles trying to nest where they actually crawl parallel across the (Follets Island) dune and they can’t dig, the structure’s too hard,” Steinhaus said.
Satisfying the diverse array of stakeholders affected by this project is the conundrum the Corps will have to solve before it submits a final proposal for the coastal barrier to Congress for funding in 2021, all while sea level rise and powerful storms continue to pose a threat.
“This is a problem we’re gonna live with,” Anderson said. “Unfortunately, Texas has to deal with this problem by engineering our way out of it.”