Dredged Material Used to Restore Historic San Jacinto Marsh in Houston
The Barbours Cut Dock Expansion & San Jacinto Marsh Restoration was a combination capital and beneficial use project in the Houston Ship Channel (HSC) that expanded a petroleum transfer facility, and used all the dredged material to restore 150 acres of subsided wetland at the San Jacinto Battleground State Historic Site.
When the Texas Parks and Wildlife Department (TPWD) planned to restore the marsh, it listed one of the benefits as “providing a buffer from storm surges such as those that affected the battleground during Hurricane Ike” in 2008.
Nine months after the restoration was complete, on August 25, 2017, the project was tested when the Category 4 Hurricane Harvey made landfall on the Texas Coast near Houston, and stalled over the area, dropping 40 to 61 inches of rain on Southeast Texas and Louisiana and causing massive flooding.
“The San Jacinto project site did not experience any lasting impacts from Hurricane Harvey,” said Mark Stroik, engineering project manager for Atkins, design engineer on the project. “Most of the site was underwater during the flooding, but the marsh is made for exactly this type of circumstance. The vegetation is mostly … plants that are very tolerant of varying salinity levels, so it was unharmed. Our flow channels and containment dikes all had sufficient time to mature prior to Harvey, so they performed well,” he said.
The dredging expanded and deepened Enterprise LLC’s petroleum transfer dock on the north end of the Barbours Cut Turning Basin at the inner end of The Barbour’s Cut Ship Channel, a tributary of the HSC at the mouth of Buffalo Bayou on Galveston Bay, 3.5 hours sailing time from the Gulf of Mexico. It is a 1.3-nautical-mile cut with a 300-foot-wide navigation channel accessing the Barbours Cut Container Terminal. The turning basin is 1,600 feet in diameter, and allows ships up to 1,333 feet long to reverse direction.
The massive Spillmans Island Dredged Material Management Area (DMMA) surrounds Barbour Cut. The dredging expanded what had been a single slip with a 25-foot depth to 45 feet plus 2 feet of overdepth, and created a gradual slope from the 45-foot federal turning basin to dry land (+6 feet). The improved dock is designed to handle loading and offloading of petroleum products. Vessels calling at the dock range from medium draft (inland) tugs and barges to deep draft petroleum carriers.
“Portions of the turning basin are frequently used for barge staging and fleeting, as it is a convenient place to push up on the bank. We coordinated with several local tug & barge companies, the port, and the USCG to manage traffic during construction. Good communication was the only ‘special’ procedure required,” Stroik said.
The spider barge Weeks 110 loading a barge at the transfer station on the channel side of the DMMA.
The Weeks 115 Unloader empties a barge at the San Jacinto marsh restoration. It pumped a maximum of 52,500 feet to place the slurry in a thin layer over 150 acres of subsided marsh.
Weeks Uses the E.W. Ellefsen
Dredging contractor Weeks Marine began dredging in January 2016, using the 30-inch cutter suction dredge E.W. Ellefsen to dig 475,000 cubic yards of medium to stiff clays. The dredge pumped 4,500 feet to the Weeks 110 spider barge, which filled the barges at a transfer station on the channel side of Spillman’s Island. The barges moved the material 9.7 miles up channel to the marsh restoration site at the confluence of the HSC and the San Jacinto River. The Weeks 115 Unloader received scows and re-fluidized the clay for hydraulic delivery to the marsh, pumping a maximum of 52,500 feet into the marsh creation area in a thin layer that raised the elevation of 150 acres 10 to 20 inches.
“The receiving site had sufficient capacity to receive the dredge material, but the tolerances were much tighter compared to most marsh fill projects,” Stroik said. The dredged material arrives as a slurry, he said, which dewaters in the fill site.
“The overall capacity of the fill site is the most influential aspect concerning the difficulty of that decanting process,” he said. “Most marsh fill projects will have 25 to 50 percent extra capacity available to accommodate a certain dredged volume, but our tolerances at San Jacinto were much tighter,” he said.
“The dredging methods used for this project are what made it possible to work within such tight tolerances. The scow transport to hydraulic offloader technique Weeks employed … allowed for much more control during the dewatering process than a direct-pumping configuration would have. Because material was being suctioned from barges on a smaller and shorter pipeline, the slurry arrived at a slower rate with less water needed for the pump. Barge swaps also slowed the process, and the combined effect was a controlled flow into the marsh, with opportunity for resting periods when needed. Weeks’s fill crew is very experienced and talented, and managed the tight tolerances well,” he said.
The schedule was structured in a way that allowed incremental increases in the quantity depending on fill site performance, and the site was monitored closely by qualified staff. The marsh responded well to fill operations, and accepted additional capacity via thin-layer placement in vegetated areas, which raised the site to the optimum elevation for sustaining flora and fauna in the intertidal marsh.
How the Engineering Proceeded
Atkins’s final design phase began in March 2015, after 90 percent of the structural and dredge template designs were complete. Engineers established fill elevations by analyzing existing healthy marsh habitat at the site in combination with recorded water levels. They focused on the landward limit of Spartina alterniflora, which generally delineates the boundary between high and low marsh in this location, and selected target elevations based on anticipated total consolidation and compaction rates after a two-year resting period, which Atkins would monitor.
Engineers were given only seven months to complete the final design of the dock, and to establish a plan for the conveyance and placement of the dredged material. Project bids went out October 2015 and the project owner – Enterprise LLC – selected Weeks Marine to perform the dredging.
Though the obvious choice for material placement was the federal Spillmans Island DMMA, its containment dikes were in the process of being raised and it was unavailable. To avoid delaying the project, Enterprise elected to use an alternative site. DMMA availability in the region is at a premium, so the operations department of the Galveston Engineer District was in favor of this decision. Because the San Jacinto marsh restoration was ready to receive material and was compatible with the excavation and placement methods, it was chosen as the non-federal placement alternative.
The Ellefsen is shown digging in the project area, along with mechanical dredging equipment and other Weeks vessels
Project Underway in January 2016
The marsh restoration work began in January 2016 and continued through November 2016. Besides the dredging and placement activities, it included building containment levees, dewatering and resting periods to allow water to decant.
“The project coincided with the growing and germination season for Spartina grass, which was our target species,” Stroik said. New grass sprouted during construction, and park managers harvested seed from existing grass to spread during the dewatering process.
“I would estimate that we had about 10 percent coverage after one month, 50 percent by three months, and 95 percent by twelve months. The timing of construction and seeding had a lot to do with the rapid recruitment of marsh grass,” he said.
The restored vegetation increased habitat for birds, small mammals and marine species like shrimp larvae and crabs, mitigating some of the effects of industrial development in the area.
The San Jacinto site is preserved by TPWD as the location of the Battle of San Jacinto, credited as the event that won Texas independence from Mexico in 1836. It is designated as a National Historical Landmark. A crucial part of the battle was the escape of Mexican soldiers across the marsh, depicted in an illustration of the battle at the park.
“Not only does the project have wonderful ecological benefits, but the restored setting will help all visitors to have a greater appreciation for how this natural landscape contributed to the events in 1836. We are exceedingly pleased with how the project is turning out,” said Brent Leisure, director of TPWD.
“San Jacinto Marsh is one of the few functioning tidal wetlands among the heavy industries of Houston,” said Andy Sipocz, TPWD natural resource specialist. “Much of the Houston area has sunk due to past groundwater pumping, and portions of the San Jacinto Battleground were lost below the tide. (The battleground) again looks like what those who fought in the 1836 battle for Texas independence saw,” he said.
Though sending the material to the San Jacinto site was a more expensive investment, a bottom-line gain should have been realized by the owner by expediting the work. Private industry bore the incremental cost of marsh restoration because they could not wait for a less-expensive option to become available. As a result, the State of Texas received the marsh restoration at minimal cost, and valuable DMMA capacity was conserved.
The park hosts an annual reenactment in remembrance of those who fought in the 1836 battle. It is the most well attended event of the year at the park. In 2017 the event on April 22 was the first time in a generation that the site was the same as it was during the actual battle.
The project received the Western Dredging Association Environmental Award for a Navigation Project, presented at its annual meeting in June in Vancouver, B.C. Mark Stroik of Atkins, and Charles Broussard III of Weeks accepted the award on behalf of the team, which also included Enterprise Products, Texas Parks and Wildlife Department (TPWD), the Texas Historical Commission, and the Galveston Engineer District.
What had been an intertidal marsh had subsided to a shallow lake -- a result of past groundwater pumping.
The marsh after placement of the dredged material had raised the elevation of the area.Edit Module