US Army Corps of Engineers and Maryland Port Administration Partner to Restore Poplar Island
Pummeled by years of rising sea levels and erosion, a historic island in the Chesapeake Bay was disappearing, until the U.S. Army Corps of Engineers and the Maryland Port Administration (MPA) came up with a creative solution to restore Poplar Island to its former glory.
The $1.4 billion Paul S. Sarbanes Ecosystem Restoration Project at Poplar Island received the American Society of Civil Engineers' 2015 Innovation in Sustainable Engineering Award. The project was named after Senator Paul Sarbanes who led efforts to authorize the project in 1996.
"The award was for the overall approach, using dredge material for ecosystem restoration, and it's geared to the specific design features and how we're making the project resilient to climate change," says Justin Callahan, Project Manager for the U.S. Army Corps of Engineers in Baltimore, who has worked on the project for more than 22 years. "It still amazes me every time I go out there."
The unique plan involved taking dredge material from the Port of Baltimore's shipping channels, to keep it deep enough for ships to come and go, and then depositing the silt onto the island.
"That's the story of Poplar; you have these two separate issues intersect at this project," Callahan says.
The Maryland Environmental Service (MES) in Millersville, Maryland, operates, maintains and manages construction on Poplar Island on behalf of the MPA. Portions are complete while others are still under construction. MES environmental staff monitor water quality from the spillways before the water is returned to the bay, explains Lincoln Tracy, Head of Dredge Material Containment and Environmental Restoration Operations for the Maryland Environmental Service.
"There is a constant state of construction," Tracy explains.
Chesapeake Bay is about 18 to 20 feet deep, and some ships require a 50-foot channel. Maintenance dredging occurs every year. That generates about 4 million cubic yards of dredge material annually. The island is about 34 nautical miles from the Baltimore port and about 40 miles east of Washington, D.C. The Corps and the port share costs on the associated expenses. The material that comes out of the channels has to be disposed of somewhere. Sometimes in years past, it was placed in a deeper area of the bay.
"Dredge material was never really looked at as a resource, as something useful, until now," Callahan says.
An Island Worth Saving
During the 1800s, about 1,140 acres of fields, forests and marsh covered Poplar Island, which later served as a presidential retreat for Franklin D. Roosevelt and Harry S. Truman. The island was used as a farming village, fishing spot and hunting club. But as the years passed, nature took a toll.
By the early 1990s, when the Corps began studying the situation, the island was down to about 5 acres, broken into three pieces, with 13 feet of island falling into the bay annually.
"You had this incredible loss of remote island habitat on the Chesapeake Bay," Callahan says. Overall, about 10,000 acres of island habitat had been lost in the region.
The Corps completed a feasibility and environmental impact study and came up with a plan to save the island. Congress authorized funding in 1996 and reauthorized money several times since then. Construction began in 1998 and is scheduled to continue until the early 2040s.
Congress in 2014 authorized in the Water Resources Reform and Development Act, expanding the island by another 575 acres during the next several years. The work includes a vertical expansion of the upland dikes by 5 feet and a lateral expansion of the exiting island. That will entail several contracts to complete the work on the island, which is scheduled to begin in 2016. The work will include taking sand from a borrow pit to construct dikes. The lateral expansion will start in 2017 or 2018 and include an open-water habitat.
All together, the island will feature 840 acres of uplands, 737 acres of tidal marsh and about 138 acres of open water embayment. Thousands of people visit the island every year during the warmer months.
About 200 species of birds have returned, and other animals including diamondback terrapins. As many of 15,000 birds visit the island each day. All of that wildlife has contributed to construction challenges.
"We may have a rare or endangered bird nest in a section we were going to work on, and then work has to stop" Tracy says. "We have to vacate the area and let the wildlife use the area."
Restoring the Island
The Corps began the project by building perimeter containment dikes in 1998. These outlined the island's 1847 boundaries. Kiewit Construction, based in Omaha, Nebraska, completed the first, $54.8 million containment dike on the island's 640 northern acres.
Another $41.4 million contract was let in 2000 to Tidewater Construction Corp. in Chesapeake, Maryland, which completed placing approximately 1.9 million cubic yards of sand around a 24,000-foot perimeter and interior dikes in 2002. The upland cells are along the western edge of the island. The dikes hold the dredge material and contain about 1,140 acres.
"That set the stage for us to pump in dredge materials," Callahan says. That pumping of materials began in 2001. The Corps has added 28 million cubic yards of dredge materials since then, about 2 million cubic yards a year. Various dredging contractors have held those annual maintenance contracts, which are unrelated to the island restoration contracting. The first inflow of dredged material totaled about 7 million cubic yards.
"We've had tons of challenges," Callahan reports. "The maintenance material we get is like a silty clay. It is not the material anyone would chose as a substrate."
As the material is hydraulically pumped into the containment cells, it appears soupy, like chocolate milk. It's about 90 percent water and 10 percent solid. Multiple cells, upland and wetland, are filled each year. In the second year, more material is brought in and dewatered.
"The excess water is decanted," Callahan says. "It's a matter of drying it out and creating a crust on the material."
The Corps designed and constructed spillways and weirs, which MES uses to dewater and consolidate the silt material, which takes several years. The silt will settle to the bottom of the cell, then MES slowly skims the water off the top and releases the water back to the Chesapeake Bay if it meets water quality standards. If it does not meet standards, the water will be placed in a holding cell.
"The challenge was to take material that didn't seem in the past to have much value and deal with the engineering challenges you would face to create this sustainable habitat," Callahan says.
MES also manages the crust formation. By year four or five, MES will dig the channel network through the wetland area. In year six, low-ground pressure equipment is used to do the grading of the marsh plain and creating finer networks and opening the cell to tidal flow.
"We're becoming a fine-tuned machine at this point," Tracy says.
In about year seven, after MES has achieved the proper grade, a Corps subcontractor plants marsh grasses in the cell. Construction equipment is brought in on tugboats and barges. The Corps and MES have completed restoring 232 acres of wetland. MES is working with academic researchers to keep an adaptive management plan in place to improve function or cut construction costs.
"We are pioneering this process," Tracy says. "Poplar is one of the largest island restorations in the country and is one of the only ones in the country using fine silt dredging materials to construct uplands and tidal wetland habitat. The engineering of achieving steady state, precise elevations has been trial and error, but we have been successful in achieving that."