Corps Partners with Clemson to Monitor Marshes for Harbor Dredging

Thanks to a partnership with Clemson University and the U.S. Army Corps of Engineers, scientists are collecting valuable data in the Savannah River estuary for the Savannah Harbor Expansion Project (SHEP).

The research is part of an extensive pre-construction monitoring plan to establish a baseline of environmental data in advance of the harbor deepening.

“Our partnership with Clemson University allows us to collect continuous data at key marsh sites in the estuary and sample wetland vegetation in those areas,” said William Bailey, chief of planning for the Corps’ Savannah District. “The data will be used to measure impacts from the harbor deepening, evaluate the performance of the mitigation features, and identify whether any additional actions are needed.”

This April, Clemson researchers completed the installation of 12 monitoring stations in the estuary. The stations cover the full range of marsh types: freshwater, brackish and salt marsh.

“Each monitoring station collects data for water elevation, above ground salinity and below ground salinity on an hourly basis,” said Jamie Duberstein, Clemson research assistant professor with 14 years of experience monitoring the Savannah River.

Duberstein’s team includes Clemson professor Dr. William Conner and technician Josh Salter. They represent the Clemson Baruch Institute of Coastal Ecology and Forest Science, based in Georgetown, South Carolina.

The team is also collecting vegetation samples at the 12 marsh sites and at three tidal freshwater forest areas upstream. Most of the sites are located on the Savannah National Wildlife Refuge, since the refuge contains much of the marsh that is predicted to be impacted by the deepening. The monitoring work is being closely coordinated with the refuge staff, which helped select the monitoring locations.

“We are looking for species that are indicative of salinity conditions and drawing a correlation between below-ground salinity levels and plant community composition in those areas,” Duberstein said.

Duberstein said that freshwater marsh contains a higher diversity of plants and a higher density of spike rush—a small, grass-like plant common to the estuary. In general, as salinity increases, spike rush becomes less abundant and other plants (such as bull rush and smooth cord grass) grow in larger numbers.

The data collected by Clemson University will establish a baseline for SHEP pre-construction conditions, allowing the Corps to measure changes in salinity and vegetation during and after harbor deepening.

The SHEP will deepen the federal shipping channel to 47 feet, 5 feet deeper than the current channel depth. The Corps’ Environmental Impact Statement (EIS) identified that deepening the harbor would allow additional saltwater to enter the harbor and travel further upstream. To mitigate for the increased salinity, the Corps will modify several tidal creeks in the upper harbor to re-route the flow of freshwater into the estuary.

“Flow re-routing will significantly reduce the amount of impacts to freshwater marsh, which the Wetlands Interagency Coordination Team determined to be the highest priority wetland resource in the Savannah River Basin,” Bailey said.

That team included representatives from Georgia, South Carolina, the Environmental Protection Agency, the U.S. Fish and Wildlife Service, and the National Marine Fisheries Service.

Without flow re-routing, the harbor deepening would increase salinity in 1,177 acres of freshwater tidal wetlands, converting it to brackish (more salty) marsh. However, with flow re-routing, the project will only convert 223 acres of freshwater wetlands to brackish marsh.

The Corps anticipates the additional freshwater in the back river will convert 740 acres of salt marsh to brackish marsh. Over time, more diverse plant communities are expected to be seen in that area.