Ensuring healthy water quality is an essential part of environmental monitoring for the Savannah Harbor Expansion Project (SHEP). The U.S. Army Corps of Engineers is partnering with the U.S. Geological Survey (USGS) to monitor water quality in the estuary using a sophisticated network of continuous monitoring stations.
The monitoring network allows the Corps to assess river conditions using real-time data, which will be used to monitor the estuary during construction and determine whether any adaptive management may be needed.
“ After years of field studies by a diverse group of federal, state, and local stakeholders, we worked with the Corps to develop a comprehensive monitoring network to ensure the SHEP functions as intended ,” said Brian McCallum, assistant director with the USGS Georgia Water Science Center.
The USGS is responsible for installing and maintaining the network of surface-water sites, which will be the primary indicators of change in the estuary. The network provides reliable data and capitalizes on many years of USGS expertise in hydrologic monitoring.
“ The water quality monitoring is the backbone of 95 percent of the environmental monitoring that the Corps will perform to monitor the SHEP ,” said William Bailey, chief of planning for the Corps’ Savannah District. “We are very glad to have the USGS working with us on this critical mission.”
Completed in November 2013, the USGS deployed five new stations and upgraded eight existing stations throughout the estuary. Three of the new stations were designed to assess water quality near the City of Savannah’s industrial and domestic water intake in the upper estuary, including Abercorn Creek. Two stations were sited at locations identified by the State of South Carolina. Each station includes water-quality instruments that measure tidal discharge, conductance, salinity, dissolved oxygen, and more.
Harbor deepening will allow additional saltwater to enter the harbor and travel further upstream. The Corps worked with other state and federal agencies to develop an extensive mitigation plan that avoids, minimizes and compensates for environmental impacts expected from the deepening.
One of the mitigation features is the installation of a dissolved oxygen (DO) system in the estuary. The system will mix river water with oxygen and then disperse it back into the river. The system will add oxygen to the estuary in three locations: one in the front river across from International Paper; another in the back river upstream of the old railroad bridge; and the third in the front river just downstream from Georgia-Pacific. The technology set up at each location will inject super-oxygenated water into the river during the hot, dry months, when oxygen levels typically drop.
The Corps of Engineers performed hydrologic modeling that indicated oxygen levels would be impacted by the harbor deepening; but that same modeling also indicated that DO levels would exceed the existing conditions in more than 90 percent of the estuary once the DO system is in place. The water quality data collected by the USGS gages will measure dissolved oxygen across the estuary to help the Corps assess the performance of the DO system.
The gages will also monitor salinity levels. Salinity data will provide a basis for measuring the extent of change in the estuary between salt marsh, brackish marsh and freshwater marsh.
“ The estuary’s tidal wetlands provide many valuable functions and services, including fishery and wildlife habitats, ” said Bryan Robinson, Corps’ civil engineer. “ Those functions can differ depending on salinity levels. While the harbor deepening is expected to shift some marsh from one type to another, the salinity data would be able to show a trend change in salinity, as compared to model-predicted values .”
The water quality monitoring will take place during all three phases of the harbor deepening: pre-construction, during construction, and post-construction. The post-construction monitoring will span 10 consecutive years.
Additionally, a subset of the monitoring stations will continue collecting data well beyond the post-construction phase.
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