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Savannah Harbor officials face a difficult decision—how to maintain shipping access to the nation’s fourth largest port facility while considering the ecological implications of this use in a highly complex estuarine environment. Since 2002, various member agencies have relied on Tetra Tech’s modelers to build the first three-dimensional (3-D) modeling system to support forecasting and decision making in the region.

Applying Tetra Tech’s 3-D modeling system and watershed tools, we have provided the first comprehensive representation of the harbor area and the contributing watersheds. This modeling system was used to evaluate the implications of deepening the harbor’s navigation channel to accommodate growth in container volume and total tonnage and to compete with other deep-draft ports on the eastern coast.

Savannah Harbor is located at the border of South Carolina and Georgia at the confluence of the Savannah River and the Atlantic Ocean. Numerous municipal and industrial facilities discharge into the harbor, which has a complex estuary system with large tidal fluctuations (13 feet on a spring tide) that travel through a long, narrow channel. At the navigational channel’s upper extent, extensive fresh and salt water marshes constitute the Savannah National Wildlife Refuge, where some of the largest American alligators in the Southeast are found.

Our 3-D Estuary Model—Environmental Fluid Dynamics Computer Code—provides detailed 3-D representation of the water movement in the complex estuary system. This model has been at the forefront of more than 125 Tetra Tech studies, accepted by the U.S. Environmental Protection Agency (EPA) as a basis of their modeling toolbox, and broadly applied throughout the world.

The models assessed the environmental impacts due to the six-foot deepening in the following resource areas: elevated salinity in the river and marsh; lowering dissolved oxygen in the channel; impact on striped bass and shortnose sturgeon endangered species; and increased chloride at Savannah’s water intake. Tetra Tech’s models were used to examine mitigation alternatives to the environmental impacts including “re-plumbing” the river system and acquiring wetlands in the surrounding refuge. The models are a useful tool when examining these “what-if” scenarios and quantifying the cumulative benefits of the alternatives.

Tetra Tech is currently designing a mitigation strategy for injection oxygen from a land-side facility. These facilities contain eight- to 12-foot diameter cones that pump water out of the river, supersaturate under pressure in the cone, and discharge water back into the river to elevate the dissolved oxygen. Savannah Harbor would be the technology’s first estuary application. The models determine the amount and timing for the oxygen injection to offset the effects of the deepening project.