A Hydrodynamic Model Calibration Study of the Savannah River Estuary With An Examination of Factors Affecting Salinity Intrusion (original) (raw)
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Calibration of a 3-D Hydrodynamic and Salinity Model of the Savannah River Estuary
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In support of an Environmental Impact Statement (EIS) for a proposed harbor expansion project a three-dimensional hydrodynamic model was applied to serve as a tool to determine potential project impacts. The hydrodynamic model simulated salinity, currents, water surface elevation, and volume flows for the entire Lower Savannah River Estuary system (over 60 river miles). The model was calibrated and validated over two 100-day periods in 1999 and 1997, respectively. The model proved to be capable of reproducing complex, transient physical phenomena in this extremely dynamic system and provided good agreement with observed values of surface elevation, currents, and salinity. The model will be used to directly calculate project induced changes to the hydrodynamic and salinity environment, and will also provide the input to several other studies, including: a water quality model, a marsh vegetation model, and a river sedimentation model.
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The Army Corp of Engineers (ACOE) hired CDM to develop a 3-dimensional ground water model of the Savannah harbor area, with the intent to use the model to simulate saltwater intrusion from the Savannah River harbor area, both under present conditions and under the proposed conditions after dredging. The model includes modules to simulate flow, transport (using particle tracking), and density driven flow using a coupled flow and transport code suitable for simulation of saltwater intrusion and leakage. Model simulations were designed to assess the rate and magnitude of downward leakage of saltwater along the river caused by the steep decline in heads in the Upper Floridan Aquifer in the Savannah area due to pumping. Comparative runs were made under present day conditions, and after proposed dredging of the harbor, which would result in a decrease in the thickness of underlying Miocene Confining Unit deposits.
Development of a Three Dimensional Dissolved Oxygen Model for the Lower Savannah River Estuary
Proceedings of the Water Environment Federation, 2002
WEF 2002 Manuscript_6-ALT1.doc 11/16/01 3 1.2 CHARACTERIZATION OF THE LOWER SAVANNAH RIVER ESTUARY The study area for the Savannah Harbor Modeling Effort is shown in Figure 1-1. The primary area of interest for all of the studies is the upper portion of the Lower Savannah River Estuary, which is characterized by the transition between the saline and freshwater environments. For the purposes of the SHEP modeling efforts that area is defined between River Mile (RM) 10 (Fort Jackson) and RM 30 (immediately above Interstate-95). The delineation of this study area is derived from the ecological interests of concern, which were defined in the Tier I EIS as: • Impacts of salinity changes upon the freshwater marsh species within the Savannah River National Wildlife Refuge. • Impacts of salinity changes upon the striped bass spawning areas within the Front, Middle, Back, and Little Back Rivers. • Impacts of salinity changes upon the shortnose sturgeon population within the upper Estuary. • Impacts of dissolved oxygen changes upon the striped bass spawning areas within the Front, Middle, Back, and Little Back Rivers. • Impacts of dissolved oxygen changes upon the shortnose sturgeon population within the upper Estuary.
The Savannah Harbor is one of the busiest ports on the East Coast of the United States and is located downstream from the Savannah National Wildlife Refuge, which is one of the Nation's largest freshwater tidal marshes. The Georgia Ports Authority and the U.S. Army Corps of Engineers funded hydrodynamic and ecological studies to evaluate the potential effects of a proposed deepening of Savannah Harbor as part of the Environmental Impact Statement. These studies included a three-dimensional (3D) model of the Savannah River estuary system, which was developed to simulate changes in water levels and salinity in the system in response to geometry changes as a result of the deepening of Savannah Harbor, and a marsh-succession model that predicts plant distribution in the tidal marshes in response to changes in the water-level and salinity conditions in the marsh. Beginning in May 2001, the U.S. Geological Survey entered into cooperative agreements with the Georgia Ports Authority to ...
Estimating salinity intrusion effects due to climate change on the Lower Savannah River Estuary
2010
The ability of water-resource managers to adapt to future climatic change is especially challenging in coastal regions of the world. The East Coast of the United States falls into this category given the high number of people living along the Atlantic seaboard and the added strain on resources as populations continue to increase, particularly in the Southeast. Increased temperatures, changes in regional precipitation regimes, and potential increased sea level may have a great impact on existing hydrological systems in the region. Important freshwater resources are located proximal to the freshwater-saltwater interface of the estuary. The Savannah National Wildlife Refuge is located in the upper portion of the Savannah River Estuary. The tidal freshwater marsh is an essential part of the 28,000-acre refuge and is home to a diverse variety of wildlife and plant communities. Two municipal freshwater intakes are located upstream from the refuge. To evaluate the impact of climate change on salinity intrusion on these resources, inputs of streamflows and mean tidal water levels were modified to incorporate estimated changes in precipitation patterns and sea-level rise appropriate for the Southeastern United States. Changes in mean tidal water levels were changed parametrically for various sea-level rise conditions. Preliminary model results at the U.S. Geological Survey (USGS) Interstate-95 streamgage (station 02198840) for a 7½-year simulation show that historical daily salinity concentrations never exceeded 0.5 practical salinity units (psu). A 1-foot sea-level rise (ft, 30.5 centimeters [cm]) would increase the number of days of salinity concentrations greater than 0.5 psu to 47 days. A 2-ft (61 cm) sea-level rise would increase the number of days to 248.
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Ecologists are studying the response of tidal wetlands of the Savannah Harbor watershed (Figure1) as part of the potential deepening of the Savannah Harbor. The information derived will be used to help interpret results of marsh studies, particularly the marsh hydrology studies that are to be used in conjunction with the hydrodynamic modeling to extrapolate project impacts spatially across the marsh-floodplain surface. These data will be converted into a "marsh succession model" that will be used with inputs from a three dimensional (3D) hydrodynamic model to predict the overall impact of the harbor deepening on the area's ecosystem. The linkage between the water level and specific conductance of the tidal marshes to the Savannah River is critical to developing a successful marsh succession model.
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The Savannah Harbor is one of the busiest ports on the East Coast of the United States and is located downstream from the Savannah National Wildlife Refuge, which is one of the Nation’s largest freshwater tidal marshes. The Georgia Ports Authority and the U.S. Army Corps of Engineers funded hydrodynamic and ecological studies to evaluate the potential effects of a proposed deepening of Savannah Harbor as part of the Environmental Impact Statement. These studies included a three-dimensional (3D) model of the Savannah River estuary system, which was developed to simulate changes in water levels and interstitial (or pore-water) salinity in the system in response to geometry changes as a result of the deepening of Savannah Harbor, and a marsh-succession model that predicts plant distribution in the tidal marshes in response to changes in the water-level and interstitial salinity conditions in the marsh. Beginning in May 2001, the U.S. Geological Survey entered into cooperative agreement...
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A three-dimensional (3-D) suspended sediment model was coupled with a 3-D hydrodynamic numerical model and used to examine the spatial and temporal distribution of suspended sediments in the Satilla River estuary of Georgia. The hydrodynamic model was a modified ECOM-si model with inclusion of the flooding-drying cycle over intertidal salt marshes. The suspended sediment model consisted of a simple passive tracer equation with inclusion of sinking, resuspension, and sedimentation processes. The coupled model was driven by tidal forcing at the open boundary over the inner shelf of the South Atlantic Bight and real-time river discharge at the upstream end of the estuary, with a uniform initial distribution of total suspended sediment (TSS). The initial conditions for salinity were specified using observations taken along the estuary. The coupled model provided a reasonable simulation of both the spatial and temporal distributions of observed TSS concentration. Model-predicted TSS concentrations varied over a tidal cycle; they were highest at maximum flood and ebb tidal phases and lowest at slack tides. Model-guided process studies suggest that the spatial distribution of TSS concentration in the Satilla River estuary is controlled by a complex nonlinear physical process associated with the convergence and divergence of residual flow, a non-uniform along-estuary distribution of bottom stress, and the inertial effects of a curved shoreline.
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Three-dimensional modeling of hydrodynamic processes in the St. Lucie Estuary
Estuarine, Coastal and Shelf Science, 2007
Comparing with the studies on large estuarine systems, such as the Chesapeake Bay and the San Francisco Bay, the processes of stratification and transport in small and shallow estuaries are relatively less studied. The St. Lucie Estuary (SLE) is a riverine estuary located on the east coast of south Florida. It is small and shallow, with mean depth of 2.4 m. To study the estuarine processes in the SLE, a hydrodynamic model was developed based on the Environmental Fluid Dynamics Code (EFDC) . A three-dimensional environmental fluid dynamics computer code: theoretical and computational aspects. The College of William and Mary, Virginia Institute of Marine Science, Special Report 317, 63 pp.]. The model was calibrated and verified using observational data obtained in 1999 and 2000, respectively. The model variables used for model data-comparisons are water elevation, velocity, temperature, and salinity. The model is then applied to study the hydrodynamic processes in the SLE. It is found that freshwater inflow plays a major role in the stratification and net flushing of the SLE. Stratification generally increases with freshwater inflow. But when the inflow is persistently large for a relatively long period, the estuary can suddenly change from very stratified to well mixed within a few tidal cycles and the stratification collapses. This finding suggests that large and persistent freshwater inflows do not always increase estuarine stratification. Instead, it may cause the stratification to collapse within a short period of time. In addition to gauged tributaries, ungauged lateral inflows can also be important to small and shallow estuaries like the SLE. Although small individually, the ungauged streams and surface runoffs can be a significant portion of the total inflow and affect salinity distribution significantly. Flushing time affects a wide range of hydrodynamic and water quality processes in the estuary. The model results indicate that commonly used formulas, such as the tidal prism formula and the Knudsen formula, may significantly underestimate the flushing time.