Exposure Assessment Models

EFDC

Introduction

The Environmental Fluid Dynamics Code (EFDC) is a multifunctional surface water modeling system, which includes hydrodynamic, sediment-contaminant, and eutrophication components. EFDC has been applied to over 100 water bodies including rivers, lakes, reservoirs, wetlands, estuaries, and coastal ocean regions in support of environmental assessment and management and regulatory requirements.

EFDC is a state-of-the-art hydrodynamic model that can be used to simulate aquatic systems in one, two, and three dimensions. It has evolved over the past two decades to become one of the most widely used and technically defensible hydrodynamic models in the world. EFDC uses stretched or sigma vertical coordinates and Cartesian or curvilinear, orthogonal horizontal coordinates to represent the physical characteristics of a waterbody. It solves three-dimensional, vertically hydrostatic, free surface, turbulent averaged equations of motion for a variable-density fluid. Dynamically-coupled transport equations for turbulent kinetic energy, turbulent length scale, salinity and temperature are also solved. The EFDC model allows for drying and wetting in shallow areas by a mass conservation scheme. The physics of the EFDC model and many aspects of the computational scheme are equivalent to the widely used Blumberg-Mellor model and U. S. Army Corps of Engineers' Chesapeake Bay model.

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Audience

Environmental/Civil/Coastal Engineers and Scientists

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Abstract

EFDC can simulate water and water quality constituent transport in geometrically and dynamically complex water bodies, such as rivers, stratified estuaries, lakes, and coastal seas. The code solves the three-dimensional primitive variable vertically hydrostatic equations of motion for turbulent flow in a coordinate system which is curvilinear and orthogonal in the horizontal plane and stretched to follow bottom topography and free surface displacement in the vertical direction that is aligned with the gravitational vector. A second moment turbulence closure scheme relates turbulent viscosity and diffusivity to the turbulence intensity and a turbulence length scale. Transport equations for the turbulence intensity and length scale as well as transport equations for salinity, temperature, suspended cohesive and non-cohesive sediment, dissolved and adsorbed contaminants, and a dye tracer are also solved. An equation of state relates density to pressure, salinity, temperature and suspended sediment concentration.

The computational scheme utilizes an external-internal mode splitting to solve the horizontal momentum equations and the continuity equation on a staggered grid. The external mode, associated with barotropic long wave motion, is solved using a semi-implicit three time level scheme with a periodic two time level correction. A multi-color successive over relaxation scheme is used to solve the resulting system of equations for the free surface displacement. The internal mode, associated with vertical shear of the horizontal velocity components is solved using a fractional step scheme combining an implicit step for the vertical shear terms with an explicit step for all other terms. The transport equations for the turbulence intensity, turbulence length scale, salinity, temperature, suspended sediment, dissolved and adsorbed contaminants, and dye tracer are also solved using a fractional step scheme with implicit vertical diffusion and explicit advection and horizontal diffusion. A number of alternate advection schemes are implemented in the code.

Features of EFDC are its ability to simulate wetting and drying cycles, it includes a near field mixing zone model that is fully coupled with a far field transport of salinity, temperature, sediment, contaminant, and eutrophication variables. It also contains hydraulic structure representation, vegetative resistance, and Lagrangian particle tracking. EFDC accepts radiation stress fields from wave refraction-diffraction models, thus allowing the simulation of longshore currents and wave-induced sediment transport.

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Applications and Possible Uses

  • The EFDC model has been used for a study of high fresh water inflow events in the northern portion of the Indian River Lagoon, Florida, and a flow through high vegetation density-controlled wetland systems in the Florida Everglades.
     
  • The model has been used for discharge dilution studies in the Potomac, James and York Rivers.
     
  • Salinity intrusion studies include the York River, Indian River Lagoon and Lake Worth.
     
  • Sediment transport studies include the Blackstone River, James River, Lake Okeechobee, Mobile Bay, Morro Bay, San Francisco Bay, Elliott Bay - Lower Duwamish Waterway, and Stephens Passage.
     
  • Power plant cooling studies include Conowingo Reservoir, the James River and Nan Wan Bay.
     
  • Contaminant transport and fate studies include the Blackstone and Housatonic Rivers, James River, San Francisco Bay, and Elliott Bay - Lower Duwamish Waterway.
     
  • Water quality eutrophication studies include Norwalk Harbor, Peconic Bay, the Christina River Basin, the Neuse River, Mobile Bay, the Yazoo River Basin, Arroyo Colorado, Armand Bayou, Tenkiller Reservoir, and South Puget Sound. The Peconic Bay water quality application is particularly noteworthy:
    • The model was calibrated using a one year data set and subsequently validated by simulation of an eight year historical period having extensive field data.
    • The model was then executed for 10 year management scenarios to develop a Comprehensive Conservation and Management Plan for the estuary system.

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Model History

EFDC was originally developed at the Virginia Institute of Marine Science (VIMS) and School of Marine Science of The College of William and Mary, by Dr. John M. Hamrick. This activity was supported by the Commonwealth of Virginia through a special legislative research initiative. Subsequent support for EFDC development at VIMS was provided by the U.S. Environmental Protection Agency and the National Oceanic and Atmospheric Administration's Sea Grant Program. Tetra Tech, Inc. became the first commercial user of EFDC in the early 1990's and upon Dr. Hamrick's joining Tetra Tech in 1996, the primary location for the continued development of EFDC. Tetra Tech has provided considerable internal research and development support for EFDC over the past 10 years. Primary external support of both EFDC development and maintenance and applications at Tetra Tech has been provided by the U.S. Environmental Protection Agency including the Office of Science and Technology, the Office of Research and Development, and Regions 1 and 4. The ongoing evolution of the EFDC modeling system has to a great extent been application driven by a diverse group of EFDC users in the academic, governmental, and private sectors.

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Technical Support / Training

Questions regarding EFDC and its supporting software and documents should be submitted to the Center for Exposure Assessment Modeling (CEAM) that is located at the Ecosystems Research Division of EPA's National Exposure Research Laboratory in Athens, GA.

Currently, there are no planned EFDC training sessions.

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Quality Assurance/Quality Control

The EFDC model has been validated using analytical solutions, simulations of laboratory experiments and verified prototype applications. An extensive bibliography of referred journal and conference proceedings articles exist. (See the document linked in the References of Published EFDC Applications and Uses section below.)

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Related Sites

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References of Published EFDC Applications and Uses

View a list of references, EFDC_References.
 

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Go to EFDC model download page.

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