EEMS - Version EFDC+ -Environmental Fluid Dynamics Code Software
Based on the Environmental Fluid Dynamics Code (EFDC) originally developed in the late 1980s by Dr. John M. Hamrick, DSI’s EFDC+ has become the gold standard for water systems modeling.
According to U.S. Environmental Protection Agency:
“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.”
DSI created EFDC+ by taking the original version of EFDC and vastly improving its speed, stability, and accuracy. EFDC+ now far surpasses the features and performance of the legacy code. EFDC+ is also full open-source and available online.
EFDC+ is the most up-to-date, enhanced version of EFDC, one of the most popular 3D hydrodynamic and water quality models available. The U.S. Environmental Protection Agency (EPA) has described the original EFDC as “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.” DSI has taken the EPA version of EFDC and greatly improved on it, creating EFDC+. Since 1998, DSI has been continuously upgrading the model’s hydrodynamics and stability, while also decreasing run times.
Water temperature is one of the most important physical characteristics of surface waters, impacting both density effects and thermal effects on water quality kinetics and solubility.
EFDC+ provides you a range of options to accurately simulate surface heat exchange and solar radiation attenuation in the water column. Multiple computed evaporation options are available to better represent your system.
Variations in salinity often impact estuarine stratification more than variations in temperature. In hundreds of studies, EFDC+ has been shown to successfully predict the response of rivers and estuaries to ocean salinity changes related to seasonal variation in freshwater inflow and human activities such as harbor and ship channel deepening.
To produce a realistic simulation of actual physical conditions, you may need to account for man-made structures such bridges, sluice gates, culverts, pipes, and/or weirs. With EFDC+, you can simulate these structures using a standard lookup table approach or take advantage of the enhanced EFDC+ feature that uses standard hydraulic equations of typical hydraulic structures to calculate the appropriate flow for each time step.
One advantage of EFDC+ over the EPA version of EFDC is that EFDC+ incorporates a wind-wave sub-model. This allows for temporally and spatially varying wave conditions to be directly coupled to the EFDC+ hydrodynamics. In your EFDC+ model, you can choose to allow these conditions to impact just the bed shear stress or you can also model wave-generated currents by inclusion of the radiation shear stresses on the water column.
Waves action can have a significant impact on hydrodynamics and sediment transport. EFDC+ can be linked to external wave modeling results or you can compute wind-generated waves internally.
EFDC+ has been enhanced to efficiently link to external wind models such as SWAN model output. As with the internal wind wave sub-model, you can choose to include or exclude wave-generated currents.
EFDC+ can serve as a 1-, 2-, or 3-dimensional (D) hydrodynamic model. For 3D simulations, two different vertical layering schemes are supported, providing you the ability to appropriately represent the vertical structure of your system.
A new vertical layering approach, called the Sigma-Zed approach (SGZ), has been developed and applied to the EFDC+ model, reducing the horizontal pressure gradient error. The Sigma-Zed approach allows for the number of layers to vary over the model domain. Each cell can use a different number of layers, though the number of layers in that cell remains constant over time. This is computationally efficient and is now recommended as the standard approach, ensuring greatly improved accuracy.
Learn more about Sigma-Zed and see examples of how it has been applied to water bodies in North America such as Lake Washington and Lake Mead here.
The sigma coordinate (SIG) approach uses the same number of vertical layers everywhere in the model domain, regardless of the water depths. This is the conventional EFDC approach and is common in most modern hydrodynamic modeling codes, but it is subject to horizontal pressure gradient errors when your system has steeply sloping beds relative to the horizontal grid size. This can be seen in Figure 2, to the right, which demonstrates how the thermocline is not as realistically represented using the SIG method.
You can compare the layering options for sigma coordinate and Sigma-Zed in the figures to the right.
EFDC+ no longer supports the General Vertical Coordinate (GVC), which was available in the EPA version of EFDC. The GVC and the Sigma-Zed approaches are similar, though the Sigma-Zed approach produces more accurate results and is significantly faster than a similarly configured GVC model. Although there is no advantage to using GVC with EFDC+, EE continues to support the GVC capability for users of EFDC_EPA.