The DSI version of EFDC (called EFDC+ or formerly EFDC_DSI) has a number of significant enhancements compared to the EPA and GVC versions of EFDC. These new features have been implemented in EFDC+ over the past 15 years to aid model development and application. The following summarize the main enhancements in EFDC+

What’s the Difference?

Dynamic memory allocation allows the user to use the same executable between modeling applications without having to always recompile the EFDC source code. This helps prevent inadvertent errors and provides more traceability for the source code. This features was added after 2004 for EE3 which initially still required recompiling of source code for each new model. More details on dynamic memory allocation can be found on here
Enhanced heat exchange options utilizing equilibrium temperatures for the water/atmosphere interface and spatially variable bed temperatures are coupled to the Water Quality Model. This feature was added in 2009 for EE5.
EFDC+ has been enhanced to include the ability to internally generate wind induced waves. An advantage of the EFDC+ wind-wave sub-model is that it has been incorporated into the source code of the EFDC hydrodynamic model instead of running a separate wave model. This means that the changes in hydrodynamic parameters are immediately updated in the wave calculations. The internal wave model internally computes the wind-induced waves with wind data provided in a wind series file and calculation time is low compared to other wave models. This feature was added in 2010.

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EFDC+ implements a robust ice sub-model. Previously EFDC_DSI had relatively limited ice modeling ability such that the ice conditions had to be fully specified by the user for every cell for the model simulation period. The creation of the input files was also external to EE. With EFDC+, ice formation and melt is simulated using a coupled heat model and fully handled by EFDC_Explorer. Options include Heat Coupled Ice Model (ISICE = 3) and Heat Coupled Ice Model with Frazil Transport (ISICE = 4). Ice sub-model was added in 2015 for EE7.3.

(Note that ice dynamics are not modeled at this stage. An ice dynamics sub-model would simulate the constriction of the channel by ice and the resulting bed shear caused by the transport of ice chunks. An ice dynamics sub-model is being considered for a later release of the EE modeling system).

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A new vertical layering approach, which is computationally efficient, has been developed and applied to the EFDC model, thereby reducing pressure gradient errors. In the EFDC_SGZ model, part of EFDC+, the vertical layering scheme has been modified to allow 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 for each cell is constant in time. This feature was added in 2014 and made publicly available from release of EE8.

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The EFDC_DSI incorporates a Lagrangian Particle Tracking (LPT) sub-model which replaced an earlier particle tracking code. The LPT sub-model implements options that allow particles to freely move in full 3D, or be fixed at a user specified depth. A random walk component can be added to either of these two options (free and fixed). The LPT sub-model has been further modified to model oil spill simulation. LPT was first added in 2009 for EE5 with the oil spill capability added in 2014.

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EFDC code has now been upgraded to allow multi - threading capabilities for vastly improved model run times. Depending on the machine topology, application, and operating system, thread affinity can have a dramatic effect on the application speed. The Intel® runtime library binds OMP threads to physical processing units. DSI typically produces run times up to 4 times faster on a six core processor than the conventional single-threaded EFDC model. This capability was first added in 2011 with more subroutines progressively parallelized since that time.

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EFDC has the ability to import grids with multiple sub-domains. EE checks for disconnected sub-domains and generates an IJ map of the cells with discrete subdomains. EE then allows the user to create the manual North-South face cell connections and save the information in the MAPPGNS.INP file. With EFDC+ the user may also connect E-W as well the N-S subdomains. N-S connectors were added in 2009 for EE5 and E-W connectors in 2016 for EE8.

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The EFDC code has been streamlined in a number of places in the code for quicker run times, and the FORTRAN77 code has been updated to FORTRAN90. At the same time a number of important bug fixes have implemented. EFDC+ has been optimized for Intel FORTRAN and is available in two versions, one for Windows and one for Linux.
Linkage of model results to the pre/post processor has been customized. This allows the linkage of any 2D/3D EFDC variable to the post processing tools.
• Hydraulic Structures governed by equations (EE8)

• Continuation Runs (EE7.2)

• High Resolution Data Snapshots (EE7.1)

• Rooted Plant & Epiphyte Model (RPEM) (EE7)

• Addition of dye modeling capability (EE5)

• Water Quality Boundary Conditions can now be loaded as concentrations in addition to Mass Loadings (EE5)

• Addition of Withdrawal/Return Boundary Condition (EE5)

• Internally compute bed shear stress and currents due to wind generated waves (EE6).

• Includes recent EFDC enhancements by EFDC development partners including sediment transport, SEDZLJ and hydro-mechanical devices (HMK) for EE6.

• Withdrawal/Return Boundary Condition for reversing flows (i.e. bi-directional flows) in EE6

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