Jet/Plume Boundary Condition

Jet/Plume BC Editor

One of the options available when a user creates a new boundary condition is type 8, Jet/plume. The form for editing the Jet/plume BC is shown in Jet/Plume Boundary Condition#Figure 1. EFDC+ has been enhanced to work smoothly with the EE defined jet/plume settings.

Although similar to a flow boundary condition or withdrawal/return user interfaces, the settings for jet/plume boundary conditions are unique to this boundary condition and associated sub-model (described below). In the Jet/Plume Type drop-down menu the user specifies the flow data of a jet plume boundary to link to with the time series options. These options include by-passing (ICAL=0), using a flow time series (QSER, ICAL=1), using a withdrawal return time series (W/R, ICAL=2). The user may also specify the frequency, in number of time steps, to update the jet/plume calculations.

When using the J/P with W/R Series option the user should set the location of the withdrawal and discharge locations as they would for a W/R boundary. However, it should be noted that the vertical layer setting for the discharge is not used by EFDC, though withdrawal layer setting is used. This is because J/P boundary automatically distributes the discharge flow from the plume over the vertical layers based on the flow characteristics and ambient temperature.

In the Diffuser Port Settings for Current Cell frame the user may specify the settings for each discharge cell including the number of ports, the elevation and the diameters of the port outlets, as well as the horizontal (azimuth) and vertical (altitude) angles.  It should be noted that the flow in the QSER file is multiplied times the number of ports for the total flow for that BC cell. So for example, if a user has 10 ports with each port having a time series of 0.15 cms assigned for the jet, then the total flow is 10 * 0.15 cms = 1.5 cms.

The setting for the jet/plume discharge cell is not dependent on the K value. It is only dependent on the "Elevation" set for the port. For this reason he K box for the cell is greyed out.

Figure 1  Modify/Edit Jet Plume BC Properties.

The Control Parameters frame allows the user to set various parameters relating to the plume entrainment. The user can set the #Elements, which is the maximum number of vertical computational elements along the length of the jet or plume. The entrainment calculation is an iterative process, the maximum number of iterations to be made if convergence is not obtained is set in the #Iterations form.

In the Entrainment Option menu the user sets whether to use the maximum of shear and forced entrainment, or to use the sum of shear and forced entrainment.

The Entrainment Stop menu provides three options for stopping the entrainment: stop at a specified number of elements (ISTJP=0), stop when the center-line penetrates the bottom or the surface (ISTJP=1), or stop when the boundary penetrates the bottom or the surface (ISTJP=2).

Other options include setting the Entrainment Error Criteria, which is a factor used in the iterative solution. An adjustment factor for the Froude Number may also be set. EFDC can write out a log file of the Jet/plume in various formats. Specify 1 for full ASCII, 2 for compact ASCII output at each update, 3 for full and compact ASCII output, and 4 for binary output.

Jet/Plume Boundary Condition#Figure 2 illustrates an application of the jet/plume BC for a temperature distribution in the case of two diffusers in a weak flow stream.

Figure 2   Thermal Discharge from Multiport Diffusers using Jet/Plume BC.

EFDC Jet/Plume Sub-model

The Jet/PIume sub-model in EFDC is partly described in EPA's "Review of potential modeling tools and approaches to support the BEACH program." Here an early version of the sub-model is described as providing a buoyant jet near-field dilution and mixing zone sub-model that is incorporated directly into the EFDC. The model simulates single-port and merging multi-port discharges using a three-dimensional extension of the Lagrangian formulations used in the UM model (Baumgartner et al.. 1994) and the JETLAG model (Lee and Cheung. 1990). The jet/plume model is unique in its use of unsteady fully three-dimensional ambient velocity density and concentration fields and realistic bathymetry for trajectory, entrainment, and dilution calculations. For multi-port discharges the merging of individual port plumes into multiple coalesced plumes is simulated. In addition to simulating the near-field and far-field concentration of dissolved contaminants, the jet/plume sub-model simulates sediment transport and the transport and fate of sorptive contaminants including the settling and bed exchange of the suspended and sorbed material (note that water quality parameters are not simulated at this stage).

The Jet/Plume sub-model automatically updates multiple outfalls as ambient conditions and outfall discharges evolve in time. The near-field solution is automatically coupled to the EFDC model's far-field transport and fate simulation, allowing the ambient concentration field to represent the historical influences of all unsteady discharges.  The Jet/Plume sub-model is particularly well suited to near-shore coastal simulations. The hydrodynamic component of the EFDC model is capable of simulating unsteady tide-driven, wind-driven, and wave-driven currents including long-shore and across-shore currents associated with incident wave transformation and surf zone wave breaking.