2.3 Linkage with TUFLOW FV

2.3.1 Process

Support is currently provided for linkage of the WQ Module with TUFLOW FV. Within this linkage, TUFLOW FV considers the WQ Module as a peripheral model with which it interacts at arm’s length. The role of TUFLOW FV is that it (in approximate run time order):

  • Requests the number of water quality constituents from the WQ Module at start up, based on user setup specifications (e.g. the setting of the simulation class instance, with any constituent model modifications)
  • Automatically sets up the corresponding number of tracers (one for each computed variable) within its simulation (users do not specify these tracers)
  • Is then responsible for the:
    • Application of WQ Module initial conditions
    • Conservative advection and dispersion of these tracers (that represent the WQ Module’s computed variables)
    • Application of WQ Module boundary conditions
    • Calling the WQ Module at a user specified time step for the WQ Module to execute non-conservative transformation calculations on the suite of passive tracers
    • Writing of WQ Module results files

For example, if a WQ Module simulation was set to consider only dissolved oxygen, then TUFLOW FV would automatically allocate one tracer for the dissolved oxygen variable (the user does not need to specify passive tracers within TUFLOW FV), and advect and disperse that tracer throughout the model domain in response to initial and boundary conditions. At a user defined interval, TUFLOW FV would send the two- or three-dimensional tracer concentration field to the WQ Module for it to be modified in response to non-conservative ecological processes. The WQ Module would then return this modified tracer field to TUFLOW FV for subsequent advection and dispersion, with this exchange process continuing to simulation end.

2.3.2 Treatment of light

The TUFLOW FV heat module must be activated in order to use the WQ Module. One reason for this (beyond the need to compute water temperature) is that the heat module includes calculation of the light field within the model domain. This light field is used by various WQ Module constituent models.

In order to provide this light field, TUFLOW FV splits the shortwave radiation specified in the heat module into four bands:

  • near infrared (NIR)
  • photosynthetically available radiation (PAR)
  • ultraviolet A (UVA), and
  • ultraviolet B (UVB)

This split can be executed using TUFLOW FV defaults (recommended), or be user specified (not recommended). The corresponding band extinction coefficients in water with zero suspended sediment can also be specified in TUFLOW FV. Defaults are also available for all these coefficients and are recommended. TUFLOW FV uses these coefficients, along with other simulation properties, to compute the four light band intensities at the faces and centroids of each computational cell. The WQ Module uses the same split into bands as the TUFLOW FV defaults and ensures consistency in the treatment of light between TUFLOW FV and the WQ Module.

The WQ Module can also modify the light field sent to it from TUFLOW FV via calculation of phytoplankton self shading (section M.1), the absorption of light due to the presence of organic matter and other processes. If this occurs, the WQ Module returns a modified light extinction coefficient field to TUFLOW FV that is then used in subsequent hydrodynamic heat and light calculations. This modification of light by water quality computed variables only occurs for simulation classes beyond DO.