7.4 Tracer
7.4.2 Description
A range of tracer models are available to support simulation of dissolved quantities other than salt or temperature, without feedback to hydrodynamics. A tracer model might be deployed in settings that require flushing analyses or flow path investigation.
One or more tracers are activated using the
The maximum number of tracers is 100, but less than 10 would typically be deployed. Supported tracer implementations are summarised in Table 7.5, with links to the relevant implementation sections below. Commands are listed in Table 7.6.
| Model Implementation | Description |
|---|---|
| Conservative | Tracer simulated as conservative (no decay or settling). |
| Decay | Tracer simulated with first-order temporal decay. |
| Settling | Tracer simulated with settling velocity. |
| Water Age | Tracer simulated as water age. |
| Command | Description |
|---|---|
| NTracer | Optional - Specifies the number of tracers to be simulated. |
| Tracer | Conditional - Required for the decay, settling or water age implementations or when disabling evapo-concentration. Starts a tracer block for the specified tracer ID(s). Not required for conservative tracers with default behaviour. |
| Decay Rate | Conditional - Required for the decay tracer model implementation. Specifies first-order decay rate for tracers in the active tracer block. |
| Settling Velocity | Conditional - Required for the settling tracer model implementation. Specifies settling velocity for tracers in the active tracer block. |
| Evapo-Concentrate | Optional - Controls whether tracer concentration increases due to evaporation. The default is evapo-concentrate behaviour on. |
| Water Age | Optional - Enables water age source term accumulation for tracers in the active tracer block. |
| End Tracer | Conditional - Required if using tracer blocks. Closes a tracer block if using decay, settling, water age or evapo-concentrate tracer settings. |
7.4.3 Conservative
This model is the default and allows for the initialisation and/or delivery of a tracer within a simulation where the tracer is entirely inert. As such, the tracer simply advects with the mean flow and disperses in response to spatial velocity gradients and the specified mixing model (see Section 7.5). No additional tracer process commands are required beyond
7.4.4 Decay
This model allows for the linear temporal decay of a tracer according to Equation (B.9). It can be used to simulate a dissolved quantity that follows a linear decay process pathway.
The decay rate (in units of g/day) is specified within a tracer block (which is similar in style to a material or boundary block).
Multiple tracers can be assigned the same decay rate in a single block.
7.4.5 Settling
This model allows for the settling of a tracer according to Equation (B.9). It can be used for rudimentary simulation of a quantity that settles, such as suspended sediment. Once settled, a tracer cannot resuspend.
The settling velocity (in units of m/s) is specified within a tracer block (which is similar in style to a material or boundary block) for tracer number N as follows.
Multiple tracers can be assigned the same settling velocity in a single block using the method presented in Section 7.4.4.
7.4.6 Water Age
For studies that need to track retention time, a special tracer type is available using the
Multiple tracers can be assigned as a water age type in a single block using the method presented in Section 7.4.4.