Coupling a Network of Cell Pathways to a Network of Reservoir or Pool Elements

The Contaminant Transport Module is a mass transport model. That is, it tracks the mass of the species The chemical (or non-chemical, such as bacterial or viral) constituents that are stored and transported through an environmental system in a contaminant transport model. In GoldSim, the Species element defines all of the contaminant species being simulated (and their properties). as it moves them through the pathway network. However, GoldSim does not automatically impose a mass balance on the transport media Materials (such as water, sand, clay, air) that constitute (are contained within) transport pathways. GoldSim provides two types of elements for defining media: Fluids and Solids. that it is moving between pathways (e.g., water). Mass balances for transport media must be specifically imposed by the user.

In practice, this simply means that when specifying the media amounts (typically volumes of water) and media flow rates for Cells (and other pathways), you must be careful to ensure that there is a flow balance. For some systems, ensuring a flow balance may be quite straightforward. For example, if the Cells represented portions of a saturated aquifer, the volume of water in each Cell remains constant, and you need to only ensure that the flows between Cells are consistent. In many cases, you may not even require a separate calculation for the flow rates, as they may be simply specified (or perhaps read from a Time Series).

However, if your Cells represent surface water bodies, or other compartments in which the quantity of media (e.g., water) varies with time, then you will need to build a parallel calculation in your model that tracks the water balance. This will almost always be done using Pool A stock element that integrates and conserves flows of materials. A Pool is a more powerful version of a Reservoir (it has additional features to more easily accommodate multiple inflows and outflows). or Reservoir A stock element that integrates and conserves flows of materials. elements.

In this case, it is necessary to couple the network of Pool or Reservoir elements (representing the flow system) to the network of Cells (representing the mass transport system). This can be done as follows:

• The Amount of each medium in a Cell (e.g., water) should be defined using the corresponding element (e.g., a Reservoir or Pool) that is being used to track that medium:
  
  

• The Outflow Flow Rates for each Cell should be defined using the appropriate rates for the corresponding element (e.g., outflow/withdrawal rates and/or overflow rates associated with a Reservoir or Pool).

Note: It is highly recommended that you use Pools, rather than Reservoirs when building a flow network that will link to a Cell network. This is because Pools have a number of distinct advantages (in particular, they have separate output for each outflow and they have total inflow and total outflow outputs) that make the coupling process much simpler.

Warning: If the media amounts (e.g., volumes of water) within your flow system )that you are modeling using Reservoirs or Pools and linking to Cells) change very rapidly over a timestep A discrete interval of time used in dynamic simulations. or go to zero (e.g., due to evaporation), Cells can compute incorrect concentrations and mass transfer rates. In these cases, GoldSim will write warning messages to the Run Log Text that is stored with a GoldSim model once it has been run. It contains basic information regarding the simulation, and any warning or error messages that were generated., and there are actions you can take to minimize such errors.