Pipe Pathway Outputs

• Mass_in_Pathway. This is a vector by species with dimensions of mass. It represents the total mass of each species in the Pipe.

Note: The Laplace transform algorithm for Pipes directly computes the flux rate leaving the Pipe. In order to track the amount of mass in the Pipe, we assume that the mass enters or exits the Pipe at a uniform rate over the timestep. If you use a large timestep and/or there is low dispersivity, this assumption may not be appropriate, and this can result in small errors in the amount of mass reported in the Pipe. This assumption does not affect the accuracy of the Pipe discharges, just the value of the reported amount of mass in the Pipe.

• Concentration. This is a vector by species with dimensions of mass per volume. It represents the concentration of each species in the Reference Fluid at the point where it exits the Pipe. This is a “total concentration”, and includes species sorbed onto suspended solids.

Note: The computed concentration is an approximation, equal to the mass outflux divided by the flow rate. Because the mass flux includes a dispersive component, the concentration will be slightly overestimated during periods of increasing concentrations, and slightly underestimated during periods of decreasing concentrations.

In addition, for every advective mass flux link in which the Pipe is the Outflow (upstream) pathway, an output is created on the Pipe:

• Medium_to_Path2, where Medium is the name of the flowing medium, and Path2 is the name of the linked (Inflow) pathway. This is a vector by species, and has dimensions of mass/time. It represents the mass flux of each species from the Pipe to the downstream pathway.

It is important to understand that the mass flux outputs from a Pipe represent the mass rate over the previous timestep. This can have implications if you choose to integrate one of these outputs (using an Integrator).