GoldSim allows you to control the manner in which mass enters a Pipe. In particular, you can specify the Source Zone Length parallel to the flow direction in the pathway. Hence, if your pathway had a length of 100m, and you specified a Source Zone Length of 40m, mass would enter the pathway uniformly over the first 40m (rather than at the beginning of the pathway):
This is useful, for example, if your Pipe represents an aquifer which is being loaded from above with mass from source which is of such an areal extent (e.g., a landfill) that it extends over a significant portion of the pathway and therefore cannot be treated as a point source.
By default, the Source Zone Length for a Pipe is zero. In this case, any mass entering the Pipe is treated as a point source which is applied at the beginning of the Pipe. If the Source Zone Length for a Pipe is greater than zero, the mass is distributed uniformly over the specified length.
Two points regarding the use of the Source Zone Length are worth noting:
•The Source Zone Length is applied to all forms of mass that enter the Pipe: mass that enters as an initial or boundary condition, mass that enters the Pipe from other pathways via a mass flux link, and mass that enters the Pipe as a specified discrete change via the Discrete Changes field.
•If the Source Zone Length is larger than the Pipe Length, the Source Zone Length is assumed to be equal to the Pipe Length (and a warning message is written to the Run Log).
Warning: The Source Zone
Length should only be used if the total flow in the Pipe is substantially larger
than the flow associated with the incoming mass. This is because that the
Source Zone Length does not change the flow rate along the Pipe; it only impacts
where the mass is input. Hence, it is equivalent to assuming that the amount of
flow associated with the mass entering the pathway is negligible relative to the
total flow in the pathway (e.g., associated with “clean” upgradient
water).