How does WaterGEMS and WaterCAD calculate the water age in a looped system? For instance, a case where flow from two pipes in converging on one junction. How is the water age mixed?
WaterGEMS and WaterCAD use a Lagrangian algorithm to track parcels of water whose “quality” (in this case age) value is sufficiently different from the other parcels around it. Think of a pipe divided into sections along the pipe. For flow coming into one junction, from parcels within two pipes with different ages results in a blended (flow-weighted) age at the node. New parcels that leave the node attain the node’s calculated value for age.
The details for these calculations are handled in WaterGEMS and WaterCAD can be found in the EPANET User’s Manual, pages 41-46, as well as pages 194-199. Mixing at the confluence of two pipes is described in detail on page 194 of the manual.
How can I troubleshoot my model when my water age results don't appear correct?