Problem

In a branched system that comes back together at a single point, the losses through the manhole do not appear to be taken into effect. Why is this happening?

Problem ID#: 76837

Solution

This is related to how dynamic wave solver in SewerGEMS and CivilStorm handles loops. There is a section on this in the Help documentation under the topic "Network
Algorithms".

In short, SewerGEMS and CivilStorm consider loops as a series of branches. When solving a looped branch for a time step, the Implicit solver does the normal relaxation for the downstream boundary and uses an estimated flow as the upstream boundary condition. The iterative upstream flow is based on the diversion junction flow distribution factors which are derived by estimating the exiting link dynamic flow capacities.

For this reason, when two branches come together at a single point, SewerGEMS and CivilStorm will consider the losses across the manhole where the branches come together for only one loop. As a further test of this, you can try making the branch that does have losses across it inactivate is eliminating the branch and loop. When you recompute the model, you should see a losses are now accounted for.

See Also

Troubleshooting unstable SewerGEMS and CivilStorm results using the Implicit solver