	Applies To
	Product(s):	SewerGEMS, CivilStorm, StormCAD, SewerCAD
	Version(s):	08.11.XX.XX
	Original Author:	Mark Pachlhofer, Bentley Technical Support Group

Problem

Upstream conduit has less flow than downstream conduit when using the GVF - Convex, Implicit, and SWMM solvers.

Flow increases going from upstream to downstream.

Solution

This result is likely due to the trailing limb of an attenuated hydrograph. In the graph in the screen shot below, the upstream conduit (blue line) flow peaks faster and sooner than the downstream conduit flow (red line), which peaks later and with a flatter peak. This is due to attenuation effects, flattening the downstream hydrograph.

Sometimes this brings up the questions of, "What happened to the flow if none was added?" and "Is the volume of water being retained?". The volume of water at the end of the downstream conduit is the same (unless some flow is added or lost along the way), but takes a longer time to get to the end due to later or flatter peak. You're just observing the time lag of the flow pulse.

Conduit flow increases as you move downstream, with no additional inflow

Problem

Solution

See Also