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Spike in the pipe flow when analysing pipe network with iDAS in Civil 3D

When you analyse the stormwater or sewer networks in Autodesk® Civil 3D® with Devotech iDAS, you may experience a spike at the beginning of the analysis in the pipe flow hydrograph when you run the Dynamic Wave routing model.


In the example below, the total inflow coming from the upstream manhole is 0.2 l/s, but the spike shows a higher flow:


This problem may be caused by:

  1. The EPASWMM engine (used by iDAS) can generate a spike in the flow as it fills the pipe at the beginning of the analysis

  2. Backwater effect

  3. The effect of flooded node

  4. The downstream depth is above the upstream depth


If the EPASWMM engine as mentioned above is causing the problem, the following options are available to resolve it:


OPTION 1

Set the Start Report Time a few time steps after the analysis begins. In the example below, the reporting starts 30 minutes after the analysis begins:


OPTION 2

Set the Initial Flow in the Pipes tab to the flow you expect in the system. This might stabilise the analysis at the beginning:


Result:


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