Applies To Product(s): Bentley PondPack Version(s): 08.11.xx.xx Environment: N/A Area: Output and Reporting Subarea: Original Author: Scott Kampa, Bentley Technical Support Group Problem Description What does the following user notification mean and how can I fix the issue? "Mass balance for routing volumes vary by more than 0.5% " Reason This user notification typically occurs when there is an instability in the interconnected pond routing (ICPM)calculations. Below are some possible steps to resolve the issue Steps to Resolve 1) Make sure that the ponds connected to the ICPM outlet structures are not flooding. This can cause instability in the calculations and make it difficult for the program to achieve mass balance. 2) You can try adjusting the calculation options. For instance, try a different value for Output Increment and ICPM time step. A smaller value will take longer to compute, but will results should be more stable since the calculation is able to capture the smaller changes in headwater and tailwater values. 3) Try to make all the pond outlet links ICPM routing. This includes all the links that go to outfalls. If the outfall was originally set a free outfall what you will need to do is set the outfall to the boundary condition type of "Time-Elevation Curve" and enter a time elevation curve such that the elevations still create the free outfall effect. This means that you will have your elevation be lower than the lowest elevation of the upstream outlet structure. Example: The lowest elevation of the upstream outlet structure is 5.00 ft. In this case you could set up your outlet structure with a time elevation curve as follows: Time Elevation 0.0 hours 0.00 ft. 12 hours 0.00 ft. 24 hours 0.00 ft. 4) You can adjust the ICPM settings in the outlet structure itself. Go to Components Composite Outlet Structures and click on the outlet structures that are mentioned in the user notifications. If you click on the name of that outlet structure you have the option to change the increment at which the headwater and tailwater are calculated. You can try to make this smaller than what it is at. A value of .5 ft. or .25 ft. usually works well for outlet structures that have very fast changes in flow vs. elevation that need to be captured on a smaller scale, but this value will be different depending on your outlet structures.
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