I am currently attempting to model a stormwater system that has a high likelihood of backflow because the proposed basins are interconnected and there are no intervening structures which would impede flow from moving backwards in larger storm events.
To model this, I've connected my ponds to each other with primary discharges going towards downstream basins, however, I've added identical discharges in the downstream basins (as a secondary and tertiary discharge) which are identical to the upstream flow controls (usually some kind of broad-crested weir).
For smaller storms (i.e. 2-year), the output data has been pretty clean and not indicated that there are any issues worth noting.
However, when I crank this up to large storm events (i.e. 100-year), the oscillations are absurd to the point that I'm questioning whether these results are valid. The overall hydrograph appears correct, however, I have been unable to completely eliminate the oscillations.
At this point, I've attempted the following:
- Reduced the time step all the way down to the minimum of 0.01 hours.
- Ensured that none of the basins are undersized and have sufficient defined volume.
- Applied a phase-in depth of 0.01' to all infiltration basins.