I'm a new user to SWMM and i'm currently trying to model SSO events at a waste water treatment plant. I've been using dynamic routing and I've been having trouble modeling the diversion structure. Currently I have a storage node acting as a wet well that feeds a type 3 pump. The pump is connected to an orifice which regulates the the pump to 4.0 MGD (anything over that would risk washing out the plant). Also coming out of the wet well i have a weir that is offset from the invert elevation of the storage tank. After some adjusting of that elevation I am able to match the volume of diverted flow for specific events. The problem comes in that very small adjustments of that height (as little as 0.5%) has a major impact of the simulated volume (around 50%) which makes the model impossible to calibrate and useless for a design event. Does anyone have any suggestions on how better model the diversion structure? Any help would be appreciated.