A typical collection system may include many gravity mains connected by pump stations pushing flow into a complex network of force mains. The EPA standard SWMM5 engine can solve this complex case, but it can be very expensive and time consuming. In most force main networks the solution time improves significantly by separating or “decoupling” the gravity network from the force main network. “Decoupling” can improve speed 3-5 times. Larger networks have much larger increases in solution time speed for the decoupled network.
Results for the decoupled model can be slightly different. In particular, wet-well levels in the gravity network will impact the pump operations for the forcemain network. Ignoring the storage available in gravity conduits can lead to oversized pump designs, because the overall storage volume is much larger than the volume available in the wet-well alone.
In this paper, a rigorous dynamic conduit storage synthesizer that takes the conduit volume and applies it to the wet-well depth-area curve to reduce the impact of decoupling the model on pumping simulations is developed. This paper will discuss the new method and present case study results showing coupled, de-coupled and de-coupled with synthesized results.