Abstract

A typical collection system may include many gravity mains connected by pump stations pushing flow into a complex network of pressurized conduits or forcemains (ASCE, 1982). The EPA standard SWMM5 engine solves this complex case, but it can be very expensive and time consuming. In most forcemain networks, the solution time improves significantly by separating or “decoupling” the gravity network from the force main network. Decoupling can improve computational speed three to five times. Larger networks have much larger increases in solution time speed for the decoupled network, up to twenty times faster.

Results for the decoupled model may differ from the original model. In particular, wet-well levels in the gravity network influence 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.

This chapter develops a rigorous dynamic conduit storage synthesizer approach that estimates the conduit volume available for storage and applies it to the wet-well depth-area curve to reduce the impact of decoupling the model on pumping simulations. We discuss the new method and apply it to a decoupled system with and without synthesized storage.

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