Improve 1D SWMM Hydraulic Modeling with Hydraulically Challenging Structures and Designs

The Metropolitan Sewer District of Greater Cincinnati (MSDGC) plans to divert CSOs 430 and 431 overflows from the downstream portion of McLean Avenue Sewer via various modifications to CSO 666 with a dynamic underflow control connection to the EBORI to drain the McLean Avenue Sewer. The project ensures hydraulic grade line increase is less than 2-feet for the 10-year, 24-hour design storm.

Computational Fluid Dynamics (CFD) modeling was necessary to understand the physical geometry and associated losses at the key junctions/diversion structures. CFD modeling was based on the 10-year design storm conditions. The results were implemented into the SWMM model for the 10-year design storm simulations. Figure 1 shows the model progression schematic.

Figure 1. CFD Model Components

lipped SWMM models were created to match the domain of the CFD model. The same inflows and boundary levels were applied to match the CFD models. The minor loss coefficients and/or pipes’ roughness coefficients were adjusted so the flow split at each junction and the HGL at each node match the CFD results. Table 1 summarizes the model updates as a result. Figures 2 and 3 show the peak HGL comparison between the SWMM and CFD results.

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