Field evaluation of discretized model setup for the stormwater management model

Robson L. Pachaly, Jose G. Vasconcelos and Daniel Allasia


The Stormwater Management Model (SWMM) is a hy-drologic-hydraulic model often used to simulate flows in collection systems, as well changes in water quality in these systems. Regarding the hydraulic solver used by SWMM, mass and momentum conser-vation equations are solved for each conduit, along with mass conservation at each junction. At each rout-ing time step, SWMM calculate water levels at junc-tions and, for each conduit, flow rate and depth. This standard link-node approach adopted by SWMM does not allow for discretization (i.e. intermediate cal-culation points) between consecutive junctions. In gradual filling scenarios this approach has been proven to be accurate with appropriate calibration and selection of adequate routing time steps. Yet, with more rapid filling, it is possible that some of the details of the filling process could be missed without any type of intermediate discretization. This work presents the result of a field investigation where an upstream reservoir was rapidly emptied into a 400-mm collection system. Level loggers were placed to measure flow depth and outflow rates in these tests. These results were compared with SWMM modeling results obtained with traditional link-node approach with varying time steps. Comparisons are also made with alternative SWMM modeling setup, where inter-mediate dummy nodes are added. The goal is to as-sess the potential benefits of SWMM discretization in the context of the rapid filling of collection systems.

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