Field evaluation of discretized model setups for the storm water management model

Abstract

The Stormwater Management Model (SWMM) is a hydrologic–hydraulic model often used to simulate water flows in urban drainage systems and changes in water quality. The unsteady flow hydraulic solver in SWMM solves mass and momentum conservation equations for the entire conduit length, and mass is conserved at each junction. This link–node approach used by SWMM does not allow for discretization (i.e. intermediate calculation points) between consecutive junctions, which is adequate in gradual filling scenarios with appropriate calibration and suitable selection of routing time steps. However, because there are more rapid filling scenarios that are associated with intense rain events, the link–node solution approach will affect the accuracy of the hydraulic calculations. This work presents the results of a field investigation in which predetermined volumes of water were suddenly released into a physical stormwater collection system. Level loggers were installed to measure flow depth and outflow rates in these tests. The results were compared with SWMM modeling results obtained by the link–node approach using alternative SWMM model setups which included additional intermediate discretization. The goal was to assess the potential benefits of SWMM discretization in the context of rapidly filling collection systems.