A Suite of Tools for Efficient Modeling of Complex Collection Systems using SWMM
The U.S. Environmental Protection Agency’s Storm Water Management Model (SWMM) model uses a non-linear reservoir algorithm to compute runoff by dynamically routing flows while taking into account the backwater and pressurized flow conditions. These abilities of SWMM enable detailed modeling of complex urban collection systems. Advancement in the computer memory and processing speed has encouraged development of complex collection system models. As complexity increases, detailed representation of the system is often limited by the ability of the available tools in SWMM to prepare large input datasets for the model simulation as well as to perform adequate quality assurance checks on the model simulation results. Moreover, some of the unique methodologies utilized in such complex models cannot be handled by the in-built functionalities of some readily available third party software which are designed to address the more general applications of the models. Experience with modeling large urban collection systems suggests that the one-size-fits-all concept does not always work. This paper presents a discussion of some of the customized tools developed to assist with the hydrologic and hydraulic (H&H) modeling of complex urban service area for the Allegheny County Sanitary Authority (ALCOSAN) in south-western Pennsylvania using SWMM5.
The customized tools presented in this paper include those devel-oped to prepare the model, the input datasets and the post-processing of the model simulation results. The tools or programs were developed using the Statistical Analysis Software (SAS). Programs were developed to process the GIS information to create slope categories for the sub-catchments, process the calibrated radar rainfall data to develop area-weighted precipitation time-series for each sewershed and process the quality assured flow monitoring data to develop the dry weather flow hydrographs at all point of connections to the collection system for direct input into the model. Post-processing programs were developed to facilitate the hydrologic validation of the monitored sewersheds, to generate various types of plots to assist with the quality assurance checks of the model simulation results and to generate overflow discharge summary reports for all outfalls in the system to quantify the combined sewer overflow (CSO) and separate sewer overflow (SSO) discharges into the receiving waters.
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