Model Conversion from SWMM4 to SWMM5
Client: Private Client (subconsultant to LevelUp Consulting, LLC)
LevelUp’s development project was in the Alafia River Watershed and got permits through the Southwest Florida Water Management District (SWFWMD) and Hillsborough County by using a model in ICPR4 software. However, FEMA denied the use of ICPR4 and requested to use the current effective model for the Alafia River Watershed in HC-SWMM4 software. LevelUp contacted LAGO for converting the model to HC-SWMM5.
A script was developed to convert most of the SWMM4 input features and parameters into the SWMM5 format. The original model had to be cleared for wrong cards and zero values in the irregular channel cross section data.
Suspected duplicated conduits and weirs, as well as wrong weir crest elevations and basin areas were not corrected with the purpose of comparing the results between the two models.
The converted HC-SWMM5 model was run for the 100-year return period design storm, and the results for peak stages and flows were compared with the predecessor HC-SWMM4 model results.
The conversion approach was fine tuned to get better concordance between the two model outputs. The simulation time step was reduced to reduce flow routing errors to reasonable levels. Horseshoe and Egg conduit shapes in SWMM4 were converted to elliptical and arch shapes, respectively.
At the end of the conversion process, peak stages around the project area had typical absolute differences of less than a foot, which is reasonable considering that the two software versions use different equations and numerical methods. Some the numerical instabilities and mass balance errors may have been removed in the SWMM5 model version that may have also contributed to the differences observed in model results.