Stormwater　drainage　systems　are　typically　consisted　of　a　network　of　closed　conduits　designed　to　operate　in　an　open-channel,　free-surface　flow　regime　under　normal　conditions.　Nevertheless,　during　intense　rain　events,　the　conduits　may　fill　completely　undergoing　a　transition　to　a　pressurized　pipe　flow.　This　regime　transition　is　characterized　by　the　propagation　of　a　pressurization　front　in　the　form　of　a　non-linear　wave,　or　hydraulic　bore.　During　this　process,　high-pressure　peaks　may　occur　inside　sewers,　potentially　cab　cause　structural　damages　to　the　system,　pouring　through　manholes　or　other　vertical　shafts,　and　other　operational　problems.　On　the　other　hand,　flooding　caused　by　system　surcharge　has　become　an,　important　issue.　With　increased　property　values　of　buildings　and　other　structures,　potential　damage　from　prolonged　flooding　can　cause　millions　of　money.　The　complexity　of　the　system　geometries　and　the　flow　dynamics　requires　the　use　of　numerical　models　to　simulate　this　phenomenon.　A　detailed　simulation　model　was　described　based　upon　hydraulic　flow　routing　procedures　for　free　surface　and　pressurized　flow.　Special　consideration　was　given　to　the　interaction　between　free　surface　and　pressurized　flow　in　order　to　accurately　compute　water　pressure　in　the　conduits　as　a　basis　for　further　assessment　of　possible　damage　costs.　The　model　application　was　presented　for　small　case　study　in　terms　of　algorithm　designs,　equations　solution　method　and　preliminary　simulation　results.