1. Create flood damage extent
The InfoSWMM Risk Assessment Manager is laid out according to the duties required for risk assessment. Four options are found in the drop-down menu of the risk assessment. Each of these instructions launches a new dialog box where users can submit further information. The following passages explain how each of these instructions works. The commands listed below should generally be used in the sequence shown.
A flood damage extent map shows areas subject to flooding at the current simulation time of the network model. The current simulation time is shown on the InfoSWMM Output Toolbar, and it can be adjusted using the date and time drop-down selectors or the slider bar.
InfoSWMM's flood flow calculations are given for each node when the hydraulic depth is larger than the total of the invert height, the maximum depth, and the surcharge depth, except where ponding is simulated. Ponding presumes that floodwater will be stored in the pond area and then reintroduced to the storm drainage system.
The flood damage extent only computes the flood surface using nodes with a flood flow greater than zero. The hydraulic grade line (HGL) is interpolated between flooded nodes at these points using an inverse distance weighting scheme. The result of this interpolation is a flood elevation that may or may not rise above the ground surface as defined by the elevation raster layer. Any parts of the flood elevation above the surface elevation are flooded, while those below are dry.