xpdrainage 2017.1 Help Documentation XDH2017v1
The following flowchart describes the successive steps that happen during the analysis. The steps shown on the flowchart are repeated at each Analysis Interval for each Stormwater Control.

The Inflow Hydrograph may be defined by the user as an Input Hydrograph or may be calculated from the Runoff Method selected when using a Catchment Area. Each Runoff method is described in detail under these headings.

The hydrograph will first reach an inlet, either to a Simple Junction, Manhole or Stormwater control. The Inlet may restrict the flow based on a range of methods described via links to the Inlet types on the Inlet page. There may be multiple inlets which are treated separately and then summed to create the total inflow into the Junction, Manhole or Stormwater Control.

For hydrographs entering a Simple Junction or Manhole, a volume and water level are calculated based on the dimensions. For a Simple Junction, the plan area is fixed at 1.2 m2. For Manholes, the user can enter the area.
For a Stormwater Control, a more complex analysis takes place. Multi-layered Stormwater Controls are treated as having separate subsystems and the water levels and volumes are calculated separately in each subsystem. For example, a Swale with a Trench is treated as having two separate subsystems.

The computation routine used to calculate the outflows and the updated volume is derived from the Modified Puls method.

More details on the Analysis of Connections and Analysis of SWC/Junctions are available by following the links.