RDII Unit Hydrograph Editor

Unit Hydrographs (UHs) estimate rainfall-derived inflow/infiltration (RDII) into a sewer system. A UH set contains up to three such hydrographs - one for a short-term response, one for an intermediate-term response, and one for a long-term response.

A UH group can have up to 12 UH sets, one for each month of the year.

Each UH group is considered as a separate object by SWMM, and is assigned its own unique name along with the name of the rain gauge that supplies rainfall data to it.

Each unit hydrograph is defined by six parameters:

R - The fraction of rainfall volume that enters the sewer system.
T - The time from the onset of rainfall to the peak of the UH in hours.
K - The ratio of time to recession of the UH to the time to peak.
DMax - The maximum initial abstraction depth available in mm.
Drec - The initial abstraction recovery rate in mm/day.
Do - The initial abstraction depth filled at the start in mm.

Option	Description
Name of UH Group	Enter the name assigned to the UH Group.
Rain Gauge	Select the name of the rain gauge that supplies rainfall data to the unit hydrograph in the group. This is compulsory.
UH Group Selector	Select the UH Group to edit.
Rain Gauge Editor	Click to display the Rain Gauge Editor.
Add	Click to add a new UH Group to the project.
Delete	Click to delete a UH Group from the project.
Month	Select a month from the list box for which hydrograph parameters will be defined. Select All Months to specify a default set of hydrographs that apply to all months of the year. Then select specific months that need to have special hydrographs defined.
R-T-K Parameters Grid	Use this data grid to provide the R-T-K shape parameters for each set of unit hydrographs in selected months of the year. The first row is used to specify parameters for a short-term response hydrograph i.e. small value of T, the second for a medium-term response hydrograph, and the third for a long-term response hydrograph - largest value of T. It is not required that all three hydrographs be defined. The shape parameters for each Unit Hydrograph consists of: R - The fraction of rainfall volume that enters the sewer system. T - The time from the onset of rainfall to the peak of the UH in hours. K - The ratio of time to recession of the UH to the time to peak. DMax - The maximum initial abstraction depth available in mm. Drec - The initial abstraction recovery rate in mm/day. Do - The initial abstraction depth filled at the start in mm.