The Unit Hydrograph Editor is used to create and edit Unit Hydrograph objects, which define the shape parameters and rain gauge information for a group of triangular unit hydrographs. These unit hydrographs are crucial for calculating rainfall-derived inflow/infiltration (RDII) flow at specific nodes within the drainage system.

Click the Unit Hydrograph button to open the Unit Hydrograph Editor.

Button Description
Add one unit hydrograph
Delete selected unit hydrographs. Please note to use Ctrl and Shift keys for multiple selection.
Import a group of unit hydrographs
Export all the unit hydrographs

In the field Storm Index type the index of storm in the rain group.

Here are the key details of the Unit Hydrograph Editor:

  • Name: Assign a name to the Unit Hydrograph Group.
  • Storm Index: Specify the rain gauge that provides rainfall data for the unit hydrographs in this group. You can either type the name or select it from a dropdown list.
  • Hydrographs For: Select a specific month or choose “All Months” to define hydrograph parameters that apply to all months of the year. Some months may already have assigned hydrograph.

This editor allows you to configure parameters for different unit hydrographs, including short-term, intermediate-term, and long-term responses, as well as initial abstraction losses. These hydrographs are essential for simulating the flow of rainfall-derived water in the drainage system.

To view or edit the RTK table, click the button next to the Unit Hydrograph field in the Unit Hydrograph Editor.

The “Unit Hydrographs” tab allows you to configure the R-T-K shape parameters for different sets of unit hydrographs in specific months of the year. Each set of unit hydrographs includes parameters for short-term, medium-term, and long-term responses. You have the flexibility to define these parameters for one or more of the response hydrographs, and the sum of the R-values for each set of unit hydrographs does not necessarily have to equal 1.

The shape parameters for each unit hydrograph are as follows:

R: Represents the fraction of rainfall volume that enters the sewer system.
T: Indicates the time interval, in hours, from the beginning of rainfall to the peak of the unit hydrograph.
K: Denotes the ratio of the time it takes for the unit hydrograph to recede to the time it takes to reach its peak.

To view or edit the Initial Abstraction Depth table, click the button next to the Initial Abstraction Depth field in the Unit Hydrograph Editor.

The “Initial Abstraction Depth” tab allows you to specify parameters related to the reduction of rainfall before it enters the unit hydrographs for a specific month of the year. This reduction accounts for initial abstraction, including interception and depression storage. You can assign different initial abstraction parameters to each of the three unit hydrograph responses (short-term, medium-term, and long-term).

The parameters for initial abstraction are as follows:

Dmax: This represents the maximum depth of initial abstraction available, measured in units of rainfall depth (e.g., inches or millimeters).
Drec: It indicates the rate at which any utilized initial abstraction is replenished or made available again, measured in units of rainfall depth per day.
Do: This parameter represents the amount of initial abstraction that has already been used up at the beginning of the simulation, measured in units of rainfall depth.