RDII Hydrographs¶
For SWMM models, Rainfall Dependent Inflow/Infiltration (RDII) are stormwater flows that enter sanitary or combined sewers due to inflow from direct connections of downspouts, sump pumps, foundation drains, etc. as well as infiltration of subsurface water through cracked pipes, leaky joints, poor manhole connections, etc.
RDII for SWMM models can be computed for a given rainfall record based on a set of triangular unit hydrographs (UH) that determine a short-term, intermediate-term, and long-term inflow response for each interval of rainfall. Each unit hydrograph is defined by three 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 hour
- K: The ratio of time to recession of the UH to the time to peak
Figure: RTK concept for unit hydrographs
A SWMM RDII Hydrograph can contain up to 12 sets of unit hydrographs (one for each month of the year), and each set may consist of up to 3 individual hydrographs (for short-term, intermediate-term, and long-term responses, respectively).
Figure: The SWMM RDII Hydrographs editor
The SWMM RDII Hydrographs Editor organizes the related input data for the RDII Unit Hydrograph approach into following groups:
- Identification
- Tabular Data
Identification¶
Figure: RDII Hydrographs Identification group
| Edit field | Description | Used or required by simulations | Field name in datastructure |
|---|---|---|---|
| ID | RDII Hydrograph ID | Yes | MUID |
| Raingauge ID | ID of the associated Raingauge | Yes | RaingageID |
| Description | User descriptive text | No | Description |
Table: Edit fields in the RDII Hydrographs Identification group (mss_Hydrograph)
Tabular Data¶
Define hydrograph characteristics in the secondary table on the RDII Hydrographs editor. Use the Insert and Delete buttons to add or remove records from the table, respectively. The Up and Down buttons may be used to reorder the table entries.
Figure: Define RDII hydrograph characteristics in the secondary table on the editor
| Edit field | Description | Used or required by simulations | Field name in datastructure |
|---|---|---|---|
| MonthNo | Individual Months or all months | Yes | MonthNo |
| R1 | The fraction of rainfall volume that enters the sewer system | Yes | R1 |
| T1 | The time from the onset of rainfall to the peak of the UH in hour | Yes | T1 |
| K1 | The ratio of time to recession of the UH to the time to peak | Yes | K1 |
| R2 | The fraction of rainfall volume that enters the sewer system | Yes | R2 |
| T2 | The time from the onset of rainfall to the peak of the UH in hour | Yes | T2 |
| K2 | The ratio of time to recession of the UH to the time to peak | Yes | K2 |
| R3 | The fraction of rainfall volume that enters the sewer system | Yes | R3 |
| T3 | The time from the onset of rainfall to the peak of the UH in hour | Yes | T3 |
| K3 | The ratio of time to recession of the UH to the time to peak | Yes | K3 |
| IA_Max1 | Short term maximum depth | Yes | IA_Max1 |
| IA_Rec1 | Short term recovery rate | Yes | IA_Rec1 |
| IA_Init1 | Short term initial depth | Yes | IA_Init1 |
| IA_Max2 | Medium term maximum depth | Yes | IA_Max2 |
| IA_Rec2 | Medium term recovery rate | Yes | IA_Rec2 |
| IA_Init2 | Medium term initial depth | Yes | IA_Init2 |
| IA_Max3 | Long term maximum depth | Yes | IA_Max3 |
| IA_Rec3 | Long term recovery rate | Yes | IA_Rec3 |
| IA_Init3 | Long term initial depth | Yes | IA_Init3 |
Table: Edit fields in the hydrographs data table (mss_Hydrograph)