f1-Rsa Model
The f1-Rsa Model is used to calculate the effective rainfall when using the Quasi Linear Reservoir Method; a standard runoff model used in Japan.
See the Japanese Runoff Methodology technical paper for further information.
In the f1-Rsa method, an initial runoff rate, f1, is applied until the cumulative rainfall reaches a specified saturated rainfall value. A second runoff rate, fsa, is then applied.
This model is not designed for use in continuous simulations, as there is no mechanism to reduce cumulative rainfall after an event.
Using the f1-Rsa model
To use the f1-Rsa model in InfoWorks ICM, set the Runoff Volume Type field of the Runoff Surface to f1-Rsa.
Parameters are entered as follows:
- f1 - Minimum runoff field
- fsa - Maximum runoff field
- Rsa - Saturated rainfall field
Initial cumulative rainfall is set in the antecedent rainfall depth of the rainfall event, set in the sub-event properties.
Standard values of f1 and Rsa are shown below. These values can be used for a first approximation:
| Parameter | Rural area | Urbanised area |
|---|---|---|
| f1 | 1 | 0.5 |
| Rsa (mm) | 100 | 50 |
Standard values of f1, Rsa and fsa for typical land use patterns:
| Rice field | Farmland | Mountain |
Residential area 2 degree* |
Residential area 4 degree** |
|
|---|---|---|---|---|---|
| f1 | 0.0 | 0.15 | 0.25 | 0.7 | 0.9 |
| Rsa (mm) | 50.0 | 300.0 | 150.0 | 55.0 | 55.0 |
| fsa | 1.0 | 0.6 | 1.0 | 1.0 | 1.0 |
*2 degree - roads are installed quite well, drainage systems are not fully installed
**4 degree - all of the planned areas to be paved are paved, drainage systems are fully installed
