The unit hydrograph transforms excess rainfall into runoff hydrograph. It is useful when flood volume and timing are important, not only peak discharge.
Recommended workflow
- Estimate catchment lag time and time of concentration.
- Prepare design storm hyetograph for selected return period.
- Separate losses to obtain excess rainfall.
- Apply unit hydrograph ordinates and superpose rainfall blocks.
- Add baseflow if required and check peak timing against catchment response.
Quick design table
| Item | Check |
|---|---|
| Loss model | Use consistent infiltration or abstraction assumption. |
| Time step | Small enough to capture peak but not too noisy. |
| Validation | Compare with observed hydrographs if available. |
Document the selected time of concentration formula because it strongly affects peak flow.