Check these researchgate answers at this link

https://www.researchgate.net/post/How_to_use_SWMM_model_in_an_un-gauged_urban_area

Thank you Mr. Bilel

Your answer is very simple. You CANNOT calibrate without a gauge data!

While the above holds true, you still can improve your model and reduce uncertainty with some side jobs on elements of your SWMM model. For example:

- Reduce uncertainty in the hyrological forceing (rainfall, and snow)

- Conduct infiltration test (e.g. double ring) on the soil and reduce uncertainty in the soil infiltration,

- Use high quality DEM (this is very important), the coarser the data less accurate,

- Add temperature to your model,

- Find exact vegetation (doable with only field visit),

- Use a similar watershed for calibration (same elevation, same land use, same rainfall).

- Within SWMM use rainfall-runoff models which are more physical based (not the ones which have lumpsum parameters like CN method!).

All of the above will help to have a better model. Hope it helps,

Kaveh

Not having data for calibrating models is now a very common problem. Analysts and managers have almost come to accept models without calibration or verification - sad but true. I wish more resources were invested in data collection than in modeling with doubtful validity.

this might help:

Article Assessing the Performance of LISFLOOD-FP and SWMM for a Smal...