Green–Ampt Infiltration and Hourly Precipitation Input in SWAT+

[Fereshteh Kordrostami]

Hi everyone,

I am considering using the Green–Ampt infiltration method instead of the Curve Number approach. I would appreciate your guidance on a few points related to precipitation inputs and model configuration.

1) If I switch to the Green–Ampt method, is it mandatory to use hourly precipitation inputs, or can the model still operate with daily precipitation data? If hourly precipitation is required, should the daily precipitation input files also be kept in the project, or should they be removed? Additionally, are there any other settings or considerations in the model configuration that should be adjusted when using the Green–Ampt method?

2) Could you please share an example of the hourly precipitation input file format used in SWAT+? The examples I have been able to find so far are all for daily precipitation input files, so it would be helpful to see a reference for the hourly format.

3) If I switch from the Curve Number approach to the Green–Ampt infiltration method, would it be necessary to recalibrate the model, or could the existing calibration still be used?

I would greatly appreciate any guidance you could share.

Thanks,

Fereshteh 

[Alex VanDeWeghe]

Hi Fereshteh, 

The model will still run with the Green-Ampt method using daily precip, but may give significantly different results than sub-daily. You may also want to review the theoretical documentation of the method to investigate if its calculation are appropriate at a daily time step. 

If you are running subdaily, the daily precipitation files can be removed from the model folder. As for parameters, note the different between the "event" and "gampt" codes in the codes.bsn file. My understanding is that both should be 1 for the gampt method.

The subdaily precipitation file just requires an additional column for hours, to the right of the column for days and tstep set to 24. 

You will almost definitely need to recalibrate when switching the runoff method and daily to hourly precip data. 

Hope this helps!

[Fereshteh Kordrostami]

Thanks Alex! That was very helpful.

Best,

Fereshteh