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Hi,

I want to know the volume of infiltered water in a rainfall/runoff simulations. And to know that I ran two simulations, one with CN 100 and one with CN 70 keeping all the other inputs same including the rainfall file. I also added two source terms with 0.6 m3/s each.
The difference between the area under the hydrographs (volumes) from these two simulations should be the volume of infiltered water.
The water balance at the end of two simulations is as follows:

1. simulation with Curve Number 100:
FINAL BALANCE OF WATER VOLUME

RELATIVE ERROR CUMULATED ON VOLUME: 0.5971796E-11

INITIAL VOLUME : 0.000000 M3
FINAL VOLUME : 23784.51 M3
VOLUME THAT ENTERED THE DOMAIN: -1359435. M3 ( IF <0 EXIT )
VOLUME ADDED BY SOURCE TERM : 1383219. M3
TOTAL VOLUME LOST : 0.8118266E-05 M3

2. simulation with Curve Number 70:
FINAL BALANCE OF WATER VOLUME

RELATIVE ERROR CUMULATED ON VOLUME: 0.6657597E-10

INITIAL VOLUME : 0.000000 M3
FINAL VOLUME : 23678.20 M3
VOLUME THAT ENTERED THE DOMAIN: -745199.6 M3 ( IF <0 EXIT )
VOLUME ADDED BY SOURCE TERM : 768877.8 M3
TOTAL VOLUME LOST : 0.4961239E-04 M3


I am surprised to see how come the VOLUME ADDED BY SOURCE TERM is different in these two simulations because the input rainfall is exactly the same.
what does this term VOLUME ADDED BY SOURCE TERM indicate and how is it calculated?

Also, how can I calculate the volume of input rainfall from the input file rainfall.slf or the runoff volume from the result file?
Or is there any other simple way to calculate the volume of infiltered water in any simulation?


Thanks and Regards,
Nitesh

Hello Nitesh,

As you may know, I am not a specialist of rainfall-runoff modelling in TELEMAC-2D.

Anyway, what is computed behind "VOLUME ADDED BY SOURCE TERM" is an accumulation of MASSES, see PROPAG subroutine to know how it is computed.
Reading RUNOFF_SCS_CN subroutine, POTMARET may vary with CN, thus ACCFA, thus ACCROFF, RAIN_MPS_GEO, thus PLUIE. Thus T1 and MASS_RAIN in PROPAG subroutine.

This may explain the different "VOLUME ADDED BY SOURCE TERM".

Hope this helps,

Chi-Tuan

Hello Nitesh !

I hope I can complete Chi-Tuan to answer your questions.

Physically, the "VOLUME ADDED BY SOURCE TERM" mainly computes RAIN and other water sources (through the logical value YASMH to tell if there are other sources of water, and if so, take them into account in the tracer equation with the SMH variable).

Indeed, as Chi-Tuan mentioned, it is the PLUIE variable that is behind "VOLUME ADDED BY SOURCE TERM" when you are using the runoff routine as you do. This PLUIE variable represents the net rainfall (only the runoff) without the infiltration. With your different CN values you have different infiltrated volume of water, that is why the "VOLUME ADDED BY SOURCE TERM" is different.

To compute the input rainfall from the input file, you could just launch a simulation without infiltration, then the difference between the simulations with infiltration and without it is the infiltrated water volume.
Another solution (if you want to have the volume of rainfall without infiltration while using the infiltration mode) is to change the prosou.f file to print the volume of rainfall without infiltration before calling the runoff routines.

Jean-Paul

Thank you both of you for your answers.

As Jean-Paul said, 'To compute the input rainfall from the input file, you could just launch a simulation without infiltration, then the difference between the simulations with infiltration and without it is the infiltrated water volume.', I have run two simulations one with infiltration (with CN 70) and another without infiltration (with CN 100) (correct me if this is wrong way).

So now, is the difference between the volume under the hydrographs from these simulations the infiltration or the difference between the "VOLUME ADDED BY SOURCE TERM" from these simulations is infiltered water?

Regards
Nitesh

The infiltration on your whole domain is the difference between the "VOLUME ADDED BY SOURCE TERM" since a CN of 100 means that there is no infiltration (I did not notice the value of 100 at first, you could have used directly RAINFALL-RUNOFF MODEL=0 for the case without infiltration).
The volume difference under the hydrograph can be the infiltrated volume as well if all the net rainfall runs off to the outlet in both cases (without remaining water from the rainfall in your domain) where the hydrograph is measured for both simulations. You can do some cross validation, but I would suggest taking the difference between the "VOLUME ADDED BY SOURCE TERM".

Kind regards,
Jean-Paul

Hi!

If your case is simple (rainfall and CN constant in space) you can simply calculate the total infiltration losses using the CN model equation giving Pe, the net rainfall (runoff).

You can refer to your favorite hydrology handbook or look at this paper for the CN model equations:
henry.baw.de/bitstream/handle/20.500.119...quence=1&isAllowed=y

I made several checks during validation and infiltration is handled as expected in T2D.

For your set-up, a possibility would also be to cancel your source inflows and simply compare VOLUME ADDED BY SOURCE TERM for both runs. The only source term is then runoff.

Good luck!

Kind regards
PL