Rainfall sensitivity

Hello, my model seems to have no sensitivity to recharge. Even when I increase de recharge 10 or 20 times the normal rainfall, the heads have insignificant change. Can anybody tell me what could I do about that?

I also have problems when I use the first layer as phreatic. I only get convergence when using this layer as free & movable. How could I resolve this?

Hum ! :-\  I think it could be due to some think. Have you checked that your infiltration value is correct and not too low?

And if the hydraulic conductivity is high, it could be difficult too.

Perhaps could you give us more explanations on values you are using ?

regards

Hidraulic conductivity have been tested for many values found in field (mean value 0.42E-4 m/s) and even for values lower than those ones. But I do not know about the infiltration value. Where do I input these value?

Thx very muh for your answer!

Hi,

But what do you mean in your post by rainfall then?

Groundwater recharge is in the flow material menu, In(+)/out(-)flow on top for layer 1.

regards

Hi there! Yes, I mean rainfall as recharge. What I am saying is that when I rise this value (In(+)/out(-)flow on top), the heads don't respond to this change in recharge.

Right ! What are your value for recharge?  are in steady state or transient flow?  In this case, how many time are you running?

Perhaps you could explain a little bit more of the configuration of your model, boudary conditions...?

Ok, I'm running a transient simulation. The mean recharge value is 41E-4 m/d (1500mm/y) but I want to simulate changes in heads due to increasing recharge. I have input rainfall monthly too, as a time-varying powerfunction. It's a unconfined aquifer, with 25 meters thick isotropic porous media. I only used boundary condition os first type (head) for streams.

Have you set on all boundaries of your  model boundary conditions (head fixed) ?

to be sure : you have model only one geological layer?

Have you checked tthe balance when you have changed the recharge?

- In fact I didn't set a head on the boundaries because these boundaries are in a hilly topography. Do I need to do this?

- yes I have only one geological layer, which I divided into 5 layers, but they are all have the hydrological settings.

- I will check balance.

Thx again!

No, I wanted to be sure that you have not fixed all the boudaries, it could be difficult in this case !

Normaly, if you check the balance I think you should note significant change in the volume if you change only the recharge (10 to 20 times more).

Perhaps a stupid question : Have you checked all your layers to verify that there is not too high values (by mistake ).

Another stupid thing to check : Have you checked that your coordinates are in meters and not put in kilometers.  I mean that for example if you work on a  10x5 km area and you put 10 and 5 as coordinates in the model, the model "thinks" that it is 10 to 5 meters and not km.  (I did that one time, many years ago, and it took us 3 days to find it).

I suppose that you are in the calibration phase of your model, how many days you use for the run?

I haven't saved the tests I made with 10 or 20 times the recharge. But for a 4 times recharge run, I had no significant diferences in balance. I'll run again with higher recharge and check.

I am checking the heads at observation points that I have in field, through the scatterplot. Since observation points are present in all layers I think I have no differences.

And the coordinates are in meters, it's ok.

Yes, I'm in the calibration phase. I've tried many ways, with bigger periods and smaller ones too. But my final project has 1310 days.
Thx again for your attention Thierry!

Hi,

normally you can check that the volume incoming from infiltration in the model is right according to the calculation you could don with the surface.