IC and Head Reference Point

[k.gum]

Hello,

I have a question regarding the Initial Condition expressed in heads. My model is a 2D cross-section of an infiltration basin. I used the actual ortho heights in the geometry of the model, therefore the groundwater table lies somewhere around 140 mNN at the left side and 134 mNN at the ride side of the model. Based on this information I used the Hydrostatic Equilibrium Setting with a slope in X-Direction of -0.13°. My model base is at 120 mNN.

1. What is the reference point for the head value: the model base or the origin of the coordinate system? Should I use 140 mNN and 134 mNN which would use the origin as reference or is it 20 and 14 with the model base as reference point. Same question occurs to me when I am using the constant head boundary condition.
2. Is using the Hydrostatic Equilibrium Setting the right choice if the bottom of my model is not the groundwater table but it is higher within the model? I chose it because I wanted to be able to introduce a gradient in horizontal direction and it was recommended several times in this forum.

For further context: I am attempting to use measured groundwater level values for the calibration of the model. To do so I tried to set up my model in a way that it will generate a groundwater table, which is why I placed the model base at 120mNN with a no flow boundary. At approx. 120 mNN the base rock occurs. Please let me know, if this concept is essentially wrong.

I am a hydrus beginner so if these questions are too basic for this forum, kindly refer to tutorials and sections in the manual.

Kind regards,
Kristina

[Jirka]

I have no idea what mNN is. When I googled it, I got either Manhattan Neighborhood Network or Mission Network News .

But anyway. When you select a domain, the reference point is always the lowest located node, and if there are several nodes at one z-coordinate, then it is the one most to the left.

Once you have a groundwater table in the domain, you should always use hydrostatic equilibrium below the water table.

J.

[k.gum]

Sorry for the confusion, mNN referes to meters above mean sealevel.

[Jirka]

Where does the NN come from? J.

[k.gum]

"Normal Null" which is German and refers to the mean sea level.

[Jirka]

Thanks. One learns something new every day . J.

[HamidMoghimi]

Hello. I hope you are well.
I saw your question in the forum about groundwater modelling. I am trying to model groundwater and contaminant transport. I have hydraulic head measurements for calibration and am unsure about the boundary conditions. I attached the B.C I used. The model is working properly but I am not sure if this model is correct conceptually.
What did you mean by hydrostatic equilibrium? I could not find an option to have a gradient for the head at the bottom boundary. Is that possible?
That would be your kind to guide me.
Thank you
Hamid

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[Jirka]

I do not think that this will work if “hydraulic head 1” contradicts “hydraulic head 2” in the bottom left corner.

Hydrostatic equilibrium: H=h+z, where H is the total head, h is the pressure head (negative in the vadose zone and positive in the saturated zone), and z is the gravitational potential.

J.