Kasrt system

Hello everyone,

I am modeling a 3D Karst system. I used the discrete features to define my karst: thickness = 0.1m and hydraulic conductivity = 0.1 m/s ( HH BC = 0m at the left side and HH BC= -5m on the right side). As a starting point I created only one layer of karst in the middle of my model just to test the results. As a first step I ran the model in steady state to establish the equilibrium, then I ran it in transient mode and I have increased the value of my hydraulic head BC at the left side from 0m to 10m using the time series option. I placed two observation points, one at the slice containing the Karst and one 10 m below it.

I was expecting that the HH at observation point in the karst would increase earlier than the one 10 m below. However, when I plotted the HH for the two piezometers I got the exact same curve for both.

My questions are:
1) How can I see the hydraulic head in the Karst only ?
2) Is it a better method to create an additional layer with the a high enough K rather than using the DF ?
3) The result of the observation point gives the HH in the karst or in the element?

Thank you

Sam

[b]How can I see the hydraulic head in the Karst only ?
The result of the observation point gives the HH in the karst or in the element?[/b]
If you locate observation points on mesh nodes which are additionally affected by Discrete Features you take both the DF and the porous media into account. A discrimination between Discrete Features and the porous medium does not exist for observation wells. However, the calculated heads at nodes occupied with Discrete Features are strongly influenced by the highly conductive Discrete Feature. Accordingly, if you record the heads on nodes which are additionally affected by Discrete Features you actually take the Karst into account.

[b]Is it a better method to create an additional layer with the a high enough K rather than using the DF ?[/b]
It depends on the model conceptualization and the question being investigated. Both methods have pros and cons. Without doubt, a fully discretized approach allows the representation of more details within the boundaries (limitations) of the applied flow law validity. However, a fully discretized approach inevitably results in a higher computational effort due an increased number of elements.

Discrete Features provide a useful alternative to represent different spatial scales for which an equivalent single Representative Elementary Volume does not exist anymore. In this case, two different continua, one for the porous medium and one for the Discrete Feature can be applied. At the same time, this method allows you to keep the number of elements at a lower level with respect to the fully discretized approach.

Thank you for the reply.

I just have one more question regarding the discrete features.
I modeled my fractures using the Manning approach and it works perfectly, however I am having trouble with the following:

I have 2 piezometers 2Km apart in my karst and they react to a change in hydraulic head at the same second.
i.e: I have a steady state condition. I apply a varying head condition on the uphil and simulate in transient mode. I want to see the propagation of my wave. I have no head loss in my karst (which I need) but the problem is that all the points in the karst change at the same time. There is no delay in that part of the model. Is there a way to create a delay in my karst according to the distance from HH BC (without creating head loss)???
Thank you