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Problem using Modflow in transient


rdhotelans
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Hi!

I'm using Modflow in transient for a simulation: i have modeled drains to make the groundwater level decrease.

My model is quite easy: my initial piezometric state is a 1% gradient , with two constant limits (specified heads) and two "no flow limits", and with two drains.

I'm doing several tests to determine the number of drains that are necessary to make the water decrease under a specific value.

After the modflow simulation, i can observe the flow in each drain (thanks to the "flow budget" function), but although i'm using modflow in transient and with very small time steps, i cannot observe the evolution of the flow in each drain: indeed the flow should be important at the begginning of the simulation (because the piezometric charge is more important) and decrease to a constant value.

The flow that i observe is constant (like in the steady state).

I cannot either observe the evolution of the groudwater level over time, wheareas i'm in transient state: there is no difference with steady state. I only observe the "final state".

Do you understand my problem and do you see how i could observe the evolution of the flow in each drain over time (in transient state) and also the decrease of the ground water level?

thank you for your help and sorry for some english mistakes

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Make sure the "Steady State" box is not ticked for any stress periods in the MODFLOW - GLOBAL OPTIONS - STRESS PERIODS . If the box is checked/ticked in a given stress period, that stress period will run to steady-state rather than transient over the period. So if you have only one stress period and the steady state box is ticked, it will actually be a steady state solution.

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thank you for your help.

I have checked what you suggested to me and everything was already ok.

After my transient simulation, all the time steps are displayed, but there isn't any difference between the first time step (1 hour) and the final time step (1month): i tried to reduce my time steps, but it doesn't change anything. I don't know how to observe the progession of the goundwater level drawdown : i thought that modflow in transient was able to show this evolution?

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Well, I can't say why you aren't seeing a difference between the 1 hr and 1 month result - that will be for you to figure out. For the last part of your post, drawdown is handled through output control - you probably figured that out already. To see the evolution at certain locations, the easiest way is to select a cell or cells and then display one of the built-in time-series charts. That being said, it sounds like you probably won't be seeing much change, since it uses the results for each time step result output. Therefore, if you don't visually see a change between 1 hr and 1 mo, you may not get that much info from the chart.

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