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Subdivised a monolayer model to several layer

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  • Mohamed
    Hello, I have an hydrodynamic modelwhose features are as follows: 1. The aquifer is unconfined 2. The model consists of a single layer 3. the model is
    Message 1 of 3 , Aug 31, 2010
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      Hello,

      I have an hydrodynamic modelwhose features are as follows:
      1. The aquifer is unconfined
      2. The model consists of a single layer
      3. the model is simulated in transient of 35 years.

      When I subdivided the model into several layers. I kept the first layer unconfined and the lowers confined (i think i should do so). For lowers layers I subdivised the specific yield by the the thickness of each layer to obtain the specific storage). The pumping is applicated through all the layers pro rata their thickness, I have considered the kz = Kh. But I do not get the same results of the original model.
      How I could choose the parameters of my model multilayer among the original model to obtain the same results (the specific yield should become the specific storage for lower layers) and how to choose the vertical permeability of the layers?

      Thanks for any help
    • srigiriraju sriharirao
      Dear Mohamed, It is very interesting experiment you are doing. Your aquifer is unconfined and you got some results. Now, you want to test the same with
      Message 2 of 3 , Sep 4, 2010
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        Dear Mohamed,

        It is very interesting experiment you are doing. Your aquifer is unconfined and
        you got some results. Now, you want to test the same with multiple aquifers.
        What is the real story. Is the aquifer you are testing is unconfined or
        combination of both unconfined and confined. You cannot get specific storage by
        deviding specific yield with thickness of the aquifers ( You may get some figure
        which is not correct). You may try to get some realistic Storage coefficients in
        the area and try the experiment. Probably you will not get the same results as
        the aquifer thickness is different when it is a single aquifer and different
        when you converted them into multiple aquifer system.

        With best wishes,

        Dr.S.S.Rao
        Water Infotech


        ________________________________
        From: Mohamed <m.chaachoua@...>
        To: gwmodel@yahoogroups.com
        Sent: Tue, August 31, 2010 3:13:28 PM
        Subject: [gwmodel] Subdivised a monolayer model to several layer

        Hello,

        I have an hydrodynamic modelwhose features are as follows:
        1. The aquifer is unconfined
        2. The model consists of a single layer
        3. the model is simulated in transient of 35 years.

        When I subdivided the model into several layers. I kept the first layer
        unconfined and the lowers confined (i think i should do so). For lowers layers I
        subdivised the specific yield by the the thickness of each layer to obtain the
        specific storage). The pumping is applicated through all the layers pro rata
        their thickness, I have considered the kz = Kh. But I do not get the same
        results of the original model.
        How I could choose the parameters of my model multilayer among the original
        model to obtain the same results (the specific yield should become the specific
        storage for lower layers) and how to choose the vertical permeability of the
        layers?

        Thanks for any help
      • chrisli1223
        Hello, I assume you are talking about MODFLOW? The comments below are just my two cents worth. Other forum members please feel free to comment. ... If you are
        Message 3 of 3 , Sep 5, 2010
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          Hello,

          I assume you are talking about MODFLOW?

          The comments below are just my two cents worth. Other forum members please feel free to comment.

          --- In gwmodel@yahoogroups.com, "Mohamed" <m.chaachoua@...> wrote:
          >
          > Hello,
          >
          > I have an hydrodynamic modelwhose features are as follows:
          > 1. The aquifer is unconfined
          > 2. The model consists of a single layer
          > 3. the model is simulated in transient of 35 years.
          >
          > When I subdivided the model into several layers. I kept the first layer unconfined and the lowers confined (i think i should do so).

          If you are not sure whether the lower layers will remain confined or not, select type 2 or 3 (for BCF)/any non-zero value(for LPF). MODFLOW will calculate whether the layers are confined or not for you. However, if you are sure that the layers will be confined, then setting them as confined (type 0 for BCF or LPF) will speed up calculation.

          For lowers layers I subdivised the specific yield by the the thickness of each layer to obtain the specific storage).

          You do not need to perform this calculation to specific yield. This calculation is performed to storage coefficient, which is about the elastic storage of a layer. If you are using a GUI, the GUI should perform this calculation for you. Note that BCF and LPF treat storage differently.

          Elastic storage: when pressure decreases (i.e. head decreases), water will expand and the aquifer material will contract. Therefore water is released from storage.

          The pumping is applicated through all the layers pro rata their thickness, I have considered the kz = Kh. But I do not get the same results of the original model.

          Your original model uses solely specific yield. Your new model uses both specific yield (for the top layer) and specific storage (for the other layers). This may affect your result, as storage is usually importing for pumping simulation.

          > How I could choose the parameters of my model multilayer among the original model to obtain the same results (the specific yield should become the specific storage for lower layers) and how to choose the vertical permeability of the layers?

          Try using the same value for specific yield and specific storage.

          >
          > Thanks for any help
          >
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