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Re: R: [visual-modflow] Re: Simulating spring flow

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  • Rene Pericles Mbanguka
    Thanks Daniele, I will give it a try. The complication is that the springs are located somewhere inside my mode domain. From my previous experience, CHD cells
    Message 1 of 10 , Mar 8, 2011
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      Thanks Daniele, I will give it a try. The complication is that the springs are
      located somewhere inside my mode domain. From my previous experience, CHD cells
      act as sinks when they located at the downstream end of the model, and they act
      as sources once the are on the upstream boundary. For the case of a CHD inside
      the model domain, I think you always experience "In" and "Out" components!
      Regards,
      René.
      ________________________________
      Eng. René Périclès MBANGUKA
      Water Res. Eng. & Modeller
      WEMA Consult (T) Ltd
      Dar es Salaam - TZ
      Phone : +255 653 35 92 520
      Alt mail: rene@...
      Web link: www.wemaconsult.com
    • Daniele Baldi
      Well, in this case you have to use a drain to simulate spring. About your problem, have you checked the head out of the drain? In order to achieve the
      Message 2 of 10 , Mar 8, 2011
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        Well, in this case you have to use a drain to simulate spring.

        About your problem, have you checked the head out of the drain? In order to
        achieve the discharge, maybe you need to increase local gradient.

        All the best,
        Daniele



        _____

        Da: visual-modflow@...
        [mailto:visual-modflow@...] Per conto di Rene Pericles
        Mbanguka
        Inviato: Tuesday, March 08, 2011 11:38 AM
        A: visual-modflow@...
        Oggetto: Re: R: [visual-modflow] Re: Simulating spring flow

        Thanks Daniele, I will give it a try. The complication is that the springs
        are
        located somewhere inside my mode domain. From my previous experience, CHD
        cells
        act as sinks when they located at the downstream end of the model, and they
        act
        as sources once the are on the upstream boundary. For the case of a CHD
        inside
        the model domain, I think you always experience "In" and "Out" components!
        Regards,
        René.
        ________________________________
        Eng. René Périclès MBANGUKA
        Water Res. Eng. & Modeller
        WEMA Consult (T) Ltd
        Dar es Salaam - TZ
        Phone : +255 653 35 92 520
        Alt mail: rene@... <mailto:rene%40wemaconsult.com>
        Web link: www.wemaconsult.com
      • chrisli1223
        Hi Rene, Daniele s CHD approach sounds reasonable to me. I understand your concern about the fact that CHD can both act as a source and sink. I would use Zone
        Message 3 of 10 , Mar 8, 2011
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          Hi Rene,

          Daniele's CHD approach sounds reasonable to me. I understand your concern about the fact that CHD can both act as a source and sink. I would use Zone Budget to set up a zone at the CHD cells. The CHD-in value would show you only the amount of flow that goes into the CHD cells.

          Also check your CHD-out value. If it is zero, then CHD is purely a sink and we do not need to worry further. Otherwise, continue to read.

          If there is outflow from the CHD cells, then it is going to change the surrounding area and hence may affect the inflow to the CHD cells. Therefore you should only use the CHD-in value as your preliminary start point of your calibration.

          The following is just my opinion.

          Springs are simulated by drainage cells because (i) it is always a sink (ii) we do not know about the amount of spring discharge. We need drainage cells to tell us the answer.

          In your case, (i) is true but (ii) is false as you already know the discharge value.

          Another type of boundary condition that can fulfill (i)=true and (ii)=false is the Well package. It is always a sink. It requires known discharge rates.

          Since you have assigned very high drain conductance but the discharge is still too low. Therefore the next thing I would look at will be K (higher K = transmits more water = more discharge).

          I would use the Well package and vary K until the head at the wells are near the drain elevation (surface elevation of the spring). After your K is right, you can take away the wells and put the drainage cells in.

          The methodology I just mentioned, however, is purely based on theory and has not been tested yet. :p

          Feel free to comment.

          Cheers,
          Chris

          --- In visual-modflow@..., Rene Pericles Mbanguka <rmbanguka@...> wrote:
          >
          > Thanks Daniele, I will give it a try. The complication is that the springs are
          > located somewhere inside my mode domain. From my previous experience, CHD cells
          > act as sinks when they located at the downstream end of the model, and they act
          > as sources once the are on the upstream boundary. For the case of a CHD inside
          > the model domain, I think you always experience "In" and "Out" components!
          > Regards,
          > René.
          > ________________________________
          > Eng. René Périclès MBANGUKA
          > Water Res. Eng. & Modeller
          > WEMA Consult (T) Ltd
          > Dar es Salaam - TZ
          > Phone : +255 653 35 92 520
          > Alt mail: rene@...
          > Web link: www.wemaconsult.com
          >
        • Rene Pericles Mbanguka
          Hi Chris, Thank you very much for your suggestions. The well approach sounds very logical indeed. I tried a good number of runs but I ve just realised my
          Message 4 of 10 , Mar 9, 2011
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            Hi Chris,

            Thank you very much for your suggestions. The well approach sounds very logical
            indeed. I tried a good number of runs but I've just realised my spring discharge
            is perhaps too high! I had to increase K up to >100m/d which is not physically
            true. K values have been approximated to be between 5 and 10m/d in the area. The
            spring is actually said to be due to faults, so I think setting too high
            conductivity for the whole hydrogeologic unit containing the spring is may be
            not logical!
            And another question is : how do I relate my estimated K value to the drain
            conductance?

            Cheers.

            ________________________________
            Rene Pericles MBANGUKA
            Water Res. Eng. & Modeller
            WEMA Consult (T) Ltd
            Dar es Salaam - TZ
            Phone : +255 653 35 92 520
            Alt mail: rene@...
            Web link: www.wemaconsult.com


            ________________________________
            From: chrisli1223 <chris.li@...>
            To: visual-modflow@...
            Sent: Wed, March 9, 2011 12:36:25 AM
            Subject: R: [visual-modflow] Re: Simulating spring flow

            Hi Rene,

            Daniele's CHD approach sounds reasonable to me. I understand your concern about
            the fact that CHD can both act as a source and sink. I would use Zone Budget to
            set up a zone at the CHD cells. The CHD-in value would show you only the amount
            of flow that goes into the CHD cells.

            Also check your CHD-out value. If it is zero, then CHD is purely a sink and we
            do not need to worry further. Otherwise, continue to read.

            If there is outflow from the CHD cells, then it is going to change the
            surrounding area and hence may affect the inflow to the CHD cells. Therefore you
            should only use the CHD-in value as your preliminary start point of your
            calibration.

            The following is just my opinion.

            Springs are simulated by drainage cells because (i) it is always a sink (ii) we
            do not know about the amount of spring discharge. We need drainage cells to tell
            us the answer.

            In your case, (i) is true but (ii) is false as you already know the discharge
            value.

            Another type of boundary condition that can fulfill (i)=true and (ii)=false is
            the Well package. It is always a sink. It requires known discharge rates.

            Since you have assigned very high drain conductance but the discharge is still
            too low. Therefore the next thing I would look at will be K (higher K =
            transmits more water = more discharge).

            I would use the Well package and vary K until the head at the wells are near the
            drain elevation (surface elevation of the spring). After your K is right, you
            can take away the wells and put the drainage cells in.

            The methodology I just mentioned, however, is purely based on theory and has not
            been tested yet. :p

            Feel free to comment.

            Cheers,
            Chris
          • Daniele Baldi
            Hi Renè, if you know fault’s patters, you could apply local high hydraulic conductivity in order to simulate high fault’s k. Do you have any idea of
            Message 5 of 10 , Mar 10, 2011
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              Hi Renè, if you know fault’s patters, you could apply local high hydraulic
              conductivity in order to simulate high fault’s k.

              Do you have any idea of piezometric around the spring? Are you able to find
              local preferential flow way due to the faults?

              Anyway, your spring discharge isn’t too high, I mean, it’s your true data,
              so you have to play with piezometric gradient, k (locally by faults line)
              and (but you’ve just do it) spring conductance.

              All the best,
              Daniele

              _____

              Da: visual-modflow@...
              [mailto:visual-modflow@...] Per conto di Rene Pericles
              Mbanguka
              Inviato: Wednesday, March 09, 2011 3:10 PM
              A: visual-modflow@...
              Oggetto: [visual-modflow] Re: Simulating spring flow

              Hi Chris,

              Thank you very much for your suggestions. The well approach sounds very
              logical
              indeed. I tried a good number of runs but I've just realised my spring
              discharge
              is perhaps too high! I had to increase K up to >100m/d which is not
              physically
              true. K values have been approximated to be between 5 and 10m/d in the area.
              The
              spring is actually said to be due to faults, so I think setting too high
              conductivity for the whole hydrogeologic unit containing the spring is may
              be
              not logical!
              And another question is : how do I relate my estimated K value to the drain
              conductance?

              Cheers.

              ________________________________
              Rene Pericles MBANGUKA
              Water Res. Eng. & Modeller
              WEMA Consult (T) Ltd
              Dar es Salaam - TZ
              Phone : +255 653 35 92 520
              Alt mail: rene@... <mailto:rene%40wemaconsult.com>
              Web link: www.wemaconsult.com
            • Giovanni Firmani
              Theoretically a spring is a drain of the system and you should calibrate the hydraulic parameter of the drain (conductance) on the base of the observations of
              Message 6 of 10 , Mar 10, 2011
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                Theoretically a spring is a drain of the system and you should calibrate the
                hydraulic parameter of the drain (conductance) on the base of the
                observations of the measured discharges. If you are not able to repreduce
                the same or similar discharges it means that your conceptualization
                (boundary conditions or other thins) is not OK.
                Of course, for a calibration run you can use other packages like the well
                package or the EVT package to simulate the springs and to force the
                abstraction of the water you have observed . However for a predictive run
                you have to use the drain package and if the drain conductance is not
                calibrated or the conceptual model is not OK you might get wrong results.

                Gio

                On Tue, Mar 8, 2011 at 2:30 PM, rmbanguka <rmbanguka@...> wrote:

                > Hello again!
                >
                > How can I model spring discharge in Visual Modflow? I do understand springs
                > are often simulated with the drain package, but my problem is on how to get
                > the springs to deliver the observed/recorded flow! Im my model, there is a
                > spring which discharges 3.5m^3/s. I tried to assign a drain channel around
                > the spring area in my model, but the channel can only deliver very little
                > water. I tried to raise the drain conductance very high but I still can't
                > reach the recorded flow!
                >
                > Cheers!
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