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

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  • Daniele Baldi
    Hi Renè, that’s correct, I meant you can use CHD as spring if you are sure that spring will be always as sink (not source). Sometimes it’s possible, of
    Message 1 of 10 , Mar 8, 2011
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      Hi Renè,

      that’s correct, I meant you can use CHD as spring if you are sure that
      spring will be always as sink (not source). Sometimes it’s possible, of
      course you can’t simulate any dry condition of the spring because of the CHD
      (source in this case).

      You can say “spring is always as sink, never as source”, so, in my opinion,
      you could simulate as CHD.

      All the best,
      Daniele


      Da: visual-modflow@...
      [mailto:visual-modflow@...] Per conto di Rene Pericles
      Mbanguka
      Inviato: Tuesday, March 08, 2011 9:42 AM
      A: visual-modflow@...
      Oggetto: [visual-modflow] Re: Simulating spring flow

      Hi Daniele,

      From my understanding, a constant head boundary can both act as a source or
      sink, depending on the assigned head value; so that's why I thought it won't
      be
      reasonable to use this as a boundary. Can you please elaborate more on how I
      can
      use this constant head as a sink only (i.e. no inflow to the model).

      Regards

      ________________________________
      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

      ________________________________
      From: Daniele Baldi <daniele.baldi@...
      <mailto:daniele.baldi%40email.it> >
      To: visual-modflow@...
      <mailto:visual-modflow%40yahoogroups.co.in>
      Sent: Tue, March 8, 2011 10:56:02 AM
      Subject: R: [Spam][visual-modflow] Simulating spring flow

      Why don't you assign a constant head and find a k to obtain your
      discharges ?

      Cheers,
      Daniele
    • 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 2 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 3 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 4 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 5 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 6 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 7 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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