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Re: [gwmodel] Quantification of water in an unsaturated aquifer

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  • alexisvalenza@aol.com
    Hi Frederic, First, you need information about existing pumping in the area. That would give you an idea and the range of pumping rate in the unsaturated
    Message 1 of 6 , Jul 1 12:13 AM
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      Hi Frederic,

      First, you need information about existing pumping in the area. That would
      give you an idea and the range of pumping rate in the unsaturated aquifer. If
      you are not able to find this kind of information, you could try to find some
      about trial pumping in the area. The trial pumping will give you data about
      drawdown, exploration radius, permeability, and porosity. which would allow
      you to estimate the rate. Yet, the rate will depend on your pumping well
      geometry, casing, and also kind of pump.
      You need to take care of existing pumping close to your area, in order to
      keep the waterlevel high enough for the other wells.
      In a productive aquifer, you can go up to 700 m3/h and perhaps a bit more
      (this is just my experience), but you can also go down to 50 m3/h. this why
      you need information about other pumpings in this aquifer.

      ALexis
      Alexis Valenza
      SOL SYSTÈMES
      Éden Parc "Les Cèdres" - Square Vilmorin
      06160 Juan les Pins - France
      alexisvalenza@...


      [Non-text portions of this message have been removed]
    • Guarnaccia Joseph BC US
      The first step is to estimate aquifer hydraulic properties and external stress conditions (as negatively suggested by dod). Second, develop a calibrated flow
      Message 2 of 6 , Jul 1 6:12 AM
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        The first step is to estimate aquifer hydraulic properties and external
        stress conditions (as negatively suggested by dod).

        Second, develop a calibrated flow model.

        The third step is to formulate the 'hydraulic optimization problem'. This
        involves three steps:
        1.) define decision variables - in your case well pumping rate (and
        maybe location) and water table elevation.
        2.) define constraints - e.g., the water table cannot be lowered more
        than some level at a number of predefined points (nodes of the mesh). In
        addition, you can define a number of 'candidate' extraction well locations.
        3.) define objective - e.g., what is the highest rate that can I pump a
        well such that I do not lower the water table below the value defined at the
        constraint points?

        The forth step is to get an optimization package that can solve the problem
        defined above. Basically, it systematically searches for the stress
        configuration that meets the objective by sequentially setting well location
        and rate, calling the flow model to solve for the resulting flow field, and
        assessing whether the constraints are met. The algorithm stops when either
        the objectives are met (feasible solution), or cannot be met for any
        configuration (infeasible solution).

        I know of two free optimization packages that can solve your problem. They
        come with complete documentation that efficiently walk you through theory
        and practice. The only issue is that they have been written to work with
        MODFLOW (they have internal calls to MODFLOW to solve the flow problem for
        each stress configuration). So you will have to develop a calibrated MODFLOW
        model to represent the physical problem. You can find them at:
        http://www.ecs.umass.edu/modofc/
        http://www.geotransinc.com/modman.html


        Joe Guarnaccia

        -----Original Message-----
        From: Daniel O'Donnell [mailto:dodonnell@...]
        Sent: Saturday, June 29, 2002 8:55 AM
        To: gwmodel@yahoogroups.com
        Subject: Re: [gwmodel] Quantification of water in an unsaturated aquifer


        Not much to go on Fred. Have you done the hydrogeologic work up of the
        area? Have you done the aquifer testing? If not, hire a professional
        with experience, http://home.att.net/~dodonnell/odonnell.html

        If you have done the above and still don't know what to do, best of luck
        to your client...dod

        Frederic Ghogomu wrote:
        >
        > Hi everyone,
        > I am working on a project where I have to quantify
        > water that can be pumped from an unsaturated aquifer.
        > I am using FRAC3DVS. This model gives an option where
        > you can place pumping well with specified rate. But
        > the aim of our study is to determine this rate. I will
        > apreciate any advice on the procedure to use or how to
        > handle this problem.
        > Thanks
        >
        > Fred Ghogomu
        >
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      • tcudzilo
        I am troubled by Fred s approach and agree with Daniel that a basic hydrogeologic understanding is essential BEFORE modeling. The wording of the original
        Message 3 of 6 , Jul 1 4:37 PM
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          I am troubled by Fred's approach and agree with Daniel that a basic
          hydrogeologic understanding is essential BEFORE modeling. The wording
          of the original question suggested little if any hydrogeologic
          information was available.

          --- In gwmodel@y..., Frederic Ghogomu <fred_ghogomu@y...> wrote:

          > I am working on a project where I have to quantify
          > water that can be pumped from an unsaturated aquifer.

          I don't know if this statement concerns anyone else, but an aquifer
          by definition is saturated. How can an aquifer be unsaturated? If one
          were to accept a definition allowing for a portion to be unsaturated,
          there would not be one value of hydraulic conductivity; there would
          instead be characteristic curves for conductivity determined by
          wetting or drying conditions.

          > I am using FRAC3DVS. This model gives an option where
          > you can place pumping well with specified rate. But
          > the aim of our study is to determine this rate. >
          Are there any wells in this aquifer? How deep are they? Are they
          completed in the same kind of material as the proposed well? Will the
          well fully penetrate the aquifer?
          If this aquifer is "unsaturated", what portion of it is saturated and
          do those conditions change with seasons? Are there barriers to flow
          that could affect production? Are there surface water bodies that
          could affect or be affected by production?



          __________________________________________________
        • George Matanga
          I agree with Tom. A conceptual model needs to be constructed. FRAC3DVS is a finite-element variably-saturated flow and transport model. MODFLOW approach will
          Message 4 of 6 , Jul 2 10:07 AM
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            I agree with Tom. A conceptual model needs to be constructed. FRAC3DVS
            is a finite-element variably-saturated flow and transport model. MODFLOW
            approach will not work for this model. Unfortunately these days,
            groundwater modeling implies applying MODFLOW. There are other types of
            models besides MODFLOW. In FRAC3DVS, a well can be screened such that
            the screen interesects both saturated and unsaturated zones. Obviously,
            the saturated zone will contribute most of the well discharge.

            It is essential that prior to model selection, one develops a
            conceptual model. A conceptual model will lead to a thorough
            understanding of hydrogeology, data gaps, processes taking place in the
            flow domain, boundary and initial conditions, etc. Armed with a
            conceptual model, one can then select an appropriate model. This
            approach will lead to application of appropriate models and reliability
            of model results. ASTM has good standards for application of groundwater
            models.

            If FRAC3DVS is approriate, there is a need to acquire a thorough
            understanding of the physical problem and the model.



            >>> tcudzilo@... 07/01/02 04:37PM >>>
            I am troubled by Fred's approach and agree with Daniel that a basic
            hydrogeologic understanding is essential BEFORE modeling. The wording
            of the original question suggested little if any hydrogeologic
            information was available.

            --- In gwmodel@y..., Frederic Ghogomu <fred_ghogomu@y...> wrote:

            > I am working on a project where I have to quantify
            > water that can be pumped from an unsaturated aquifer.

            I don't know if this statement concerns anyone else, but an aquifer
            by definition is saturated. How can an aquifer be unsaturated? If one
            were to accept a definition allowing for a portion to be unsaturated,
            there would not be one value of hydraulic conductivity; there would
            instead be characteristic curves for conductivity determined by
            wetting or drying conditions.

            > I am using FRAC3DVS. This model gives an option where
            > you can place pumping well with specified rate. But
            > the aim of our study is to determine this rate. >
            Are there any wells in this aquifer? How deep are they? Are they
            completed in the same kind of material as the proposed well? Will the
            well fully penetrate the aquifer?
            If this aquifer is "unsaturated", what portion of it is saturated and
            do those conditions change with seasons? Are there barriers to flow
            that could affect production? Are there surface water bodies that
            could affect or be affected by production?



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