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Re: [hydforum] how steady simulation in modflow

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  • pkm
    Hi Thanks for sending me such useful discussion. For me steady state simulations are the basics to know a system, which sometimes could emerge as a calibration
    Message 1 of 3 , Jan 31, 2007
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      Hi

      Thanks for sending me such useful discussion. For me steady state simulations are the basics to know a system, which sometimes could emerge as a calibration procedure. In the country like India where groundwater exploitation is 70 to 80 percent with varied but continuous usage throughout the year, searching for a steady state condition for simulation is difficult, if not impossible. A modeller's innovative realisation only can help in extracting such informations. I do not believe in unsteady state calibrations in hydrology. I term them as a base case generation, which might be useful for answering some "if or what" type of questions in a typical setup. In a model like MODFLOW, people tend to feel overconfident when a perticular match is good or excellent. There is nothing like that, because a single parameter invariably is a function of more than one stresses. Our calibration should also look in to these stresses. Therefore steady state calibrations are the must, where the parameter becomes function of a single stress, if performed purposefuly. Once we are sure about these behaviours, unsteady simulations are ought to be useful.

      majumdar

      ----- Original Message -----
      From: Wilsnack, Mark
      To: hydforum@yahoogroups.com
      Sent: Wednesday, January 31, 2007 7:40 PM
      Subject: RE: [hydforum] how steady simulation in modflow


      Hebauhyk:

      I've generally used steady state simulations under two sets of
      conditions. First, if you have a system that responds very rapidly to
      stresses that remain nearly constant for a period of time after their
      onset, then a steady state simulation compared to measured system
      responses would be appropriate. Haitjema (1995) provides some
      discussions on identifying these situations. You may also want to have a look at Anderson & Woessner (1992).

      Another reason to simulate steady state is that you're removing storage and the time derivative from the governing PDE. Hence, errors in these terms cannot mask errors in hydraulic conductivity or spatial
      discretization. Calibrating to steady state conditions therefore
      provides another way of verifying these aspects of your model. If you
      want to history match over a long period of time where steady state
      conditions don't exist, you may want to try what we've done in several
      large ground water modeling projects. That is to apply long term average stresses to you model (boundary conditions, recharge, ET, etc.) and ensure that computed system responses at least fall within the range of corresponded measured responses (preferable not too far from the historical average). If you model doesn't pass this test, it would undoubtedly signify that there are problems with either the model or the data.

      Best wishes,
      Mark Wilsnack
      South Florida Water Management District
      ===============================================================

      From: hydforum@yahoogroups.com [mailto:hydforum@yahoogroups.com] On
      Behalf Of hebauhyk
      Sent: Sunday, January 28, 2007 10:42 PM
      To: hydforum@yahoogroups.com
      Subject: [hydforum] how steady simulation in modflow

      hello everyone

      I am a fresh man about using modflow ,I wanna do a steady
      simulation to rectify the parameters of my model ,so ,is there anyone
      could tell me something about it? like why steady simulation ,and how?
      Can steady simulation calibrate the model?and where can i get some
      useful paper or information? thanks !
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