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Uses of Modeling

A model designed to represent reality and predict the effects of changes to a groundwater system, allowing for estimation of certain aspects, determination of causes, and analysis of observed conditions.

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Uses of Modeling

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  1. A model is designed to represent reality in such a way that the modeler can do one of several things: Quickly estimate certain aspects of a system (screening models, analytical solutions, ‘back of the envelope’ calculations) Determine the causes of an observed condition (flow direction, contamination, subsidence, flooding) Predict the effects of changes to a system (pumping, remediation, development, waste disposal) Uses of Modeling

  2. Analytical Models (Exp and ERF functions) 1-D solution, Ogata and Banks (1961) 2-D solution, Wilson and Miller (1978) 3-D solutions, Domenico & Schwartz (1990) Numerical Models (Solved over a grid - FDE) Flow-only models in 3-D (MODFLOW) MODPATH - allows tracking of particles in 2-D placed in flow field produced from MODFLOW Types of Ground Water Flow Models

  3. MODFLOW is a modular 3-D finite-difference flow code developed by the U.S. Geological Survey to simulate saturated flow through a layered porous media. The PDE solved is for h(x,y,z,t): where Kxx, Kyy, and Kzz are defined as the hydraulic conductivity along the x, y, and z coordinate axis, h represents the potentiometric head, W is the volumetric flux per unit volume being pumped, Ss is the specific storage of the porous material and t is time. GROUNDWATER FLOW GENERAL EQUATION

  4. Problem identification and description Model conceptualization Data Model development Model calibration & parameter estimation Model verification & sensitivity analysis Model Documentation Model application Present results MODEL PROCESS • Problem identification • Important elements to be modeled • Relations and interactions between them • Degree of accuracy • Conceptualization and development • Mathematical description • Type of model • Numerical method - computer code • Grid, boundary & initial conditions • Calibration • Estimate model parameters • Model outputs compared with actual outputs • Parameters adjusted until the values agree • Verification • Independent set of input data used • Results compared with measured outputs

  5. Starting New Model

  6. Importing a site map Marking Inactive cells

  7. Assign Boundary Constant Heads (East 2-3 m West (0 m) North & South inactive cells

  8. Assign Recharge Start from GIS

  9. Importing Wells (Agricultural, Domestic and Observation

  10. Running the Model Head output

  11. Model Calibration Through Calibration, a revision for the recharge by changing the rate and running the model until Observed values almost equal to Calculated values

  12. Results: Head, Velocity, Drawdown, etc.

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