5441336988

Model Calibration

Process of evaluating initial and boundary conditions and aąuifer hydraulic properties to verify that the model can reproduce measured heads or fluxes

-    There is a package in GMS capable of performing inverse modeling, but it is not available under the present UT liscense.

Inverse modeling is the process of adjusting model inputs until the optimum set of inputs are determined for a partiticular condition.

-    The inputs are optimized by comparing the residuals computed using a number of pairs of predicted and measured values.

Residuals are usually computed by sąuaring the differences between the predicted and measured values so that positive and negative residuals do not produce a false optimum.

After a model is calibrated, then the model can be used to simulate other conditions.

Conducting a Sensitivity Analysis for a Ground-Water Flow Model Application (D 5611 - 94)

-    used to calculate the sensitivity of a system when evaluating a model for initial and

boundary conditions and for aąuifer hydraulic properties

-    used to calculate the sensitivity with respect to a futurę prediction Process

Identify inputs to be varied Identify variations of the inputes Perform simulations

Compare predicted values with measured values Calculate residuals

Determine sensitivity type (Type I, II, III, IV)

Type I sensitivity occurs whtn variation of an input causes insignificant changes in the residuals as well as the modePs conclusions. Type I senstitivity is of no concern because, regardless of the value of the input, the conclusion will remain the same.

6-4