The HOB: Head Observation package pane is on the MODFLOW Features tab of the Object Properties dialog box. All cells intersected by the object will be part of the observation.
The data that can be specified for the Head observation package include the Observation Name, the method used to print the observations, the observed heads and their corresponding times and the data on how the simulated head should be calculated for multilayer head observations.
The Observation Name is used to identify the observation in the printout of the observation results. Only ASCII characters are allowed in Observation Name.
The Observation type determines whether a particular observation will be used in a simulation. The observation will only be used if the Observation type of the observation matches the Observation type of the model.
ITT is used to specify how the observed heads will be analyzed. If ITT equals 1, all the observed heads will be analyzed in the same way they were specified. If ITT equals 2, the first head will be analyzed as a head. For the remaining heads, the observed head will be subtracted from the first observed head to give an observed drawdown. Regardless of which choice is selected, however, the observations are always specified as heads, not as drawdowns.
If more than one head was observed at a particular location, the user specifies the Time and the Observed Head for each observation. The Observed Head is always a head (not a drawdown) even if ITT is set to 2.
For a multilayer head observation, specify the Higher Z-coordinate and Lower Z-coordinate to the top and bottom elevation of the well screen.
For multilayer observations, the simulated head is calculated using a weighted average of the heads in all the layers making up the multilayer observation. The user can specify the weights used in the calculation. If the weights do not add up to 1, ModelMuse will scale them so that they do add up to 1 in the MODFLOW input file. If no weights are specified for a multilayer observation, the heads in all the layers will be weighted equally. However, specifying a weight for a layer does not make that layer part of the multilayer observation. Instead, the cells that are part of the multilayer observation are those that are intersected by the object.
For each observation you must specify the observation time and the observed head. If you want to use UCODE for automated parameter estimation, you will also need to specify the Statistic and StatFlag. The observed time for steady-state stress periods should be at the end of the stress period. The Statistic and StatFlag are used to calculate the weight applied to each observation. The statistic should represent the uncertainty with regard to the observation in question.
See: HOB: Head Observation package.
See also: Manage Head Observations dialog box.
