The Manage Flow Observations dialog box is used to specify observations of flow at groups of specified-head, drain, general-head boundary, or river cells in MODFLOW. It is also used to specify mass-flux observations in the MT3DMS Transport Observations package. To view the dialog box, select Model|Manage Flow Observations... or click the Add or remove flowobservations button on any of the panes related to flow observations in the Object Properties dialog box. The Manage Flow Observations dialog box is displayed automatically whenever one of the flow observation packages in MODFLOW (CHOB, DROB, GBOB, RVOB, or STOB) or the Transport Observations (TOB) package in MT3DMS is first selected. The dialog box can not be viewed unless at least one of the flow observation packages or the TOB package is selected
For each observation collection, the user must specify
1.the name of the observation location,
2.whether the observation is to be used as an observation, prediction or is inactive. (See Observation Type)
3.the observation times,
4.the observed values,
5.the objects that have been used to specify the related boundary condition,
6.the fraction of the simulated value at any cell to be included in the observation (Factor)
7.the statistic used to define the uncertainty or weight associated with the observation (MODFLOW) or the weight (MT3DMS), and
8.the "StatFlag" identifying the type of statistic (MODFLOW only).
The observation name can only contain ASCII characters.
The statistic and StatFlag are not used by MODFLOW-2005. However, these values may be exported to ModelMate files for use in calibration programs.
In MT3DMS, if [weight_fobs] is assigned a negative value, the observed mass flux at the target massflux object is not used and only the calculated mass flux is saved.
Factor is specified using a formula thus allowing the fraction to vary from cell to cell. In most cases, however, Factor should be set to 1. If only some of the flow cells specified by an object should be part of an observation, it is generally easier to break the object into separate pieces that each are entirely included in the observation than it is to specify Factor correctly.
Flow observations must not be specified for the very first time step of a simulation. In addition, it is generally best to avoid specifying flow observations for the first time step of any stress period especially if the boundary conditions change significantly at the start of the stress period because the simulated flows are likely to be poorly estimated.
Positive values of observed flow represent flow into the aquifer whereas negative values represent flow out of the aquifer. With drain observations only negative flows are expected.
The objects used to specify an observation and the associated factors can also be specified in the Object Properties dialog box.
The Manage Flow Observations dialog box has a tree control on the left each of the selected flow observation packages is listed in the tree control. The individual observation locations can be viewed if the node for one of the flow packages is expanded. New observation locations can be added by clicking the Add button. An observation collection can be deleted by selecting it and clicking the Delete button. When one of the observation locations is selected, the properties of that location will appear in the controls to the right of the tree control. Each observation location has a series of observation times associated with it. For each time, the user must specify an observed value. Each such observation also receives a name that is assigned automatically based on the name that the user assigns to the location. The user can change the number of observations times associated with a an observation location using the control beneath the table where the observation times and values are specified.
To specify the cells for the observation location, the user specifies the objects used to specify the associated boundary in the Objects tab. On the left side of the Objects tab is a list of all the objects that specify a boundary of the appropriate type that are not used to specify the selected flow observation. On the right side is a list of all the objects that are used to specify the selected flow observation. The buttons between the two lists can be used to move the selected objects (single arrows) or all the objects (double arrows) from one list to the other. The direction of the arrows indicates the direction in which the objects will be moved. The user can also select objects in one list and drag them to the other list to move them. If the user selects one or more objects in the list of used objects the Factor edit box beneath the lists becomes enabled and the user will be able to edit the formula used to define the Factor. The user can either type a formula or click the Edit F()... button do display the Formula Editor dialog box.
For either list of objects, you can select one or more of the objects and right-click. A pop-up menu will appear. You use the pop-up menu to select, edit, go to or hide the object in question. You can select multiple objects but you can only edit or go to a single object.
