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Define Observations

 

At the Define Observations step, you can define and edit observation data that can be used to compare your model to historical/expected values for various model outputs and evaluate your model results. The following types of observations can be added to a numerical model:

Well Observations: heads or concentrations

Boundary Obs: net volumetric flow exchange between the groundwater domain and a specified boundary condition

Zone Budget Obs: net volumetric flow exchange of groundwater

oin/out of a specified zone,

obetween a specified zone and another zone, or

obetween a specified zone and specified boundary condition type

Surface Water Flow Obs: observations defined in the Surface Water Workflow:

oStream (SFR): stage, depth, outflow, head difference between stream midpoint and associated groundwater cell centroid, flow diverted (diversion segments only), groundwater head, streambed seepage through the unsaturated zone

oLakes (LAK): stage, volume, inflow, outflow

 

Following a successful model run, assigned observations can be compared to simulated values to facilitate model evaluations including history matching/calibration.

 

 

Toolbar

Observations can be defined at the Define Observation step by selecting the type of observation to be defined under the toolbox and selecting the assign option:

Under the Toolbox, use the combo box to select from the various Observation types:
 

oWell Observation

oBoundary Obs

oZone Budget Obs

oSurface Water Obs

 

Then use the Assign button to assign the appropriate object type (described below) defining the observation location.

 

Well Observations

Well observations include groundwater data collected from wells and piezometers and consist of four components:

Location: x- and y-coordinates of the sampling point

Elevation: the elevation at which the observation occurred. For monitoring wells, this is typically the midpoint elevation of the screen. For piezometers, this is typically the elevation of the open-ended bottom of the piezometer.

Time: the time as an absolute date/time or more commonly as elapsed time relative to the model start date

Value: the value of the observation:

oHead: the hydraulic head measured in the well or piezometer as top of casing elevation minus depth to water

oConcentration: solute concentration of the specified species (note that an extra field must be present to define the species)

 

Prerequisites

To define well observations, you must first have a well data object in the Data Explorer with observation data. You can either import the well observation data or create a new well data object and then add/edit the observation data. The "raw" observation well data can be viewed/edited in the Well Data section.

All other boundary conditions can be fully defined at the Define Observations step; however, you may find that using an imported Time Schedule object in the Data Explorer makes the process significantly more efficient.

 

Assigning the Well Observations

Once you have imported or created a Well observation data object with heads or concentrations, navigate to the Define Observations step in the numerical model workflow. Below the toolbox, select Well Observation and select Assign > using data object.  The Create/Add Well Observations dialog will appear:

 

The Create/Add Well Observations dialog contains two controls:

The assign button (): allows you to specify a well data object with observations in the Data Explorer

The radio button allows you to specify which observation group the well observation object will be added to in the model tree.

 

The observation wells should then appear a new node on the numerical model tree on the Model Explorer and any observation well points located in the active layer, row, or column will be also be displayed in the appropriate view(s).

Please Note: If you add Observations that are defined in Absolute times and if some or all of the observation times occur before the model start date defined in the modeling objectives, then you will receive a warning message during creation.  These head/concentration observations cannot be included in the numerical model and will be filtered out.

 

Specifying a Well Observation Group

You will be prompted with a choice to append the observations to an existing well group or create a new well group. Well groups can be used to group observation data into logical sets of data based on a meaningful criteria that may facilitate model calibration, analysis, or evaluation.  For example you may wish to group observations by watershed, hydrostratigraphic unit/zone, land use, or property type.

 

Viewing and Editing Well Observations in CSV Format

Once defined, head or concentration observation data can be viewed/modified in a CSV format:

Right-click on the Head (or Concentration) Observations node from the Model explorer

Select "Edit Attributes..." as shown below.

 

 

The data contained inside the Observations data object will be displayed in a .CSV file; this should appear in either Notepad or Excel depending on your system configuration; an example is below:

 

You can use this interface for numerous types of edits/additions:

Adding a new observation point at a defined XY location

Change existing data

Add a new observation time to an existing observation point.

 

Please Note: the Layer number for the observation point is calculated based on the Obs. Elev; changing the layer number will not change the vertical location of the observation point.

 

When you are finished with the edits in the .CSV file, you need to save and close this file.  Then re-import back the changes into Visual MODFLOW Flex using the steps below:

Right-click on the Head (or Concentration) Observations node from the Model explorer

Select "Reload Attributes..."

 

The modified data will now appear and will be utilized for any charts the next time you translate and run the model.

 

Defining Boundary Condition Observations

Visual MODFLOW Flex allows you to define observations of net volumetric flows between a specific boundary condition (and its associated collection of cells) and the groundwater flow domain.

 

Assign Boundary Condition Observations

To define a boundary condition observation data set:

At the Define Observations step, select the Boundary Obs option in the toolbox

Click Assign > Using data object...

The Explorer object select will appear
 

 

Select a specific boundary condition object in the Model Explorer (e.g. select "Constant Heads 1" under the Model Explorer tree: Grid > Run > Boundary Conditions > Constant Heads > Constant Heads 1) and use the assign button () to add that boundary condition object

Click OK and the Gage Editor window will be displayed allowing you to define the observations

 

Boundary Condition Observation Types

The gage editor window includes two parts, the left side includes controls to define the observations themselves (i.e. time of observation and the data observed) as described below. In the case of boundary conditions, the only observation type supported is the (net) volumetric flow rate between the groundwater system and the specified boundary condition. By MODFLOW convention, positive values indicate the net flow is from the boundary condition into the groundwater flow system and negative values indicate the direction of flow is from the groundwater system to the specified boundary condition. For example a extractive pumping well and evapotranspiration  boundary conditions should produce negative values, while an injection well should produce positive values.

 

Boundary Condition Observation Spatial Representation

For boundary condition observations, the right side of the gage editor includes the collection of cells associated with the selected boundary condition.  You may use the checkboxes and toolbar buttons to toggle which cells associated with the specified boundary condition are included in the observation. The corresponding simulated value will be calculated base on the total net groundwater flow between the groundwater flow cells and the selected boundary condition using information from the output budget file. By MODFLOW convention observations By default, all cells associated with the boundary condition are included.

 

Please Note: if the specified collection of cells includes other boundary conditions of the same type, then the affects of these other boundary conditions will be included in the observation as the output budget file produced by versions of MODFLOW lump flow terms for boundary conditions of the same type.

 

Defining Zone Observations

Visual MODFLOW Flex allows you to define observations of net volumetric flows using ZoneBudget zones.

 

Assign ZoneBudget Observations

To define a boundary condition observation data set:

At the Define Observations step, select the Zone Budget Obs option in the toolbox

Click Assign > Using data object...

The Gage Editor window will be displayed allowing you to define the observations

 

Zone Budget Observation Types

The gage editor window includes two parts, the left side includes controls to define the observations themselves (i.e. time of observation and the data observed) as described below. In the case of Zone Budget zone observations, the only observation type supported is the (net) volumetric flow rate. By MODFLOW convention, positive values indicate the net flow is into the groundwater domain of the specified  ZoneBudget zone.

 

Zone Budget Observation Spatial Representation

The right side of the Gage Editor includes the spatial definition of the observation.  For ZoneBudget zone observations, the right side of the gage editor includes two dropdown selectors:

Selected Zone (From): The "from" zone selection allows you to specify the zone where groundwater flows are to be observed.

Selected Zone (To): The "to" zone selection (shown in red) is optional and allows you to specify a different ZoneBudget zone or a boundary condition type present in the model.  If not selected, then the net groundwater flows to all adjacent zone budget zones will be observed.
 

 

Defining Surface Water Observations

Visual MODFLOW Flex allows you to define observations of various types of data observed in streams and lakes developed in the Surface Water Workflow.

 

Assign Surface Water Observations

To define a boundary condition observation data set:

At the Define Observations step, select the Surface Water Obs option in the toolbox

Click Assign > Using data object...

The Surface Water Workflow will open allowing you to create stream reach and lake observation gages using the surface water network tools.

Once a gage has been created, you can add/edit observation data using the surface water gage editor window.

 

Gage Editor

The gage editor includes several controls allowing you to define and edit observations. The left side of the panel allows you to define the observations (e.g. time, value, and target residual) while the right side of the panel allows you to define the spatial scope over which the observation(s) apply (e.g. the collection of cells where the volumetric flow is to be measured).

 

 

Observation Schedule

The left side of the Gage Editor dialog includes the following controls for all supported types of observations (boundary conditions, zone budget zones, stream, and lake gages):

 

Gage Type: allows you to select the type of observation to be measured and associated project units. The stream and lake gages support a variety of observation types as described above and the remaining gages/observation types are limited to volumetric observations.  Note that well observations are handled separately using well objects (see above).

 

Toolbars: the gage toolbars include the following buttons:

o Add interval: adds an observation time at the end of the table

o Insert interval after selection: adds an observation time after the selected row

o Delete selected row(s): deletes selected row(s) from the table

o Clear sort: clears the sort order (if any) on fields in the observation table

o Expression builder: opens the Expression builder

o Assign to column: evaluates the Expression for all cells in the current column

o Assign to current cell: evaluates the Expression for all selected cells in the current column (press and hold SHIFT or CTRL buttons with left mouse clicks to select multiple cells)

 

Table: the table in the left hand side of Gage Editor includes three fields:

oTime: elapsed time relative to the model start date

oValue: the value of the observation. Note that positive flow values for volumetric observations follow the standard MODFLOW convention that positive values indicate flow into the groundwater flow system

oTarget Residual: the target difference between observed values and simulated results (based on project goals, stakeholder input).

 

Load Schedule Object: Selecting this option will allow you to load the data from a time schedule object in the Data Explorer and map fields from the schedule object (using the dropdown selectors) to the value and target residual fields.
 

 

Observation spatial scope

With the exception of certain stream and lake observations, the observation types apply generally apply over a defined area rather than at a discrete point.  As such, the right side of the panel is used to define the spatial extent/scope of the observations that will be used for extracting simulated equivalent values to be compared to the observations. Since the various observation types have differing contexts, the applicable interface is dependent on the type of observation:

Boundary Condition: allows you to define a specific boundary condition for observations

Zone Budget Zone: allows you to define the primary zone from which flows may be leaving (or entering) and (an optional) secondary zone or boundary condition type to which flows are entering.

Steam: allows you to define a stream reach for observations (via the gage package)

Lake: allows you to define a specific lake for observations (via the gage package)

 

Script

The Script tab allows you to quickly add or modify data based on a script. If you are interested in using the script, try to define a simple gage to observe the structure and add complexity.  An example is shown below:

 

The header defines the type of observation and (other than the name, which should be wrapped in "quotes") should not be edited.

The Observation Scope section defines which objects are associated with the observation gage.

The Location section defines where the observation will be rendered in views when displaying residuals

The Observation Type defines which observation data are used. You can specify more than one Observation Type block

The Observation Data includes the set of times, observations, and target residuals for the time above.

 

Similar to a macro builder, any edits you make on the Edit tab will be reflected at the Script tab. In this way you can experiment with the Gage Editor and learn to build your own scripts.

 

 


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