ETS: Evapotranspiration Segments Package Pane

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The ETS: Evapotranspiration Segments package pane is on the MODFLOW Features tab of the Object Properties dialog box.

The data that can be specified for the Evapotranspiration Segments package are the Starting time, Ending time, Evapotranspiration rate, Evapotranspiration surface, Evapotranspiration depth, several copies of Fractional rate[i] and Fractional depth[i] and sometimes Evapotranspiration layer. Whether or not Evapotranspiration layer is present depends on the choice of return location in the ETS: Evapotranspiration Segments package pane of the MODFLOW Packages and Programs dialog box. If Specified layer was selected on the ETS: Evapotranspiration Segments package pane but Time varying ETS layers was not selected, the layer at any location will be determined by the layer of the lowest cell selected by the object at that location. The number of copies of Fractional rate[i] and Fractional depth[i] that are present depends on the Number of segments defined in the ETS: Evapotranspiration Segments package pane of the MODFLOW Packages and Programs dialog box. The number of copies of Fractional rate[i] and Fractional depth[i] will each be one less than the Number of segments.

Of these data, all but Fractional rate[i] and Fractional depth[i] are also present in the Evapotranspiration package and are described in the help for the EVT: Evapotranspiration Package Pane.

Starting time and Ending time are explained in the help for the MODFLOW Features tab.

Fractional depth[i] is a proportion of the extinction depth (dimensionless), measured downward from the ET surface, which, with Fractional rate[i], defines the shape of the relation between the evapotranspiration rate and head. The value of Fractional depth[i] must be between 0.0 and 1.0, inclusive. Repetitions of Fractional depth[i] and Fractional rate[i] are read in sequence such that the first occurrence represents the bottom of the first (uppermost) segment, and subsequent repetitions represent the bottom of successively lower segments. Accordingly, Fractional depth[i] values for later repetitions (representing lower segments) should be greater than Fractional depth[i] values for earlier repetitions.

Fractional rate[i] is a proportion of the maximum evapotranspiration rate (dimensionless) which, with Fractional depth[i], defines the shape of the relation between the evapotranspiration rate and head. The value of Fractional rate[i] should be between 0.0 and 1.0, inclusive. Repetitions of Fractional depth[i] and Fractional rate[i] are read in sequence such that the first occurrence represents the bottom of the first (uppermost) segment, and subsequent repetitions represent the bottoms of successively lower segments. Accordingly, Fractional rate[i] values for later repetitions (representing lower segments) generally would be less than Fractional rate[i] values for earlier repetitions.

If parameters are used with an object, a multiplier for Evapotranspiration rate must be defined for each parameter. MODFLOW will multiply the multiplier by the parameter value (specified in the MODFLOW Packages and Programs dialog box) to determine the evapotranspiration rate to apply.

Time-series interpolation

In MODFLOW 6, time series files can specify the times and values to use for a boundary condition.

When MODFLOW 6 needs data from a time series or time-array series for a time interval representing a time step or subtime step, the series is queried to provide a time-averaged value or array of values for the requested time interval. For each series, the user specifies an interpolation method that determines how the value is assumed to behave between listed times. The interpolation method thus determines how the time averaging is performed. When a time-array series is used, interpolation is performed on an element-by-element basis to generate a 2-D array of interpolated values as needed.

The supported interpolation methods are STEPWISE, LINEAR, and LINEAREND. When the STEPWISE interpolation method is used, the value is assumed to remain constant at the value specified in one time-series record until the time listed in the subsequent record, when the value changes abruptly to the new value. In the LINEAR interpolation method, the value is assumed to change linearly between times listed in sequential records. LINEAREND is like LINEAR, except that instead of using the average value over a time step, the value at the end of a time step is used.

ModelMuse uses time-series interpolation when parameters are used. The parameter value becomes the SFAC (scale factor) in the time-series file.

ModelMuse sets the interpolation method to STEPWISE for all boundary conditions in which it is used except for the CHD package in which it is set to LINEAREND.

ModelMuse does not currently support time-series interpolation because it slows down MODFLOW to much as implemented in ModelMuse. Support for time-series interpolation may be supported in a future version of ModelMuse but in a different form.

hmtoggle_plus1For MODFLOW experts

When parameters are used to assign the EVT, RCH, and ETS boundary conditions, the objects used to define the values of the parameters also define the spatial extent where the parameters apply by assigning the values to a hidden zone array that is used by MODFLOW to determines where each parameter applies.