The Time Series dialog box is used to specify time series for MODFLOW 6 models. The Time Series dialog box is displayed by selecting "Model|Edit Time Series."
The Time Series dialog box has a tree control on the left. Initially the right side of the dialog box is empty. To define a times series, the modeler first clicks the "Add Group" button. Each time series group is used to specify a series of times and as many associated time series as desired. The modeler can change the number of time series by increasing the value displayed in the "Number of time series" edit box. The user can also delete a time series by selecting a column in the table for a time series and clicking the "Delete time series" button. The user can change the number of times by changing the value displayed in the "Number of times" edit box. The user can also insert or delete times by selecting a row and clicking the "Insert time" or "Delete time" buttons.
A video about this topic is available at https://www.usgs.gov/media/videos/using-modflow-6-times-series-modelmuse.
A time series is an alternative method in MODFLOW 6 for specifying time-varying data. The modeler specifies a series of times along with a corresponding series of values. The times do not need to correspond to the beginning and ending times of any stress period. Instead, MODFLOW will interpolate the values in the time series to determine the value applied to any time step. Three different interpolation methods can be used: STEPWISE, LINEAR, and LINEAREND.
•With STEPWISE, the values change abruptly at each new time and the value that is applied to a time step is a weighted average of the values for a time step.
•With LINEAR, values are interpolated linearly among the times and the value applied to any time step is a weighted average of the values for that time step.
•With LINEAREND, the values are also interpolated linearly but the value applied is the value for the end of the time step.
The times must be in ascending order. The value 3E30 can be used to indicate missing values in a time series.
For example, suppose that the following time series was specified as the well pumping rate in which the time steps each had a length of 1 and the starting time of the first time step was zero.
Time |
Values |
0 |
-1 |
0.5 |
-2 |
2 |
-3 |
If STEPWISE was used, the value applied for the first time step would be ‑1.5 for the first time step and ‑2 for the second time step. If LINEAR was used, the value applied for the first time step would be ‑1.8333 for the first time step and ‑2.6667 for the second time step. If LINEAREND was used, the value applied for the first time step would be ‑2.3333 for the first time step and ‑3 for the second time step.
An example of when STEPWISE might be appropriate would be for a well pumping rate in which the pumping rate is changed abruptly from time to time but in which there is no gradual change. An example of when LINEAR might be appropriate would be for representing seasonal change in the maximum evapotranspiration rate. An example of when LINEAREND might be appropriate would be for a specified head boundary such as a lake where the lake level changes gradually.
Time series can also have a scale factor. MODFLOW will modify all the values in a time series by multiplying them by the scale factor. PEST parameters can be used with time series. The PEST parameter will modify the scale factor for the time series. The scale factor can be a formula for dynamic time series define for an object.
In ModelMuse, certain time varying values can depend on the length or area of intersection of the object with a cell. However, this does not apply when a time series is used. In such cases, the time series is used without modification. Similarly, if a PEST parameter is applied in the Object Properties dialog box, it will not apply to any time series. Instead only PEST parameters in the Time Series Dialog box or the Time Series tab of the Object Properties dialog box will apply to a time series.
