Computing a Drawdown Surface

RockWorks | Utilities | Hydrology | Drawdown Surface

This program is used to generate a potentiometric surface model based on pumping and/or injection wells using the Theis non-equilibrium equation. Data for multiple wells is read from the main datasheet. Fixed or varying saturated thickness and/or transmissivity measurements are allowed. The resulting surface can be displayed as a 2D map or 3D surface.

Menu Options
Step-by-Step Summary

Rules & Filters
Use the buttons at the top of the window to apply spatial filters, time/date filters, or stratigraphic rules to data being displayed in your map or diagram. (More info)
3D Log Design
If you decide to include logs with the 3D surface diagram ("Striplogs" setting, below), click on this button at the top of the window to set up how you want the 3D logs to look.
See Visible Item Summary and Using the 3D Log Designer for details.
Anisotropy: Click this tab to select the type of drawdown model to be created and the input columns.
- Model Type
  - Constant: Choose this option to assign a constant transmissivity value and saturated thickness for all wells.
  - Isotropic: Choose this option if you have pumping duration, transmissivity, storativity, and saturated thickness values listed in the datasheet; they can vary from well to well.
  - Anisotropic: Choose this option if you have pumping duration, X transmissivity, Y transmissivity, storativity, and saturated thickness values listed in the datasheet.
- Data Columns: Use these prompts to specify the names of the columns in the current datasheet that contain the calculation parameters:
  - X (Easting): Click on this item to select the column in the datasheet that contains the X-coordinates for the wells.
    Be sure you define your coordinate system and units for all columns except Storativity and Duraton.
  - Y (Northing): Click on this item to select the column in the datasheet that contains the Y-coordinates for the wells.
  - Elevation: Click on this item to select the column that contains the well's pre-pump water elevation.
  - Pumping Rate: Select the column in the datasheet that contains the pumping rates for the wells. Specify your units in gallons (Imperial units) or liters (metric units) per minute in the datasheet. Note: If the well is an injection well, the rate can be entered as a negative value.
  - Well Radius: Select the column that contains the well radius measurements.
  - The next set of variables will differ, depending on the model type you have selected.
    - Model Type = Constant
      - Storativity: Type in the storativity for all wells.
      - Duration: Type in the number of days that pumping/injection occurred. Note: Decimal days (e.g. 0.5 = 12 hours) are acceptable.
      - Imperial Units: Choose this option if your input units are in feet and gallons.
        
        Saturated Thickness: Enter the saturated thickness in feet.
        
        X-Transmissivity: Enter the gallons per day per foot transmissivity for the east-west axis.
        
        Y-Transmissivity: Enter the gallons per day per foot transmissivity for the north-south axis.
      - Metric Units: Choose this option if your input units are in meters and square meters.
        
        Saturated Thickness: Enter the saturated thickness in meters.
        
        X-Transmissivity: Enter the square meters per day transmissivity for the east-west axis.
        
        Y-Transmissivity: Enter the gallons per day per foot transmissivity for the north-south axis.
    - Model Type = Isotropic or Anisotropic
      - Storativity: Choose the column in the datasheet that contains the storativity values.
      - Saturated Thickness: Select the column in the datasheet that contains the saturated thickness measurements. Required: Units in feet or meters.
      - Duration: Click here to select the column that contains the pumping duration. Required: Units in days. Note: Decimal days (e.g. 0.5 = 12 hours) are acceptable.
      - Transmissivity: These prompts will differ depending on your model type.
        
        Isotropic Model
        
        Transmissivity: Click on this item to select the column that contains the transmissivity values. Required. Units are entered in gallons per day per foot (Imperial units) or square meters per day (metric units).
        
        Anisotropic Model
        
        X-Transmissivity: Select the column in the datasheet that contains the transmissivity values for the X axis. Required. Units are entered in gallons per day per foot (Imperial units) or square meters per day (metric units).
        
        Y-Transmissivity: Select the column that contains the transmissivity values for the X axis. Required. Units are entered in gallons per day per foot (Imperial units) or square meters per day (metric units).
Grid Name: Click to the right to type in the name to assign to the grid model (.RwGrd file) that the program will create, containing the model of the drawdown surface.
Grid Dimensions: Click this tab to establish the drawdown grid's dimensions. You will see the current project dimensions displayed here. In general, the larger the number of grid cells (the "finer" the grid), the smoother the resulting map, but the slower the processing. Similarly, a smaller the number of grid cells will enhance the program’s speed but will produce a more discontinuous map.
2D Grid Map
Check this box to display the output grid as a 2D map at this time.
Click this tab to set up the 2D map layers (bitmap, symbols, labels, line contours, color-filled contours, labeled cells, map border, etc.).
3D Grid Diagram
Check this box to display the output grid as a 3D surface at this time.
Click this tab to set up the 3D map layers (surface colors, images, reference cage, etc.).
! You can request both a 2D and 3D representation of the grid model.

Access the RockWorks Datasheet program tab.
Create a new datasheet and enter or import your drawdown data.
Or, open one of the sample files and replace that data with your own. See Data Layout for datasheet examples.
! Click the Example button at the top of the window to load a sample file that is installed with the program.
Select the Utilities | Hydrology | Drawdown Surface menu option.
Enter the requested menu items, described above.
Click the Continue button to proceed.

The program will computed the drawdown grid model, reading the source data from the current spreadsheet, and using the requested grid dimensions. The model will be saved on disk under the file name you specified.

The program will read the completed drawdown grid model and, if requested, create a 2- or 3-dimensional image representing the grid model. The requested diagram(s) will be displayed in a RockPlot2D tab and/or RockPlot3D tab in the Options window.
View / save / manipulate / print / export the map in the RockPlot2D or RockPlot3D window.

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