Load the model of lesson 8 (click Lesson 8.fpr)   We will show how to draw 3D flowlines. Before starting with this, we need:a a steady-state model with its heads computed;b a thickness unit with the thicknesses of all aquifers and aquitards;c for each flowline a starting point in 3D space. A starting point requires the x-, y- and z-coordinates of a point somewhere in the model. MicroFEM uses the x- and y-coordinate of the current node. The z-coordinate is given in a different way. The flowline starts in the aquifer indicated by the active cell in the Param Table. There is only one aquifer in our model. We select H1 (T1 or Q1 have the same effect). The z-coordinate also depends on the depth within that aquifer. This has to be specified as a "dimensionless depth". A dimensionless depth of 0 means at the upper boundary of that aquifer, 1 means at the base of that aquifer and 0.5 means right in the middle. A dimensionless depth can be any value on the interval [0 ... 1].   Drawing mode / [Del] / [F2] / Click at a node near (2000, 3000) Select H1 in the Table / [Draw flowlines (F9)] A window appears "Drawing 3-dimensional flowlines". Possible settings are:- Direction: Forward or Backward. Forward is with the flow. Select "Forward".- Save file: Flowline file is the default. The default filename is given near the base: "Lesson 8.#01"- Time step (y) = 10. There will be dots on the flowline indicating travel time steps of 10 years.- Levels = 0.5. A level on the interval [0 ... 1] is the dimensionless depth of the starting point. Set level = 0.- Porosity = 0.3. To compute travel times an (average) value for the porosity is required.- Max time (y) = 0. A maximum travel time can be specified, but here 0 (zero) means: "no time limit".   By selecting Forward and Level = 0 we indicate that we start at the water table and go with the flow. (An alternative way to start at the water table is to select H0; the Level is not required then).   Check that "Forward" is selected and that Levels = 0 / [OK] The 3D flowlines window disappears. A yellow flowline is drawn in the map. When counting the dots, the travel time must be between 50 and 60 years. Zooming is allowed.   [F10] / [F12]     In the map the yellow Profile line is bordered by two parallel red lines. Any 3D flowline between the red lines will be projected on the vertical 2D plane of the Section. In the left (western) part of the Section the same flowline with time steps is displayed in white. Zooming in the Section is also allowed (start with right-click).   [F10] / [F12] / Click a node at the model boundary, just north of the flowline / H1 / [F9] Backward / Time step = 1 / Level = 0.5 / [OK] [F10] / [F12]     The computation of the new flowline starts at a depth of 5 m. The line is computed Upstream. It represents a rain drop that infiltrated some 800 m east of the boundary. Travel time 6 or 7 years. Here are some further details about 3D flowlines: One or more flowlines: Usually there is only one flowline (forward and backward) through one point in 3D space. Wells are an exception. When you start in a well, you can specify any number of flowlines (Lesson 10) Flowlines will start in the current node and ALSO in all nodes with the same label. Flowline files: Information of each flowline is saved in a #nn-file. Each new file has a follow-up number. You can use the [Browse ..] button to specify a different name or number The filenames of flowlines are added to the Drawing components list (Map options). The flowline files are saved. They can be read again with: Main menu / Import / Flowlines. Colour of flowlines: The flowline colour in the map depends on the aquifer: Aquifer 1 = yellow, 2 = blue. These colours can be found and modified in: Options / Map / Colors The colour of a loaded flowline files depends on the Palette colour. The flowline colour in a Section also depends on the Palette colour. Save the model.