Drain Design Tools
When designing drains, there are several aspects that you will find that are across all the different Drain Design tools. 

The most important feature of the drain design tools that you will find will be the cross section found at the bottom of the screen.  The cross section displays all the ups and downs along the drain surface.

The cross section is made up of three different lines. The Red line is the proposed design that you are currently working on. The Blue line is the existing surface that has been surveyed. The Yellow dotted line is the current design surface, when starting a new design this will be overlapped with the Blue line and when a design is applied it will overlap with the Red line UNLESS a second design is being made on top of that.

Auto-Drains Design
Auto-Drains automatically generates drain paths for wet areas in your field, calculating optimal ditch lines to drain depressions.
Auto-Drains has two tabs:
Create controls the parameters that must be met before drains are applied to the surface.
Edit Drains lets you edit drain paths.
Create
Edit

Create Drains
Line smoothing strength controls sharp turns and the smoothness of drain lines. Move the slider farther right to make the lines rounder, with fewer sharp turns.
Surface smooth strength applies an averaging filter to the field surface to remove bumps and dips without creating a full field earthwork design.
Min. drain length sets the minimum length a drain must have to be displayed on the surface.
Min. depression area sets the minimum surface area a depression must cover before T3RRA software will consider draining it.
Min. depression volume sets the minimum volume a depression must have before a drain is implemented.
Press Add Stop Line to create a black line with large red anchors at each end. Drain lines will not cross this line.
To confirm placement, press Lock Stop Lines, which appears next to Add Stop Line.
Press the white anchor in the center of the lines to create another red anchor so the lines can be adjusted. To add more stop lines, press Add Stop Line again.
A depression is drained only if it meets all minimum length, area, and volume criteria.

Edit Drains
The Existing Drains list contains every drain in the current project.
Select, delete and move drains
Tap a drain in the list to select it; tap again to unselect it. You can select multiple drains.
Delete removes all selected drains. Delete All removes every drain in the list, including unselected drains.
Choose Move Lines to change all drain lines on the surface, as illustrated below. Blue dots along the lines identify points you can move to adjust the path.
Start at the origin point, which can also be moved, and work downhill.
Move the points to adjust the path. The lines automatically adjust to your changes so that they flow off the edge of the surface.
Choose Save Changes to keep the changes, or Discard Changes to restore the original paths.
NOTE: If you adjust a drain line, then make a second adjustment closer to the origin point, the first adjustment reverts to the line’s original state. Auto-drains ALWAYS flow downhill from the point of the last change.
When the drain paths are satisfactory, return to the wizard page. Use Drain Design to set the profiles and cross sections.

Pattern Drain Design
Use this design tool to design many parallel drains at the same time.
Select specific drains in the pattern drain window when you want to delete them.
Delete removes the selected drains; Clear All removes all pattern drains.
Set drain parameters
Set Drain length in the window, or move the red circle on the design map to set it.
Drain Heading specifies the direction in which the drains run, in degrees.
Link or separate the directions
The Padlock button controls how copied drains behave in relation to the original drain.
Locked: Drain Heading and Offset Direction are linked. Adjust either one and the other changes to match.
Unlocked: Set Drain Heading and Offset Direction independently.
Offset Direction specifies the direction in which drain copies are created from the original.
Drain Count sets how many drain copies to add. It does not include the original drain.
Drain Offset (Parallel) sets the distance between the lines of the copies. If the padlock is unlocked, this will not appear in the example until it is manually updated.
Drain Offset (Origin) sets the distance between the origin points of the copies.
Apply and design the profiles
After entering the parameters, press Apply, shown as the pattern drain icon.
When the paths are satisfactory, use Drain Design to design the drains’ profile and cross section.

Manual Drains
Place a manual drain
On a full field elevation surface, place the drain line along the path you want. Tap a white node to create more purple nodes for a nonlinear drain line. For reference, the purple nodes’ elevation height values are shown in the Design parameters.
Press Apply to create the drain path.
Delete drains individually, or use Delete All.
Choose Edit to relocate the drain path.

Drain Design
Prepare the drain paths
Create drain paths in any of these ways:
Survey paths in the Collection wizard step.
Import paths.
Use the Auto drains tool.
Use the Pattern drains tool.
Drain Design lets you choose the slope profile and cross section before “burning” (embedding) drains into the map for implementation.
Create design wizard screen.
Note: When both a surface and a drain exist, design the surface first, then the drain. To edit drain elevation data, return to the Collect wizard step and edit the drain line. Doing so loses the current project designs.
Select a drain to display its depth/elevation profile in the bottom-right plot; you may need to drag the chart up into view. Use AB Reverse so the drain falls from left to right in the profile chart. This makes the slope values positive and adjustments easier.
A negative backslope inverts the drain design, turning a drain path into a road.
Drain design pane and profile.
Note: Positioning and laying out drain paths is not part of Drain Design. Adjust driven drains in the surfacing step, or adjust paths in auto drains/pattern drains.
Choose a fit mode
The three modes for applying drain designs and adjusting the drain path are Linear fit, Best fit and Multi fit.
Linear fit
Linear fit creates one straight plane along the drain path.
Slope sets the installation gradient so water flows in the intended direction.
Offset moves the drain vertically. A positive value raises it, producing fill along the entire drain. A negative value lowers the design height, producing a deeper cut drain.
Linear fit.
Best fit
Best fit adjusts the slope to try to follow the field's natural curve, similarly to multi-fit field design. The source also states: “Cutta Ditch”.
Note: Best-fit in drains is equivalent to Multi-fit in full field design. The naming incongruity comes from an attempt to match the John Deere SWP+ naming conventions. SWP+ is superseded by T3RRA Cutta and T3RRA Ditch.
Min. Slope is the lowest acceptable drain slope gradient.
Max. Slope is the highest acceptable drain slope gradient.
Min. Cut ensures that the design consistently cuts at least the specified amount.
Max. Cut limits the depth of the design cut so it never exceeds the specified maximum.
Best fit.
Multi fit
Multi fit uses both cut and fill to remove problem points of erosion and build-up. It is best suited to maintaining existing drains.
Min. Slope sets the minimum allowable slope gradient.
Max. Slope sets the maximum allowable slope gradient.
Start Elevation is the desired elevation at the beginning of the design (point A). Set it to be greater than, equal to, or less than the set value. The source describes this as adjusting the start elevation to be “no higher or lower than the set value”.
End Elevation is the desired elevation at the final design point (point B). Set it to be greater than, equal to, or less than the set value. The source describes this as ensuring the final elevation is “not higher or lower than the set value”.
Note: Multi fit tries to balance cuts and fills using the start and end elevations. If the design parameters cannot work, the message is “Model is too constrained”.
Multi fit.
General settings
The general settings are available in all drain design modes.
For the definition of Cut/Fill ratio, refer to the appendix. The following settings and buttons are the same in all three Drain Design modes.
Settings shared by all three modes.
Copy To All copies the selected drain's settings to every other drain in the project. Use it to save time when drains need similar parameters.
Backslope (batter) is the gradient of the drain walls. Higher values produce a sharper drop into the drain. Leave the Backslope box unchecked if no backslope is wanted. Enter a negative value to make a road.
Symmetric mirrors the batter design when checked. When unchecked, the batter slope on each side can be adjusted independently.
Lock Backslope is mainly intended for drain lines, not full surfaces. It ignores the surface and creates backslopes to their maximum extent. The drain bottom is always burnt in regardless of surface elevation: for example, offsetting a drain up 5m still burns in a drain bottom whether Lock Backslope is on or off.
Drain Width sets the width of the drain bottom, which is always horizontal. For a defined non-zero bottom cross slope, manually set the implement's cross slope control during the Implementation stage.
Cut/fill ratio compensates for soil compaction characteristics.
Apply All applies every drain in the field, rather than only the selected drain.
Choose on elevation or on design to select the elevation profile used to calculate the designed surface. For example, if one drain needs a different design, first apply the design on elevation to All. Then select that drain from the drop down and apply its different design on design to that drain alone.
Note: Designing on a design continues to lower the drain surface.
Reverse reverses the profile display and the drain direction used for calculations. This affects the design because the software always tries to slope the design from left to right. It is useful when a drain was surveyed from low to high elevation.
Press Apply All (three cogs) to apply all drains at once.
Press Apply (one cog) to apply only the selected drain.
After editing drains in the surveying step, return to the Design wizard step to create a new drain design. If both a surface and a drain exist, design the surface first, then the drain.
Implement or export
Designing and applying a drain embeds (“burns”) it into the field surface model. You can then implement it like a normal field design. With a constant-depth drain cutting implement, you may only need the paths for guidance, not the depth profile or elevation control. In that case, you need not create a drain profile unless you want to examine the drains' effects in the rainfall simulation.
Optionally, use the wizard screen's Export button to export drain paths as an RCD folder structure (JD Guidance lines). Exported ditch track guidance lines can steer the tractor along the correct path to remove wet areas accurately and efficiently; John Deere AutoTrac™ is required.
Watch the video on Drain Design Tools.