The user defines the channel that is the main valley bottom channel draining all discharge to the watershed’s base level. The user also specifies the point at which the main valley bottom channel makes its transition from a lower gradient (<0.04) channel type to a steeper gradient (>0.04) channel type. The Select Main Channel button becomes active after the user has selected the GeoFluv Boundary polyline.
Command Prompt
Select main valley bottom channel polyline. Select objects: The
user moves the cursor to cross the main valley bottom channel
polyline anywhere along its length and left-clicks to define the
main valley bottom channel to GeoFluv™.
When executed correctly, the command prompt reads, “Choose the forced transition point between channel types. (Press Enter to find automatically.)” if the cursor has covered and left-clicked a closed polyline. The user then either specifies the forced transition point between channel types (reaches with >-0.04 and <-0.04 slope) by placing the cursor crosshairs on the valley bottom polyline and left-clicking, or presses enter to allow GeoFluv to find a transition point based on the Pre-Disturbed Surface file elevations.
Command Prompt:
Choose the forced transition point between channel types: The user
moves the cursor crosshairs to the point at which he wants the main
valley bottom channel to transition to its steeper (A/Aa+ type)
reach and left-clicks to select that point. Alternately, the user
can press the Enter key and GeoFluv will determine a transition
point using the Pre-disturbed file data. When executed correctly,
the main channel length and drainage density for that channel in
the entire GeoFluv Boundary area are calculated and displayed in
the “Data for main channel:” fields and the reads, “Main channel
has been accepted.” GeoFluv will compare this drainage density to
the target value in Settings and, will highlight the value in red
if it is too low or will highlight the value in green if it is
within the acceptable range. If the value is too low, the user can
lengthen the main channel, decrease the GeoFluv Boundary area, or
add more channels using the Channels tab's Add button.
The command prompt reads, “Main channel polyline must not be a closed polyline” if the polyline the user selected is closed, and the channel length is not calculated and displayed. The command prompt reads, “Main channel must cross watershed boundary” if the user has clicked on a segment that does not leave the watershed at its base level, and the channel length is not calculated and displayed.