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.