Module Valley Depth
Valley depth is calculated here  vertical distance to a channel network base level. The algorithm consists of two major steps:
 1. Interpolation of a channel network base level elevation
 2. Subtraction of this base level from the original elevations
- Author: O.Conrad (c) 2012
 
- Specification: grid
 
- Menu: Terrain Analysis|Channels
 
Parameters
|   | Name | Type | Identifier | Description | Constraints | 
| Input | Elevation | Grid (input) | ELEVATION | - | - | 
| Output | Valley Depth | Grid (output) | VALLEY_DEPTH | - | - | 
 | Ridge Level (*) | Grid (optional output) | RIDGE_LEVEL | - | - | 
| Options | Tension Threshold [Percentage of Cell Size] | Floating point | THRESHOLD | - | Minimum: 0.000000 Default: 1.000000 | 
 | Keep Ridge Level above Surface | Boolean | NOUNDERGROUND | - | Default: 1 | 
 | Ridge Detection Threshold | Integer | ORDER | - | Minimum: 1 Maximum: 7 Default: 4 | 
| (*) optional | 
Command-line
Usage: saga_cmd ta_channels 7 -ELEVATION <str> [-VALLEY_DEPTH <str>] [-RIDGE_LEVEL <str>] [-THRESHOLD <str>] [-NOUNDERGROUND <str>] [-ORDER <num>]
  -ELEVATION:<str>    	Elevation
	Grid (input)
  -VALLEY_DEPTH:<str> 	Valley Depth
	Grid (output)
  -RIDGE_LEVEL:<str>  	Ridge Level
	Grid (optional output)
  -THRESHOLD:<str>    	Tension Threshold [Percentage of Cell Size]
	Floating point
	Minimum: 0.000000
	Default: 1.000000
  -NOUNDERGROUND:<str>	Keep Ridge Level above Surface
	Boolean
	Default: 1
  -ORDER:<num>        	Ridge Detection Threshold
	Integer
	Minimum: 1
	Maximum: 7
	Default: 4