Tool Flow Accumulation (Top-Down)

Top-down processing of cells for calculation of flow accumulation and related parameters. This set of algorithms processes a DEM downwards from the highest to the lowest cell.

Flow routing methods provided by this tool:

Deterministic 8 (aka D8, O'Callaghan & Mark 1984)
Braunschweiger Reliefmodell (Bauer et al. 1985)
Rho 8 (Fairfield & Leymarie 1991)
Multiple Flow Direction (Freeman 1991, Quinn et al. 1991)
Deterministic Infinity (Tarboton 1997)
Triangular Multiple Flow Direction (Seibert & McGlynn 2007
Multiple Flow Direction based on Maximum Downslope Gradient (Qin et al. 2011)

References

Bauer, J., Rohdenburg, H. & Bork, H.-R. (1985): Ein Digitales Reliefmodell als Vorraussetzung fuer ein deterministisches Modell der Wasser- und Stoff-Fluesse. Landschaftsgenese und Landschaftsoekologie, H.10, p.1-15.
Fairfield, J. & Leymarie, P. (1991): Drainage networks from grid digital elevation models. Water Resources Research, 27:709-717.
Freeman, G.T. (1991): Calculating catchment area with divergent flow based on a regular grid. Computers and Geosciences, 17:413-22. ScienceDirect.
O'Callaghan, J.F. & Mark, D.M. (1984): The extraction of drainage networks from digital elevation data. Computer Vision, Graphics and Image Processing, 28:323-344. ScienceDirect.
Qin, C. Z., Zhu, A. X., Pei, T., Li, B. L., Scholten, T., Behrens, T. & Zhou, C. H. (2011): An approach to computing topographic wetness index based on maximum downslope gradient. Precision Agriculture, 12(1), 32-43. ResearchGate.
Quinn, P.F., Beven, K.J., Chevallier, P. & Planchon, O. (1991): The prediction of hillslope flow paths for distributed hydrological modelling using digital terrain models. Hydrological Processes, 5:59-79. ResearchGate.
Seibert, J. & McGlynn, B. (2007): A new triangular multiple flow direction algorithm for computing upslope areas from gridded digital elevation models. Water Resources Research, Vol. 43, W04501,
C++ implementation in SAGA by Thomas Grabs (c) 2007, contact: thomas.grabs@natgeo.su.se, jan.seibert@natgeo.su.se. Wiley.
Tarboton, D.G. (1997): A new method for the determination of flow directions and upslope areas in grid digital elevation models. Water Resources Research, Vol.33, No.2, p.309-319. Wiley.

Author: O.Conrad (c) 2001-2016, Portions by T.Grabs (c) 2010
Menu: Terrain Analysis|Hydrology|Flow Accumulation

Parameters

	Name	Type	Identifier	Description	Constraints
Input	Elevation	Grid (input)	`ELEVATION`	-	-
	Sink Routes (*)	Grid (optional input)	`SINKROUTE`	-	-
	Weights (*)	Grid (optional input)	`WEIGHTS`	-	-
	Input for Mean over Catchment (*)	Grid (optional input)	`VAL_INPUT`	-	-
	Material for Accumulation (*)	Grid (optional input)	`ACCU_MATERIAL`	-	-
	Accumulation Target	Grid (input)	`ACCU_TARGET`	-	-
	Linear Flow Threshold Grid (*)	Grid (optional input)	`LINEAR_VAL`	optional grid providing values to be compared with linear flow threshold instead of flow accumulation	-
	Channel Direction (*)	Grid (optional input)	`LINEAR_DIR`	use this for (linear) flow routing, if the value is a valid direction (0-7 = N, NE, E, SE, S, SW, W, NW)	-
Output	Flow Accumulation	Grid (output)	`FLOW`	-	-
	Mean over Catchment	Grid (output)	`VAL_MEAN`	-	-
	Accumulated Material (*)	Grid (optional output)	`ACCU_TOTAL`	-	-
	Accumulated Material (Left Side) (*)	Grid (optional output)	`ACCU_LEFT`	-	-
	Accumulated Material (Right Side) (*)	Grid (optional output)	`ACCU_RIGHT`	-	-
	Flow Path Length (*)	Grid (optional output)	`FLOW_LENGTH`	average distance that a cell's accumulated flow travelled	-
	Loss through Negative Weights (*)	Grid (optional output)	`WEIGHT_LOSS`	when using weights without support for negative flow: output of the absolute amount of negative flow that occurred	-
Options	Grid system	Grid system	`PARAMETERS_GRID_SYSTEM`	-	-
	Step	Integer	`STEP`	For testing purposes. Only generate flow at cells with step distance (each step row/column).	Minimum: 1 Default: 1
	Flow Accumulation Unit	Choice	`FLOW_UNIT`	-	Available Choices: [0] number of cells [1] cell area Default: 1
	Method	Choice	`METHOD`	-	Available Choices: [0] Deterministic 8 [1] Rho 8 [2] Braunschweiger Reliefmodell [3] Deterministic Infinity [4] Multiple Flow Direction [5] Multiple Triangular Flow Directon [6] Multiple Maximum Downslope Gradient Based Flow Directon Default: 4
	Thresholded Linear Flow	Boolean	`LINEAR_DO`	apply linear flow routing (D8) to all cells, having a flow accumulation greater than the specified threshold	Default: 1
	Linear Flow Threshold	Integer	`LINEAR_MIN`	flow accumulation threshold (cells) for linear flow routing	Minimum: 0 Default: 500
	Convergence	Floating point	`CONVERGENCE`	Convergence factor for Multiple Flow Direction Algorithm (Freeman 1991). Applies also to the Multiple Triangular Flow Directon Algorithm.	Minimum: 0.000000 Default: 1.100000
	Prevent Negative Flow Accumulation	Boolean	`NO_NEGATIVES`	when using weights: do not transport negative flow, set it to zero instead; useful e.g. when accumulating measures of water balance.	Default: 1
(*) optional

Command-line

Usage: saga_cmd ta_hydrology 0 [-ELEVATION <str>] [-SINKROUTE <str>] [-WEIGHTS <str>] [-FLOW <str>] [-VAL_INPUT <str>] [-VAL_MEAN <str>] [-ACCU_MATERIAL <str>] [-ACCU_TARGET <str>] [-ACCU_TOTAL <str>] [-ACCU_LEFT <str>] [-ACCU_RIGHT <str>] [-STEP <num>] [-FLOW_UNIT <str>] [-FLOW_LENGTH <str>] [-LINEAR_VAL <str>] [-LINEAR_DIR <str>] [-WEIGHT_LOSS <str>] [-METHOD <str>] [-LINEAR_DO <str>] [-LINEAR_MIN <num>] [-CONVERGENCE <double>] [-NO_NEGATIVES <str>]
  -ELEVATION:<str>     	Elevation
	Grid (input)
  -SINKROUTE:<str>     	Sink Routes
	Grid (optional input)
  -WEIGHTS:<str>       	Weights
	Grid (optional input)
  -FLOW:<str>          	Flow Accumulation
	Grid (output)
  -VAL_INPUT:<str>     	Input for Mean over Catchment
	Grid (optional input)
  -VAL_MEAN:<str>      	Mean over Catchment
	Grid (output)
  -ACCU_MATERIAL:<str> 	Material for Accumulation
	Grid (optional input)
  -ACCU_TARGET:<str>   	Accumulation Target
	Grid (input)
  -ACCU_TOTAL:<str>    	Accumulated Material
	Grid (optional output)
  -ACCU_LEFT:<str>     	Accumulated Material (Left Side)
	Grid (optional output)
  -ACCU_RIGHT:<str>    	Accumulated Material (Right Side)
	Grid (optional output)
  -STEP:<num>          	Step
	Integer
	Minimum: 1
	Default: 1
  -FLOW_UNIT:<str>     	Flow Accumulation Unit
	Choice
	Available Choices:
	[0] number of cells
	[1] cell area
	Default: 1
  -FLOW_LENGTH:<str>   	Flow Path Length
	Grid (optional output)
  -LINEAR_VAL:<str>    	Linear Flow Threshold Grid
	Grid (optional input)
  -LINEAR_DIR:<str>    	Channel Direction
	Grid (optional input)
  -WEIGHT_LOSS:<str>   	Loss through Negative Weights
	Grid (optional output)
  -METHOD:<str>        	Method
	Choice
	Available Choices:
	[0] Deterministic 8
	[1] Rho 8
	[2] Braunschweiger Reliefmodell
	[3] Deterministic Infinity
	[4] Multiple Flow Direction
	[5] Multiple Triangular Flow Directon
	[6] Multiple Maximum Downslope Gradient Based Flow Directon
	Default: 4
  -LINEAR_DO:<str>     	Thresholded Linear Flow
	Boolean
	Default: 1
  -LINEAR_MIN:<num>    	Linear Flow Threshold
	Integer
	Minimum: 0
	Default: 500
  -CONVERGENCE:<double>	Convergence
	Floating point
	Minimum: 0.000000
	Default: 1.100000
  -NO_NEGATIVES:<str>  	Prevent Negative Flow Accumulation
	Boolean
	Default: 1