Tool Name	Flow Path Length
Tool ID	6
Library ID	ta_hydrology
Version	1.0
Author(s)	O.Conrad (c) 2005

Description

This tool calculates the average flow path length starting from the seeds, that are given by the optional 'Seeds' grid and optionally from cells without upslope contributing areas (i.e. summits, ridges). Seeds will be all grid cells, that are not 'no data' values. If seeds are not given, only summits and ridges as given by the flow routing will be taken into account. Available flow routing methods are based on the 'Deterministic 8 (D8)' (Callaghan and Mark 1984) and the 'Multiple Flow Direction (FD8)' (Freeman 1991, Quinn et al. 1991) algorithms.

References

Freeman, G.T. (1991): Calculating catchment area with divergent flow based on a regular grid. Computers and Geosciences, 17:413-22. doi:10.1016/0098-3004(91)90048-I

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. doi:10.1016/S0734-189X(84)80011-0

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. doi:10.1002/hyp.3360050106

Parameters

Name	Type	Identifier	Description	Constraints
Input
Elevation	grid, input	ELEVATION
Seeds	grid, input, optional	SEED
Output
Flow Path Length	grid, output	LENGTH
Options
Seeds Only	boolean	SEEDS_ONLY	Use only seed cells as starting points.	Default: 0
Flow Routing Algorithm	choice	METHOD		Available Choices: [0] Deterministic 8 (D8) [1] Multiple Flow Direction (FD8) Default: 1
Convergence (FD8)	floating point number	CONVERGENCE	Convergence factor for the 'Multiple Flow Direction' algorithm (after Freeman 1991)	Minimum: 0.001000 Default: 1.100000