Length Area Stream Source

Summary

Creates an indicator grid (1,0) that evaluates A >= (M)(L^y) based on upslope path length, D8 contributing area grid inputs, and parameters M and y. This grid indicates likely stream source grid cells. This is an experimental method with theoretical basis in Hack's law which states that for streams L ~ A^0.6. However for hillslopes with parallel flow L ~ A. So a transition from hillslopes to streams may be represented by L ~ A^0.8 suggesting identifying grid cells as stream cells if A > M (L^(1/0.8)).

Usage

Command Prompt Syntax:


					mpiexec -n <number of processes> LengthArea
					-plen <plenfile>
					-ad8 <ad8file>
					-ss <ssfile>
					[-par 0.03 1.3]

Parameters:

plenfile: File name for longest upslope path grid (generally from Gridnet) (input)
ad8file: File name for contributing area file (generally from AreaD8) (input)
ssfile: File name for indicator (1,0) output grid with A >= M L^y. Short. (output)
par: Array of input parameters with p[0] being M coefficient and p[1] being the y exponent on length

Note: The default parameter values of 0.03 and 1.3 are assumed unless -par is specified.

Syntax

LengthAreaStreamSource (Input_Length_Grid, Input_Contributing_Area_Grid, Threshold__M, Exponent__y, Input_Number_of_Processes, Output_Stream_Source_Grid)

Parameter	Explanation	Data Type
Input_Length_Grid	Dialog Reference A grid of the maximum upslope length for each cell. This is calculated as the length of the flow path from the furthest cell that drains to each cell. Length is measured between cell centers taking into account cell size and whether the direction is adjacent or diagonal. It is this length (L) that is used in the formula, A >(M)(L^y), to determine which cells are considered stream cells. This grid can be obtained as an output from the "Grid Network" tool. There is no python reference for this parameter.	Raster Layer
Input_Contributing_Area_Grid	Dialog Reference A grid of contributing area values for each cell that were calculated using the D8 algorithm. The contributing area for a cell is the sum of its own contribution plus the contribution from all upslope neighbors that drain to it, measured as a number of cells. This grid is typically obtained as the output of the "D8 Contributing Area" tool. In this tool, it is the contributing area (A) that is compared in the formula A > ML^y to determine the transition to a stream. There is no python reference for this parameter.	Raster Layer
Threshold__M	Dialog Reference The multiplier threshold (M) parameter which is used in the formula: A > (M)(L^y), to identify the beginning of streams. There is no python reference for this parameter.	Double
Exponent__y	Dialog Reference The exponent (y) parameter which is used in the formula: A > (M)(L^y), to identify the beginning of streams. In branching systems, Hack's law suggests that L = 1/M A^(1/y) with 1/y = 0.6 (or 0.56) (y about 1.7). In parallel flow systems L is proportional to A (y about 1). This method tries to identify the transition between these two paradigms by using an exponent y somewhere inbetween (y about 1.3). There is no python reference for this parameter.	Double
Input_Number_of_Processes	Dialog Reference The number of stripes that the domain will be divided into and the number of MPI parallel processes that will be spawned to evaluate each of the stripes. There is no python reference for this parameter.	Long
Output_Stream_Source_Grid	Dialog Reference An indicator grid (1,0) that evaluates A >= (M)(L^y), based on the maximum upslope path length, the D8 contributing area grid inputs, and parameters M and y. This grid indicates likely stream source grid cells. There is no python reference for this parameter.	Raster Dataset

Code Samples

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Use limitations

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Title Length Area Stream Source