Slope Area Stream Definition

This input is a grid of flow directions that are encoded using the D8 method where all flow from a cells goes to a single neighboring cell in the direction of steepest descent.

A grid giving the specific catchment area value for each cell taken as its own contribution (grid cell length or summation of weights) plus the proportional contribution from upslope neighbors that drain in to it. This grid is typically obtained using the D-infinity multiple flow direction method that is used by the "D-Infinity Contributing Area" tool. In this tool, it is this area (a) that is used in the formula (S^m)(a^n) >= T to determine the transition to a stream.

This input is a grid of slope values. This is measured as drop/distance and it is most often obtained as the output of the "D-Infinity Flow Direction" tool. In this tool, it is this slope (S) that is used in the formula (S^m)(a^n) >= T to determine the transition to a stream.

This optional input is a grid that is used to mask the domain of interest and output is only provided where this grid is valid, i.e. does not contain a no-data value and whose value is greater than 0. A common use of this input is to use a D-infinity contributing area grid as the mask so that the delineated stream network is constrained to areas where D-infinity contributing area is available, replicating the functionality of an edge contamination mask.

This input is a grid of elevation values. As a general rule, it is recommended that you use a grid of elevation values that have had the pits removed for this input. Pits are generally taken to be artifacts that interfere with the analysis of flow across them. This grid can be obtained as the output of the "Pit Remove" tool, in which case it contains elevation values where the pits have been filled to the point where they just drain. This grid is only needed if drop analysis is being performed and is used to evaluate elevation drops along streams.

This input is 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 or the sum of weight loadings. This grid can be obtained as the output of the "D8 Contributing Area" tool. This input is required only when using drop analysis and is used to evaluate drainage density.

This input parameter is used as the area exponent (n) in the formula: (S^m)*(a^n) >= T, that is used to identify the beginning of streams.

This output is an indicator grid (1,0) that indicates the location of streams, with a value of 1 for each of the stream cells and 0 for the remainder of the cells.

This output grid contains the value of (S^m)*(a^n) for each grid cell.

This output grid contains the maximum value of the Slope-Area grid upslope of each grid cell in the domain using D8 flow directions.

This output is a comma delimited text file with the following header line:

Threshold, DrainDen, NoFirstOrd, NoHighOrd, MeanDFirstOrd, MeanDHighOrd, StdDevFirstOrd, StdDevHighOrd, T

The file then contains one line of data for each threshold value examined, and then a summary line that indicates the optimum threshold value. This technique looks for the smallest threshold in the range where the absolute value of the t-statistic is less than 2. For the science behind the drop analysis see Tarboton et al. (1991, 1992), Tarboton and Ames (2001). This output is only generated if drop analysis is used.

The number of steps to divide the search range into when looking for possible threshold values using drop analysis. This technique looks for the smallest threshold in the range where the absolute value of the t-statistic is less than 2. For the science behind the drop analysis see Tarboton et al. (1991, 1992), Tarboton and Ames (2001).