Input layers

The Input layers group includes the following parameters:

• Input surface raster is the elevation raster that will be used for calculation. It can be a digital elevation model (DEM) with no prior sinks filled or a hydroconditioned DEM.

  The tool is not sensitive to errors in the surface raster that can act as depressions or sinks where flow terminates; filling sinks or depressions is not necessary.

  If the input surface raster contains real depressions, the locations of the depressions must be specified in the Input depressions raster or features parameter to be considered cells where water can flow into but not out from.

  NoData cells in the input surface raster do not have an associated value. These cells are ignored when identifying the direction of the least steep uphill neighbor, as well as the determination of flow direction and accumulation.

The Optional layers group includes the following parameters:

• Input depressions raster or features is the dataset that defines real depressions or sinks, where water can flow into but not out from.

  If the input is a raster layer, the depression cells must have a valid value, including zero, and the areas that are not depressions must be assigned NoData.

  If the input is a feature layer, it can be point, polyline, or polygon. Feature input will be converted to a raster internally before performing the analysis.

• Input weight raster is a raster layer that defines the fraction of flow that contributes to flow accumulation at each cell.

  The weight is only applied to the accumulation of flow.

  If no accumulation weight raster is provided, a default weight of 1 will be applied to each cell.

Flow direction settings

The Flow direction settings group includes the following parameters:

• Flow direction type specifies the type of flow method that will be used when computing flow direction.

  • D8—The D8 method assigns flow direction to the steepest downslope neighbor calculated by taking the difference in z-value divided by the path length between cell centers (1 for cardinal cells and the square root of 2 for diagonal cells). The values in the Output flow direction raster name layer will be integer values in the range of 1 to 255. The values from the center of each direction are specified in the following diagram:

    

    If a cell has the same change in z-value in multiple directions, the D8 flow direction will be undefined. In this case, the value for such cell will be the sum of the possible directions.

    This is the default.

  • MFD—The MFD flow method partitions the flow direction across downslope neighbors according to an adaptive partition exponent. The adaptive component is estimated as a function of maximum slope gradient, which considers local terrain conditions (Qin et al., 2007). The values in the Output flow direction raster name layer will be integer values in the range of 1 to 255, showing the predominant flow direction (toward the cell that receives the largest fraction of flow according to the partition scheme) for ease of interpretation. However, the values in the Output flow accumulation raster name layer reflect accumulation based on the flow partition scheme.

• Force edge cells to flow outwards specifies whether edge cells will always flow outward or follow normal flow rules.

  • Unchecked—The flow direction will be toward the inner cell with the steepest drop in z-value. However, if the drop is less than or equal to zero, the cell will flow outward from the surface raster. This will be the same for all cells across the raster.
  • Checked—Flow direction at edge cells will always be outward from the surface raster.

Result layer

The Result layers group includes the following parameters:

• Output flow accumulation raster name is the name of the output raster that will contain the flow accumulation result.

  The name must be unique. If a layer with the same name already exists in your organization, the tool will fail and you will be prompted to use a different name.

• The Optional layers group includes the following parameter:

  • Output flow direction raster name is the name of the output raster that will contain the flow direction result.

    The name must be unique. If a layer with the same name already exists in your organization, the tool will fail and you will be prompted to use a different name.

• Save in folder specifies the name of a folder in My Content where the result will be saved.