The Flow Accumulation tool generates a raster of accumulated flow into each cell from a flow direction raster.
The output is a hosted imagery layer.
Learn more about how Flow Accumulation works
Examples
Example scenarios for using this tool include the following:
- Identify stream channels at cell locations with high flow accumulation.
- Identify ridges at cell locations with zero flow accumulation, which are local topographic highs.
Usage notes
Flow Accumulation includes configurations for input layers, accumulation settings, and the result layer.
Input layers
The Input layers group includes the following parameters:
The Input flow direction raster parameter specifies the raster that shows the direction of flow out of each cell. The flow direction raster can be created using the Flow Direction tool with the D8, Multiple Flow Direction (MFD), or D-Infinity (DINF) method. Use the Flow direction type parameter to specify the method that was used when the flow direction raster was created.
The Optional weight layer group includes the Input accumulation weight raster, which is a raster layer that defines the fraction of flow that contributes to flow accumulation at each cell.
If no accumulation weight raster is provided, a default weight of 1 will be applied to each cell.
Accumulation settings
The Accumulation settings group includes the following parameters:
- The Flow direction type parameter specifies the type of flow method that will be used when computing flow direction. Specify the method (D8, MFD or DINF) that was used when creating the raster specified in the Input flow direction raster.
Flow accumulation data type specifies the data type of the output flow accumulation raster. The options are as follows:
- Float—The output raster will be floating-point type. This is the default.
- Integer—The output raster will be integer type.
- Double—The output raster will be double type.
Result layer
The Result layer 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.
- Output layer type specifies the type of raster output that will be created. The output can be either a tiled imagery layer or a dynamic imagery layer.
- Save in folder specifies the name of a folder in My content where the result will be saved.
Environments
Analysis environment settings are additional parameters that affect a tool's results. You can access the tool's analysis environment settings from the Environment settings parameter group.
This tool honors the following analysis environments:
- Output coordinate system
- Processing extent
Note:
The default processing extent in Map Viewer is Full extent. This default is different from Map Viewer Classic in which Use current map extent is enabled by default.
- Snap raster
- Cell size
- Mask
Credits
This tool consumes credits.
Use Estimate credits to calculate the number of credits that will be required to run the tool. For more information, see Understand credits for spatial analysis.
Output
The Output flow accumulation raster name layer stores the value of accumulated flow as determined by accumulating all upstream cells that flow into each cell. The target cell is not included in the accumulation value. If an input weight raster was specified, the weight at each cell is considered in the accumulation value.
Cells of undefined flow direction will only receive flow; they will not contribute to any downstream flow.
For an input D8 flow direction raster, a cell is considered to have an undefined flow direction if its value in the flow direction raster is anything other than 1, 2, 4, 8, 16, 32, 64, or 128. For an input D-Infinity (DINF) flow direction raster, a cell is considered to have an undefined flow direction if its value in the flow direction raster is -1.
Usage requirements
This tool requires the following user type and configurations:
- Professional or Professional Plus user type
- Publisher, Facilitator, or Administrator role, or an equivalent custom role with the Imagery Analysis privilege
Resources
Use the following resources to learn more:
- How Flow Accumulation works
- Flow Accumulation in ArcGIS REST API
- flow_accumulation in ArcGIS API for Python
- Flow Accumulation in ArcGIS Pro with the Raster Analysis extension
- Flow Accumulation in ArcGIS Pro with the Spatial Analyst extension