ArcMap

Stream Order

Available with Spatial Analyst license.

Summary

Assigns a numeric order to segments of a raster representing branches of a linear network.

Learn more about how Stream Order works

Usage

  • The output of Stream Order will be of higher quality if the input stream raster and input flow direction raster are derived from the same surface. If the stream raster is derived from a rasterized streams dataset, the output may not be usable because, on a cell-by-cell basis, the direction will not correspond with the location of stream cells.

  • The results of the Flow Accumulation tool can be used to create a raster stream network by applying a threshold value to select cells with a high accumulated flow. For example, cells that have more than 100 cells flowing into them are used to define the stream network. Use the Con or Set Null tool to create a stream network raster where flow accumulation values of 100 or greater go to one and the remainder are put to the background (NoData). The resulting stream network can be used in Stream Link and Stream to Feature.

    An analytical method for determining an appropriate threshold value for stream network delineation is presented in Tarboton, et al. (1991).

  • The Stream Order tool only supports a D8 input flow direction raster. D8 flow directions can be created using the Flow Direction tool, run with default flow direction type D8.

  • See Analysis environments and Spatial Analyst for additional details on the geoprocessing environments that apply to this tool.

  • References:

    Tarboton D. G., R. L. Bras, I. Rodriguez–Iturbe. 1991. On the Extraction of Channel Networks from Digital Elevation Data. Hydrological Processes. 5: 81–100.

Syntax

StreamOrder(in_stream_raster, in_flow_direction_raster, {order_method})
ParameterExplanationData Type
in_stream_raster

An input raster that represents a linear stream network.

The input stream raster linear network should be represented as values greater than or equal to one on a background of NoData.

Raster Layer
in_flow_direction_raster

The input raster that shows the direction of flow out of each cell.

The flow direction raster can be created using the Flow Direction tool, run using the default flow direction type D8.

Raster Layer
order_method
(Optional)

The method used for assigning stream order.

  • STRAHLER —The method of stream ordering proposed by Strahler in 1952. Stream order only increases when streams of the same order intersect. Therefore, the intersection of a first-order and second-order link will remain a second-order link, rather than creating a third-order link. This is the default.
  • SHREVE —The method of stream ordering by magnitude, proposed by Shreve in 1967. All links with no tributaries are assigned a magnitude (order) of one. Magnitudes are additive downslope. When two links intersect, their magnitudes are added and assigned to the downslope link.
String

Return Value

NameExplanationData Type
out_raster

The output stream order raster.

This output is of integer type.

Raster

Code sample

StreamOrder example 1 (Python window)

This example assigns a numeric order to segments of a raster representing branches of a linear network.

import arcpy
from arcpy import env
from arcpy.sa import *
env.workspace = "C:/sapyexamples/data"
outStreamOrder = StreamOrder("stream", "flowdir", "STRAHLER")
outStreamOrder.save("c:/sapyexamples/output/outstrmordr01")
StreamOrder example 2 (stand-alone script)

This example assigns a numeric order to segments of a raster representing branches of a linear network.

# Name: StreamOrder_Ex_02.py
# Description: Assigns a numeric order to segments of a raster 
#              representing branches of a linear network.
# Requirements: Spatial Analyst Extension

# Import system modules
import arcpy
from arcpy import env
from arcpy.sa import *

# Set environment settings
env.workspace = "C:/sapyexamples/data"

# Set local variables
inStreamRast = "stream"
inFlowDirectionRaster = "flowdir"
orderMethod = "STRAHLER"

# Check out the ArcGIS Spatial Analyst extension license
arcpy.CheckOutExtension("Spatial")

# Execute StreamOrder
outStreamOrder = StreamOrder(inStreamRast, inFlowDirectionRaster, orderMethod)

# Save the output 
outStreamOrder.save("c:/sapyexamples/output/outstrmordr02")

Environments

Licensing information

  • Basic: Requires Spatial Analyst
  • Standard: Requires Spatial Analyst
  • Advanced: Requires Spatial Analyst

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