Stream Order

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

Usage tips

Command line and Scripting

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

The results of the Flow Accumulation function 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 functions 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 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.

In the STRAHLER order method, all links with no tributaries are assigned an order of one and are referred to as first order. When two first-order links intersect, the downslope link is assigned an order of two. When two second-order links intersect, the downslope link is assigned an order of three, and so on. When two links of the same order intersect, the order will increase. This is the most common method of ordering.

The output from the Stream Order tool is an integer raster.

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

The following environment settings affect this tool:
- General: Current Workspace, Scratch Workspace, Output Coordinate system, Output Extent, Snap Raster.
- Raster Analysis: Cell size.
- Raster Storage: See the Raster Storage settings for the particular output raster format selected.

Map Algebra

The <net_grid> can be created by "thresholding" the results of FlowAccumulation. Refer to the FlowAccumulation command reference for an example.

The output of StreamOrder will be of higher quality if the net_grid and dir_grid are derived from the same surface. If the net_grid is derived from a rasterized streams coverage, 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 raster linear network should be represented as values greater than or equal to one on a background of NoData.

In the STRAHLER method, all links with no tributaries are assigned an order of one and are referred to as first order. When two first-order links intersect, the downslope link is assigned an order of two. When two second-order links intersect, the downslope link is assigned an order of three, and so on. When two links of the same order intersect, the order will increase. This is the most common method.

Learn more about how to specify the input raster dataset in the Map Algebra expression of Raster Calculator.

ArcObjects

The streamRaster can be created by thresholding the results of FlowAccumulation. Refer to the FlowAccumulation command reference for an example.

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

The output of StreamOrder will have higher quality if the streamRaster and directionRaster are derived from the same surface. If the streamRaster 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.

With orderType STRAHLER, all links with no tributaries are assigned an order of one and are referred to as first order. When two first-order links intersect, the downslope link is assigned an order of two. When two second-order links intersect, the downslope link is assigned an order of three, and so on. When two links of the same order intersect, the order will increase. This is the most common method.

The output from the ArcObjects method is a raster object.

Syntax

StreamOrder_sa (in_stream_raster, in_flow_direction_raster, out_raster, order_method)

Parameter	Explanation	Datatype
Input stream raster (Required)	An input raster that represents a linear stream network.	Composite Geodataset
Input flow direction raster (Required)	The input raster that records the direction of flow out of each cell. This can be created with the Flow Direction function.	Composite Geodataset
Output raster (Required)	The output stream order raster.	Raster Dataset
Method of stream ordering (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 create 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

Data types for geoprocessing tool parameters

Script Example

# StreamOrder_sample.py
# Description: 
#   Assigns a numeric order to segments of a raster representing
#   branches of a linear network.
# Requirements: None
# Author: ESRI
# Date: Sept 6, 2005

# Import system modules
import arcgisscripting

# Create the Geoprocessor object
gp = arcgisscripting.create()

try:
    # Set local variables
    InStreamRaster = "C:/data/stream"
    InFlowDirectionRaster = "C:/data/flowdir"
    OutRaster = "C:/data/streamorder"
    InMethod = "STRAHLER"

    # Check out Spatial Analyst extension license
    gp.CheckOutExtension("Spatial")

    # Process: StreamOrder
    gp.StreamOrder_sa(InStreamRaster, InFlowDirectionRaster, OutRaster, InMethod)

except:
    # If an error occurred while running a tool, then print the messages.
    print gp.GetMessages()

Map Algebra syntax

StreamOrder(<net_grid>, <dir_grid>, {STRAHLER | SHREVE})

Parameter	Explanation
<net_grid>	A grid representing a linear stream network.
<dir_grid>	A grid showing direction of flow out of each cell. This can be created using the FlowDirection function.
{STRAHLER \| SHREVE}	Keyword indicating the method for assigning 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 create 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.

Parameter

Explanation

<net_grid>

A grid representing a linear stream network.

<dir_grid>

A grid showing direction of flow out of each cell. This can be created using the FlowDirection function.

{STRAHLER | SHREVE}

Keyword indicating the method for assigning 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 create 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.

Map Algebra example

streamorder(channel_grid, flow_dir, strahler)
streamorder(channel_grid, flow_dir, shreve)

ArcObjects syntax

IHydrologyOp::StreamOrder (streamRaster As IGeoDataset, directionRaster As IGeoDataset, orderType As esriGeoAnalysisStreamOrderEnum) As IGeoDataset

Parameter	Explanation
streamRaster	An input Raster, RasterDataset, RasterBand, or RasterDescriptor representing a linear stream network.
directionRaster	An input Raster, RasterDataset, RasterBand, or RasterDescriptor showing the direction of flow out of each cell. This can be created using the IHydrologyOp::FlowDirection method.
orderType	An esriGeoAnalysisStreamOrderEnum indicating the method for assigning order. esriGeoAnalysisStreamOrderStrahler — The method will be the 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 create a third-order link. This method is commonly used. esriGeoAnalysisStreamOrderShreve — The method will be 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.

Parameter

Explanation

streamRaster

An input Raster, RasterDataset, RasterBand, or RasterDescriptor representing a linear stream network.

directionRaster

An input Raster, RasterDataset, RasterBand, or RasterDescriptor showing the direction of flow out of each cell. This can be created using the IHydrologyOp::FlowDirection method.

orderType

An esriGeoAnalysisStreamOrderEnum indicating the method for assigning order.

esriGeoAnalysisStreamOrderStrahler — The method will be the 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 create a third-order link. This method is commonly used.

esriGeoAnalysisStreamOrderShreve — The method will be 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.

ArcObjects example

' Create the RasterHydrologyOp object
Dim pHydrologyOp As IHydrologyOp
Set pHydrologyOp = New RasterHydrologyOp

' Declare the input stream raster object
Dim pInputStream As IGeoDataset

' Calls function to open a raster dataset from disk
Set pInputStream = OpenRasterDataset ("D:\SpatialData", "inputstream")

' Declare the input direction raster object
Dim pDirection As IGeoDataset

' Calls function to open a raster dataset from disk
Set pDirection = OpenRasterDataset	("D:\SpatialData", "direction")

' Declare the output raster object
Dim pOutputRaster As IGeoDataset

' Calls the method
Set pOutputRaster = pHydrologyOp.StreamOrder (pInputStream, pDirection, esriGeoAnalysisStreamOrderShreve)