Stream Networking and Segmentation

This page defines terminology used in GNAT for stream networking and segmentation.

Stream Branches

Stream Branch: A continuous series of reaches, sections, segments, etc. along a stream. Branches should not be broken up by trib junctions, rather branches help differentiate 'main stem' vs tributary at confluences.

###Benefits of using Stream Branches:

• Segmenting the line network along continuous reaches (not stopping at each trib junction)
• Transferring attributes between line networks with different geometries
• Defining the continuous sections of the stream for the Moving Window Analysis Tool.

###Workflow for Generating Branches The general workflow for defining Stream Branches:

1. Determine how to proceed with networking and segmentation of the network. Many of the Attributes are affected by how the stream is segmented, how things like braids, tributary junctions etc. are defined.
2. Make sure the Stream Linework is clean. [How to clean NHD Networks for GNAT][CleanNHDDocumentLink]:

• All parts of the Line Network is fully connected.
• All Braids are removed.
• Fix all "Crossing" streams or more than 3 streams at a junction.
• Be careful for "hidden" duplicate features in the line network.
• "Dangles" removed.
• Attributes are properly transferred from original Line Network (NHD)

3. Generate Stream Order on the cleaned up network.
4. Run the Generate Stream Branches Tool to define the stream branches using Stream Order and named stream attributes.

Once the Stream Branches are defined for the network, they can be copied or transferred to another line network using the Copy Stream BranchID Tool. The two networks do not need to have the same geometry.

Copying Stream BranchID's

Once the Stream Branches are defined for the network, they can be copied or transferred to another line network using the Copy Stream BranchID Tool. The two networks do not need to have the same geometry. Copying Stream Branch ID's is useful for improving the results of the Transfer Line Attributes Tool

1. Make sure the following apply:

   • Clip to Focus Area both inputs files– Smaller is better.
   • Project “To” and “From” lines to a Projected coordinate system
   • Use the Multi-part to Single part tool or “Explode” tool to ensure you do not have multi-part features on both layers
   • Disable Z and M values on the both layers

2. (Temporary Step) Use the Dissolve tool to Create continuous lines between network junctions in the "To" network

3. Use the Copy Stream Branch IDs tool to copy the brand id to the “To” network.

4. (Temporary Step) Use the Intersect tool to move the original "To" network segments to the "To" network with copied BranchID's

5. QA Check

   1. Symbolize the NHD layer by BranchID

      • Lines with a Branch ID 1 color
      • Lines without a Branch ID a second color.
      • Label layer with Branch ID

   2. Symbolize the ICB layer by BranchID

      • Label layer with Branch ID.

   3. Make sure that the ends of the NHD layer fully cover the fish layer.

   4. If they do not, then update the NHD layer with the corresponding Branch ID from the ICB layer.

6. Use the Transfer Line Attributes tool to move the attributes between the line networks.

   This process take awhile, it is a good idea to look at the highest branch id so you can track progress.

Stream Segmenting/Reach Breaks

Segmenting the stream network provides the basic 'units' that are used for calculating Geomorphic Attributes. Analysis can be conducted on segments of uniform or varying lengths, and it may be desirable to have different segmentation of the network for calculating different Geomorphic Attributes.

###Types of Segmentation

• Uniform Segments: Branch is broken up at regular intervals. The length of the interval size could be variable by stream size or some other attribute, but should be the same within each branch.

• Reach Breaks or "Smart Segments": Branch is broken up using a natural feature, process, or geometry. Reaches vary by length.

  GNAT is in the process of developing Reach Breaks.

Tools for Segmenting

There are a number of tools available for segmenting the stream network.

• GNAT Segmentation Tool: The GNAT Segmentation Tool can be used to divide the Stream network into segments based on a target length. This tool provides a couple options for dealing with the remaining lengths of the lines during segmentation.

• GNAT Reach Break Tool: Potentially coupled with moving window analysis. >In Development.

• Fluvial Corridor Segmentation Tool

• ArcGIS Editing Tools

Stream Network / Sequencing

Sequencing refers to the upstream/downstream arrangement of segments or reach breaks.

Tools/Process

In Development

1. Build table (or attribute table) that describes upstream/downstream reaches
2. Incorporate tributary branches and braided reaches.