Confinement Tool

Valley confinement is a primary control on river morphology and describes the degree to which confining margins constrain the active channel’s ability to adjust laterally.

The tool clips the channel polygon by the Valley Bottom to align the Valley Bottom and Channel Polygon edges; this product is called the Confined Channel. The Valley Bottom and Confined Channel are intersected to identify the Confined Margins, which are the segments of Confined Channel and Valley Bottom edges that overlap. These are then identified as part of the left or right stream banks.

The Confinement Tool calculates two versions of Confinement from the specified inputs: Channel Confinement and Summed Margin Confinement.

• Channel Confinement is the proportion of channel length in which the channel abuts a confining margin on either side of the channel.
• Summed Margin Confinement is the proportion of the total channel edge length (left and right stream bank) that is confined.

In other words, Summed Margin Confinement considers the sum of the left and right bank length as the total possible length that could be confined, while Channel Confinement considers the stream length as the total possible length that could be confined, which is roughly 1/2 the length considered for Summed Margin Confinement.

Usage

• All input data should be in the same projected coordinate system.
• Do not use a Geographic coordinate system (causes problems with Thiessen Polygons).

Parameters

Input Stream Network (Segmentation Optional)

This is the line network for which confinement will be calculated. Requirements include:

• Segmented appropriately for confinement. > * Note that this segmentation can be different than segmentation required for other Geomorphic Network Analyses. > * Also note that calculating confinement could be an iterative process using the Moving Window Analysis to define the appropriate segmentation interval or to create Reach Breaks. If this is the case, the segmentation does not matter for the initial run(s) of the tool.
• All tributaries must connect to the line network.
• All tributary lines start from the junction of the tributary with the main stem.
  > Note that the mainstem segment does NOT need to be split at this junction.
• A File GDB Polyline Feature Class to meet field requirements
• NOT be Z or M enabled.
• (Untested) Entirely contained within the Channel and Valley Bottom Polygons.

Input Valley Bottom Polygon

This polygon defines the valley bottom area and margins which may confine a stream channel. Requirements include:

• Single Valley Bottom polygon feature
• a File GDB Polygon Feature Class
• NOT Z or M enabled.
• (Untested) Singlepart feature

Input Channel Polygon

Area of digitized or estimated channel calibrated to valley bottom extent. This is done by buffering the Channel Polygon to the extent needed to accurately reflect confined margins (e.g. overlap between Valley Bottom and Channel Polygon).

Requirements:

• Buffered as needed to calibrate channel polygon to valley bottom
• a File GDB Polygon Feature Class to meet field requirements
• NOT Z or M enabled.
• (Untested) Singlepart feature

Output Raw Confining State Along Stream Network

This is the name of a Polyline Feature Class that will be created in the GDB to store the raw confining state of the Stream Network.

Note: This is does not contain the "Calculated Value" for confinement, even though this is the only required output for this tool. In order to calculate confinenemt, you must Segment the network and specify a value for the Output Confinement Calculated by Segments parameter.

• The feature class will be overwriten if it already exists.
• None of the Original Segments or their attributes are retained in this feature class.

Output Confinement Calculated by Segments (Optional)

Specify the name of a new Feature Class in a File GDB that will be created using the confinement by segments calculation.

• The feature class will be overwriten if it already exists.
• In addition to new Confinement Calculation attributes, all of the original fields in the input Stream network are retained.
• If no output is specified for this parameter, confinement will not be calculated for segments in the Stream Network.

Output Confining Margins (Optional) Specify the name of a new Feature Class in a File GDB to save the 'confining margins' that define Confinement.

• The feature class will be overwriten if it already exists.

Scratch Workspace

Name of a file GDB that will be created to store temporary processing files

Geoprocessing Environments

• 64bit python Geoprocessing is recommended.
• Disable Z and M values if topology or memory errors are encountered.

Technical Background

Calculations

Calculation of Channel Confinement

To determine the proportion of the stream length that has a Confining Margin, the tool identifies whether a confining margin is on the left bank, right bank, or both banks. To do this, the confined margin segments from each bank margin are 'projected' onto the same network line, using a nearest point method to split up the network. There is potential error caused by curves in the stream, but this does provide a relative comparison of confinement along the stream. Once the left and right bank confined margins have been identified on the same stream network line, each segment is identified has having left, right or both banks confined.

Once the Confined Margins have been identified, The Confined Channel polygon is segmented into smaller polygons using perpendicular cross sections at the stream network line segment endpoints. Alternatively, a pre-segmented polygon may be specified in the tool if it already exists. The Channel Margins are split with the Segmented Confined Channel Polygon and the Summed Margin Confinement is calculated for each segment of the stream network.

Outputs

Raw Confining State Along Stream Network

This output contains the 'raw' confining state of the network, rather than calculation of actual Confinement Values.

This output can be used to support other types of confinement analysis, including moving window confinement calculations.

Attribute Fields:

• Confinement_Left and Confinement_Right: (Boolean)
  • True = section is confined on that side of the stream.
  • False = section is not confined on that side of the stream.
• Confinement_Type: (String)
  • None = Not confined on either side of the stream.
  • Right = Confined on right side of stream.
  • Left = Confined on left side of the stream.
  • Both = Confined on both sides of the stream.
• IsConfined: (Boolean)
  • True = section is considered confined (i.e. Confinement_Type = Right, left, or Both).
  • False = section is considered unconfined.

Confinement By Segments

The actual confinement calculation is run on this line by using the segments in the input stream network.

Confinement Calculation by using the Raw Confining State:

• Confinement_LineNetwork_All: Confinement as calculated by transferring the attributes from the Raw Confining State to the segmented network.

  • Confinement = Sum of length of Confined margins divided by the Sum of the total length of segment, Expressed as a ratio:
    • 0 = unconfined
    • 1.0 = completely confined
  • This method does not double count the lengths of the confining margins if the stream is confined on both sides of the channel at that location.

• Confinement_LineNetwork_Both: Confinement is calculated where both sides of the stream are considered “Confined”.

• Confinement_LineNetwork_Left: Confinement is calculated where the left side of the stream is considered “Confined”.
• Confinement_LineNetwork_Right: Confinement is calculated where the right side of the stream is considered “Confined”.

Confinement Calculation by Segmenting Channel Polygon:

• Confinement_Margin_Summed Simplified method for calculating confinement using channel margin lengths. Length of confined margins on both sides of channel divided by total length of channel margins on both sides of channel. Values is a ratio 0 (unconfined) to 1.0 (confined on all margins). This method does not exclude double counting of confinement if confined on both sides of the channel at that location.
• Length_ConfinedMargin_Left and Length_ConfinedMargin_Right Length of confined margin for Left and Right sides of the channel for that segment.
• Length_ChannelMargin_Left and Length_ChannelMargin_Right Length of channel margin for Left and Right sides of the channel for that segment.
• Confinement_Margin_Left and Confinement_Margin_Right Confinement expressed on each side of the bank separately.

Troubleshooting and Potential Issues

• Tributary Junctions
• Channel completely outside of valley bottom (if using different networks)
• No Valley Bottom
• Network completely outside of channel

Tool Revisions

• GNAT 1.3
  • Removed Cross Section Method of splitting segments
  • Added Confining Margin Output
  • Renamed/Modified/removed some Input Parameters
    • Output Raw Confining State Along Stream Network
    • Output Confinement Calculated by Segments
    • Removed Calculate Confinement by Segments (tool will only do this if an output Confinement Calculated by Segments is specified.)
    • Removed Polygons already Segmented? (tool will always segment the polygon internally)
• GNAT 1.1
• Accepts Segmented Polygons or Use cross section method
• Option to only generate Confinement by centerline (for quicker results).
• Additional confinement calculations added
• Field Name Changes: New format: Attribute_MethodOrType_BankOrLocation

• Version 0.9
• Changed output confinement from percent to ratio