Methods for Analyzing Stream Channel Change through Time Using Georeferenced Imagery
Price River, Utah
Abstract:
To familiarize reader with the methods and analyses used to assess channel change width and area for specified stretches of river (reaches). This document looks specifically at the Price River of east-central Utah, where damming, diversion, invasive species introduction/spread, or a combination of some or all of these factors have caused significant channel narrowing over the course of 78 years (1938-2016).
Objective:
The purpose of this tutorial is to explain the process of analyzing the change in bankfull area and width of a stream channel from 2 or more different points in time.
Methods:
A. For Most Current River Scenario/Condition:
1. Find adequate imagery. The most current NAIP (National Agriculture Imagery Program) imagery, which is 1m resolution, will suffice. Here is a link to the imagery:
https://gis.apfo.usda.gov/arcgis/rest/services
To load:
Abstract:
To familiarize reader with the methods and analyses used to assess channel change width and area for specified stretches of river (reaches). This document looks specifically at the Price River of east-central Utah, where damming, diversion, invasive species introduction/spread, or a combination of some or all of these factors have caused significant channel narrowing over the course of 78 years (1938-2016).
Objective:
The purpose of this tutorial is to explain the process of analyzing the change in bankfull area and width of a stream channel from 2 or more different points in time.
Methods:
A. For Most Current River Scenario/Condition:
1. Find adequate imagery. The most current NAIP (National Agriculture Imagery Program) imagery, which is 1m resolution, will suffice. Here is a link to the imagery:
https://gis.apfo.usda.gov/arcgis/rest/services
To load:
- Open ArcCatalog, Navigate to “GIS Servers”, double click then copy and paste the above address in the “Server URL” box.
- A new server titled “arcgis on gis.apfo.usda.gov (user)” will appear in the Arc Catalog menu.
- Open, navigate to the NAIP folder, Open it then find desired state and drag it onto the map. This will load the imagery as a basemap.
- Once loaded into ArcMap, take note of the year the NAIP Imagery was taken in the Table of Contents
Figure 1: Loading NAIP
2. Create a new polyline feature class using the following directions:
http://desktop.arcgis.com/en/arcmap/10.3/manage-data/shapefiles/creating-a-new-shapefile.htm
http://desktop.arcgis.com/en/arcmap/10.3/manage-data/shapefiles/creating-a-new-shapefile.htm
- Here is a video tutorial on how to digitize a polyline or polygon in ArcMap.
Video 01: Digitizing Centerline
3. Create bankfull polygon for current imagery/stream channel scenario:
For a tutorial on how to create a bankfull polygon, please refer to the following link:
https://usu.box.com/s/wsmpg604lvx7v8193ki8py1z3ossj78u
For a tutorial on how to create a bankfull polygon, please refer to the following link:
https://usu.box.com/s/wsmpg604lvx7v8193ki8py1z3ossj78u
- Note that using the bankfull Channel Tool is only applicable if the stream channel lacks width variability, in other words, the channel is of a uniform width. A good example of this is depicted in the figures below:
- The tool combines a flow accumulation raster (pixelated imagery where a value is assigned to a pixel based on accumulation of all uphill pixels) with a precipitation shapefile to determine the width of the stream along a digitized line network (stream network). Given this, the polygon from the bankfull tool will likely still require editing.
- Islands: If the line network used does not have side channels, the tool will not pick them up. (See figure 2).
Figure 2: Side Channel
- Here is another quick video on how to edit bankfull polygons with side channels.
- Raster-Line Network Differences: Sometimes the flow accumulation raster and imagery were (likely) collected at different points in time and/or the stream channel may have shifted to a different area in the floodplain (accretion, anabranching, wholesale shift). The bankfull polygon will have to be edited to fix these discrepancies. (Figure 3 below displays flow Accumulation Raster with white pixels as higher values on the left, Imagery on the Right)
Figure 3: False Widths
- Here is a video about this issue and how to edit:
B. Create Bankfull Polygon Based on Historic Imagery:
1. Obtain Historic Imagery: Depending on the source, historic imagery may have to be georeferenced in a GIS. These procedures will not be covered in this tutorial.
- For this analysis, georeferenced historic imagery were provided as raster feature classes.
- In Utah, there is quite a bit of historic imagery available via web server. Directions below.
2. Load Historic Imagery:
- In Utah, the AGRC website provides these datasets
- Visit the following website for directions on how to load the server.
https://gis.utah.gov/image-server/
1. Obtain Historic Imagery: Depending on the source, historic imagery may have to be georeferenced in a GIS. These procedures will not be covered in this tutorial.
- For this analysis, georeferenced historic imagery were provided as raster feature classes.
- In Utah, there is quite a bit of historic imagery available via web server. Directions below.
2. Load Historic Imagery:
- In Utah, the AGRC website provides these datasets
- Visit the following website for directions on how to load the server.
https://gis.utah.gov/image-server/
- To load Imagery:
Figure 4: Loading Historic Imagery #1
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Figure 5: Loading Historic Imagery #2
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3) The overall trend of river condition throughout the past century has been increased channelization and floodplain disconnect. This means that we look at past imagery as reference for natural stream condition and behavior. Figure 6 below is a good example of this
Figure 6: Reduction in Width, Width Variability, and Area on the Price River, UT
- If there is width variability/diversity across a larger spatial extent, or throughout the stretch of stream analyzed, the bankfull polygon must be digitized by hand.
- Use fluvial geomorphic knowledge to determine and digitize the bankfull channel from imagery
- Vegetation (appears black to dark gray on imagery) Presence vs. Absence OR Abundance vs. Scarcity along stream corridor
- Depositional Bars, in black and white imagery, appear bleached (bars below the water surface appear darker.
- Bars with sparse vegetation
- Use fluvial geomorphic knowledge to determine and digitize the bankfull channel from imagery
- Vegetation (appears black to dark gray on imagery) Presence vs. Absence OR Abundance vs. Scarcity along stream corridor
- Depositional Bars, in black and white imagery, appear bleached (bars below the water surface appear darker.
- Bars with sparse vegetation
Figures 7 and 8: Clues Identifying Active Stream Channel Extent and an Example
of Distortion.
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Figure 9: Prime Example of Imagery Distortion.
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C. Clip Both Polygons Using Specified Reach Breaks:
1. Reach Breaks can be derived from several sources, in this case, a Valley Bottom Polygon
broken up by Management Reaches was provided. Here is a list below:
1. Reach Breaks can be derived from several sources, in this case, a Valley Bottom Polygon
broken up by Management Reaches was provided. Here is a list below:
Figure 10: List of Management Reaches
2. Other examples of potential reach breaks include:
- GPS Waypoints (UTM-Northing, Easting) (Lat,Long)
- Property Ownership Boundaries
- Natural Geomorphic Breaks (Gradient, Valley Width, Substrate, Sinuosity)
- Fixed Length Segmentation (ex. 500m segments)
3. Cut historic and current bankfull channel polygons at reach breaks
- Video demonstrating how to clip reaches by reach breaks:
Video 04: Clipping Reach Breaks
- GPS Waypoints (UTM-Northing, Easting) (Lat,Long)
- Property Ownership Boundaries
- Natural Geomorphic Breaks (Gradient, Valley Width, Substrate, Sinuosity)
- Fixed Length Segmentation (ex. 500m segments)
3. Cut historic and current bankfull channel polygons at reach breaks
- Video demonstrating how to clip reaches by reach breaks:
Video 04: Clipping Reach Breaks
4. Populating Attribute Tables with Data:
- Videos demonstrating how to populate the attribute tables of historic and current bankfull channels with necessary data:
How To video on Naming:
Video 05: Attribute Table Naming
- Videos demonstrating how to populate the attribute tables of historic and current bankfull channels with necessary data:
How To video on Naming:
Video 05: Attribute Table Naming
…And On Calculating Area
Video 06: Attribute Table Area
Video 06: Attribute Table Area
Calculating Average Width (optional):
Video 07: Historic Channel Centerline
- Although Slightly more involved, assessing change in average channel width can be a useful analysis
Video 07: Historic Channel Centerline
Joining attribute tables and performing calculations
Video 08: Width Calculation
Video 08: Width Calculation
***ALWAYS REMEMBER to CALCULATE GEOMETRY before performing CALCULATIONS, to ensure each feature has correct area and length values***
(In attribute table- right click on field header- calculate geometry)
5. Populating Data on Flowline, and calculating Area and Width Departures/Reductions:
- Here is the formula for calculating channel area departure/reduction for a given stretch of river at two (2) different points in time.
Figure 11: Analysis Formulas
- Video for Populating flowline with data from channel polygons:
Video Setting proper Symbology:
Video 10: Proper Symbology
Video 10: Proper Symbology
Figure 12: Displayed Reaches of the Price River
