Spatial Imagery Consolidation and Channel Feature Delineation

Lead Scientist

Tony Thatcher

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study objectives

This study consisted of three primary tasks, with one additional task (#4) added during the study:  


  1. Identify and compile available data and aerial photography for use in GIS. 

  2. Map banklines and physical features. 

  3. Analyze data and summarize results. 

  4. Create a Bighorn River Atlas. 


The resulting data and maps provide the spatial context for assessing historic and current conditions throughout the river corridor. 

Figure 1. Bankline mapping showing changes through time.

Figure 2. Relative Elevation Modeling using LiDAR elevation data with cross section location (Figure 3).

Figure 3. LiDAR cross section showing multiple channels.

 Figure 4. Change in channel and island area through time.

findings

To assess historic river locations, migration, and conditions, banklines were digitized from the 1954/1956, 1979/1980, 1996,  2005, and 2017 imagery (Figure 1). Additionally, river channel centerlines, including secondary channels, were digitized from  the 1954/1956 and 2017 imagery High-resolution LiDAR elevation data was collected  in Fall 2018 by the NRCS for the Bighorn River  corridor from Yellowtail Dam to the confluence with  the Yellowstone River. These data were mosaicked  into a single Digital Elevation Model (DEM) and used  to create a Relative Elevation Model for the corridor  (Figure 2). The data is useful for assessing connectivity  of side channels, inundation potential, and avulsion risk  (Figure 3).  


Figure 3 displays a topographic cross section through  the Juniper side channel (see Figure 2 for cross section  location). The main river channel and the smaller  Juniper Channel, along with various perched historic  swales are clearly visible. These data are key for a variety  of tasks such as understanding channel connectivity  and potential for reactivation. 


The study area is divided into seven  defined reaches numbered upstream  to down. These reaches are used  to analyze changes in channel  morphology through time as defined  by the bankline and centerline  mapping. The following are some  preliminary findings of the analysis.  

  1. Visual inspection of the imagery  indicates a clear loss of open bar area  and channel complexity through time.  

  2. Bankline mapping shows a  consistent loss in both channel and  island area from the mid-1950s  to 2005, with a slight rebound in  2017. Figure 4 presents the bankline  mapping data for reach BH3 (Bighorn  FAS to Mallards FAS), showing the  loss of both channel and island area.  

  3. Approximately 13.8 miles of  secondary and anabranching channel  length has been lost between the mid-  1950s and 2017 between the Afterbay  Dam and the Yellowstone River.

implications

The work completed under this part of the Research Initiative provides a foundation for future research efforts related to aquatic and floodplain habitats, channel stability, bank erosion, armoring effects, side channel evolution, and agricultural land loss. The data provide some historic context regarding longer-term system evolution as well as a modern snapshot of river conditions. The results are intended to help guide the development of effective management/restoration strategies as well as identify optimal locations for specific project implementation. 

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