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River Flattening

This tutorial describes how to edit a river in a Digital Surface Model (DSM). Flowing water like rivers must be flattened into steps due to the changing elevation of the water surface along the river course.

Prior to commencing a project perform the following steps.

Review the Getting Started tutorials to learn more about loading and interacting with data using uniDEM.

This lesson will take approximately 10 minutes.

The following video executes the steps in the tutorial.

1. Load and View DSM

  1. Click uniDEMlogoLoad DEM
  2. Open ConodoguinetCreek_DSM.tif
  3. Display "ConodoguinetCreek_DSM" in the View
  4. Turn colors off in shader by clicking into view and press "H"
  5. Click uniDEMlogoLoad Shapes
  6. Open "2DRiver.shp"
  7. Display "2DRiver.shp" in the View
Conodoguinet Creek DSM and River Shape

Help references:

Load DEM | Load Shape | Shader Color Scheme (H)

2. Classify Water from 2D Shapefile

Water identification can be done manually or shapefile polygons can be used to create a selection and applied to a classification mask.

The Classification Mask is created to align spatially with the DSM being edited the first time a mask value is assigned.

  1. Within the Selection tab click the Load From File tool
  2. Select 2DRiver.shp to add all river pixels within the shapefile to the selection mask
  3. Within the Classification tab click the shortcut "2" for River classification
  4. Press Esc to clear the selection
  5. Click the CLASS mask in the ConodoguinetCreek_DSM dataset
classified river
Observe: The River class is assigned within the intersecting pixels of ConodoguinetCreek_DSM and the 2DRiver.shp

Help references:

Load (Selection) From File | Classification Shortcuts

4. Create River Centerline

Flowing water like rivers and streams can be editing using river centerlines drawn manually or semi-automatically.

Start Collection

  1. Click 2DRiver.shp in the TOC to remove from the View
  2. Navigate to the western most portion of the river
  3. Within the Shapes tab click Trace In Class
  4. Press Shift + Left Click over a non-void pixel within the river to start the centerline.
Note: The height of the node is taken from the DSM. If all water is void the elevation can be set manually.
start of river centerline

End Collection

River centerlines can be collected between a start and end node saving time delineating the river.

  1. Navigate to the eastern most portion of the river
  2. Within the Shapes tab click Trace In Class
  3. Press Shift + Left Click over a non-void pixel nearest the end of the river
river centerline
Notes:
  • The centerline is delineated from the first node to the last node along the river classification
  • The height of the last node is taken from the DSM. If all water is void the elevation can be set manually
  • All elevations within the River shape are intepolated between the first and last node

Review and Control River Elevations Along Centerline

River slopes vary along the coarse of flow. To ensure that river elevations do not "float" above the shoreline it is recommended that the elevation of some of nodes along the river coarse are set.

In some instances such as when a river has been void filled the river must be lowered below neighboring tree heights.

  1. Working from the western portion of the river (top to bottom)locate nodes intermittently that are over non-void river pixels
  2. Mouse over the node and nearby non-void water heights. If they are close to one another continue down the river
  3. When the centerline height does deviate from the river perform the following:
    • Press Shift + Right Click over the node to be changed
    • Select Set Elevation
    • Select Fixed for the Z mode
    • Enter the new height for the node
    • Repeat as required
set centerline node elevation
Notes:
  • All elevations within the River shape are intepolated between the manually set elevation nodes
  • The centerline can be applied (below) and this step can be revisited as needed.

Help references:

Select By Class | Clean Up | Classification Shortcuts

4. Flatten Water

Rivers must be made to flow downhill.

  1. Press Ctrl-A to select all pixels
  2. Within the Shapes tab click Apply Centerline
  3. Select Classification as the constraint
  4. Select 27: River as the class to use when modifying
  5. Click OK to use 1000m as the maximum distance
  6. Click OK to use 0m as the step size
  7. Press Esc to clear the selection
Observe: All pixels classified as River are edited and no longer contain void.
apply centerline to flatten river

Help references:

Select By Class | Set To | Make Void (V) | Perimeter Void Fill

5. Adjust Shorelines

Many derivative products such as contours and flood modelling require land to be equal to or higher than neighbouring water pixels.

  1. Press Ctrl-A to select all pixels
  2. Within Classification tab click Enforce Boundaries
  3. Enter 1.0 raise all elevations by 1.0m in Group 2 (land types) is lower than Group 1
  4. Click Hydro to separate groups 1 and 2
  5. Click OK to apply the shoreline corrections
  6. Hit Esc key to clear the selection mask
Observe: All pixels that are of class Unknown are now equal to or higher than the height of the Ocean
contain water

Help references:

Select By Class | Enforce Boundaries