Geoprocessing Tools

Objective - This tutorial will take the user through an introduction to tools available in HEC-RAS for geoprocessing vector data.

The data for this tutorial are provided below.

WorkshopData.zip

These data are for demonstration purposes only and should not be used for engineering analysis.

Steps

Step 1: Getting Started

Start a New Project

Open HEC-RAS
Create a new Project
Set the Folder name
Provide a Project Name
Set the projection by dragging and dropping the projection.prj file onto the space "Drop a file here".
Press the Create button to create your new RAS project

Create a Terrain Layer

Create a new Terrain by pressing the Add button next to the Terrains group
Provide a Name and press Create
Select the Terrain layer
Press the +Add button next to the new Terrain layer and select Import File option
Select the Terrain_100ft.tif file
Press the Import button
Zoom to the extents of the new Terrain layer.

Step 2: Working with Shapefiles

Importing a Shapefile

Create a new Geometry by pressing the Add button next to the Geometry group
Provide a Name and press Create
Turn on the Conceptual Mesh
Right-click the Conceptual Mesh and select the Import | Polylines/Polygons menu item
Select the HUC12s.shp shapefile
Select the Import Without Merge option
Press the Import button
In the Components window, note the issues with the Arcs (there are a multitude of over overlapping Arc issues)
Select the Edit tool - you will see all of the Arcs that do not satisfy a Conceptual Mesh topology symbolized with red dashed lines
An example of the map view is shown below

You could proceed by manually splitting arcs and deleting overlaps, however, each of the polygons is going overlap with an adjacent polygon. This could be a tedious workflow.
Delete all of the Arcs, by selecting them all and pressing the Delete key
1. Draw boundary box over the study area
2. Press the Delete key
Right-click the Conceptual Mesh and select the Import | Polylines/Polygons menu item
1. Select the HUC12s.shp shapefile
2. Select the Import and Merge option
3. Press Import

Creating a Shapefile

Add the Rivers.shp shapefile to the map (drag/drop or Add through the file dialog)
Create a new/empty shapefile
1. Click on the Add button next to the Map Layers group
2. Select the Create New Shapefile option
3. Choose the Line Type
4. Provide a Name for this new layer ("NewRivers")
5. Press the Create button
6. A new shapefile will be created in the "/Exports" folder
Copy features FROM the Rivers layer TO the NewRivers layer
1. Select the Rivers layer
  1. Select the features for the single subbasin
  2. Press Ctrl+C to copy the features to the clipboard
2. Select the NewRivers layer
  1. Press Ctrl+V to paste the features or right-click on the layer and choose Paste Features

Editing a Shapefile

Select the NewRivers layer (shapefile)
Remove small tributaries
1. Choose the Edit tool
2. Select the feature(s) to delete
  1. Practice using the Box Selector and the Freeform Selector (aka "fruit ninja")
3. Press the Delete key
  The D key can be used to Delete the selected features (Arcs, Nodes, Regions). Make sure the feature you wish to delete is selected.
  The Shift key will allow you to Pan while in Edit mode.
Continue deleting features that you wouldn't need to model separately
An example set of features is shown below

Step 3: Geoprocessing Tools

There are several geoprocessing tools available. Filter, Smooth, and Buffer will be frequently used tools. You will use a couple of them to gain an understanding of usage. The Tools all work similarly where there is a dialog that works on the selected layer features.

Smooth

The smoothing tool is helpful to create meshing that transitions well from cell to cell. Sharp changes in Arcs can result in poor triangulation and poor meshing.

Right-click on the NewRivers layer
Choose the Tools | Smooth option
1. Choose Input Lines (All or Selected)
2. Choose the Method and Parameters
Choose the Output location

Map Layer will create a shapefile and add it to the map
Press the Run button

Buffer

The buffer tool is convenient for growing or shrinking polygons, but it can also be used to create a polygon from a polyline. This is helpful when trying to define the channel portion of your 2D mesh using the Quadrangle meshing type.

Right-click on the Geometry | Conceptual Mesh and select the Import | Polylines/Polygons menu item
Select the Smoothed Lines shapefile you created in the previous step ("SmoothedRivers.shp" is on disk, if you need it)
Select the Import and Merge option
Press the Import button

The imported NHD lines come in many pieces. The Import and Merge option connected the end Nodes, but also created unwanted intersections at the downstream end of the river.
We want continuous river reach segments. A Merge Tool would assist with connecting segments.
Select the Edit tool
Fix the downstream portion of the river
1. Delete the Arcs (red arrows)
2. Delete the Node (circled in red)
3. Move the end Node (yellow arrow)
4. Delete any additional Nodes
5. Clean up any vertices that are close to other arcs
Fix the 3 river reaches by merging the individual portions of the river
1. Delete each of the nodes along a river reach.
  The result should be a 3 reach river system with Nodes at the end points and at the junction, as shown below
Use the Measure tool to find the appropriate channel width
High resolution ground surface elevation data would be helpful. Aerial imagery is also helpful.
Select the river Arcs
Right-click on the Conceptual Mesh and select the Tools | Buffer menu item
1. Choose the Selected Arcs option
2. Enter the Buffer Width
3. Choose a Smoothing Method
4. Choose the Clipboard for the output
5. Press the Run button
Paste the new features into the Conceptual Mesh (Ctrl+V or right-click layer and choose Paste Features)
Clean up the channel regions
1. Delete the river centerline Arcs
2. Delete extra Arcs and Nodes
3. An example figure (before and after) of how to handle the junction is shown below
4. Each end of the river reach should have 2 points, as shown in the figure (before and after) below

In order to use the Quad meshing approach, each regions must have at least 4 sides.

Step 4: Tagging

Tagging is useful for labeling portions of your model with distinctive characteristics or parameters which you can later quickly identify. For this part of the exercise, tag the well-defined channel regions and those that are larger subbasins.

Setting Tags

Select the Conceptual Mesh layer and choose the Edit tool
Select a Region (not the channels)
In the Component pane, press the Add Tag button.
In the pop-up panel, choose Create New Tag
Name the tag
Enter a Value - "Subbasin"
Press the Set Value button
Assign the tag to each of the larger (subbasin) regions
1. Select the Region
2. Press Add Tag
3. Click the Tag "RegionType Subbasin"
Zoom into the channel regions
Add the RegionType tag to each channel region
1. Press the Add Tag button
2. Select the RegionType tag
3. Type in the Value with "Channel"
4. Press the Set Value button
Assign the tag to the other channel regions
1. Select the Region
2. Press Add Tag
3. Click the Tag "RegionType Channel"

Working with Tags

Zoom out to the full Conceptual Mesh
With the Conceptual Mesh selected, choose the Regions tab in Components
Type in the filter "Subbasin"
Note that the filter will immediately take affect
1. Select one of the regions from the Regions tab
2. Select All of the regions (use Ctrl+A or click on each one)
3. Set the Cell Type to Triangular
4. Set the Cell Size (and Secondary) to 1000
5. Set the Cell Stretching Rate to 0.3
Clear the Filter
Type in the filter "Channel"
1. Select one of the regions from the Regions tab
2. Select All of the regions (use Ctrl+A or click on each one)
3. Set the Cell Type to Quad
4. Set the Cell Size to 500
5. Set the Count to 1
Press the Regenerate Mesh button
Utilize the Tagging and Filtering to change the meshing properties and Regenerate, as time allows