Tips for Manually Editing Stream Arcs
Did you generate stream arcs in your Watershed Modeling System (WMS) model that you discovered later needed to be adjusted? Or maybe the outlet point’s position needs to be slightly adjusted. You can manually edit streams without using any of the wizards available in WMS, but you do need to be careful. Here are some tips on how to do it and what to watch for.
To manually edit your stream arcs, you will need to use the tools in the Map module. You can select and move a stream node or vertex to alter the path of a stream. You can also change a node to a vertex, create new feature points where needed, and manually edit properties in the Properties screen. You may wish to change your Display Options so that you can see the stream arcs, and vertices more clearly. Used carefully, you can make minor adjustments without using the wizards.
If you need to shift a stream outlet point or other major node, you can use the Select Feature Point/Node tool to select the stream outlet point and drag it to a new position. When the stream outlet point is originally on an arc but then moved away from the arc, the arc can snap to the new outlet location. Be careful where you move your stream outlet point, (or any stream arc vertex), especially if you accidentally shift it to a higher elevation, as this can create digital dams or break the model.
If you have extremely long stream arcs, or need to make precise corrections around obstacles, land formations, or buildings, you can manually add one or more vertices to the arc using the Create Feature Vertex tool. Then, you can then use the Select Feature Vertex tool to select and move them to better locations within the bounds of the model. This can be especially useful if you discover that one or more of your steam arcs now cross outside the bounds of the delineation arcs after manually editing them.
If you’ve changed a stream arc by adding vertices or just moving locations, you’ve also changed the vertex distribution along the arc. It may be necessary to redistribute the vertices again.
You will want to check elevation values against the DEM. If you have moved a stream arc point, you may have shifted it from its elevation. You may need to re-interpolate elevations back onto the stream arcs.
It is also recommended that manual edits be done prior to defining the model, otherwise you may discover that making these edits, while improving the stream arcs, has broken the model. If that happens, you may need to re-delineate the watershed. You can go back to the wizard that you used to delineate your watershed model and skip to the appropriate step to rework your model from there.
This manual editing of stream arcs is different from the GSSHA’s Smooth Stream/Pipe Arcs tool and works outside of any wizards within WMS.
Try out any of the tips with your watershed projects in WMS today!
