The Upstream Flow Paths command can be used to compute and trace the upstream overland flow path from a user-defined terminus point(s) to a point of intersection with the current subbasin upstream boundary.
This command is also useful in determining the longest flow path from anywhere within the subbasin, which can then be used to define the TOC (Time of Concentration) or Lag Time flow path for the subbasin. However, the true TOC flow path may not be obvious for various reasons and using this command alone may be insufficient to represent the situation on the ground. There may be roadways, bridges, culverts, buildings, and other manmade and natural obstructions that may alter the actual TOC flow path of a subbasin, but which may not be immediately apparent from the elevation grid. However, the user can piece together a true representative TOC flow path by using parts of the upstream flow paths created using this command, raindrop flow paths, and manually-digitized flow lines where obstructions exist. Refer to this article to learn more about the Automated Flow Paths command.
To use the Upstream Flow Paths command, follow these steps:
- From the Watershed ribbon menu, select the Upstream Flow Paths command.
- The Upstream Flow Paths dialog box will be displayed.
- In the Layer group name field, a default layer name will be displayed which may be edited. Once the results are computed, the software will add an Overland Flow Paths layer group to the Map Data Layers panel.
- The Delete previously computed overland flow paths option allows the user to delete previously computed upstream overland flow paths and defined terminus points.
- Once the General Specifications are defined, click on the [Draw] button and the dialog box will temporarily disappear, allowing the user to place the terminus point(s) on the Map View.
- After defining the terminus point(s) on the Map View, right-click and select Done from the context menu or press the [Enter] key.
- Now, the dialog box will be redisplayed and the number of terminus point(s) drawn will be displayed in the Terminus points field.
- On clicking the [OK] button, the terminus point(s) and the computed upstream overland flow path will be displayed on the Map View as shown below.
- The Overland Flow Paths layer will be created in the Map Data Layers panel containing the Upstream Flow Paths and Terminus layers that reference the computed upstream flow path and selected downstream terminus point.