Making the Stream Arc Directions Consistent

Another important topologic relationship that must exist for arcs used to define a stream network is consistent connectivity. WMS (and WMS-Hydro) uses the convention of downstream to upstream to define the stream arc directions. In other words, the "from" node should be the downstream node and the "to" node should be the upstream node. Many times, stream arcs created for other purposes will not use this convention; you can use the Stream Directions… dialog to check and modify the direction of stream arcs if necessary. The Stream Directions dialog is shown in Figure 1.

The directions of all stream arcs can be displayed as shown in Figure 2, by selecting the Show All Directions button. If you discover an arc that is backwards then with the arc selected choose the Reverse Flow Direction button. An easy way to insure that all arc directions are defined correctly is to select the downstream most node of the stream using the Select Outlet tool  and then choose the Define Direction button. WMS-Hydro will trace all stream arcs from that point upstream and reverse all arcs that are required to make sure the network "drains" to the selected node.

The Show Connectivity button allows you to identify places where the stream arc topology is not consistent, and where you may need to edit using the edit tools described previously. At a first glance it may appear that all stream arcs are properly connected, but it may be difficult to tell for sure unless you zoom in very tight on each intersection. To display continuous stream arcs from any point in the network you should first Show All Directions, second select one of the direction nodes using the connectivity tool , and then select the Show Connectivity button.

The Clear Directions button can be used to erase or eliminate the node direction markers displayed at each end of the arc.
 

These materials may be used for study, research, and education, but please credit the authors and the Environmental Modeling Research Laboratory, Brigham Young University. All commercial rights reserved. Copyright 1999 Environmental Modeling Research Laboratory.