WMS:Topologic Trees

A topological tree is one way to represent a watershed in the absence of terrain data. When a digital terrain model or feature objects are being used to automate basin delineation and build a particular sub basin configuration, a tree is simultaneously generated. The tree representation uses icons for confluences (outlet points) and basins, and should be clear to both experienced and inexperienced users of hydrologic models such as HEC-1 or TR-20.

The public domain version supports the building of a hydrologic model using a topologic tree as the only means of developing the model.

An equivalent tree representation is also shown and can be selected from the Project Explorer.

Building Trees

A topologic tree can be used to create a watershed configuration in the absence of digital terrain or feature object data (the only possibility for the public domain version of WMS). The tree representation can then be used to select basins and outlet points for entry of all basin and routing data, in the same way the digital terrain based watershed map can be used. Geometric parameters such as areas, lengths, and slopes, which can be automatically computed when a digital terrain model is used, must be entered interactively. However, all other features of the hydrologic modeling interfaces work in the same fashion.

All of the functions for building and/or editing trees (except diversions and reservoirs) cannot be used when a digital terrain model is used. In this case, all new basins and outlet points must be created from the digital terrain model.

Adding

Adding Basins

The Add | Basin command of the Tree menu defines a new drainage basin for the selected outlet point. Any number of sub basins can be associated with each outlet point. Typically, there are either one or two (a sub basin for each upstream branch), depending on whether or not the outlet point represents a branch in a stream network.

Adding Outlets

The Add | Outlet command of the Tree menu allows entering a new outlet "upstream" from the currently selected outlet node. This represents a new confluence or sub-basin outlet which is upstream from the selected outlet. In this fashion, a network of outlet points can be built which actually represent the stream network of the watershed.

Adding Reservoirs

A reservoir can be created for an outlet by selecting the outlet and choosing the Add | Reservoir command from the Tree menu. By creating a reservoir at an outlet storage, routing for the outlet can be done followed by routing from the outlet of the reservoir to the next downstream outlet point.

Adding Diversions

Diversions are defined in a two step process: by defining the diversion at the outlet or basin where flow is to be diverted, and then assigning a previously defined diversion (retrieving a diversion) to another outlet. Diversions are defined by first selecting an outlet point or a drainage basin where the flow is diverted and then selecting the Add | Diversion command from the Tree menu.

After adding a diversion, a link will be drawn from the outlet or basin selected to the side of the Graphics Window, indicating that no retrieval outlet has yet been specified for that diversion.

The retrieval outlet point can be specified when defining diversions from one outlet to another by multi-selecting the retrieval outlet before issuing the Add Diversion command.

Adding Sources

The Add | Source command of the Tree menu allows defining a source at an "upstream" outlet. No basins or outlets may exist upstream from a source outlet as they are intended to represent the headwaters of a stream within a basin and the source is that flow entering the modeled watershed through the stream.

Adding Sinks

The Add | Sinks command of the Tree menu allows defining a sink at a "downstream" outlet. No outlets may exist downstream from a sink outlet as they are intended to represent the discharge of a stream within a basin and the sink is that flow leaving the modeled watershed through the stream.

Deleting

Deleting Basins

The Delete | Basin command of the Tree menu can be used to delete a selected drainage basin from a given outlet. The Select Drainage Basin tool should be active to select a basin icon.

Deleting Outlets

The Delete | Outlet command of the Tree menu allows deleting selected outlet points. The Select Vertices tool can be used to select outlet points which are to be deleted.

Deleting Reservoirs (Tree)

The Delete | Reservoir command of the Tree menu can be used to delete a selected reservoir from a given outlet. The Select Outlets tool should be active to select an outlet icon where a reservoir has been defined from the Tree menu.

Deleting Diversions

The Delete | Diversion command of the Tree menu can be used to delete a selected diversion. The Select Diversions tool should be active to select a diversion icon.

Deleting Sources

The Delete | Sources command of the Tree menu is used to delete a defined source from an outlet.

Deleting Sinks

The Delete | Sinks command of the Tree menu is used to delete a defined sink from an outlet.

Inserting Outlets

The Insert Outlet command of the Tree menu allows entering a new outlet between two selected outlet points. This makes it possible to insert a confluence which may have been inadvertently left out or to simply subdivide a watershed into smaller sub basins. The Insert Outlet command can also be used to insert a new outlet at the base of a tree. In such cases then only the bottom most outlet should be selected before issuing the Insert Outlet command.

Merging Outlets

The Merge Outlets command of the Tree menu can be used if wanting to connect the downstream-most outlet of one watershed into an outlet of another watershed. This will effectively join the two watersheds into a single a watershed.

This can be used to combine information from two model (HEC-1) files into one. In order to do this, open the first HEC-1 file into an editor, then would insert the second file below (or above the first). Eliminate the job control records and the zz record in the middle of the new file and save. When opening this new file into WMS, it will contain two trees that can be merged together at the appropriate location.

Retrieving Diversions

To retrieve a diversion at an outlet point, select the outlet point where the diverted flow is to be retrieved and then select the Retrieve Diversion command from the Tree menu. If more than one diversion not yet retrieved exists, a list of defined diversions without retrieval outlet points (a diversion cannot be assigned to more than one retrieval outlet) will appear in the diversion selection dialog. Select the name of the desired diversion and choose OK.

After retrieving a diversion, the diversion link will now be drawn from the outflow outlet or basin to the retrieval outlet point. HEC-1 only allows inflow to be defined at outlet points.

Rebuilding the Display

When creating a topologic tree WMS tries to default the display according to the width and breadth of the tree, placing an icon in each quadrant. Some may wish to move individual icons around in order to display the tree differently. However, if wanting at anytime to have WMS rebuild the default display, choose the Rebuild Tree Display command of the Tree menu.

Related Topics

• Tool Palette