Overview

A common schematic is used to share data between HEC software programs (such as HEC-HMS and HEC-ResSim) for models within a watershed. This shared schematic ensures consistency in the representation of computational nodes, routing reaches, and other key elements. You can create the common schematic using tools available in the Setup module. These tools allow you to visually define elements of the schematic, but they do not alter the configurations of the original (native) models. Any changes made using these tools are not reflected in the native model computations.

The first component to create in the common schematic is the stream alignment. This alignment serves as the foundation for all other schematic elements.

Components

Stream alignments represent the stream network within a watershed. They show the direction of flow and indicate locations of confluences and bifurcations. Alignments also help convey a sense of distance and scale.

A stream alignment is made up of:

  • Stream elements: Segments of the stream network. Each begins or ends at a confluence, bifurcation, or the boundary of the river system. Stream elements are defined by a series of vertex points, with the start and end points designated as stream nodes.
  • Stream nodes: Points that mark the beginning or end of a stream element.
  • Stream junctions: Special types of stream nodes where two stream elements connect.

Each stream element must have at least two stream nodes - one at each end. The alignment is drawn using segments between vertex points. These components are illustrated in the figure below.

Relationships of Stream Elements, Stream Nodes, and Stream Junctions

Stream Nodes

Stream nodes are key components in representing the stream network within a watershed. HEC-RTS automatically creates stream nodes at:

  • The start and end of each stream element
  • Junctions where stream elements connect

Stream nodes are used to define stream stationing, which assigns reference values along the stream. You can adjust stationing by editing stream nodes using the Stream Node Tool. These tools allow you to fine-tune the structure and reference points of your stream network for accurate modeling and analysis.

Stream nodes are not the same as computation points. While computation points represent locations for exchanging time-series data between analysis tools, stream nodes help support and guide the placement of computation points.

Stream Junctions

A stream junction forms when two or more stream elements connect. It represents a point where multiple stream nodes come together. On the map, a stream junction is shown as a dark green circle with a light green halo, like in the example below. You can move or edit a stream junction to adjust the stream’s stationing.

Example of a Stream Junction within a Stream Alignment

Stream Stationing

HEC-RTS automatically creates and labels stream stations (also called river stations, depending on user settings) along each stream element. Stationing provides a reference system for locating features along the stream.

By default:

  • The downstream end is Station 0.
  • Station values increase upstream based on the linear distance between vertices in the watershed’s coordinate system.

You can override this default stationing by manually editing the station values of stream nodes or by adding additional nodes along the stream element.

The stationing units match those of the map layer used when drawing the stream element (e.g., feet or meters), though the units are not displayed on the map. If no map layer is used, the alignment will use the default X-Y coordinate system, which has no defined units.

Additional Resources

Refer to the Working with the Stream Alignment guides for step-by-step instructions on creating, editing, and customizing the appearance of your watershed's stream centerline.