Streams can be defined for a TIN by manually connecting, or linking, consecutive channel edges together. They appear similar to stream feature arcs, but are not. On a TIN the streams are defined simply as connected vertices.
Because TINs are created from a sparse set of points, it is often difficult to explicitly define channel edges, particularly in urban areas where well defined channels may not even exist. For this reason, a stream can be created by manually selecting a set of vertices which defines a channel. This method also allows a street or storm drain to be incorporated into the TIN and used as part of the "stream network."
When the Create Streams command is chosen, a stream network for the current selected string of TIN vertices is created. The vertex string is made by connecting points which are known to lie in a stream, street, or other drainage structure. If the entered vertex string crosses triangle edges, a prompt will ask if wanting to insert a breakline. The breakline is inserted by creating new points where the line crosses a triangle edge. The elevation of the new points is determined by linear interpolation along the edge. Inserting the breakline in this fashion alters the topology without affecting the geometry.
Since flow through a stream network is defined strictly by the “linked” set of vertices, a downstream vertex does not even have to be lower than the upstream vertex. However, care should be taken to ensure that the general direction of the stream is downhill. The intent of creating streams in this fashion is to eliminate the need of defining a continuous set of channel edges with the TIN editing techniques described above. This type of stream creation is particularly important when doing basin delineation for urban areas.
Deleting Stream Segments
The Delete Stream Segments command deletes the segment of the stream between two selected stream nodes. An outlet point is inserted at the upstream node. If a single stream node is selected this command deletes the portion of the stream network from the selected stream node upward, including the selected stream node.
When the Create Pipe command is chosen, a pipe connecting stream nodes in the current selected string of TIN vertices is created. A pipe can be used to create a "stream" from any stream node to another without enforcing a continuous set of triangle edges between the two stream nodes. Pipes differ from streams in that when a flow path intersects a stream it then continues down the stream from node to node, whereas when a flow path intersects a pipe it continues overland across the pipe.
Displaying the Stream Profile
The Display Stream Profile command is used to display the elevation profile between two selected stream nodes. Because of the limited resolution of most elevation datasets, it is difficult to get a continuous set of stream bed elevations. Within this dialog, select and edit the elevation of individual stream nodes or can select two different stream nodes from the profile plot and linearly interpolate the elevation of all nodes in between. In this way it is possible to smooth out pits in the stream that may exist only because of a lack of resolution.
When using this command, It's necessary to select at least two stream nodes and the second one selected must be upstream of the first.
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