About River Flattening
The River Flattening command opens the River Flattening dialog that captures input for flattening river polygons perpendicular to the flow. A river polygon layer, and centerline layer is required to execute the flattening process.
Note: The River Flattening command is only available in LP360 for ArcMap. In LP360, as of v2018.2, it is called Double Line Drain, but works in a similar manner.
How to Flatten River Polygons
River Flattening Command
1. Click the River Flattening command on the Digitize Breaklines Toolbar.
2. The River Flattening dialog will open.
The River Flattening dialog captures the inputs required to flatten river polygons in a polygon layer perpendicular to a selected centerline layer.
The flattening process consists of projecting z values perpendicular from the centerline onto vertices of river polygons. The result is the flattening of the river polygon surface perpendicular to the flow of the centerline. The flattening process requires the centerlines to be located within the river polygons (so the centerline(s) can be located using simple intersections) and are assumed to be populated with z values using a method similar to the downstream conflation method. Likewise the river polygons must be z enabled, and only those existing vertices are modified. The process does not create new vertices. Vertices can be added to the polygon features prior to flattening using a drape conflation method for example.
The characteristics of the flattening algorithm is very sensitive to the relationship between the polygon and its centerline(s). For example, as the polygon edges (i.e., bank lines) become more perpendicular to its centerline, the flattening process begins to work more poorly. Therefore, in backwater areas it is suggested to add centerlines to achieve the full expectations of the flattening process. It is also advised but not required to add centerlines around islands, particularly if the islands have undulations that deviate significantly from the centerline.