Generate geometric representations of streams

[richpsharp]

This issue comes from prototyping a flood risk model that requires backfill from each of the junctions in a Strahler stream system. It will also be useful for automatic derivation of flow accumulation parameters by studying the statistical difference in drop depths from Strahler stream order 1s to 2s (this comes form https://www.researchgate.net/publication/2329568_Advances_in_the_Mapping_of_Flow_Networks_From_Digital_Elevation_Data)