Outlines/outfalls overview

[barneydobson]

There are a lot of issues that relate outline/outfall derivation. Furthermore, this choice has an enormous impact on the derived network. There is a sense that the current method needs improvement. In this PR I will explain the current processes and bring together existing issues. Here we can also discuss proposed improvements.

Three current options exist (two on swmmanywhere - which primarily take place in graph_utilities.py/clip_to_catchments):

• Clip to subbasin (i.e., parameters.py/SubcatchmentDerivation.subbasin_clip_method='subbasin'). Where subbasin is derived either using pyflwdir.snap or, if a non-None parameter is provided, using SubcatchmentDerivation.subbasin_streamorder=<int>. In this method, all potential pipe carrying links that span two subbasins are removed - thus flows always stay within a subbasin.
• Community threshold (SubcatchmentDerivation.subbasin_clip_method='community'). Subbasins are derived, as are communities using nx.louvain_communities. Communities with less than subcatchment_derivation.subbasin_membership proportion of nodes in a subbasin have their links to all other nodes in that subbasin removed.
• Bypass this issue by providing a user defined outline, and removing all nodes/catchments outside of that outline (see trim_to_real here ).

In addition to the processes above, if there are rivers near the street network, then further processing to identify which outfalls should be used takes place in graph_utilities.py/identify_outlets.

Grouping these issues below:

• General DEM-related features (these will inherently interact closely with subcatchment_derivation since both rely on DEM, but it is important to note that subbasins relate to the overall drainage of the network, while subcatchment refers to the individual catchment that drains to a given manhole):
  • Derive rivers from DEM rather than OSM #154
  • More efficient conditioning #141
  • Use RichDEM for conditioning #137
  • Add option to carve in clip_to_catchments #165
  • Downsample for prettier catchment outlines #138
  • Subcatchment derivation parameters #226
  • Match streets to rivers with attention to underlying DEM #201 (also related to below)
• Outfall identification-related features:
  • Enable switching of outfall detection method #203
  • Ensure each subbasin has an outfall #190
  • Match streets to rivers with attention to underlying DEM #201
  • outfall identification behaviour #314
• Louvain communities features:
  • Louvain community parameters #188
  • Louvain community performance #153
  • Using Leiden instead of Louvain for community detection #319