Longest flow length in ArcPy?

Question

I have to generate LONGEST FLOW PATH(polyline) within watershed. What is the procedure to generate this ? After generating longest flow length , I will divide polygon with polyline. I have :

• watershed layer(polygon)
• stream layer(polyline)
• Digital Elevation Model (DEM) layer

I am using .NET and python in ArcGIS 10. I have tried "FlowLength()" http://pro.arcgis.com/en/pro-app/tool-reference/spatial-analyst/flow-length.htm method , but it gives raster output. I tried to convert this raster dataset to polyline. this was my procedure.

I have attached an image to simplify this problem.

enter image description here

• Nxaunxau: Have you tried the ArcHydro toolkit?
• Hornbydd: You will have a problem when it comes to cutting your catchment into the 2 halves. Unless the initiation of the river path is generated upstream of the catchment then it will almost certainly be the case that the rivers upstream end does not cross the catchment boundary and you won't be able to do the cut...

Answer 1

Input: enter image description here

Catchments table:

enter image description here

WORKFLOW TO DERIVE LONGEST FLOW PATHS:

arcpy.PolygonToRaster_conversion(in_features="subcatchments", value_field="ID", out_rasterdataset="D:/Scratch/CATCHM")
arcpy.gp.FocalStatistics_sa("CATCHM", "D:/Scratch/RANGE", "Rectangle 3 3 CELL", "RANGE", "DATA")
arcpy.gp.RasterCalculator_sa("""Con("RANGE" == 0,"CATCHM")""", "D:/Scratch/ISLANDS")
arcpy.gp.RasterCalculator_sa("""Con( ~IsNull("ISLANDS"),"dem")""", "D:/Scratch/FENCED")
arcpy.gp.Fill_sa("FENCED", "D:/Scratch/FILLED", "")
arcpy.gp.FlowDirection_sa("FILLED", "D:/Scratch/FDIR", "NORMAL", "")
arcpy.gp.FlowLength_sa("FDIR", "D:/Scratch/FLEN", "DOWNSTREAM", "")
arcpy.gp.ZonalStatistics_sa("ISLANDS", "VALUE", "FLEN", "D:/Scratch/LENMAX", "MAXIMUM", "DATA")
arcpy.gp.RasterCalculator_sa("""Con("LENMAX" == "FLEN","ISLANDS")""", "D:/Scratch/MAXPNTS")
arcpy.DeleteIdentical_management(in_dataset="SOURCES", fields="GRID_CODE", xy_tolerance="", z_tolerance="0")
arcpy.gp.CostPath_sa("SOURCES", "FDIR", "FDIR", "D:/Scratch/CPATHS", "EACH_CELL", "GRID_CODE")
arcpy.gp.StreamToFeature_sa("CPATHS", "FDIR", "D:/Scratch/LongFPs.shp", "SIMPLIFY")

SPLIT CATCHMENTS (DEM cell size = 1*1):

arcpy.FeatureToLine_management(in_features="subcatchments", out_feature_class="D:/Scratch/ARCS.shp")
arcpy.Merge_management(inputs="ARCS;LongFPs", output="D:/Scratch/MERGED.shp", field_mappings="""ID "ID" true true false 10 Long 0 10 ,First,#,ARCS,ID,-1,-1""")
arcpy.ExtendLine_edit(in_features="MERGED", length="15 Meters", extend_to="EXTENSION")
arcpy.FeatureToPolygon_management(in_features="MERGED", out_feature_class="D:/Scratch/splits.shp", cluster_tolerance="", attributes="ATTRIBUTES", label_features="")
arcpy.SpatialJoin_analysis(target_features="splits", join_features="subcatchments", out_feature_class="D:/Scratch/FINAL.shp", join_operation="JOIN_ONE_TO_ONE", join_type="KEEP_ALL", field_mapping="""Id "Id" true true false 6 Long 0 6 ,First,#,splits,Id,-1,-1;ID_1 "ID_1" true true false 10 Long 0 10 ,First,#,subcatchments,ID,-1,-1""", match_option="WITHIN", search_radius="", distance_field_name="")

OUTPUT LABELLED BY COUNT OF PARTS:

enter image description here

As one can see some manual editing of MERGED lines (no split happened to catchment 4) or FINAL (too many splits of catchment 10) will be needed

• FelixIP: If it solved your problem, mark it please
• Monir: I have tried your code to arcgis python console with my data set. I have done successfully upto : .... .... arcpy.gp.RasterCalculator_sa("""Con("LENMAX" == "FLEN","ISLANDS")""", "D:/Scratch/MAXPNTS") I can not understand your input "SOURCES" at this execution and got exception : arcpy.DeleteIdentical_management(in_dataset="SOURCES", fields="GRID_CODE", xy_tolerance="", z_tolerance="0"). Is "SOURCES" input my "watershed", "DEM" or "Stream" ?? Thanks.
• FelixIP: There is a missing line, sorry. Raster MAXPOINTS has to be converted to points (raster to points) and called SOURCES
• Monir: Many many thanks . It works perfectly. If I have any inquiry , contact with you later. :)
• Monir: I have faced trouble in different data source. I have another data set and when I tried this code statement : arcpy.gp.ZonalStatistics_sa("ISLANDS", "VALUE", "FLEN", "D:/Scratch/LENMAX", "MAXIMUM", "DATA") ; It gives this error : arcpy.gp.ZonalStatistics_sa("ISLANDS", "VALUE", "FLEN", "D:/Scratch/LENMAX", "MAXIMUM", "DATA") Runtime error <class 'arcgisscripting.ExecuteError'>: ERROR 000864: Input raster or feature zone data: The input is not within the defined domain. ERROR 000367: Invalid GP data type . Have you any suggestion ??