Update graph_utilities.py

Fix new double_directed

swmmanywhere/graph_utilities.py

@@ -371,8 +371,22 @@ def __call__(self, G: nx.Graph, **kwargs) -> nx.Graph:
         Returns:
             G (nx.Graph): A graph
         """
+        # Convert to directed
         G_new = G.copy()
         G_new = nx.MultiDiGraph(G_new)
+
+        # MultiDiGraph adds edges in both directions, but rivers (and geometries)
+        # are only in one direction. So we remove the reverse edges and add them
+        # back in with the correct geometry.
+        # This assumes that 'id' is of format 'start-end' (see assign_id)
+        arcs_to_remove = [(u,v) for u,v,d in G_new.edges(data=True)
+                          if f'{u}-{v}' != d.get('id')]
+
+        # Remove the reverse edges
+        for u, v in arcs_to_remove:
+            G_new.remove_edge(u, v)
+
+        # Add in reversed edges for streets only and with geometry
         for u, v, data in G.edges(data=True):
             include = data.get('edge_type', True)
             if isinstance(include, str):