Relationship to relevant (feature) models 
  HY_Features 
HY_Features model has some logical connection points through the related features in the HY_SurfaceWaterBody package: E.g. HY_River, Reach etc. There is also a HY_CrossSection which provides some geometric properties (area) and the reach geometry:
 
If sections are included in the scope it would be possible to relate some relevant features here. 
  INSPIRE 
INSPIRE is similarly focussed on the network structure and topology, but does identify core featuers that are relevant. E.g. water courses, physical features and man-made features (embankments, fords, dams etc.). All these types of objects are able to carry geometries but specifics are not defined. 
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PeterTaylor - 18 May 2012