Hydrographic sections [BD TOPO®] - Department of the Channel

Definition of IGN: Axis of the bed of a river, stream or canal, homogeneous for its attributes and links and
not including a confluence outside its extremities.

Selection: All permanent streams, natural or artificial, are included

• Temporary natural streams are included, with the exception of stretches of less than 200 m located at
  extremities upstream of the network.
• Temporary artificial or artificialised watercourses are selected on the basis of their importance and
  the environment (sections along a communication route are excluded, as well as ditches).
• Talwegs that are not marked by the regular presence of water are excluded.
• Underground or busted sections more than 25 m long are retained.
• All watercourses over 7.5 m wide are included. They are represented by a Hydrographic Section
  of attribute Fictif="True" superimposed on an object of class Hydrographic surface.

In their downstream part, the rivers are represented at least up to the leash of the highest seas.

Ditches: large ditches more than 2 m wide are included when they sink permanently. The ditches
whose flow rate is not permanent are selected according to the environment. They are generally excluded
when they walk along a communication route.