Hydrographic sections — Metropolitan 2016 — BD Carthage

An elementary hydrographic section is a related portion of rivers, streams or canals, homogeneous for the relationships involving it and for the attributes it bears. It corresponds to the axis of the bed of a river, stream or canal. This concerns: — on national territory: — all main axes, including in the estran area up to zero NGF and in marsh areas. ‘Sack cups’, whatever their length (at least 20 metres), are sufficient to ensure completeness in the case of traps longer than one kilometre or belonging to a river of more than one kilometre in length. — In addition to the main axis, the axes of the secondary arms or which delimit an island with an area greater than 10 hectares when a watercourse is subdivided into several. — Abroad: — all hydrographic sections which ensure the continuity, upstream or downstream, of the network of the national territory; — all sections of navigable canals; — major stretches of watercourses. Continuity of the network is ensured when water bodies, marshes, drainage areas and agglomerations are crossed. An elementary hydrographic section is represented by an arc. On the other hand, an arc may correspond to several basic sections where there is an overlay of the watercourses. The elements of the hydrographic network are cut into portions with the same attributes. The change in value of a attribute shall result in the creation of a section only if the new value remains the same over a length of at least 20 metres; Otherwise, the previous section is extended. The elementary hydrographic section is characterised by a set of attributes managed by the IGN: Condition, direction of flow, width, nature, airworthiness, gauge, position in relation to the ground. An elementary hydrographic section is not to be confused with the hydrographic section, a concept introduced by Circular No 91-50.