Hydrographic sections — Metropole 2017 — BD Carthage

An elementary hydrographic section is a related portion of rivers, streams or canals, homogeneous for the relationships involved, and for the attributes it carries. It corresponds to the axis of the bed of a river, creek or canal. These are: — within the national territory: — all main axes, including in the foreshore zone up to zero NGF and in the marshes areas. ‘Sacks’, regardless of their length (at least 20 metres), completeness for culs de sacs over one kilometre in length or belonging to a watercourse 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 of more than 10 hectares when a watercourse is subdivided into several. — abroad: — all hydrographic sections that ensure the continuity, upstream or downstream, of the network of the national territory; — all sections of navigable canals; — important stretches of watercourses. Continuity of the network is ensured when crossing water bodies, marshes, drainage and agglomerations. An elementary hydrographic section is represented by an arc. On the other hand, an arc can correspond to several elementary sections when there is an overlay of streams. The elements of the hydrography network are divided into portions with the same attributes. The change in value of an attribute only results in the creation of a section 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, flow direction, 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.