Elementary hydrographic sections — Mayotte 2013 — 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 harbours. 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.

The geometry is close to the BDTopo IGN, which has been used for its implementation.The BDCarthage Mayotte is maintained by DEAL Mayotte.The Carthage Mayotte is a version validated by the EIS but not by the IGN and therefore problems of incompatibility with IGN REFERENTIELS may arise (and an update “will formalise” the Carthage BD with IGN validation).

基本水文河段（elementary hydrographic section）指河流、溪流或运河中具有统一相关关系与固有属性的关联区段，对应河槽、溪槽或运河槽的轴线。

本数据集涵盖范围如下：
一、本国领土范围：
1. 所有主河道轴线，包括潮间带（estran）区域至法国零水准面（NGF）的区段，以及沼泽区域内的主河道轴线。对于长度超过1千米的汇水洼地，或隶属于长度超过1千米的河流的区段，无论其自身长度如何（至少需为20米）的"囊状蓄水段"（Sack cups），均可纳入以保证数据完整性。
2. 除主河道轴线外，当水网被分流形成多个汊道时，分隔面积大于10公顷岛屿的次级汊道轴线也需纳入。

二、境外范围：
1. 所有可衔接本国领土水网上下游连续性的水文河段；
2. 所有通航运河区段；
3. 大型河道区段。

当水网跨越水体、沼泽、汇水区与城镇建成区时，即可视为保持了网络连续性。

基本水文河段以弧段（arc）形式表示。反之，当存在河道重叠时，单个弧段可对应多个基本水文河段。水文网络的元素会被切割为属性一致的区段：仅当属性变更后的新值在至少20米的长度内保持稳定时，才会生成新的水文河段；否则，原河段将延续。

基本水文河段由法国国家地理研究院（IGN）管理的一系列属性表征，包括：河道状态、流向、宽度、河道性质、通航性、水位标尺、与地面的相对位置。

需注意，基本水文河段不可与1991年第50号通告（Circular No 91-50）引入的"水文河段"概念相混淆。

该数据集的几何数据近似于法国国家地理研究院BDTopo IGN数据库（BDTopo IGN），并以此为基础实现。马约特迦太基数据库（BDCarthage Mayotte）由马约特环境、规划与住房局（DEAL Mayotte）维护。该版本仅通过欧洲环境署（EIS）验证，未获得法国国家地理研究院（IGN）认可，因此可能出现与IGN参考基准（IGN REFERENTIELS）不兼容的问题——后续更新将通过IGN验证，正式完成马约特迦太基数据库与IGN标准的统一。