Hydrographic Zones — Guyana 2015 — BD Carthage

Circular No. 91-50 of 12 February 1991 on hydrographic codification and spatial identification of surface aquatic environments in metropolitan France defines the hydrographic zone as follows:

“The whole French territory is divided into elementary zones called hydrographic zones. Their boundaries are based on those of the topographic watersheds (in whole or in part)”.

A zone is a partition of a subsector that can include up to 10. It is entirely within a river basin boundary and serves, together with other elements, to delineate various programming or regulatory areas such as the Water Planning and Management Schemes, sensitive areas, water bodies mentioned in the European Framework Directive of 23 October 2000.

A hydrographic area covers, in part or in whole, the territory of one or more municipalities. Conversely, the territory of a municipality is either fully included within a hydrographic zone or split between several zones.

Different scenarios of the hydrographic area may exist:

a — The main watercourse of the hydrographic zone has its source within the area: it is an upstream area whose contour corresponds to that of the topographic catchment area of the main stream at the exit point of the area.

B — The hydrographic area is crossed by the main watercourse and the downstream pk is not 1000: it is an intermediate watershed,

C — The hydrographic area is crossed by the main stream whose downstream point corresponds to pk 1000: this is the downstream area of the catchment area,

D — The hydrographic area is on the shoreline. Three scenarios:
* or it is a main stream that has its source in the area: this is then case (a),
* or this downstream area is the last intermediate basin before the mouth of the main river: this is then case (c),
* or the area includes a coastal line with the mouth of the coastal river and areas drained by “ruses” directly entering the sea,

e — The area does not have surface discharge but nevertheless receives endoreic streams located upstream.

The list of hydrographic areas shows two specific cases:

— To avoid the creation of frontier hydrographic regions, five hydrographic zones on the border border with Italy or Spain (codes Y670 and Y680 corresponding to two ends upstream of the Po basin, S910, S911 and S912) have been linked to the coastal hydrographic regions (codes S and Y) of the basin districts on which they depend,
— Although the hydrographic logic would require the zone U204 (sub-basin of the Jougnena belonging to the Rhine basin) to be attached to the Rhine-Meuse basin district, it is nevertheless attached to the district of Rhône-Méditerranée-Corse (Regional Region “Saône”) given the small size of this area and its remoteness from the Rhine-Meuse basin,
— Although the hydrographic logic would require that the areas of sector D0 (Sambre basin in France) be allocated to region B (Bassin de la Meuse) they are administratively linked to the Artois Picardie basin district in view of the remoteness of the Meuse and Sambre basins in France and the confluence of these two rivers operating abroad.

1991年2月12日发布的第91-50号通告，针对法国大都市地区地表水环境的水文编码与空间标识工作，将水文区域（hydrographic zone）定义如下：
“法国全境被划分为名为水文区域（hydrographic zone）的基础单元，其边界以地形流域（topographic watershed）的边界（全部或部分）为依据划定。”
单个水文区域是子流域的划分单元，单个子流域最多可包含10个此类区域，且所有水文区域均完整处于某一河流流域（river basin）的边界范围内，可与其他要素共同划定各类规划或监管区域，例如《水规划与管理计划》、敏感区域，以及2000年10月23日发布的《欧盟水框架指令（European Framework Directive）》中提及的水体（water bodies）。
单个水文区域可覆盖一个或多个市镇的全部或部分辖区；反之，单个市镇的辖区要么完整隶属于某一个水文区域，要么被分割至多个水文区域之中。
水文区域存在以下多种类型：
a. 水文区域的主干河道的源头位于该区域内部：此类区域为上游区域，其边界与主干河道在区域出口处的地形汇水区（topographic catchment area）边界一致。
b. 主干河道穿过该水文区域，且下游里程桩号（pk）未达1000：此类区域为中间流域。
c. 主干河道穿过该水文区域，且其下游终点的里程桩号为1000：此类区域为汇水区的下游区域。
d. 该水文区域位于岸线地带，包含以下三种子情形：
* 主干河道的源头位于该区域内部，此类情形即上述a类；
* 该下游区域为主干河道入海口前的最后一个中间流域，此类情形即上述c类；
* 该区域包含沿海岸线，涵盖沿海河道入海口以及由直接入海的"ruses"汇水形成的区域。
e. 该区域无地表径流，但承接上游的内流河（endoreic streams）来水。
水文区域名录中存在两类特殊情形：
—— 为避免形成边境水文区域，与意大利或西班牙接壤的5个水文区域（代码Y670、Y680对应波河（Po basin）流域上游的两个端点，以及S910、S911、S912）已被划归至其所属流域片区的沿海水文区域（代码S与Y）。
—— 尽管按水文逻辑，隶属于莱茵河流域（Rhine basin）的若格纳（Jougnena）子流域U204应划归莱茵-默兹流域片区（Rhine-Meuse basin district），但鉴于该区域面积狭小且距离莱茵-默兹流域片区较远，其实际被划归至罗讷-地中海-科西嘉流域片区（Rhône-Méditerranée-Corse，对应"Saône"行政区）。
—— 尽管按水文逻辑，法国境内的桑布尔河流域（Sambre basin）片区D0的区域应划归B片区（默兹河流域（Bassin de la Meuse）），但鉴于法国境内的默兹河与桑布尔河流域相距较远，且两河的汇流点位于法国境外，因此该区域在行政上被划归至阿尔图瓦-皮卡第流域片区（Artois Picardie basin district）。