Integrated Hydrological Units of the United Kingdom: Hydrometric Areas with Coastline

This dataset is part of Integrated Hydrometric Units (IHU) of the UK. Hydrometric Areas are used to organise river flow measurement and hydrometric data collection in the UK. Hydrometric Areas are either integral river catchments having one or more outlets to the sea or tidal estuary, or they may include several contiguous river catchments having topographical similarity but separate tidal outlets. In mainland Britain they are numbered from 1 to 97 in clockwise order around the coast commencing in north east Scotland. The larger islands and groups of islands are numbered from 100-108. Ireland has a unified numbering system from 1 to 40 commencing with the River Foyle catchment and circulating clockwise; not all Irish Hydrometric Areas, however, have an outlet to the coast. Only those Hydrometric Areas covering Great Britain and Northern Ireland are included in this dataset. The boundaries between hydrometric areas correspond to catchment boundaries as digitally-derived from CEH Integrated Hydrological Digital Terrain Model (IHDTM) using a catchment definition program. It should be noticed that the Northern Ireland data are clipped to its political boundary so not every Hydrometric Area in this region is completely represented.

The naming and numbering convention for the hydrometric areas in Great Britain was originally defined by the Inland Water Survey Committee (and first published in the Surface Water Year-Book of Great Britain 1936-37). For Northern Ireland the system was developed by a multi-agency working group in the 1970s (and first published in Surface Water: United Kingdom 1971-73. Note that full citations of those two publications are provided as additional information source.

This dataset represent the same entities as the IHU Hydrometric Areas of the UK without Coastline, however, the outer boundaries of the units follow coastline published by the Ordnance Survey (Meridian 2), rather than the boundaries of the CEH Integrated Hydrological Digital Terrain Model.

本数据集隶属于英国综合水文单元（Integrated Hydrometric Units, IHU）。水文区域（Hydrometric Areas）用于统筹英国的河流流量监测与水文数据采集工作。此类区域既可以是拥有一个或多个入海口或潮汐河口的完整河流集水区，也可以包含多个地形特征相似但拥有独立潮汐出水口的毗邻河流集水区。在英国本土，水文区域以苏格兰东北部为起点，沿海岸顺时针编号1至97；较大的岛屿及群岛则编号为100至108。爱尔兰采用统一的编号体系，以福伊尔河流域为起点顺时针编号1至40，但并非所有爱尔兰水文区域均拥有海岸出水口。本数据集仅涵盖覆盖大不列颠及北爱尔兰的水文区域。水文区域间的边界由CEH综合水文数字地形模型（CEH Integrated Hydrological Digital Terrain Model, IHDTM）通过集水区定义程序数字化提取所得，需注意的是，北爱尔兰的数据已按其行政边界进行裁剪，因此该区域内并非所有水文区域都能得到完整呈现。

大不列颠地区水文区域的命名与编号规则最初由内陆水文调查委员会制定，并首次刊登于1936-1937版《大不列颠地表水年鉴》。北爱尔兰的编号体系则于20世纪70年代由多机构工作组制定，首次发表于《地表水：英国1971-1973》。上述两份出版物的完整引用信息已作为附加数据源提供。

本数据集所涵盖的实体与英国不含海岸线的综合水文单元水文区域一致，但该单元的外边界采用英国地形测量局（Ordnance Survey）发布的子午线2号（Meridian 2）海岸线数据，而非CEH综合水文数字地形模型的边界。