Kral, F.; Fry, M.; Dixon, H.

Integrated Hydrological Units of the United Kingdom: Hydrometric Areas without Coastline

This dataset is part of Integrated Hydrological Units (IHU) of the UK, a set of geographical reference units for hydrological purposes including river flow measurement and hydrometric data collection. 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. Hydrometric Areas are the coarsest units of the IHU in terms of spatial resolution. This dataset represents the same entities as the Hydrometric Areas with Coastline. The coastline of Hydrometric Areas without Coastline follows the boundaries of the CEH Integrated Hydrological Digital Terrain Model, from which IHU were derived, while the coastline used in Hydrometric Areas with Coastline was derived from Ordnance Survey data. The Hydrometric Areas without Coastline currently covers Great Britain only as no dataset with river geometries and names with suitable detail is available for Northern Ireland.

Publication date: 2015-02-03

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You must cite: Kral, F.; Fry, M.; Dixon, H. (2015). Integrated Hydrological Units of the United Kingdom: Hydrometric Areas without Coastline. NERC Environmental Information Data Centre.


This dataset is part of the following


Study area
Temporal extent
2014-08-20    to    …


The main inputs for development of Integrated Hydrological Units (IHU) of the UK were data held by the Centre for Ecology and Hydrology. Specifically, the cumulative catchment area raster and outflow raster from the Integrated Hydrological Digital Terrain Model (IHDTM) [1]. The vast majority of the watercourse names come from the subset of CEH UK river centreline network enriched by names from Ordnance Survey 1:50K Gazetteer [2]. Some names were obtained from or verified using other readily available sources like OpenStreetMap ( and WikiPedia ( Bespoke FORTRAN functions, part of the CEH Flood Estimation Handbook code set, were used for catchment delineation. These functions enable sensible interlocking catchments boundaries to be created for the whole IHDTM surface. The option that does not leave gaps between catchments was specified [1]. Except for the catchment delineation, ArcGIS was used as the main GIS platform. Custom Python code was developed to drive the whole process and to perform hierarchical and network tasks. The full name of each IHU Section was derived from three rivers defining the section: the largest (in terms of cumulative catchment area) inflowing river other than the main river in the Section, the main river in the Section, and the largest river flowing into the downstream Section. If no such inflows exist, words ‘Source’, ‘Sea’, or the name of the main river in the downstream Section are used as appropriate. A similar approach was adopted for IHU Group names, although group names were edited manually to a great extent to ensure they are simple and readily understood. [1] Morris, D.G. and Flavin, R.W. 1990. A Digital Terrain Model for Hydrology. Proc 4th Int. Symposium on Spatial Data Handling. Zurich, 1, 250-262. [2] Moore R V, Morris D G and Flavin R W, 1994. Sub-set of UK digital 1:50,000 scale river centreline network. NERC, Institute of Hydrology, Wallingford.


Kral, F.
Centre for Ecology & Hydrology
Fry, M.
Centre for Ecology & Hydrology
Dixon, H.
Centre for Ecology & Hydrology

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Point Of Contact
Centre for Ecology & Hydrology
Maclean Building, Benson Lane, Crowmarsh Gifford
OX10 8BB
United Kingdom
Centre for Ecology & Hydrology
Environmental Information Data Centre
NERC Environmental Information Data Centre
Environmental Information Data Centre


Spatial reference system
OSGB 1936 / British National Grid


Topic categories
Inland Waters
Other keywords
Geospatial / Map
Catchments and Topography
CEH Topic
Rees Section
Discipline keywords
Place keywords
United Kingdom
Great Britain

Dataset identifiers



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