Catchment Spatial Information Catchment Spatial Information - Index of Stations

Catchment Spatial Information - Overview

Each spatial information page features a small map showing the distribution of a given spatial dataset within the catchment. Gauging station locations are shown as a red dot. Gauged catchment boundaries were generated using the IHDTM (see Elevation below). Tabular statistics, which accompany the maps, were automatically calculated from their respective datasets; they are consistent across catchments but could differ to a small extent from similar statistics featured elsewhere. Each page has a link (top and bottom of the page) to the station's Summary Sheet; in a few instances, Summary Sheets may await derivation.

Elevation:

Elevation data were derived from the CEH Wallingford Integrated Hydrological Digital Terrain Model (IHDTM). The IHDTM is based on a 50 m grid interval (i.e. each cell represents 50 x 50 m²) with a 0.1 m vertical resolution. It is designed to be hydrologically consistent and is a core component of the Flood Estimation Handbook; given a user-supplied catchment outlet location, a grid of flow directions toward the outlet can be generated, from which the catchment boundaries are calculated. Each CSI page features an elevation map (Fig. 1), a hypsometric curve (Fig. 2), and a statistical table (not shown here). The hypsometric curve and the tabular data were derived from the IHDTM; some values (e.g. maximum elevation) may therefore differ slightly from those featured on other NRFA website components.

Example of elevation map

Fig. 1. Elevation map of station 2001

Example of hypsometric curve

Fig. 2. Hypsometric curve of station 2001

To order elevation data or to get further information, please follow this link

Geology:

The geological maps were derived from 1:625000 British Geological Survey (BGS) datasets. Two datasets were used: hydrogeology and superficial deposits (‘Drift’). These hydrogeological characterisations were chosen because of their water resource’s significance and influence on flow regimes. In collaboration with BGS, a bespoke key has been agreed which emphasises the influence of hydrogeology on river flow behaviour (distinguishing, in particular, between permeable/impermeable bedrock). Because many catchments do not have superficial deposits, it was decided to feature Drift as an additional layer optionally displayed on top of the hydrogeology rather than as a stand-alone map. Users can interactively display either the hydrogeology alone, or the hydrogeology and the superficial deposits by ticking a box (Fig. 3). Each CSI page features a statistical table in addition to the map. Note: many adjacent polygons, originating from different outcrops in the underlying dataset, were reclassified as the same hydrogeological category, therefore are displayed with the same colour; however, their boundaries were maintained on the maps (see Fig.3, left). The hydrogeological categories are based on the 1:625 000 hydrogeological maps of England and Wales, and of Scotland. The hydrogeological maps have six subdivisions, which are featured in the CSI module as detailed in Table 1. These directly correspond to the original categories with one exception; those formations that are of very low permeability but overlie aquifers (concealed aquifers) were moved from pale brown to dark brown, as the latter represents the permeability of the formation itself.

Hydrogeological subdivisions	CSI subdivisions	Colours

Highly productive fissured aquifers	High permeability (fissured)	Dark green

Locally important fissured aquifers	Moderate permeability (fissured)	Pale green

Highly productive aquifers with intergranular flow	High permeability (intergranular)	Dark blue

Locally important aquifers with intergranular flow	Moderate permeability (intergranular)	Pale blue

Areas underlain by impermeable rocks, generally without groundwater except at shallow depths	Very low permeability	Dark brown

Concealed aquifers; aquifers with limited or local potential	Mixed permeability	Pale brown

Table 1. Original and CSI hydrogeological subdivisions, and associated colour scheme

Example of hydrogeological map

Example of hydrogeological map with drift

Fig. 3. Geological map of station 2001; hydrogeology alone (left), hydrogeology and superficial deposits (right)

To order BGS data or to get further information, please follow this link

Land Use:

Land-use information were derived from the Land Cover Map 2000 (LCM2000). The satellite-generated LCM2000 was produced by CEH Monks Wood as part of the Countryside Survey 2000. The dataset has a 50 m resolution (one square represents 50 x 50 m²) and has 27 land cover categories. The categories have been grouped into seven broader classes (e.g. six distinct categories of grasslands were merged) that have significance from a hydrological point of view (Table 2). Each land-use CSI page features a land-use breakdown map (Fig. 4) and a statistical table. Note: Built-up areas tend to be overestimated.

Example of land-use map

Fig. 4. Land-use map of station 2001

Land Use	LCM2000 Classes

Woodland	Broad-leaved/mixed woodland Coniferous woodland

Arable & horticulture	Arable cereals Arable horticulture Arable non-rotational

Grassland	Improved grassland Setaside grass Neutral grass Calcareous grass Acid grassland Bracken Fen, marsh, swamp

Mountain, heath, bog	Dense dwarf shrub heath Open dwarf shrub heath Bog (deep peat) Montane habitats Inland bare ground

Built-up areas	Suburban/rural development Continuous urban

Water (inland)	Water (inland)

Coastal	Supra-littoral rock Supra-littoral sediment Littoral rock Littoral sediment Saltmarsh

Table 2. Land-use groups used in the website and their original LCM2000 categories

To order land-use data or to get further information, please follow this link

Rainfall:

Rainfall information were derived from the Standard-period Average Annual Rainfall (SAAR) map for 1961-1990, a 1 km grid based on data from the Met Office, from which isohyets were generated using a GIS 'contour' function. Each rainfall CSI page features an isohyet map (Fig. 5); the isohyets are colour coded using a standard template.

Example of isohyet map

Fig. 5. Rainfall map of Station 2001

To order Met Office data or to get further information, please follow this link

Catchment Spatial Information Catchment Spatial Information - Index of Stations