Catchment
Catchment
Definition
A catchment is an area of land that is drained by a river and its tributaries.
Delineation criteria
Delineation can be made based on the topographic divide (watershed) using digital elevation models (DEM) and a Geographic Information System (GIS), or with an existing catchment boundary database.
Methods and Data sources
- Digital elevation models (e.g. EU-DEM) using GIS algorithms to delimit the divide
- EU-wide CCM2 River and Catchment Database (v2.1) or EEA Ecrins (connected watersheds, rivers, lakes, monitoring stations, dams) data set
Simple GIS tools are available to create a river network and delineate the catchment boundary for any location on a river network based on a DEM. In theory, this process should be relatively easy using existing DEMs and widely available GIS algorithms. In practice the process is often quite difficult. In particular, delineation of headwater streams can be problematic if valley width is less than DEM resolution, while vertical accuracy of DEMs often causes problems in flat, plain regions. Further complications in terms of subsequent interpretation of hydrology can arise due to water transfer infrastructure and changes in underlying geology, which may lead to the effective watershed not coinciding with the topographic watershed.
Accurate digital mapping products could also be utilised. At pan-European scale, the CCM2 River and Catchment Database v2.1 (Table 3.2) is a purpose-designed product. The CCM2 database was originally defined using the SRTM 90 m DEM but it has been refined continually to remove errors in river line positions. While exact channel planform boundaries are not defined in CCM2, the database can be utilised to define catchment boundaries and quantify the upstream contributing areas to any point on a river network.
The River Frome catchment is a medium-sized, lowland, calcareous catchment located in southern England.
