Administrative Boundaries - Water Management Areas

asNeeded

The Environment Agency Water Management Boundaries are based on amalgamations of river sub-catchments derived from a Digital Elevation Model (NextMap DEM) and a set of 1:10 000 scale river centrelines improved using local knowledge. The national outline is delineated to the Mean High Water Mark (OS Boundary-Line). The boundaries have been generated using hydrological modelling techniques using the data listed above as input datasets to define many small sub-catchments. Each of these sub-catchments has been combined with many others to create larger catchments. The pure river catchments have however been modified in a number of places for improved accuracy of the watershed delineation and more importantly for operational needs. Then the polygons of the areas for each area are merged to create the area boundaries.