| Attribute name | Label | Description |
|---|---|---|
| waterbody | ||
| wb_type | ||
| sac | ||
| wb_id | ||
| geom |
Marine SAC Freshwater Catchments Requiring Nitrogen Neutrality
Natural Resources Wales
The Marine SAC Freshwater Catchments Requiring Nitrogen Neutrality layer is a subset of the Nutrient Sensitive Marine SAC Freshwater Catchments layer. It only shows the three freshwater catchments that require nitrogen neutrality based on NRW’s advice letter of 25th July 2025 and maybe subject to future changes.
The Nutrient Sensitive Marine SAC Freshwater Catchments layer has been created in QGIS largely using the PCRaster toolset.
Data sources from DataMapWales:
- ‘LIDAR data download’ - comprising Welsh Government LIDAR 2020-2023
- ‘Wales Boundary’ (High Water Mark),
- ‘Wales National Marine Plan Boundary’ - (Normal Tidal Limit) - ‘SACs’
- ‘WFD Cycle 2 TraC Waterbodies’.
All Open Government Data sources.
Data Processing: (QGIS largely using PCRaster toolset)
- Native resolution LIDAR Digital Terrain Model (DTM) geotiff data was resampled at 10m x 10m resolution.
- DTM converted to PC raster format.
- DTM clipped to High Water using Wales (High Water Mark) polygon.
- DEM converted to Local Drain Direction (LDD) raster having filled pits in DTM (using ‘LDDcreate’ tool for both tasks)
- LDD raster processed (using ‘pit’ tool) to identify drainage outlets to the DTM boundary, creating an ‘outlets’ raster.
- LDD and Outlets rasters processed (using ‘catchments’ tool) to create upstream catchments flowing to the outlet points, one for each outlet. Created ‘catchments’ raster.
- Converted Catchments raster to vector format.
Tidying up and adding data attributes:
- The Catchments vector layer was clipped using the National Marine Plan boundary (Normal Tidal Limits) to better represent the land/sea interface and create a closer match with WFD Transitional water body boundaries.
- Catchment polygons were assigned values representing the SAC and WFD Transitional or Coastal waterbody they flowed into, or could directly affect (i.e. where adjacent) – created using the SAC and WFD Cycle 2 WB layers.
Adjustment for Marine SAC nutrient use:
- Catchments (polygons) with common combined Waterbody and SAC values were merged.
Where there was an obvious deviation between the freshwater catchment vector layer and the existing WFD river catchment layer, resulting from man-made interventions viewable on the map data, the freshwater catchment boundary was adjusted to align with the WFD river catchment water body boundary.
Attribution statement:
Contains Natural Resources Wales information © Natural Resources Wales and Database Right. All rights reserved. © Crown Copyright and Database Rights. Ordnance Survey Licence number AC0000849444, © Crown Copyright: Welsh Government.
Use this data in another application
Please refer to the licence to understand the conditions of using this data.
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- Type:
- Spatial data
- Category:
- Environment
- Publication date:
- 08 September 2025
- Licence:
- Open Government Licence for Public Sector Information (OGL)
-
Copyright:
- Point of contact:
- opendata@naturalresourceswales.gov.uk
- Language
- English
- Spatial Representation Type
- Vector data is used to represent geographic data