Saltmarsh Extent & Zonation

Saltmarsh Extent and Zonation Summary:

The Saltmarsh Extent & Zonation V4_10 layer was mapped from aerial photography collected predominantly between 2016 and 2019.

Dataset Description:

Polygon data layer showing the extent of saltmarsh in England, for use in flood and coastal risk management, and for ecological monitoring and reporting. Saltmarsh extent has been interpreted from aerial imagery (typically 20 x 20 cm resolution), collected predominantly between 2016 and 2019. The demarcation of the landward extent is aimed to be the point at which the upper most zones give way to terrestrial plants (often at the foot of a seawall), and where saltmarsh plants become ≤5% of the predominantly terrestrial community. At the seaward end, the final demarcation is aimed to be where the saltmarsh vegetation cover has become so sparse it only represent <5% of the ground cover. How the saltmarsh has been defined is described in detail in the ‘Saltmarsh mapping standardisation for the Water Framework Directive’ document (Hambidge and Phelan, 2014), available online at https://www.nmbaqcs.org/scheme-components/under-development/reports/.

Over 95% of the national extent has been mapped to zonation level. Zonation classes are as follows: • Pioneer • Spartina • Mid-low • Upper Marsh • Reedbeds • Unclassified (saltmarsh; but not classified to zonation level)

These zones reflect ecological communities within saltmarsh habitats required for ecological assessment purposes. The mapped extent and zonation has been ground-truthed with data collected by the Environment Agency and Natural England.

The aerial imagery used was primarily collected through the Regional Coastal Monitoring Programmes and other estuarine and coastal strategy monitoring programmes.

What has changed since the last update:

This layer was published in August 2022 to coincide with the release of the report 'The extent and zonation of saltmarsh in England 2016 - 2019' https://www.gov.uk/government/publications/the-extent-and-zonation-of-saltmarsh-in-england-2016-2019.

The layer was also updated in 2023 and 2024, to view the Water Environment Regulation (WER, formally WFD) water body extent and zonation changes in these versions 4_09 and 4_10 please see the Saltmarsh_Extent_and_Zonation_Documentation.doc under the files section. If you require information on WER water body attributes associated with this salmarsh layer please contact Deborah Coates, contact in contacts section.

Guidance and Limitations: The dataset includes saltmarsh within 63 managed/unmanaged realignment and regulated tidal exchange sites (including Medmerry, Hesketh and Steart). Users should be aware that in some cases, local aerial mapping outputs have been fairly simply embedded into the national layer. In other cases, full mapping using aerial imagery was undertaken.

Users should refer to the 'Year' attributes for the timing of image capture, from which extent and zonation mapping has been undertaken. Extent and zonation were typically mapped from the same year of imagery. However, in some instances these years do differ.