Saltmarsh Change

Saltmarsh Change Summary:

The Saltmarsh Change layer shows the recent change in saltmarsh extent across England, since a baseline inventory was completed in 2006 to 2009.

Dataset Description:

The Saltmarsh Change layer was created by comparing the 'baseline' version (v1_08) of Saltmarsh Extent with its 'most recent' version (v4_10). The baseline version was mapped from aerial imagery, primarily collected between the 2006 and 2009. The most recent version is based on imagery captured predominantly between 2016 and 2019. Since the production of the baseline (2006–09), almost 100% of England's saltmarsh has been remapped using later imagery. This dataset allows users to easily identify the differences between the two versions of the mapped extent, and identifies where areas of gain and loss have occurred. Each feature within the dataset contains one of the following change attribute classes:

• Gain • Loss • No Change • Not Remapped

The dataset provides valuable evidence of where saltmarsh is accreting and eroding across the whole of England, which is vital for flood and coastal risk management, and for ecological monitoring and reporting.

What has changed since the last update:

This change 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.

It has also been updated in 2023 and 2024, please see Saltmarsh_Change__Dataset_Documention.doc on the file tab for details of Water bodies updated in Version 4_09 and Version 4_10. If you require Water Environment Regulation (WER formally WFD) water body attribute information for the salmarsh change layer please contact Deborah Coates, contact details in contacts section.

Limitations & Other Guidance:

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' and ‘Month’ attributes for the timing of image capture of both the 'baseline v1_08' (Year 1) and 'most recent v4_10' (Year 2) inventory.

Users should bear in mind that some instances of change may be a result of the seasonal differences in the timing of image capture.

Further Information:

Saltmarsh extent has been interpreted (using a consistent technique) from aerial imagery, primarily collected through the Regional Coastal Monitoring Programmes, and other estuarine and coastal strategy monitoring programmes. 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 represents <5% of the ground cover. Mapped extents have been ground-truthed using data collected by the Environment Agency and Natural England. 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/.