As Britain\u2019s coastlines face growing pressure from heavier rainfall, rising sea levels and increasingly dynamic shorelines, Ordnance Survey\u2019s new continuous tidelines dataset offers a timely tool for understanding where land meets sea \u2013 and how that boundary is changing. By providing a consistent, up-to-date view of the coastline, the dataset has the potential to support more informed approaches to managing coastal erosion and flood risk across Great Britain. \n<\/p>\n
Earlier this year, the Environment Agency updated its national flood risk assessment (NaFRA), incorporating climate-related changes in flood risk for the first time. The assessment highlighted that a substantial share of homes and businesses in England are already located in areas vulnerable to flooding, with that exposure expected to increase over the coming decades. Alongside this, updated national coastal erosion risk mapping indicates that thousands of properties could be affected by coastal change within a single generation. \n<\/p>\n
Accurate coastal change monitoring<\/p>\n
The current OS National Geographic Database (OS NGD) Tidal Boundary line features have been automatically aggregated with the source features dissolved into continuous lines which form two new feature types within OS NGD Water \u2013 Tidal Boundary Continuous High and Tidal Boundary Continuous Low. The new dataset can also be used as overlay layers in the Tiles API, offering a clean, intuitive visual experience. They complement the NGD base layer and provide added value for contextual mapping and macro analysis.<\/p>\n
The dataset will support environmental monitoring & regulation including: \n<\/p>\n
\nCoastal erosion modelling – to understand impacts on people, property and infrastructure, enabling better risk management and strategic planning;
\nCoastal flooding modelling – to enhance preparedness and response; \u00a0
\nUpdating boundary features – to align with coastal change,\u00a0enabling accurate and effective environmental monitoring and regulation, and better management of natural resources;
\nClimate change assessments – to identify and evaluate the impact of climate change, enabling informed decision-making and effective adaptation strategies; and
\nUnderstanding the foreshore – to identify areas that provide natural flooding defences, essential for implementing flood risk management.
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William Russell,\u00a0senior coastal process scientist at the Wales Coastal Monitoring Centre, welcomed the new dataset. He said: “One of our core values is ‘data, not opinions’. When information is missing, we seek out or collect the data needed to support sound decision-making. The OS Continuous Tidal Boundaries dataset is a great example: it removes uncertainty from our strategic monitoring programme and gives us clearer insight into intertidal extents, delivering cost savings and efficiencies for our survey contractors.” \n<\/p>\n
\u00a0The new tidelines data is a valuable asset for those customers in environmental policy and regulation, and supporting evidence-based decisions relating to water discharge for example, whether from a regulatory or flooding perspective. Understanding where tidelines are helps in defining the intertidal zone, which provides a natural line of defence against coastal erosion and flooding. This in turn provides essential protection for coastal communities and ecosystems. Intertidal data has also been enhanced in the Land feature of the OS NGD. Adding data around obscured areas delivers a more complete and accurate coastal dataset across GB.<\/p>\n
Changing size of riverbanks<\/p>\n
Lily Brown,\u00a0product manager at Ordnance Survey, said: \u201cThe digital master map of Britain \u2013 the OS National Geographic Database\u00a0\u2013 contains trusted, accurate features that support a wide range of public and private sectors, from climate resilience and infrastructure planning to coastal management. This wealth of data delivers critical insights and by incorporating authoritative tideline data, we are enabling evidence-based decisions which will protect and monitor the nation\u2019s evolving coastlines.” \n<\/p>\n
Following the release of the continuous tidelines dataset, OS has ranked all ceremonial counties in GB by their percentage change in size between high and low tide.\u00a0Merseyside comes out top, much higher than the others, with a nearly 17% difference in high and low tidelines. Orkney has the second highest difference of 7%. Interestingly, counties considered to be landlocked, like Nottinghamshire and South Yorkshire, have rivers which are tidal for a long way upstream (the Trent and the Don respectively), so the changing size of the riverbanks causes a significant change in the size of the counties. \n<\/p>\n
The new datasets can also be overlaid with other information to enable essential location-based insights.\u00a0Combining the tidelines data with UPRNs in ceremonial counties shows that Greater London has by far the highest number of commercial and residential properties within 15 metres of high tides \u2013 around 5,500. \u00a0Cornwall ranks second, with just over 3,000 properties, followed by Devon with 2,400. [See table below]<\/p>\n
The new location data has been released as part of the\u00a0Public Sector Geospatial Agreement<\/a>\u00a0(PSGA). The PSGA is a contract between Government Digital Service, managed on behalf of the UK Government, and OS for the provision of geospatial data and services to the emergency services and wider public sector organisations. \n<\/p>\n
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