Coastal Flooding and Erosion
What is Coastal Flooding? Coastal flooding happens when the sea overflows onto the land. This can be caused by high tides, storms, and rising sea levels. It’s a growing concern in Wales due to climate change.
Profiles
Beach profiles are 2D measurements of elevation and distance (chainage) along a pre-determined line. The beach profile is measured from the back of the beach such as a sea wall and extend seaward until the Mean Low Water Spring (MLWS) elevation is reached (this is known as a vertical datum). You can find detailed instructions for profile surveys in the documents section for more information.
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We conduct two types of survey:
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BASELINE: High-density profile distribution. These surveys are costly and performed less frequently, but they provide high detailed and comprehensive data.
INTERIM: Low-density profile distribution. These surveys are cheaper and performed more frequently (bi-annually), offering insights into shorter-term trends (seasonal).
Over time beach profiles are repeated and their changes can be compared in a graph.
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We use the 4 vertical datums and the 'back of beach' chainage, shown here, to calculate cross sectional area.
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Cross Sectional Area (CSA)
Cross Sectional Area (CSA) is the area underneath the profile line from the back of the mobile beach to a specific vertical datum e.g. MLWS. Four examples of CSA are shown for the four datums below.
CSA is a single value to represent each profile. The time series chart displays a MLWN CSA from multiple survey dates.
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This allows us to see how that CSA trends over time.
What can I learn from changing the datum?
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If I use the datum selection in the menu I can choose;
MHWS - Mean High Water Spring is the average height of 'high waters of the spring tides'. Using this datum will show you changes above the intertidal area e.g. if a dune system is evolving.
MHWN - Mean High Water Neap is the average height of 'high waters of the neap tides'. Using this datum will show you changes to the top of the beach, e.g., this could inform you of changes closest to a sea wall.
MLWN - Mean Low Water Neap is the average height of the 'low waters of the neap tides'. A lot of historic data was collected to this datum and using this datum will provide data across most of the intertidal area.
MLWS - Mean Low Water Springs is the average height of 'low waters of the spring tides'. Using this datum will provide the most informed changes across the intertidal. The Wales Coastal Monitoring Centre have been surveying beaches to this datum since 2019. Data prior to 2019 may not exist for this datum. To unlock historic data, the MLWN datum can be selected.
Standard Deviation
In statistics, the Standard Deviation (SD) measures the amount of variation expected around a variable's mean. We use the SD values shown on the x-axis of this normal distribution plot to represent the variability of each profile's Cross Sectional Area.