Data Platform Wiki

Data Platform Wiki

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Welcome to our wiki page, offering supplementary explanations and guidance to our data platform:

Glossary

CSA - Cross Sectional Area
MLWN - Mean Low water Neaps
MHWN - Mean High Water Neaps
MLWS - Mean Low Water Springs
MHWS - Mean High Water Springs
NNR - National Nature Reserves
SD (Std. Dev.) - Standard Deviation
SMP - Shoreline Management Plan
SAC - Special Area of Conservation
SSSI - Sites of Special Scientific Interest

Shoreline Management Plans (SMP)

SMP

Our data supports the strategic approach to flood and coastal erosion risk management, detailed in the Shoreline Management Plans (SMP). Our 'Survey Units' are geographically bounded coastal cells established in the SMPs (aka 'Policy Units'). To learn more about SMPs click here.

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.

We conduct two types of survey:

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.

We use the 4 vertical datums and the 'back of beach' chainage, shown here, to calculate cross sectional area.

CSA

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.

This allows us to see how that CSA trends over time.

What can I learn from changing the datum?

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.

Datums

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.

The box and whisker graph (right) displays the CSA SD values from multiple surveys, which describes the distribution or natural variability of the profile. Values >2 or <-2 SD would be considered 'high variability'.

Survey Unit Status

SU Status

Survey unit 'Status' calculates a value from the most recent survey and compares it against all previous surveys, to give an indication of the survey unit's current state of variability.

Survey units can contain multiple profiles spatially, (see the satellite image below). Our survey unit 'Status' averages profile standard deviation values of all the profiles in that survey unit from the most recent survey only. For Example, in the Survey Unit 8c15.1 shown in the satellite image below, the average SD is calculated across 17 profiles. The scale is 'absolute' which means any negatives SD values have been transformed to positives. This is to allow for alongshore variability within a survey unit where positive and negative profile SD values could average to zero - avoiding a misleading score for a beach where a lot of change is occurring.

Low Variability; 1 SD from the mean (68% of all results fall within this range)
Moderate Variability; between 1-2 SD from the mean (95% of all results fall within 0-2)
High Variability; is more than 2 SD from the mean (only 5% of all results will have an SD over 2)

Hydrodynamics

Wave power data demonstrates the short term antecedent hydrodynamic conditions. Long term seasonal wave events are also shown to provide context. The graphs are generated using E.U. Copernicus Marine Service Information.

Dates of named storms are from the Met Office UK Storm Centre.

Wave Power Equation

The return period of extreme wave height events has been calculated using extreme value analysis in python using the pyextremes package. The 'storm' threshold value was selected as the 95th percentile value (the top 5% of significant wave height values were classified as 'storm'). The peaks over threshold (POT) method was used, classifying any top 5% value within 16hrs of another to be one storm event to avoid capturing the same event multiple times. A return period of 1 year (365.2425 days) was used with a Weibull distribution in order to give the return period of each significant wave height 'storm' event. The return periods were then grouped by size of the event and the number of events in each year (from September to August to include an entire storm season) was counted e.g. a 2.568 return period value was grouped as a 1 in 1 year event, a 11.450 return period value is grouped as a 1 in 10 year event.
More details

What do the wave return periods mean?

Return periods are an estimate of the likelihood of an event to occur;

1 in 1/4 year (400% annual chance of occurrence)

1 in 1 year (100% annual chance of occurrence)

1 in 10 year (10% annual chance of occurrence)

Count of Extreme Wav Events by Winter Period.png

Plot Downloading

Hovering your mouse pointer over a plot will reveal additional buttons in the top corner of the plot. Here, you are provided the option to 'copy' an image for your own use or records.

Data Downloading

Ascii format data and reports are hosted by the National Network Regional Coastal Monitoring Programme (NNRCMP) and can be downloaded from their data download portal. Wales started collecting NNRCMP compliant data in 2019. For data prior to 2019 please use the contact us form

This video is an aid to downloading data from the NNRCMP portal

Data Use

CSA - It's important to clarify that the reported values represent theoretical Cross Section Area (CSA). This means the actual amount of mobile sediment on the beach might differ due to factors like underlying structures or local geology. However, theoretical CSA provides a valuable shorthand for comparing changes between profiles, especially when detailed information about the subsurface isn't available.
CSA - Profile height measurements have a vertical accuracy of ±30mm as detailed in our survey specification, available on our contractors page.
Timescales - Coastal systems exhibit natural variability across various timescales, including seasonal fluctuations and long-term cycles. Short datasets may not capture this full range of variability, potentially limiting assessments of climate change impacts.
Hydrodynamic Data Resolution and Limitations - This dataset provides offshore wave information on a grid with a resolution of approximately 1.5 kilometers. This means the data represents average conditions within each grid cell and may not reflect the specific wave conditions experienced at a particular point, especially near the coast. The data can only be taken as an indicator of trends.
Hydrodynamic Data Source - The wave data used here is hindcast reanalysis, which means it's a computer simulation of past wave conditions based on historical data. Find more information on quality here.
The data visualizations presented in this report are intended for preliminary assessment of coastal change. Due to inherent uncertainties in beach profile data, such as theoretical Cross Section Areas (CSA) and ±30mm vertical accuracy in height measurements, these visualisations should not be used in isolation for critical decision-making. As described above, all data can be downloaded for comprehensive analysis.