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Data Platform Wiki

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

Profiles

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.

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.

Profile Graph3.png

Cross Sectional Area (CSA)

CSA

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.png

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.

CSA over time.png

Standard Deviation

SD
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In statistics the Standard Deviation (SD) is a measure of the amount of variation of a variable expected about its mean. We use the SD values shown on the x-axis of this normal distribution plot to represent the variability of each profile CSA.

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

CSA SD.png

Survey Unit Status

SU Status

Survey units can contain multiple profiles spatially, see the satellite image below.

Our 'survey unit status' averages profile SD values of all the profiles in that survey unit from the most recent survey. 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 the 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. That would be a misleading score for a beach where a lot of change is occurring. 

SUStatus.png
Alongshore Distribution.png

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 (5% remaining)  

Hydrodynamics

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.

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

Plot Downloading

Plot Downloading
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Hovering your mouse pointer over a plot will reveal additional buttons in the top corner of the plot. We are provided the option to 'copy' and image for our own use or records. Please reference our website if plots are used for reporting.

Data Downloading

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

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 in our documents, 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 LimitationsThis 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. For more information on quality.

  • 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 visualizations should not be used in isolation for critical decision-making.  As described above, all data can be downloaded for comprehensive analysis. 

Glossary

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 - Standard Deviation

  • SMP - Shoreline Management Plan

  • SAC - Special Area of Conservation

  • SSSI - Sites of Special Scientific Interest

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