Physical measurement of cliff loss in the glacially deposited clays of the East Yorkshire coast began in 1951 using a series of erosion posts. Prior to this date, estimates of recession of the land relied on a comparison of cliff lines drawn on Ordnance Survey maps.
An improved system employing GPS technology was introduced in 1999, becoming fully applied at regularly spaced monitoring profiles in 2003. Almost all erosion posts were abandoned in 2010, with the remainder gone by 2013.
Information on cliff loss measurement since the middle of the nineteenth century is available at data in detail.
Only a few erosion posts and monitoring profiles approximate as regards location. An Excel spreadsheet has been prepared which attempts to overcome the difficulty and combine the two data sets.
the combined data sheet
Rows represent the coast from just south of Bridlington to the neck of the Spurn peninsula, each row standing for a 100 metre stretch. There are 580 such rows.
Columns represent full years from 1951 to 2016. There are 66 such columns.
A year is deemed to be that in which the erosion occurred, not the year of measurement. Readings from twice-yearly monitoring are added together to make the year.
Annual cliff loss figures in metres for erosion posts and for monitoring profiles are inserted relative to location within the 100 metre scheme. Brief descriptions of locations appears at the right of the data (coordinates can be obtained from respective data sheets: posts and profiles).
Gaps appear in the posts data when no readings were taken. Sometimes, posts were lost to erosion and had to be renewed.
Cumulative readings following breaks in measurement have been averaged out, or ‘smoothed’, over the period to which they relate. Although not entirely satisfactory, smoothing does at least prevent untrue peaks of erosion appearing in the data.
The data set for monitoring profiles is, apart from a couple of brief instances, complete from 2003 to 2016.
sediment migration and cliff loss
The design of the above spreadsheet may seem a somewhat unwieldy way to present cliff loss data. However, a representation of the coast in 100 metre units allows for the depiction of related sediment movement.
Two pages, sediment segmentation and migration chart, set out a model to explain the way in which material that forms the beach is drifted southwards down the coast in the form of long bodies or segments of sediment that curve towards the low water line.
As segments pull away from the near cliff, beach level is lowered and increased erosion may be expected.
pace of sediment movement
Earlier researchers, notably Ada Pringle and Anne Scott, referred to the sites of reduced beach as ord systems, or ords. Crucially, an estimate of the rate of ord movement resulted from their observations.
Calculated from a number of surveys conducted between 1969 and 1983, particularly 1977 to 1983, average migration is put at 496 metres per year, with variation from 5 to 775 metres. Perusal of beach contour levels for recent years would support the figures.
It follows that an estimate of the rate of ord movement can be applied to the sediment segments that define ords.
Trend paths for salients are added to the combined data spreadsheet using a coloured cell fill. ‘Salient’ is the term adopted for the northern end of a segment, nearest the cliff, regarded in the migration chart as lying within a contour minimum of +3.5 metres OD.
At steps of 100 metres, the average pace of migration appears as 500 metres per year. Over the 66 years covered, the difference from the estimated rate of 496 metres amounts to 264 metres, about half the length of a monitoring profile.
migration in the data
The chart on the left presents average annual rates of cliff loss when cells are totalled through the combined data spreadsheet along paths that imitate those of the colour filled cells representing sediment movement.
These averages should not be confused with linear row and column averages included in the combined data spreadsheet, which indicate rates for a particular location (rows) or for a specific year (columns).
Each path reflects the condition of the cliff line dynamically through time and over distance as sediment is drifted down the coast.
Path totals that produce the chart are available in a separate list. The period covered is 1951 to 2015.
On the chart, locations of trend lines for salients are shown as at 2015, placed opposite relevant monitoring profile numbers located from north of Barmston to Neck of Spurn.
Peaks of cliff loss tend to occur below a trend line, or a little south of a sediment salient, as the model describes. Some peaks coincide with a trend line. Possibly, there are elements of delayed erosion, or adjustment as a sediment segment passes through a terminal groyne effect zone.
The bottom part of the chart continues with paths associated with segments now lost and dispersed beyond the southern end of the coast. Data becomes increasingly partial, but the peak and trough sequence of cliff loss remains intact.