Information CCMA: Frequently Asked Questions

Content

1. What’s this about in a nutshell?
2. What is coastal change?
3. Why is the CCMA erosion rate in most places, much higher than long term study areas, such as Pennington Point and East Beach, and Seaton Hole?
4. Why is there so much difference in areas such as East Beach and Seaton Hole between the CCMA data and existing studies?
5. Can we use the CCMA rates to help better fund our Beach Management Schemes?
6. What is the national approach to dealing with coastal change?
7. Can coastal change be predicted?
8. How is coastal change predicted at the moment?
9. Why is a new approach being considered?
10. Who has produced the new coastal change maps?
11. Have coastal change maps been produced for the whole of East Devon?
12. How have the new coastal change maps been produced?
13. How likely is it that the changes shown will happen?
14. How has the additional work been funded?
15. Where are the places most at risk of coast change?
16. How will the new information be used?
17. Can you explain in detail why the erosion rates differ at East Beach in Sidmouth?
18. Since the CCMA only uses data since 1998, does it suggest that erosion has increased since the 1994 flood scheme?

What’s this about in a nutshell?

The University of Plymouth have undertaken research that gives new predictions of coastal change. This indicates that, if erosion rates continue as they have for the past 20 years, more properties may be risk of coastal erosion than previously thought. These ‘frequently asked questions’ help to explain why new coastal change maps have been produced and what it might mean for future plans.

What is coastal change?

Our coastline is constantly altered by waves, tidal currents and the changing climate. Coastal change is the term used to describe any permanent physical change to the shoreline caused by processes such as erosion, landslip or flooding. It is anticipated that climate change will create increasing pressure on coastal and estuarine environments.

Why is the CCMA erosion rate in most places, much higher than long term study areas, such as Pennington Point and East Beach, and Seaton Hole?

Fundamentally, the difference is due to a reasonable worst case scenario being modelled for the CCMA, and a most likely (actual) erosion rate being used for our studies.  The CCMA rate also has additional 10m safety buffer, which is not included on our existing local studies.

Why is there so much difference in areas such as East Beach and Seaton Hole between the CCMA data and existing studies?

Aside from the differing (worse/likely) case scenarios and buffer zone, there is a fundamental difference in the way the data has been collected and analysed. The CMMA method is designed to be the same method wherever it is used on the UK coastline, therefore it only uses recent historical data (as this is available nationwide)  The existing studies at East Beach and Seaton Hole use historic data from the last 100 years including mapping and aerial photography studies, which were not included in the CCMA.

Can we use the CCMA rates to help better fund our Beach Management Schemes?

Unfortunately not. The majority of the funding for the BMPs come from central government and its administered by the Environment Agency. Current guidance indicates that reasonable worst case erosion rates cannot be used to justify funding.  Also larger funding requirements will attract greater scrutiny, therefore the CCMA study will unlikely be enough without additional study, taking in longer term erosion rates.

What is the national approach to dealing with coastal change?

The emphasis is on working with natural processes to adapt to coastal change rather than trying to prevent it. Local authorities are expected to identify the areas at risk of coastal change within 100 years and to use their planning powers to carefully control what is built and to allow development to move to a safer location where feasible.

Can coastal change be predicted?

To a degree, yes. This is the most accurate and up to date prediction, which has been produced using multiple data sources, agencies and expert judgement, but there is no guarantee that we can anticipate exactly what will happen in a local area and in what timescale.

How is coastal change predicted at the moment?

The government advises local authorities to use the shoreline management plan (SMP) as the main source of evidence for identifying areas at risk of coastal change. The SMP is a large-scale assessment of the risks associated with coastal processes and includes maps showing the expected shoreline position in 0-20 years, 20-50 years and 50-100 years (short, medium and long term). In East Devon the SMP does not show any significant loss of property or infrastructure in the short term, although it was adopted in 2011 and so we are already half way through the first 20 years and it is currently being refreshed to include the latest projections for climate change and sea level rise.

Why is a new approach being considered?

The SMP took a broad brush approach in order to achieve national coverage so it did not include the detailed work that is sometimes necessary to fully understand and predict complex coastal systems like the East Devon coast. Also, since the work was done on the SMP, there have been technological advances that enable much more accurate mapping of the coastal change that is actually happening. Plymouth University believe that these advances, coupled with factoring in the latest expectations of climate change, will result in a more accurate plan of the areas likely to be at risk from coastal change.

Who has produced the new coastal change maps?

The Coastal Processes Research Group in the School of Biological and Marine Sciences, University of Plymouth have undertaken the work in association with the Environment Agency, Natural England, the Marine Management Organisation and the local authorities of East Devon, North Devon and Torridge.

Have coastal change maps been produced for the whole of East Devon?

No, at the moment we only have new maps for the area from the east of the River Sid (Sidmouth) to the Dorset boundary at Lyme Regis. This has been used as a pilot study area by the University to pilot the new method for calculating cliff retreat, coastal change and coastal flooding.

How have the new coastal change maps been produced?

The University of Plymouth have devised a method for predicting coastal change related to the type of coast involved (estuary, cliff or beach). This is a complex process.  For example, to estimate future cliff line positions, past retreat rates are combined with predicted future sea level rise using scientific formulae. For estuaries predicted sea level rises are combined with existing flood mapping from the Environment Agency. If you want to read the papers produced by Plymouth University giving details of the methods developed they are available at South West Partnership for Environment & Economic Prosperity (SWEEP) - Plymouth Marine Laboratory. We have also produced a briefing note to guide consideration of the issues by our Strategic Planning Committee and this is available at Agenda for Strategic Planning Committee on Tuesday, 20th October, 2020, 2.00 pm - East Devon.

How likely is it that the changes shown will happen?

Plymouth University have estimated coastal change over the next 100 years using the most update information, but coastal change is a dynamic natural process so there is no guarantee that the changes will happen as predicted or that other areas won’t be affected over the next 100 years. Also, we have plans in place (through the Seaton and Sidmouth Beach Management Plans) for coastal protection works that are designed to reduce the rate of cliff erosion. It is important to note that the University work takes no account of these proposed coastal defence works.

How has the additional work been funded?

The research work has been funded by the South West Partnership for Environment and Economic Prosperity (SWEEP), which is a partnership project with the aim of delivering economic and community benefits to the South West, whilst protecting and enhancing the area’s natural resources.

Where are the places most at risk of coast change?

Generally the new maps show more variation than the Shoreline Management Plan in the extent of areas potentially affected by coastal change. This means that some areas that are not shown to be affected in the SMP are now included in the area at risk and some of the areas shown to be at risk in the SMP are not included in the new mapping. It is important to note that the new maps for cliff erosion include a ten metre ‘buffer’ inland of the predicted coastal change and all references to places refer to the land within this buffer.

Areas that are predicted to experience less erosion than the SMP maps include:

• The section of coast from Seaton to Lyme Regis.
• Much of the coast west of Highcliffe close in Seaton, through Beer to the east of Branscombe mouth; and
• The majority of the coast from Branscombe mouth to the cliffs east of Sidmouth (roughly south of ‘Southdown’.

Areas where more erosion is predicted in the new maps compared to the SMP are:

• In Seaton including some properties accessed off Beer Road and the Highcliffs Close area;
• Two small areas either side of Branscombe mouth; and
• Land in Sidmouth east of the River Sid including properties accessed off Cliff Road, Beatlands Road, Southway, Laskeys Lane and Alma Road.

How will the new information be used?

The main purpose of the Plymouth University work is to develop a robust method for identifying areas at risk of coastal change that can be used by councils nationwide. The case study of East Devon, as part of that project, is evidence that could be used to inform the policies of the new local plan, and could help to deliver coastal protection schemes. The main purpose of planning for coastal change is to identify the places most likely to be affected and to develop policies to reduce future risks to people and property and to help communities at risk prepare and plan for future risks.

Can you explain in detail why the erosion rates differ at East Beach in Sidmouth?

BMP (2016)

Assess erosion with two methods

• Historic maps between 1890-1991 = 0.19m/yr cliff top and 0.15m/yr cliff toe
• Aerial photograph 1946-2015 = 0.19-0.27m/yr cliff top and 0.25m /yr cliff top and 0.25m /yr cliff toe

Future prediction ~ 20.9m in 100 years or 30.9m with a nominal further 10m buffer

Initially the OBC adopted BMP values however a further study was requested to check on sensitivity of previous rates

RHDHV reassessed the Halcrow calculations by repeating their calculation and looking at the variation of these results over a short time or longer time and by section.  It was found that the erosion was quicker in recent past/short term and slower over a longer-term past.  The analysis also showed transect 31 erosion was higher than the others.  Therefore, it was suggested to be cautious and the worst transect should be used with the first 20 years based on the higher rate and the latter years on the longer-term average rates.

From transect 31 the rates for 2006-2018 are 2.1m/yr and 1946-2018 are 0.6m/yr.  The future loss is estimated at 92.5m over 100 years.  

Alternate source rates  

These elaborated on the method used in the BMP using areas rather than a simple section. This is not dissimilar to the updated values adopted above.

DCC rates (2020) are undertaken with reference to apparent crest and toe lines on aerial surveys.  These are then transacted at 3 sections to identity change in position of the area around the transect.   The aerial photos were dated 2012, 2015, 2017, 2020.   These are spilt into the rates at the top and bottom of the cliff.  The top of the cliff is likely to be a reasonably well defined line bar any overhanging vegetation, however the position of the toe will also be a reflection of the height of the beach at the bottom as much as its position, so that if the beach is higher it would appear the toe of the cliff has receded whereas this may not be the same contour. 

These have been used to come up with a high and low estimate line, where the high is and arbitrary 10m inland of the low line. 

SWEEP rates

It should be noted that SWEEP was to inform possible CCMA’s and is therefore precautionary as not to leave out any properties potentially at risk or affected by changes in the future.   This method is based on the digitisation of the cliff top form Lidar data (since 1998 and therefore resent short term data) and then an algorithm used to extrapolate this in the future including a nominal 0.5 speed up factor to account for climate change. These would appear to provide a significantly earlier loss of cliff compared to the methods above.   

Since the CCMA only uses data since 1998, does it suggest that erosion has increased since the 1994 flood scheme?

We know that the erosion rate varies over time with periods of fast and slow erosion rates. One of these periods coincides after the implementation of the 1994 scheme, however it does not necessarily mean the erosion rate has increased due to the effects of the 1994 scheme, however it is it would unreasonable to say it has had no effect, although its effect would be hard to quantify. It is likely one of the many contributory effects leading to a periodic increased rate of erosion including climate change, sea level rise, stormier weather, wetter winters, terminal erosion from the existing sea wall as well as geological variation within the rocks. We also know the Victorian rail tunnel dug through the cliffs has also largely collapsed, which would have increased erosion rates during this period.

The periodic increase in erosion post 1998 may have also led to the algorithm used in the CCMA study to predict an increased and sustained erosion rate, as it only has used data since 1998, not taking account of any other periodic increase and decrease of erosion rates prior to that.