The INFORM project: (INformation For cliff Recession Management)
A long-term monitoring and research programme for the chalk cliffs of South East England
Project Investigators:
Dr. James Lawrence, University of Leeds
Prof. Rory Mortimore, University of Brighton/ChalkRock Ltd
Mr Martin Eade, Brighton and Hove City Council
Sponsor: Brighton and Hove City Council and INTERREG IIIa
Value: £135,000
Dates: 2005 - present
Aims of the project:
The cliffs will always be subject to erosion and the cliff line will gradually recede inland as a result of the natural processes of weathering. The aims of the project are to allow coastal engineering to predict both long and short term rates of recession and to maintain and improve day to day safety around the cliffs. In order to achieve these objectives the project is employing existing and new methods of cliff monitoring (geotechnical investigations, insitu instrumentation, photogrammetry, numerical modelling and other methods). As the research and development of INFORM Project answers more questions and develops new technologies the focus of the project changes although the overall aim remains the same.
Current research focus:
The current focus of The INFORM Project is to research the impact of sea salt water weathering along protected zones of chalk cliff in East Sussex.
In partnership the University of Leeds and Brighton and Hove City Council have planned to drill two horizontal boreholes to test changes in the rockmass properties as environmental and weathering factors affect the cliff which ultimately lead to cliff failure, The focus of this work will be on the impact and depth of salt water weakening. This project has a value of £25,000 and is currently ongoing.
Background and rationale for the project:
The coast between Brighton Marina and Saltdean is dominated by chalk cliffs and an ancient raised beach at the west end of the section.
The Undercliff Walk, beaches and cliff top have high amenity value for the adjacent densely populated urban area. The coastal cliffs are of particular value to science and are designated a site of special scientific interest (SSSI) and contain the Geological Conservation Review (GCR) site the Brighton Elephant Beds and raised beach.
In the winter of 2000/2001 a series of catastrophic cliff collapses occurred mainly behind Brighton Marina. The Council as owner of the cliffs carried out a number of stabilization and safety improvement works so as to enable the reopening of the Undercliff Walk and to ensure the continuing viability of the A259.
In 2005 the Council approached the University of Brighton to discuss a collaborative research and monitoring programme aimed at improving our knowledge of the cliffs. This programme became known as The INFORM Project. Since then a number of different partners have been involved in the project, developing and utilising skills and expertise as necessary.
Coast defence and cliff engineering works prior to 2005:
The first piecemeal defences along this section of coast were believed to have been built in the late 19th century following construction of the intercepting sewer which links Brighton to the long sea outfall at Portobello to the east of Saltdean. These original defences consisted of some localised cliff toe protection and a number of long groynes, some of which are still visible. The value of these groynes in collecting shingle and building protective beaches was fairly minimal due to the limited amount of shingle in transit along this section of coast.
In the 1930s a complete and uninterrupted seawall and promenade (known as the Undercliff Walk) was built from Black Rock (the location of the Marina) to just beyond the city boundary at Saltdean. Analysis of historic Ordnance Survey data has shown that the building of this Undercliff Walk slowed the process of cliff retreat considerably.
In the 1980s the seawall was reaching the end of its maintainable life and a programme of reconstruction was begun. This involved the encasement of the old wall, removal of most of the original fairly ineffective 98 concrete groynes and reconstruction of the Walk and rear splash wall.
The final phase occurred just after the instability of 2000/2001 and so incorporated some cliff stabilization and pedestrian protection measures. These were localised bolting of chalk blocks identified as unstable; 5 sub horizontal rock catch nets at mid cliff; vertical rock catch fences and extensive lengths of shingle beds built on the new promenade.
In the area behind the Marina where the main cliff collapses had occurred 3 schemes to improve safety and cliff stability have been implemented
- The construction of 5 large shingle beds in areas below sections of the cliff that had been unstable
- In the chalk above the Asda superstore and residential flats - bolting of chalk blocks identified as unstable, reprofiling of the top section of cliff to 70 degrees, the hanging of protective mesh over the full face of the cliff and the erection of a rock catch fence on the promenade.
- In the raised beach section above the Asda car park - reprofiling of the top section of the cliff, installation of a pattern of soil nails over the full face and extension of the promenade rock catch fence.
Establishing a monitoring programme:
As funds become available a comprehensive cliff monitoring network is being established. Five main areas are identified for investigation using existing and novel monitoring techniques:
1. Borehole Instrumentation so far 2 boreholes have been established in the cliff top above the Marina containing temperature sensors, a number of further boreholes for monitoring ground water levels are already in existence but have not proved particularly useful as groundwater levels have never risen above the base of the cliff. Further boreholes containing more sophisticated instrumentation are planned once finance becomes available.
2. High Definition Surveying aerial surveying of the cliffs is carried out once a year as part of the south coast regional coastal monitoring project funded by Defra. Discussions are taking place with the regional monitoring project team on the best ways of utilising and analysing this data within the Inform project.
3. Laboratory Testing there is a range of tests being considered which are thought to be significant when considering cliff stability including moisture content and salinity.
4. Numerical Modelling this activity has value but is expensive and time consuming, consideration will be given to further work in this area.
5. Meteorological stations a met. station has been established on the cliff top above the Marina and has been recording since November 2008.
All five of these methods work hand in hand with further extensive geological fieldwork.
Impacts of sea level rise and climate change:
Many natural forces affect the cliffs and the chalk platform in front of them. These range from boring and burrowing animals up to marine and meteorological affects. These latter 2 are the most significant.
The seawall built in the 1930s has removed the usual undermining and toppling action that sea cliffs are often subject to. An evaluation of the historic record has shown a significant slowing in the recession rate once the wall was completed. However marine and weathering effects on the cliff above the wall are still considerable.
The impact of climate change will exacerbate these effects. This part of the country is subject to rising sea levels made up of 2 elements: the rise in sea level experienced globally and the sinking of the land as the north rises following the retreat of the ice sheets. These 2 elements combined are studied at a national and international level by a range of organisations whose findings will be used in this project. The changes in wind and rainfall patterns as a result of the changing climate are also significant. At present the study of these effects have been limited locally by the availability of data this will gradually change as more data comes in from the new met. station.
Monitoring and research methods employed so far:
Topographic surveys 2 sites have been established on the cliff top comprising a grid of wooden pegs. Each site has been surveyed on a regular basis to establish if any movement is taking place.
Sirovision a method of rock mass characterization using cliff face photogrammetry from digital photography - requires more detailed research to establish its value.
Laser scanning a method of rock mass characterization using cliff face laser scanning requires further investigation to establish its long term value.
Numerical modelling the programmes Elfen and FracMan have been used, future
work using UDEC is likely to be more suitable for identifying modes of failure in this cliff section.
The figure below shows a DFN Stochastic fracture geometry model for the chalk. Contains 68,200 fractures, the slope has the same orientation as the cliffs at Saltdean. An example of the fracture traces is also shown. The different colours represent the different sets of blocks. Statistically the fracture trace lengths compared well to those observed in the cliffs.
Thermal imaging identifies temperature variations in the face, further investigations will be needed to establish whether this is a viable cliff stability monitoring method.
Meteorological recording a weather station has been established on the cliff top above the Marina. From the long term analysis of its data any link between rainfall saturation of the cliff face and cliff instability can be established.
Historical recession data from old Ordnance Survey data held by the Council a comparison has been made of cliff line positions since 1873. This shows significant recession until the construction of the seawall at the base of the cliffs (see section 4 above) and minimal movement since, indicating that the principal source of recession and instability has been marine attack at the base of the cliff.
Sources of financial and technical support:
INTERREG - financed as part of the European Unions European Regional Development Fund (ERDF) the Inform project received a micro project grant of 50,000 in 2007
Brighton & Hove City Council the Council as owners of the cliffs supports and sponsors the project on a continuing basis.
The following organisations have been involved in the project so far:
Brighton & Hove City Council
University of Brighton
University of Leeds
University of Le Havre
University of Exeter, Camborne School of Mines
Findlay Irvine Ltd
ChalkRock Ltd
National Oceanographic Centre, Channel Coastal Observatory
South Downs Coastal Group
Outputs:
Stavrou, A., Lawrence, J.A., Mortimore, R.N. & Murphy, W. (In review). A new method of predicting present and future risk assessment for rocky cliffs using GIS and geotechnical hazard identification methods: A case study of the chalk cliffs of southern England. Natural Hazards and Earth System Sciences.
Mortimore R.N & Lawrence, J.A. 2008, INFORM PROJECT (INformation FOr cliff Recession Management), Long-term monitoring programme for the cliffs between Black Rock and Saltdean, Annual Report 2. 2007. March 2008. 42pp.
Lawrence, J.A., Mortimore, R.N., Eade, M. & Duperret, A. 2007. Developing a strategy for coastal monitoring and management. In McInnes, R. Jakeways, J. Fairbank, H. & Mathie, E. (eds) 2007. Landslides and Climate Change Challenges and Solutions, Taylor & Francis Group. 81-90.
Mortimore, R.N. & Lawrence, J.A. 2006 INFORM PROJECT (INformation FOr cliff Recession Management). Long-term monitoring programme for the cliffs between Black Rock and Saltdean. June 2006. 49pp.
Mortimore R.N & Lawrence, J.A. 2006 Coastal Cliff Management. Walk-over Survey from Black Rock, Brighton Marina to Saltdean. Report No. 1: October 2006. 39pp.
In addition an annual walk-over survey is conducted and nine Engineering Geology MSc. Dissertation topics have included studies of this area between 2009 and present.