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WEST COAST RESEARCH MEETING

MINUTES

by: Dr Malcolm Bray Department of Geography University of Portsmouth

April 3rd - 4th 1997 at the Fern Hill Hotel, .

1 chesil5a.doc COAST: RESEARCH MEETING

MINUTES of the meeting of April 3rd - 4th 1997 at the Fern Hill Hotel, Charmouth. by: Dr Malcolm Bray

PARTICIPANTS:

Neil Allsop (West Dorset District Council) Mike Amphlett (West Dorset District Council) Dr Malcolm Bray (University of Portsmouth) Professor Denys Brunsden (Kings' College ) Dr Alan Carr (Fleet Study Research Group) Dr Jim Chandler (Loughborough University) Tim Collins (English Nature: Peterborough) Dr Ken Coombe (Oxford University) Victoria Copley (English Nature: Dorset office) Geof Davis (West Dorset District Council) Richard Edmunds () Dr Robert Inkpen (University of Portsmouth) Mark Lee (Rendel Geotechnics) Taukir Ishaq (Babtie Group) Dr Adrian Parker (Oxford University) Nick Pittock (Posford Duvivier: Peterborough) Dr Carolyn Heeps ( University)

INTRODUCTION: A group of 17 researchers and coastal managers met with the aim to review recent research results and to consider their implications for interpretation and further study and management of the geomorphological behaviour and development of this coast. Three main themes were identified at the outset as follows:

¨ and : evolution and contemporary behaviour. ¨ Landslides of West Dorset and . ¨ The Coastal Process and Landform Systems and their management.

It was decided at an early stage that the scope was so large that full consideration of the landslides be deferred for a future meeting. The first day involved a structured meeting covering current work and discussions of future directions. The second day comprised a field visit to inspect the in progress coast protection and shoreline improvement scheme.

The meeting is summarised in terms of the following:

1. The Research Presented. 2. Future Research Directions. 3. Future Actions.

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PRESENTATION DETAILS:

Chesil Beach: evolution and contemporary behaviour. (Dr Alan Carr).

Evidence was reviewed in terms of the following:

· That the possible significance of the Portland raised beach should not be overlooked as its materials are similar to the constituants of the present day Chesil, although its vertical grading/sorting differs. The raised beach deposits are covered by head and possibly are Ipswichian (around 100,000 yrs. BP) although substantial portions could have been reworked and incorporated within the present Chesil Beach. However, the longevity of such materials on an interglacial ocean coast shoreline must be questionable.

· The evidence that has been obtained and interpreted from a series of CEGB boreholes in the 1960s. The boreholes revealed that the beach and Fleet rest upon a platform with a break of slope at -14m OD. C14 dates of 4,000-5,000 years B.P. from peats beneath the beach and Fleet (at around -4m OD) indicate that a barrier to seaward should have existed at that time to provide necessary shelter. Pollen analysis of sediments beneath the peats suggest that this shelter may have been afforded as early as 6,000-7,000 yrs. BP. Both marine and brackish faunas are present within sediments between the bedrock and the peats indicating a complex depositional history - perhaps the ancient barrier was incomplete, or of marginal stability and liable to phases of breakdown and reformation as sea-level rose - present day analogues at a smaller scale have been reported from areas of crustal subsidence such as Nova Scotia by Orford and Carter.

· That assessment of the contemporary beach levels and position should not be taken as a reliable guide to behaviour because: (i) short term variations are similar to, or of greater magnitude than many long term trends and (ii) the most significant changes are produced by extreme events of >50 year frequency so that the effects of only a very small number of such events have been measured or are contained within reliable historical records. Profile analyses nevertheless indicate a spatial variation in beach variability that could be indicative of the different foci of different wave or storm events.

· Statistical comparision of 500m beach segments from the 19th century, 1950s, 1960s, 1979 and 1990-91 in terms of their sedimentological and morphological characteristics revealed increasing variability in recent epochs - this could be indicative of the early stages of a break- up of the beach.

· A report to DCC in 1980 set out the requirements then for future research. Progress achieved towards resolving those issues may be reviewed as follows: (i) Offshore shingle sources - no significant deposits identified in west or central Lyme Bay by surveys of Dobbie (1981) or BGS (various), but surveys were at a coarse scale and did not extend sufficiently far inshore. (ii) assessment of West Dorset cliff erosion inputs and their fate using tracers - tackled by Bray in PhD thesis (1996). (iii) Repeat profile surveys - tackled by Babtie/EA study, monitoring to continue. (iv) More boreholes through Chesil and the Fleet - tackled by PhD of Coombe (1996) and continuing work by the Oxford University team. (v) Shingle attrition rates - raw cliff gravels tackled by Bray, (1996), but unresolved for beach pebbles that are already well rounded.

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Holocene palaeoenvironments of the Fleet Lagoon. (Dr Ken Coombe and Dr Adrian Parker).

Further advances were reported following a coring programme (32 cores) within the Fleet:

· The sediments of the Fleet originated from (driven in by SE storms) and not from Lyme Bay.

· A complex history of environmental changes was revealed from analyses of the cores, but could not easily be related to Holocene sea-level changes. This could be due to the variable effects of a barrier to seaward and the changing relationship between sea-levels and bedrock levels that governed depositional conditions within the early Fleet Lagoon.

· At the bottom of most cores (most were insufficiently deep to reach bedrock) black marine sands comprising angular flint and silica quartz were found. - could these be attrition products of an ancient pebble barrier perhaps including cherts?

· Peats dated at approx. 4,800BP were found at between 3-4m OD. - freshwater conditions indicative of static or falling sea-level (unlikely), or barrier buildup produced by increased sediment availability.

· A distinct shell layer was identified within brackish sediments above the peats. This is indicative of a short duration high energy event perhaps rapid barrier breakdown and reformation, possibly due to tsunami impact. The lack of coarse clastic sediments from this deposit is puzzling, suggesting either that they were absent from the barrier, or that the barrier was too far seaward for the larger, higher density washover deposits to be carried to the position of the present Fleet.

· The following points emerged from discussion:

· That the sediment types found with depth within Chesil were not well defined and comprised boulders and angular clasts with a much higher frequency of limestones than amongst the surface sediment layers. This may suggest that an earlier beach of different composition was supplemented and enlarged by a subsequent influx of flint and chert pebbles. However, since shingle beaches are known to evolve by a "rollover" process during periods of rising sea- level, it would be expected that material within the beach should have become as rounded as the surface material had the beach migrated onshore a significant distance by this process. Thus, the core materials probably were not involved in barrier transgression.

· A large cobble layer was recorded at -7.5m O.D. in those boreholes that could penetrate to this depth. The cobbles were surrounded by sediments containing marine ostracods similar to those found within Weymouth Bay. This again suggests that any barrier was further offshore and less subantantial prior to 6,000-7000 BP. Future boreholes clearly need to penetrate this layer and reach bedrock to reveal environmental conditions during the earlier stages of barrier development.

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The significance of cliff sediment inputs to the littoral system. (Dr Malcolm Bray).

The results of investigations into the types, quantities and fates of sediments released to the coast by cliff erosion in west Dorset were presented. as follows:

· Some 320,000m3a-1 of sediment are contributed, but only 6,400m3a-1 comprise beach forming gravels. The remainder being clays that are removed offshore in suspension, sands that contribute to the Lyme Bay bed and limestones that form short lived pebbles or boulders on the local beaches. The potential contribution of the gravels to the coastal system was greater than anticipated at the outset.

· Sedimentological analysis, tracer studies and beach volume analysis indicated eastward movement of gravels away from the main cliff input sites at and . Processes of sediment input and littoral transport were modelled, but this revealed a substantial shortfall of gravel remaining on local beaches between Lyme Regis and West Bay compared with that supplied from the cliffs.

· Shoreline transport is regulated by landslide activity at the main headlands of and Doghouse Hill. A model was developed that envisaged intermittent pulses of gravel bypassing these headlands at intervals of 30-50 yrs., most recently at Golden Cap between 1949 and 1962, but not recently at Doghouse Hill (connecting beaches depleted). The implication is that over long periods of time the sub-cells formed did not hinder net eastward transport so that most erosion products have been transported towards Chesil, the only substantial shingle accumulation and containing materials identical to the cliff erosion products except in their greater degree of rounding. Permanently maintained shoreline structures could interfere with this system in the long term.

· landslide deposits (boulder aprons)identified some 2-3km offshore of Golden Cap may be interpreted as indicating the extent of past cliff erosion. This might expected to have yielded approx. 32 million m3 of gravel to the retreating shore assuming similar morphology and distribution of deposits as at present. This material could be a major new factor in explaining the origin and development of Chesil Beach (estimated volume 16-60million m3).

This work raised a series of key questions identified as follows:

¨ This work again raises questions as to the source(s) of the material that comprises the present Chesil Beach.

¨ Details are needed of the true scale of cliff recession in the mid to late Holocene as this controls the gravels potentially available to nourish and sustain Chesil during that period. The boulder aprons do not yet provide conclusive evidence because their full distribution has not been mapped and their age is unknown. D.Brunsden suggests on basis of work around Lyme Regis that recession of insitu strata could be overstated and that the main erosion contribution could result from removal of formerly extensive gravel rich degraded slopes marking an ancient cliffline abandonded at the beginning of the Devensian glaciation and modified by sub-aerial processes prior to relatively recent reactivation by the Holocene marine transgression.

¨ Inshore features and deposits within 3km of the coast have largely been ignored by researchers although they have the potential to be mapped and interpreted to provide information on: (i)the extent of past cliff erosion; (ii) the previous position(s) of Chesil which may be indicated

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by relic beach base deposits, and (iii) possible pathways of sediment transport to/from the pocket beaches.

¨ Permanently maintained shoreline structures such as the Cobb, Lyme Regis and the West Bay piers could have greater long term impacts on the shingle transport than the headlands which evolve naturally. Key questions involve definition of the extent of interference produced by individual structures and whether compensatory bypassing arrangements might be neceessary in the future.

¨ Cliff recession is likely to accelerate due to (i) increased rates of sea-level rise and (ii) increased winter precipation likely to occur in the future due to global warming. Whilst such behaviour is likely to increase cliff sediment inputs, the effects upon shoreline drift at headlands are unpredictable as both debris delivery (landsliding) and removal (marine erosion) are likely to accelerate.

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Photogrammetry and digital elevation modelling of cliff landslides. (Dr Jim Chandler)

The capability of modern protogrammetric techniques and digital elevation modelling (DEM) packages to rapidly measure and analyse complex ground surfaces quickly, precisely and to a high level of detail was demonstrated by reference to studies of the Black Ven landslide complex covering several epochs within the period 1946-1995. The qualities demonstrated were as follows:

· A variety of photographic images including oblique perspectives could be accommodated providing that there was a continuity of objects of known position (control points) recognisable from one epoch to another.

· Outputs comprise 3-D co-ordinates of the ground surface that are used as inputs for DEM generation. At Black Ven, this typically involved around 10,000 user specified points per epoch with the analytical photogrammetry technique, but up to 1 million points measured automatically with the latest digital photogrammetry techniques.

· DEMs are produced of the ground surface based on interpolations between the measured points. Results are produced as 3-D plots, contour plots, profiles, distributions of slope angle etc. Comparisons of consecutive surveys permit calculation of change (differences) which may be expressed as recession rates of given contours, contour plots of elevation change or volumes of sediment lost by cliff erosion. Such data are vital inputs for process and modelling studies of landslides and unstable coastal cliffs.

· The new digital methods in particular offer great advances in the speed of data acquisition and automatic processing of some results. A typical system may cost £20,000 for necessary software and a workstation, although conventional print or diapositive photography needs to be scanned using high quality equipment (available as a service by some companies). Some photogrammetric expertise is necessary as are sufficient reliable ground control points.

· These methods hold promise for efficient survey of beaches, being especially valuable in overcoming problems of covering a large and difficult structure such as Chesil within a single low tide interval. Photography at approx 5-10 year intervals is available back to the 1940s so such methods may complement and improve on existing historical data so long as there is a continuity of ground control recognisable within photos. Tests are needed of the application of digital photogrammetry to survey Chesil. In particular to establish (i) the effectiveness on a shingle surface of the stereo matching technique by which DEMs are automatically generated, and (ii) possible limitations imposed by the minimum scanned pixel size which may be equivalent to 1-3m with 1:10,000 scale images typical of the historical photos. If successful, the photogrammetric techniques could provide the basis for development of new geomorphological mapping methods for shorelines.

· GPS is an alternative survey method that might be used to measure crest height and position along the beach and to rapidly survey profiles or indeed to establish a series of high quality ground control points for subsequent air photo studies.

· It was also noted that the photogrammetric technique could also be applied to the other major landslide complexes e.g. Stonebarrow, Broom Cliff, Golden Cap to establish whether the behaviour recorded at Black Ven was typical. At Golden Cap, links could be developed between landslides and the development of debris lobes on the foreshore that control beach drift.

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Chesil Beach Investigation. (Taukir Ishaq - Babtie Group)

A summary of the results forthcoming from a major Environment Agency funded study of Chesil beach covering 1993-97 were presented. The following data collection and analytic procedures were included in the work: 1. Annual aerial photography, photogrammetric measurement of transverse beach profiles spaced at regular longitudinal intervals. Ground control was established in support of the photography. The brief survey period revealed a stability of crest height and position. 2. Post-storm surveys of key profiles. 3. Beach surface sediment sampling from 27 profiles (five cross shore sample sites at each). 4. Installation of an offshore wave rider in eastern Lyme Bay approximately at the position of a Met. Office wave prediction point. 5. Inshore pressure type wave guages were deployed at the sites occupied by previous instruments that had recorded in the 1970s and 1980s off and . In spite of some technical problems, all three wave recording instruments were operational simultaneously during periods of significant storm and swell waves. 6. Bathymetric surveys were undertaken of the inshore area including diver and sonar surveys of selected transects corresponding to the terrestrial profiles. Results suggested that at, or shortly before the time of survey, shingle movement was confined to a zone close inshore at the toe of the shingle beach. 7. Refraction and shoaling studies of waves in Lyme Bay. 8. Beach profile modelling (HR Wallingford SHINGLE model based on physical model work of Keith Powell). 9. Longshore drift modelling (HR Wallingford BEACHPLAN?). 10. Historical data analyses of Chesil crest heights and Lyme Bay bathymmetry. 11. Archiving and secure storage of data.

The significant results reported are summarised as follows:

¨ Beach volatility expressed as the standard deviation of areas measured under the topographic profile (based on the 4 annual surveys and post-storm profiles?) was greatest at each end of the beach and also at Burton Cliff and .

¨ Significant swell wave activity (period 10-18 sec.) was recorded at all times often delivering greater energy inputs than higher short period waves.

¨ A significant increase of incoming wave energy was recorded at Wyke Regis compared to West Bexington. This was not explained by wave refraction modelling (OUTRAY) within the inshore area and therefore not attributable to focusing of locally generated wind waves.

¨ Instead, attention was foused on swell waves. Diffraction and refraction studies were undertaken of incoming swell waves from the north east Atlantic. Because such waves may have wavelengths of up to 1000m, they are influenced by the seabed in water depths as great as 50m. This meant that the model area had to be extended well seaward and that previously ignored bathymetric features were capable of affecting the waves. Results revealed that a deep hole and mound located well offshore of Lyme Bay caused significant focusing of swell, especially the larger waves. Zones of higher wave energy were identified at Portland, Abbotsbury and West Bexington, although it was reported that focusing was not significant

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further to the west (comparisons might be possible with the Lyme Regis wave recorder operated by WDDC?).

¨ Comparisons with the beach volatility data revealed reasonable agreement between zones of beach variability and areas subject to wave focusing. Zones containing irregularities of surface pebble grading also showed some relation to the zones of beach affected most by wave focusing. It appears that swell waves exert a major and hitherto overlooked influence on the behaviour of the beach during typical conditions as well as during high magnitude low frequency events as was known previously.

¨ It should be noted that only a brief summary of results could be provided in the time permitted. Full details should be available within the technical report that may be available through the Environment Agency in the summer. Alternatively, contact Babtie Group direct.

The following were presented as draft conclusions:

1. The beach and bathymetry apprared relatively stable over the periods studied. Almost all significant changes were recorded on the beach above the 5m Chart Datum contour.

2. Crosshore profile development was predicted reasonably well by the SHINGLE numerical model, although it cannot presently incorporate the effects of swell waves.

3. The wave climate of the eastern part of the beach is significantly more severe than to the west. This is attributable to focusing of swell waves by refraction and diffraction as they pass over irregularities in the offshore bed of Lyme Bay. It is clear that where swell waves are significant, the offshore bathymmetry in water depths of up to 50m can affect conditions at the shore due to wave focusing. This is a newly identified factor and may improve understanding of the behaviour of Chesil.

4. Net shingle drift along the beach appears neutral. Details were not provided of gross drift, or its variability.

The following were identified as topics for further research:

¨ Swell wave distribution and behaviour throughout Lyme Bay. Note that a wave recorder is currently operating off Lyme Regis.

¨ Greater understanding is needed of the extreme (formative) events that shape the morphology of Chesil - sensitivity testing with various combinations of swell waves, storm waves and storm surges may help to indicate the type of event, although without improved historical data its frequency of occurrence will remain uncertain.

¨ Compilation of data and information within a GIS system.

¨ Better understanding is needed of the basic processes of sediment transport so that these processes can be more reliably modelled.

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Overview and synthesis including effects of management and results from new work at West Bay. (Mark Lee - Rendel Geotechnics and Professor Denys Brunsden)

Results were presented of a desk study of the geomorphological evolution of Chesil and the west Dorset coast. Two main foci were identified: (i) the budget of littoral sediments between Lyme Regis and the Isle of Portland, and (ii) the sensitivity of Chesil to changes in sediment budget. The work comprises part of the feasibility studies for harbour and coastal defence improvements at West Bay.

Evolutionary models were presented of the behaviour through time of the coastal system as follows: 1. Fragmentation of the shoreline shingle transport system between Lyme Regis and West Bay was identified from an analysis of Admiralty hydrographic charts dating back to 1740. The earliest charts recorded a near continuous beach, but with headlands becoming more prominent and exerting greater effects upon transport with time. 2. The west beach at West Bay retreated some 90-100m and steepened significantly from 1820- 1980, involving loss of up to 500,000m3 of material - fate unknown. This is attributed to the beach becoming a relatively closed system for coarse sediments remaining open only to sediment inputs westward around the piers. Losses are attributed to scour, although precise mechanisms and pathways are uncertain. The east beach is open to sediment inputs from Chesil to the east, but is closed to the west by the harbour piers. Frequent, or prolonged storms from the west therefore cause beach loss, whilst those from the east cause accretion. 3. The present configuration of the Lyme Regis to West Bay segment is a permanent series of sub- cells so that those not nourished directly by cliff erosion gravel inputs are likely to suffer further net beach loss in the future. The causes of these changes cannot be defined precisely, but are likely to be related to a combination of the following: (i) drift interception by the Cobb at Lyme Regis and the piers at West Bay (ii) loss of shingle by beach mining and (iii) natural evolution of headlands. 4. Twentieth century losses of shingle are estimated as comprising 1.5 to 5.0% of the total volume of Chesil, but no clear response can be discerned from the beach. It could be that its sensitivity to these changes in budget is buffered by its great volume and masked by the short term variations produced by storm and swell events. 5. In the long term it is estimated that changes in budget coupled with rising sea-levels should lead to the eventual breakdown of Chesil into a series of sub-cells with pocket beaches. Although it is difficult to identify an appropriate timescale for these changes (100s to 1,000s years?), a new headland already appears to be forming at Burton cliff. The beach between Cliff End, Cogden and West Bay is likely to diminish so that cliff erosion should increase. The beach between West Bexington and Cliff End is likely migrate slowly onshore burying the lowland marshes. The beach between Abbotsbury and West Bexington may move further onshore and re-occupy a relict cliff line. The segment between Portland and Abbotsbury is likely to "rollover" into the Fleet, eventually becoming attached to the shore at Wyke Regis where a new headland could form between two new sub-cells.

Conclusions: ¨ Knowledge of changes in the shingle budget of the coastal system throughout the whole of the central and eastern parts of Lyme Bay provides important new insights into the recent development and likely future evolution of Chesil. ¨ Cliff erosion over the past 2,000-3,000 years is likely to have contributed up to 30 million m3 of shingle to the littoral drift system that fed Chesil. This would have added a veneer of shingle to an existing barrier structure (predominantly sandy and shelly) that previously sheltered the Fleet Lagoon. This makes the present beach much younger than supposed

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formerly and challenges the classic evolutionary hypothesis presented earlier - more evidence is clearly required on these issues! ¨ There has been a recent breakdown in the sediment transport system that formerly nourished Chesil. Immediate implications are difficult to discern, but over the long term Chesil is likely to break down into several sub-cells.

Implications for Managers: ¨ Changes and likely future behaviour need to be viewed in the context of variations in external forcing agents or controls such as sea-level and climate. The best available estimates of future greenhouse induced climate change suggest that sea-levels are likely to rise more rapidly and that there should be an increase in moisture availability in winter. Coasts are therefore likely to suffer accelerated rates of erosion and landsliding. ¨ If Chesil is going to break up in the future, it will behave as several increasingly independent segments (sub-cells). There would be the advantage for management that changes in one sub-cell would be less likely to be transmitted elsewhere, However, each sub-cell should become more dynamic as it would be isolated from the buffering effect of the sediment store of the whole beach. e.g. the pocket beach is extremely responsive to storm direction whilst central parts of Chesil are unaffected. ¨ In spite of the research undertaken there are still significant uncertainties involved in predicting future behaviour. It must be asked how much understanding is needed to effectively manage the coast? and whether enough will ever be known? In the meantime, coastal managers continue to face difficult decisions in tackling unavoidable coastal problems and sometimes face criticism for taking actions in advance of definitive knowledge. The Dorset coast with its juxtaposition of immense natural and scientific value with local communities that have traditionally utilised its resources provides excellent examples of these dilemmas Improved dialogue is clearly necessary between coastal managers, their consultants and the academic community to identify, obtain and factor that necessary knowledge into management programmes. The new SMPs provide a useful focus and many funders of academic work are now recognising the value of user-oriented research.

Remote sensing of active and relict landslides at Black Ven. (Dr W. Murphy and Dr R. Inkpen).

This was presented as a poster. The work demonstrated that spectral differences observed between ATM images of active and relic landslides could form the basis for a method of discrimination.

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DISCUSSION OF RESEARCH DIRECTIONS. (Chairman: Denys Brunsden)

The following are highlighted as key research questions by researchers:

1. The Origin and Modes of Development of Chesil Beach. Recent research results need to be compiled within a new evolutionary model that includes considerations of Holocene (or earlier) inheritance, together with the late Holocene evolution of a coastal system comprising changing sources, transport pathways and sinks of littoral sediment. Detailed questions are identified as follows: ¨ What material compositions, beach configurations and behaviour were characteristic of the beach at earlier stages (lower sea-level), prior to re-occupation of the previous interglacial shoreline? ¨ To what extent and over what period has the coast to the west Dorset and east eroded and supplied beach forming materials? What has been the fate of those materials? ¨ What might be the relative contributions of material inherited from the previous interglacial compared to that supplied more recently by cliff erosion? Is it feasible that shingle only arrived in substantial quantities at Chesil within the last 2,000-3,000 years? or did it simply enlarge an already substantial, but finite inherited accumulation? What are the typical long term rates of shingle attrition? ¨ What evidence of Holocene evolution might be obtained from surveys and geomorphological interpretation of the inshore seabed? or could beach transgression and coastal erosion have removed most traces of former conditions? ¨ Of what significance to the evolution of the main Chesil Beach is the second beach that formed facing Weymouth Bay? Could it have regulated sediment inputs into the Fleet affecting the lagoon bed level and thus the elevation of the surface over-ridden by the main barrier as it migrated landwards? ¨ Has Chesil evolved by: (i) progressive changes over long periods; (ii) episodic readjustments separated by intervals of stability or (iii) combinations of both?

2. How may Knowledge of the Long term Evolution of Chesil be Used by Coastal Managers? Management timescales are typically much shorter than those commonly associated with the evolution of major landforms, so there is a danger that expedient short term decisions may have adverse long term impacts. In this context it can be asked whether: ¨ Long term management strategies can be accomplished within shoreline management methodologies based on short term option testing involving cost-benefit analyses? Can strategic coastal defence options be evaluated by alternative means that take long term impacts and evolution into consideration? ¨ Long term monitoring of key parameters might provide early warning of future evolutionary changes? ¨ Knowledge of past evolution might provide indications of the consequences of future interventions?

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3. Are we Really Witnessing the Break-up of Chesil? ¨ Have recent changes in the sediment budget approached a threashold in preparing the beach for break-up that might be triggered by an extreme wave event? is the resiliance of the beach to major changes diminishing? ¨ Is there evidence that parts of Chesil are behaving as coherent units e.g. in terms of response to storm events? ¨ Are the variations recorded simply the equilibrium behaviour of a resiliant landform?

4. Have we Really Witnessed the Break-up and Fragmentation of The Lyme Regis - West Bay drift system? ¨ Are the historical data reliable and corroborated by other evidence? ¨ Was there ever a coherent drift system, or continuous beach that could have delivered shingle to Chesil? Are there any alternative sinks for gravels yielded by cliff erosion? ¨ Could break up have been accelerated or triggered by human activities?

5. To what extent is the Contemporary Behaviour of Chesil understood? ¨ What are the characteristics and frequencies of occurrence of the Formative Events that shape Chesil? ¨ Can models be developed that reproduce the known behaviour of Chesil? Are there weaknesses that need attention e.g. shingle transport modelling?

6. What are the likely, or possible Responses to Sea-level Rise and Storm Variability? ¨ Could landward migration of Chesil by "rollover" accelerate? ¨ Could break-up of Chesil accelerate? ¨ Could sediment yields from eroding cliffs increase? What would be the fate of those materials? ¨ Can reliable models be developed that might permit sensitivity testing of the impacts of future variations in external forcing agents?

The following are highlighted as key research questions by coastal managers:

1. Which Timescales are Relevant in the Study and Management of this Coast? ¨ How should study timescales be selected? (i) on basis of scheme lifetimes? (ii) on basis of prior knowledge of natural system behaviour? (iii) according to other criteria? ¨ To what extent should studies involving the appraisal and justification of schemes be extended beyond the design life of that scheme? ¨ What natural system behaviour indicators could be adopted to indicate possible timescales? Breakdown of Chesil may occur over 100s to 1,000s of years? Formative wave events may occur every 30-100 years? Headland evolution may affect beach drift over 20-80 year periods? Wave climate changes may occur every 5-15 years? Damage/flooding may occur every 5-10 years? Could some of these intervals themselves be affected by management activities and future climate changes?

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2. What are the Main Paths and mechanisms of Shingle Transport? ¨ Gross and net beach drift and its variability? ¨ Exchanges between beaches and the nearshore bed?

3. What Monitoring Arrangements would be most effective? ¨ What should be monitored and where should measurements be made? ¨ How often should measurements be taken and over what periods should they continue? ¨ What arrangements should there be for archiving and analysis of data? ¨ Who should undertake monitoring? who should pay? ¨ Is there a case for secure long term monitoring of a few key parameters such as waves and beach morphology irrespective of short term issues?

4. What might be the advantages and drawbacks associated with widespread adoption of "managed retreat" or "do nothing" coastal defence options? ¨ How would natural systems evolve? ¨ Would new resilient natural forms develop? or are the existing systems intimately dependent upon management for the foreseeable future? ¨ If a sound case could be made for retreat at specific sites, how might it be implemented e.g. set-back zones, development controls, occupation controls? ¨ Would retreat actually be feasible or fair to implement while there are no formal means available for compensating those affected adversely?

5. How should Managers and Scientists Communicate with Stakeholders? ¨ Are the Coastal Forum and forthcoming SMP consultation exercises likely to provide an appropriate framework that includes the key stakeholders? ¨ Should there be ongoing dialogues rather than one off SMP consultations? Could a scientific sub-group of the Forum achieve such objectives? ¨ Should educational public meetings be promoted to present and discuss key strategic issues as well as specific scheme proposals? e.g. long term evolution, how the coast works, future management including managed retreat, climate change and sea-level rise?

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FUTURE ACTIONS:

The following actions have been developed with the aims of consolidating and disseminating the new research results presented and discussed at this meeting as well as to begin to tackle some of the important questions identified:

1. Meetings: There is scope for regular meetings between researchers, consultants and managers working on this coast. This would provide opportunity to: (i) discuss those topics not covered at the first meeting e.g. landslides; (ii) to develop collaborative projects; (iii) to tackle special issues as they arise. Limited funding may be available for future meetings from the British Geomorphological Research Group. A second meeting has been arranged for Thursday 19th June at Oxford University - details to be distributed.

2. Publications: Publication of the research presented at this meeting is essential so as to make results available to the wider community and to establish the credentials of the collaborative group prior to applications for funding. The studies should be published collectively within single a work(s) including strong editorial overview - it is the potential for multi-disciplinary holistic overview and application of science for management that will be of most interest to others. The following formats are suggested: (a) A monograph or open file publication sponsored by an interested organisation e.g. English Nature; NERC; SCOPAC. The advantage of this type of publication is the degree of editorial control possible. (b) A special edition of a scientific journal containing a collection of individual papers written to a general theme and including an editorial. e.g. Earth surface Processes and Landforms; Geomorphology; Journal of Coastal Conservation, Journal of the Geological Society, Proceedings of the Geologists’. Association etc. The advantage of this type of publication is that it is peer reviewed and reaches an international audience. (c) A popular publication may not be appropriate yet because there are already two landform guides published recently by the Geographical Association and the Geologists' Association respectively.

3. Conference The meeting demonstrated that there is a diverse and interesting body of work that is deserving of open presentation. A one day conference or seminar would help to establish the credentials of the group to the wider community. There are several possibilities: (a) A special session or meeting within an established institution or society e.g. Royal Geographical Society (RGS), Geological Society, Geologists Association, Institution of Civil Engineers. (b) A special session at the Institute of British Geographers /RGS annual meeting at the University of Surrey, Guildford in early January 98. (c) A local conference sponsored by a local authority or University.

4. Monitoring: Academics, consultants and managers need to continue a dialogue so as to identify the most appropriate future monitoring for this coast. The evolving SMP should provide an appropriate focal point, but it will be important that those interested should have opportunity to discuss options before definitive arrangements are formulated.

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5. Collaborative Research There is the potential to develop a funded programme of collaborative research to tackle some of the research questions identified. Possible funders include the research councils, especially NERC, MAFF and possibly the EU. The following goals might be considered:

¨ To develop a sound conceptual model of the evolution of Chesil and the neighbouring coast during the mid to late Holocene. To include some quantification of former sediment budgets and associated behaviour. ¨ To develop reliable numerical models capable of simulating recent recorded changes on Chesil. Undertaking of sensitivity analyses of likely future storm and wave climate scenarios. ¨ Intermeshing of timescales to assess the future evolution of Chesil and the neighbouring coast including the effects of alternative management options. In particular, to consider the possible break-up of Chesil and is consequences.

Attainment of these goals would involve overcoming of formidable challenges involving: (i) interpretation of new forms of evidence of Holocene coastal evolution from inshore waters; (ii) rigorous application of sediment budget analysis at different scales; (iii) largescale numerical modelling using improved shingle transport functions; (iii) intermeshing of Holocene, historical, decadal, seasonal and storm event timescales (never previously achieved) and (iv) adaptation of results to include effects of past and future management.

The programme could be developed in stages the first of which might involve: 1. Development and application of monitoring methods. 2. Consolidation of existing research e.g. additional deep bore holes through Chesil and the Fleet, appraise uses of geophysical methods to provide better spatial coverage - MB to circulate details of ground penetrating radar to Oxford team; linking of new Babtie research with geomorphological research. 3. Survey of the inshore waters between the Isle of Portland and Charmouth to develop geomorphological maps of bed features and deposits to aid: (a) interpretation of late-Holocene evolution (b) contemporary sediment mobility and exchanges with beaches. Techniques to involve side- scan sonar, sediment sampling and diver inspections. The University Oceanography Department, Southampton Oceanography Centre operate at least one suitable survey vessel equipped with a variety of sidescan sonar and sediment sampling devices. It is probable that they would be interested in collaborative research - in fact, they are presently working on a major project to investigate the mobility of the sea-bed sediments to the west of the and probably already possess many of the investigative skills necessary for the west Dorset work.

Further discussions of all possibilities would be useful at the Oxford meeting to work towards compilation of a more detailed multi-disciplinary programme.

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