West Dorset Coastal Research Group
Lyme Bay and South Devon Shoreline Management Plan: comments of
West Dorset Coastal Research Group.
The following represents the WDCRG consultation response to the draft SMP. Its scope is re-
stricted to comments directed towards Chapter 6 and Appendix C of the draft SMP concerned
with recommendations for future monitoring and research. The aim is to review the recom-
mendations made, to identify possible gaps in knowledge and to indicate the opportunities for
additional research that should be of benefit to the process of shoreline management and the
development of scheme strategies. A draft document was produced initially by Dr M. Bray
and then circulated amongst group members. Comments were received from the following
and incorporated within this final document:
Professor Denys Brunsden, Chideock.
Dr Alan Carr, Wellington.
Dr Jim Chandler, Loughborough University
Mark Lee, University of Newcastle-upon-Tyne
Attention is focused primarily upon the West Dorset coast, although many comments relate to
general principles that should be applicable elsewhere along the south Devon SMP coastline.
Some of the suggestions involve quite detailed work that it probably would not be feasible to
fund in direct support of the SMP, or related Coastal Defence Strategy Plans. However, it is
anticipated that the case for support from other directions (e.g. NERC, MAFF, EU etc.)
should be strengthened considerably if relevant and valuable items can be identified and in-
cluded within the SMP recommendations.
Issues are tackled in the same order as presented in Chapter 6 of the SMP and comments are
direct responses to that material.
6.2 Areas of Uncertainty
6.2.1 Coastal Processes
The draft plan states that a good understanding has been achieved of the coastal processes.
The opinion of the group is that this statement is incorrect and should be withdrawn or altered
in the SMP. There are many uncertainties concerning the following process related issues:
1.Long term wind climate.
2.Long term wave climate, especially swell waves.
3.Long term littoral sediment transport on the beaches.
4.Attrition losses of beach pebbles.
5.Exchanges of shingle between beaches and the nearshore bed.
6.Sediment transport in the offshore zone.
7.Approximate sediment budgets of the many pocket beaches within the SMP.
8.Breaching of barriers such as Chesil and Slapton.
Furthermore, strategic management as advocated by an SMP also requires good knowledge of
the behaviour of the landforms that result from the operation of coastal processes. It is the
coastal landform e.g. beaches, cliffs, spits, dunes or saltmarshes, that provides habitats and
West Dorset Coastal Research Group
natural coastal defence and which may require management within an SMP. The following
aspects of landform behaviour are important to identify:
1. The materials of which the landforms are composed, their origin and modes of delivery.
2. The interdependence of landforms and possible linkages between management actions
and landform responses.
3. The potential scales of landform behaviour involving knowledge of the nature, magni-
tudes and frequencies of the changes that might occur.
4. The sensitivity of different landforms to external factors such as extreme events, man-
agement actions or more gradual climate changes e.g. shingle beach response to se-
quences of storm events of varying size? impacts of climate change on coastal landslide
activity? beach response to variations in wave direction?
5. The consequences for geomorphological development, coastal defence and the natural
environment of those changes considered likely or possible e.g. the threat to coastal de-
fences posed by continued landslide activity in areas such as Lyme Regis, Seatown &
Much of this landform information can be developed using palaeo-environmental reconstruc-
tion, historical analysis and interpretation of landforms. In the case of the larger beaches
(Chesil & Slapton) and spits (Dawlish Warren), late-Holocene inheritance (up to 7,000 years
before present) is important. The sediment budget (100 year timescale) is important for all
beaches. In the case of the coastal landslides both ancient failures and the occurrence or re-
currence of failures over the past 100-200 years are important. In our opinion, such knowl-
edge is not a luxury, but a necessity in a complex and dynamic environment where present
day processes may not be a reliable guide to the full range of changes and responses that are
possible. Indeed, many of the requirements for further research derive from the need to
better define the relationship between contemporary processes and responses (reasona-
bly well covered by the SMP and various engineering studies) and the longer term (50-
100yrs.) trends towards which the landforms are evolving (not well covered to date).
Monitoring will assist in the resolution of some of these uncertainties, but only slowly as the
length of record increases. In the meantime, analysis of historical and archival sources should
provide a valuable retrospective source of data.
Studies involving the Lyme Regis Environmental Improvements and the assessment of
Coastal Defence Improvements at West Bay are excellent examples of the types of holistic
landform oriented approach that we feel the SMP should promote more strongly. In another
example, all coastal cliffs on the Isle of Wight coast were classified into “behaviour units” for
that SMP using methods developed within the recent MAFF funded “Soft Cliffs” research
6.2.2 Land Use, Human and Built Environment
Two areas of uncertainty are identified: (i) detailed knowledge of ground levels in low-lying
areas - this is essential to identify areas at risk of flooding and also to indicate the likely
floodwater depths occurring under different scenarios for economic analysis and (ii) knowl-
edge of the extent of properties situated upon ancient landslides susceptible to reactivation
following marine erosion - this is being addressed at Lyme Regis, but may be relevant else-
where e.g. Charmouth, West Bay.
West Dorset Coastal Research Group
6.2.3 Natural Environment
Three areas of uncertainty are identified: (i) knowledge of ground levels in low-lying areas -
to identify habitats at risk of saline flooding and (ii) the sensitivity or tolerance of important
habitats and rare species to changes in environment - to estimate the losses or changes occur-
ring with any change in strategic coastal defence options or with 'natural' changes occurring
under a do nothing or managed retreat option (iii) the opportunities available for habitat crea-
tion (possibly required under EU Habitats directive if SMP actions lead to damage of EU
6.2.4 Coastal Defences
Reliable information relating to condition, standard of protection and residual life is much
more difficult to provide in the case of soft defences where the beach is the main defence.
Beaches vary significantly in the short term making assessments sensitive to conditions pre-
ceding the survey. Furthermore, generic assumptions of adequacy of soft defences are poorly
developed and difficult to apply as they are less predictable in their performance than hard de-
fences and the same design of soft defence may perform differently on a site by site basis. A
solution could involve development of effective links between the programmes of beach and
coastal defence structure monitoring within rolling programmes of beach management. Even
then, some work would be needed to develop a reliable set of indicators permit monitoring of
the actual standard of defence afforded by soft defences.
6.3 Recommendations for Future Monitoring
6.3.1 Coastal Processes
Appendix C provides much sound general advice on monitoring, but a significant number of
uncertainties can be identified. We have sought to indicate how future monitoring might be
improved and suggest that you add the following to the SMP:
1. The vertical aerial photography recommended should be very valuable. However, de-
tails are needed of methods of analysis and the purposes that might be served e.g. photo-
grammetric measurement to determine cliff retreat & beach volume changes - for each
pocket beach? If so, an allowance is needed for setting up a network of stable precisely
surveyed photogrammetric ground control markers. A reliable standardised analysis
routine could then be devised to process results very efficiently. Additional flights (e.g.
post storm) could easily be commissioned by individual authorities to record exceptional
events occurring in more limited areas - processing of results would be standard and
relatively cheap. A frequency in excess of once every 5 years would be preferable for ar-
eas where potential problems are identified. The choice of 1:10,000 scale photography is
a little small for beach monitoring giving maximum attainable vertical accuracy of
measurement of ±0.2m. 1:5,000 scale photography with 60% stereo overlap is preferable
as used by the EA Southern Region Beach Monitoring Programme since 1973 between
Bournemouth and the Thames. A larger number of photos would be needed to cover the
coast at this scale such that the indicative cost could increase.
2. Consideration is needed to identify the some of the morphological features that might be
monitored as indicators e.g. cliff-top, cliff-toe, edges of terraces within undercliffs,
beach crest, shingle beach toe (where exposed) etc.
3. Having identified indicators it is important to devise a means of differentiating signifi-
cant trends of concern to coastal defence from short term fluctuations or "noise."
West Dorset Coastal Research Group
Variation of indicators in excess of that attributable to “normal variability” might pro-
vide valuable early warning of major changes and future problems. For this reason it
would be useful to establish “normal variability” based on historical analysis and to al-
low provision for periodic analysis and review of monitoring results. Consideration is
needed of the possible actions that might be triggered when monitoring results exceed
pre-determined thresholds. Such a programme would alter the management philosophy
from being reactive to proactive.
4. Details are needed of the purposes to be served by the oblique photography. Its main use
should be for visual representation and qualitative comparison. Given some care in
camera and lens selection, flight paths and perspective etc., some quantitative measure-
ments may be possible from such photography. However, vertical photography is always
preferable where ease of analysis and precision of results are important.
5. The effects of any improvement or extension of the gabion matresses at Chesilton (MU
2) would need to be monitored especially carefully . Morphological changes resulting
from high magnitude low frequency wave events would be the most important as im-
pacts upon the coastal defences, natural environment and amenity values depend upon
how the beach would interact with the new structural control under such conditions. In-
deed, it could be argued that the present gabion matresses have yet to be tested fully by
major swell wave events for which they were designed - hence they could still be viewed
as experimental such that the results of extending them are uncertain and potentially
6. Greater allowance is necessary for monitoring of the effects of extreme events upon
Chesil Beach. This should involve both the responses to typical cyclonic storms ap-
proaching from the SW as well as potentially more destructive swell and long period
wave events. The coastal defence function of Chesil is dependent upon the integrity of
the whole beach so monitoring should consider the whole structure to identify potential
"weak points" that could form foci for breaching and eventual breakdown of the beach.
This is a formidable task and would be assisted greatly by thorough historical analysis to
establish natural variability and confirm the prevalence of any especially “volatile” sec-
tions as revealed by the Babtie (1997) study. Breaching and breakdown of the beach
(either gradually or catastrophically) over the forthcoming 100-200 years are felt to be
genuine risks which were not addressed adequately by the Babtie (1997) study. A dual
level approach is recommended comprising: (i) analyses of historical records of beach
morphology (especially aerial photos) together with historical data concerning extreme
events and (ii) improved monitoring of the contemporary beach (higher frequency than
hitherto to help separate short term fluctuations from long term trends). The objective
should be to develop a morphological model of beach behaviour which might improve
confidence that events indicating possible breakdown could be detected early. Costs
might be justified by the high scientific value of the results as well as by the severe con-
sequences of an unpredictable beach breakdown. Costs of profiling might be reduced by
application of new technologies to beach monitoring e.g. GPS field survey, airborne la-
ser scanning (LIDAR), digital photogrammetry. The practicality, reliability and actual
costs of these alternatives as well as their benefits of speed and resolution would need to
be established by a feasibility study. Collectively, this work could form the basis of a sci-
entific research project funded at national or European level - inclusion of this recom-
mendation within the SMP may strengthen the argument for such work.
7. Reliable automatic weather stations could be established at key coastal sites. Wind data
would be valuable for hindcasting of local wave climates. Precipitation data would be
valuable in relation to study of landslide activity - especially if there are climate changes.
West Dorset Coastal Research Group
8. Consider monitoring of the levels of the nearshore sea bed in key areas where exchanges
of shingle are suspected as at West Bay. Periodic sonar survey and sediment sampling
along fixed shore normal profiles should suffice. Side-scan surveys could be applied to
identify geomorphological features if necessary.
It is recommended that opportunities are sought for development of monitoring proposals
within the context of a regional initiative. This might provide a means of establishing com-
mon methods and standards for measurement, archiving and data analysis and be co-ordinated
by a body such as SCOPAC with an overview of the results and future requirements of sev-
eral adjoining SMPs. Costs of necessary feasibility studies could be shared. The monitoring
most amenable to regional co-ordination would include wave and wind recording and beach
monitoring. Tidal recording is already co-ordinated nationally by Proudman Oceanographic
Laboratory with their network of 'A' Class gauges, although some other local authorities
along the south coast have established their own gauges to provide improved resolution in
flood hazard areas. A plan for regular updating of key analyses is needed to derive maximum
benefit from the monitoring data e.g. beach volumes and trend analyses, sea-level rise, wave
climate and extreme wave statistics, extreme sea-levels and joint probability studies etc.
6.4 Recommendations for Future Research
A general opinion of the group is that the draft plan recommendations focus solely upon pres-
ent day processes when significant uncertainties still remain in respect of the palaeo-
environmental evolution and historical behaviour. The latter should reveal key insights into
the likely or possible long term behaviour of large and complex landforms such as Chesil
Beach and the S.E. Devon and W. Dorset landslides. By contrast, several decades or more of
monitoring data would need to be collected before similar understanding could be derived
from contemporary process measurements. It is considered that conceptual evolutionary mod-
els need to be developed to indicate the possible longer term implications of changes detected
by monitoring. Research should attempt to tackle requirements for estimates of future coastal
evolution over scales of 20-100 years as well as seeking to provide better predictions over 2-
20 year periods. Both scales are important to shoreline management - the former to provide
strategic vision and the latter to provide the knowledge to underpin specific policies and
practices developed in working towards the long term goals.
6.4.2 Coastal Processes
In research terms Chesil needs to be considered as a whole i.e. as a process unit rather than as
two or three management units as indicated by the draft plan. It is felt that the study proposed
to analyse Chesil monitoring results should be accompanied by work to develop a conceptual
geomorphological model of the beach based the latest information available from palaeo-
environmental, historical and sediment budget research. It is regarded as a serious weakness
that the long term sediment dynamics of the beach, its morphological changes and its internal
structure remain poorly understood. Such a model should include the development of realistic
scenarios involving the modes of shingle transport and breakdown of the beach - an event that
should not be ignored by the SMP. Further academic research should be encouraged to pro-
vide vital further evidence of past evolution and behaviour of the beach.
Research is needed to classify the behaviour of the coastal cliffs & landslides throughout the
SMP coastline. The stability of all the cliffs - especially those of the Permian between
Teignmouth & Torbay and the Devonian of Torbay - should be assessed. There are many se-
vere landslide situations on this coast which may be very vulnerable to sea-level rise and cli-
mate change, but they have received little attention. It is recommended that the method of
West Dorset Coastal Research Group
identifying coastal behaviour units developed within the recently completed MAFF Soft
Cliffs project (Rendel Geotechnics) is applied. This is primarily a reconnaissance level
study and has been applied previously to the 100km of varied cliff coast around the Isle of
Wight in support of its SMP.
Management Plans need to be prepared for each pocket beach within the SMP which has a
coastal defence function. They should address issues such as the long term and short term be-
haviour, sediment budgets, sensitivity to changes in environmental controls. This information
should provide a framework for predicting the future behaviour over the next 50 years - to
help identify potential conflicts between the proposed SMP policies and the longer term man-
agement objectives for the coastline (e.g. it may be possible that a particular beach will not be
able to provide sufficient protection within the next 50 years - what should be done?). The
plans, to a large extent, would be syntheses and interpretation of existing information, but
could also include primary data collection (e.g. seabed sediments in the nearshore zone,
Validation of the Meteorological Office Wave Model is an excellent idea, though it should be
acknowledged that this model cannot easily account for far traveled swell waves or other long
period waves so there may still be a requirement for long term wave recording, especially in
the vicinity of Chesil. Note that recent research suggests that this coast is exposed to tsunami
which may explain several cases reported of “large waves appearing out of a calm sea.”
6.4.4 Natural Environment
A breach study of the type proposed for Slapton should also be considered for Chesil where
the wave exposure and consequences of breaching are significantly greater.
Relevant Research Options for Inclusion within SMP Recommendations:
The following options should fill gaps in the information contained within the SMP and
should be seen as additional to the research recommendations contained within the May 98
consultation document. The group believe that the results of the work suggested here should
assist the implementation of SMP options and in time contribute strongly to future revisions
of the SMP, thereby setting a firm basis for long term sustainable management of this coast.
We therefore recommend that the following items be added to the SMP research recommen-
1. Study of the origin and development of Chesil making use of all available palaeo-
environmental historical and sediment budget information. Linking of past development
with contemporary monitoring and coastal process data. Development of a conceptual
model of beach behaviour including possible breakdown of the beach (this type of ap-
proach is likely also to be effective for other process units within the SMP where better
understanding of long term changes are needed).
2. Effects of extreme events upon Chesil Beach. Two approaches: (i) careful collection
and evaluation of historical data and (ii) monitoring of contemporary beach responses to
storms. Consideration be given to the application of new technologies for beach moni-
toring to help tackle problems caused by the size of Chesil. Items 1 & 2 should be ad-
dressed by a national or European funded scientific research project - inclusion of these
recommendations within the SMP would strengthen the argument for such work.
West Dorset Coastal Research Group
3. Evaluation of consequences of results of items 2 & 3 for scientific interest, natural envi-
ronment, built environment, coastal defence and amenity.
4. Encourage continuation of palaeo-environmental studies of Chesil and the Fleet Lagoon.
5. Encourage geomorphological investigation of the inshore seabed in support of studies of
long term coastal evolution (relevant throughout Lyme Bay - especially between Chesil
and Lyme Regis).
6. Precision measurements of ground levels in low-lying areas to identify lands, properties
and key habitats at potentially at risk (photogrammetry or LIDAR). Especially valuable
for study of consequences of Chesil Beach breakdown.
7. Continued wave monitoring to validate locally the Met. Office wave model. Give con-
sideration to development of a means of defining a long term swell wave climate for
Chesil. Consider installation of additional automatic coastal weather stations to record
local winds and precipitation.
8. Classification of all cliffs into Cliff Behaviour Units (CBUs). These should provide an
excellent first estimate of the nature and extent of ground movements possible should
marine erosion accelerate or climate change intensify. Selected landslides where likely
reactivation or possible first time failures would present a significant risk to properties
may be identified for further investigation e.g. Isle of Portland, Torbay-Teignmouth.
9. Monitor scientific, educational and amenity interests. A means of quantifying the unique
value of the SMP coast in these terms would be of great value in appraising scheme
strategies. A definitive method has yet to be agreed, but visitors and other key indicators
should be monitored in anticipation of practical methods becoming available in the fu-
10. Seek regional co-ordination of monitoring through a body such as SCOPAC to identify
best practice and standardise measurements, data archiving and analysis.
11. Promote preparation of Management Plans for each pocket beach within the SMP which
has a coastal defence function.
Any correspondence relating to this document should be addressed to the following:
Dr Malcolm Bray
Department of Geography
University of Portsmouth