Kenneth Pye
Associates
Ltd.
Scientific Research,
Consultancy and Investigations
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Sand dune processes and management for flood and coastal defence
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Project funded by Department for Environment, Food and Rural Affairs, R&D Technical Report FD1302/TR This project represents a seven year study into the sand dunes of England and Wales. The final report was published in May 2007, and can be downloaded from the DEFRA website. The Executive Summary can be viewed below.
Executive summary
Background
Sand dune systems can
provide an important natural coastal flood defence and are also of great
importance from nature conservation, recreation and tourism perspectives. This
project was based on a recognition that (a) considerable information exists
about the ecology of coastal dune systems in England and Wales but
geomorphological, sedimentological and engineering management aspects have been
relatively neglected, and (b) recent changes in coastal management philosophy
towards adaptation and risk management mean that there is increasing interest in
developing new methods of managing coastal dunes as dynamic natural defences. To
this end a better understanding of the physical nature of sand dune systems, and
of sand dune processes, is required. Project
objectives
The main objectives
were: (1) to compile information about the geomorphological and sedimentological
character, flood defence significance and management status of coastal dune
systems in England and Wales; (2) to review available methods for the management
of coastal dunes; (3) to evaluate the effects of predicted climate and sea level
change on dune systems, and to consider the implications of removing hard
defences to recreate more dynamic dune systems; (4) to examine the issues and
options for future management in relation to five case study areas; and (5) to
identify aspects of best practice and requirements for further work. Results
The results are
summarised in this report which consists of five parts. Part 1 provides an
overview of the project, the main issues addressed, the approaches used and the
main conclusions. Part 2 presents a review of sand dune processes and the
significance of coastal dunes for coastal flood risk management. Part 3
describes the methods used to obtain data and presents brief descriptions,
location maps and database summaries for each dune site. Part 4 reviews
available methods to manage and modify coastal dunes, and Part 5 discusses the
problems and management options at the five example sites (Sefton Coast, Spurn
Peninsula, Brancaster Bay, Studland, and Kenfig Burrows). Additional information
is provided in publications and a PhD thesis which arise from the work (details
given in Part 1). Coastal dunes in England
and Wales presently occupy an area of approximately 200 km2.
A total of 158 individual dune localities, grouped into 112 dune 'sites', were
identified. Coastal Cell 9 has the largest total area of dunes (c. 48 km2)
followed by Cell 11, Cell 8 and Cell 1. The largest single system is located on
the Sefton Coast (c. 20 km2),
but there are few systems larger than 5 km2
and more than 50% of the sites are <1 km2 in size. The largest systems occur on the west coasts of
England and Wales but smaller systems in eastern and southern England are also
locally of considerable flood risk management significance. Their importance in
this regard lies primarily in their function as barriers to coastal flooding,
and is dependent on the asset value of the land behind and the existence or
otherwise of other flood defences. Dune systems are especially important where
they protect high density residential or industrial developments, high-grade
agricultural land or habitats of international conservation importance. Compared
with many other forms of defence, dunes are less visually intrusive, have
greater value for wildlife and recreation, and are able to respond more readily
to changes in environmental forcing factors (e.g. climate and sea level change,
sediment supply conditions). Virtually all dunefields
in England and Wales have formed entirely in the last 5000 to 6000 years, and in
most places the present dune topography is less than a few hundred years old.
Dune migration occurred on a large scale during the Little Ice Age, but many
sites still had extensive areas of bare sand as recently as the 1970's, largely
as a result of human activities. Dune stabilisation measures since the 1950's,
and particularly in the 1980's and 90's, have stabilised most dunefields to a
high degree. Areas of aeolian activity are now restricted mainly to sections of
eroding coast and a few inland blowouts which have remained active due to local
wind acceleration and increased turbulence. Approximately 35% of the
total dune frontage in England and Wales has experienced net erosion or is
protected by hard defences, 35% has experienced net stability and 30% net
seawards accretion. The extent of frontal dune erosion may increase in the next
century as a result of increased storminess and sea level rise, and this may
have negative impacts on the extent of some dune habitats and the effectiveness
of dune systems as flood defences. However, the consequences of such changes
will vary from location to location, reflecting differences in natural processes
and beach-dune sediment budgets. Most dune systems in
England and Wales are composed of quartz sands, and marine carbonate is
important only in some systems in Devon and Cornwall and southwest Wales. The
main sources of sand in the past were marine reworking of glacial sediments on
the sea bed and in coastal cliffs. These sources are much less significant at
the present time. Increased storminess and rising sea level are likely to cause
more widespread erosion, leading to re-distribution of existing coastal
sediments. Accretion can be expected at the down-drift ends of sediment
transport cells, but dunes at the up-drift ends will experience accelerated
erosion and greater risk of breaching/overtopping. Conclusions
and Recommendations
Wherever possible, coastal dune and beach systems should be allowed to respond naturally to changes in forcing factors and sediment supply conditions. Where accommodation space exists and conditions are favourable, frontal dunes should be allowed to roll back to establish a new equilibrium. However, in areas of low wind energy or strongly negative beach sediment budget, dune dissipation is likely to occur unless nourishment with fine-grained sand and artificial dune profiling are undertaken. It is recommended that a detailed Geomorphological Evaluation Study should be undertaken at each dune site, or group of sites, to assess the requirements and to identify the most appropriate management strategy. This will require nature conservation and other interests to be taken into account. Where not in existence, systematic monitoring programmes should be set up to provide early warning of dune change. Data should be obtained in a standardised format which can be exported for centralised analysis. Click here to download the full report or Technical Summary from the DEFRA website
Printed ReportsPye, K., Saye, S.E. and Blott, S.J. (2007) Sand Dune Processes and Management for Flood and Coastal Defence. Part 1: Project Overview and Recommendations. R & D Technical Report FD1302/TR/1, Department for Environment, Food and Rural Affairs, London, vi + 35 pp, tables, figures and plates. Pye, K., Saye, S.E. and Blott, S.J. (2007) Sand Dune Processes and Management for Flood and Coastal Defence. Part 2: Sand Dune Processes and Morphology. R & D Technical Report FD1302/TR/2, Department for Environment, Food and Rural Affairs, London, vi + 21 pp, tables, figures and plates. Pye, K., Saye, S.E. and Blott, S.J. (2007) Sand Dune Processes and Management for Flood and Coastal Defence. Part 3: The Geomorphology and Management Status of Coastal Dunes in England and Wales. R & D Technical Report FD1302/TR/3, Department for Environment, Food and Rural Affairs, London, vi + 94 pp, tables and figures. Pye, K., Saye, S.E. and Blott, S.J. (2007) Sand Dune Processes and Management for Flood and Coastal Defence. Part 4: Techniques for Sand Dune Management. R & D Technical Report FD1302/TR/4, Department for Environment, Food and Rural Affairs, London, vi + 49 pp, tables, figures and plates. Pye, K., Saye, S.E. and Blott, S.J. (2007) Sand Dune Processes and Management for Flood and Coastal Defence. Part 5: Dune Management Practices at Selected Dune Systems in England and Wales. R & D Technical Report FD1302/TR/5, Department for Environment, Food and Rural Affairs, London, vi + 39 pp, tables, figures and plates.
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Sand
dune sites in England and Wales
