Engineering geomorphology on the coast: lessons from west Dorset

Geomorphology 31 Ž1999. 391–409

Engineering geomorphology on the coast: lessons from west Dorset Denys Brunsden a,) , Roger Moore b a

Department of Geography, King’s College, London, UK b Rendel Geotechnics, Birmingham, UK

Received 6 September 1996; received in revised form 12 March 1997; accepted 13 May 1997

Abstract The central aim of this paper is to describe the general context in which an applied geomorphological investigation for a management project on a Heritage coast will be set. We attempt to show how the decisions may be affected by historical legacies and public or administrative attitudes. Modern attitudes to the coast in Great Britain are summarized in the light of recent studies by the Department of the Environment and the Ministry of Agriculture, Fisheries and Food. The Dorset coast in southwest England is used to illustrate the main points. The paper describes the coastal features, explains the historical legacy of use, and examines problems of contemporary coastal management. The paper concludes with a consideration of the natural geomorphological principles of landscape design which might be employed as part of the guiding concepts. q 1999 Elsevier Science B.V. All rights reserved. Keywords: applied geomorphology; coastal geomorphology; geomorphological principles; attitudes

1. Introduction Some general lessons may be learned during the early stages of a local coastal management problem, as illustrated by a description of the Dorset coast in southwest England and the current plans for the physical management of some of its landforms. We do not intend to describe the details of a particular project, but to concentrate on how management decisions, at this early stage, can be based on sound geomorphological practice.

)

Corresponding author.

This paper explores the general contextual considerations that lie behind the development of an investigation in the inception stages of a project, and suggests that if we are unwary, the essential science may be influenced at the outset by attitudes, local needs, and planning guidelines. Although many of our comments rely heavily on the experience, attitude, and opinion of the authors, every attempt has been made to limit value judgments. We do admit that some of the views expressed are not always fully supported by scientific data, and it is not therefore expected that the stances adopted in the paper will be acceptable to all readers. However, it is valuable to discuss the problem because our experience has shown that in applied geomorphology, many decisions have to be made quickly without critical

0169-555Xr99r$ - see front matter q 1999 Elsevier Science B.V. All rights reserved. PII: S 0 1 6 9 - 5 5 5 X Ž 9 9 . 0 0 0 8 2 - 3

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D. Brunsden, R. Moorer Geomorphology 31 (1999) 391–409

information. In these circumstances, the advisor must do the best job possible with the data available, relying on experience and analogy for support, while always admitting the extent of the unknown areas of knowledge. When faced with this problem, we have found that it helps to have in mind a few simple, commonsense guidelines or rules. They may be obvious and well known to an experienced practitioner, but inexperienced consultants often neglect them. Each of the following sections summarizes the local Dorset experience and concludes with lessons for general practice.

2. The coast as ‘Created’ In the beginning, God created the heavens and the earth . . . God said, ‘‘Let the waters under heaven come together into a single mass, and let dry land appear.’’ And so it was. God called the dry land ‘earth’ and the mass of waters ‘seas’. God saw that it was good. ŽJerusalem Bible, 1994; Genesis 1:1–2.. ‘‘The significant landforms of Lyme Bay are so numerous and important that they compose the richest variety and most protected range of geomorphological sites on any coastline in the world’’. ŽD.C.C., 1996.. 2.1. The nature of the resource The first general consideration in the development of an applied geomorphological investigation Žassuming that the problem has been identified, the objectives are known, and the brief has been written!. is to determine the nature of the resource which is to be managed and to understand public attitudes toward it. For our examination, the resource is Lyme Bay and the Isle of Purbeck, which includes Chesil Beach ŽCarr, 1980; Bray 1992., the Bindon Landslide of Christmas Eve, 1839 ŽConeybeare and Buckland, 1840., and Portland Bill ŽFig. 1.. This is one of the most famous and beautiful coastal areas on the southwest coast of England, providing an area of outstanding scientific and cultural interest, especially for the Earth sciences, with an exceptional range of

wildlife habitats, biodiversity, and a rich cultural heritage ŽTownley et al., 1996.. It is one of the most regulated of all Heritage coasts, and is considered by many to be worthy of World Heritage status ŽD.C.C., 1996.. This scientific interest, beauty, and diversity are based on the remarkable geology and geomorphology, the position the coast holds in the history of geological science itself ŽLang, 1936; Purcell and Gould, 1992; Taylor, 1995., and its educational importance ŽLulworth Estate, 1996.. Between Axmouth and Swanage, there is a continuous sequence of marine sedimentation into the Channel Basin representative of the whole Jurassic system ŽFig. 2.. The junction of the Triassic and Jurassic is the reserve world stratotype reference section. Eastward are an almost unbroken internationally significant series of references exposures in the Lower Jurassic mudstones, Middle Jurassic limestones, and a sequence of Upper Jurassic limestones and clays. Here are found world stratotypes of Kimmeridge Clay, Portland and Purbeck Beds. Capping all of these beds are transgressive Cretaceous rocks, including the Chalk and the Upper Greensand and Gault of Albian–Aptian age. From the Permian to the Cretaceous in a virtually unbroken sequence, this area contains nearly 200 million years of earth history from the age of the fishes, through the amphibians, to the coming of the reptiles. It is for this reason, the contribution to our understanding of the evolution of species, that the World Heritage designation is sought. The section from Lyme Regis to Seatown in the Lower–Middle Liassic is a famous marine fossil locality ŽPurcell and Gould, 1992.. Here, Mary Anning recorded the first Plesiosaur, a Pterosaur, the Cephalopod Belemnosepia Žcomplete with ink., and the fossil fish Squaloraja ŽTickell, 1996.. The rocks regularly yield specimens of Ichthyosaur as well as new species of fish, shark, and dragonfly. Ammonites, belemnites, crinoids, and fossil wood in abundance ensure an intense public and educational interest and concern for the wise management of the coastal resources ŽTorrens and Taylor, 1986; House, 1989; Torrens, 1993.. Local Experience 1: It is obvious that the public attitude to the management and planning strategies for such a coast is heavily biased toward protection and resistance to development proposals.

Fig. 1. Location map for the Dorset coast.

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D. Brunsden, R. Moorer Geomorphology 31 (1999) 391–409

Fig. 2. The geology of the Dorset coast.

General Lesson 1: The general consideration to influence the applied geomorphologist and those responsible for the decision-making process is the realization that their actions are publicly visible, observed with concern by educated user groups firmly in the environmental arena and subject to the most stringent assessments and opinions. The intensity of this scrutiny increases in Heritage areas. 2.2. The geotechnical framework The Lyme Bay coastline is also known for the scientific interest of its landforms. The geological structure of the area also dominates the form and evolution of the landscape and provides a textbook example of the development of a space–time sequence in the evolution of coastal forms on the concordant structural coast of Lulworth and Purbeck ŽGoudie and Brunsden, 1997.. The Isle of Portland must rank as the best example in Britain of structurally controlled landsliding. The NW–SE master and conjugate joint sets in the capping Portland and Purbeck Beds are a major landform control at all

scales, from the location of individual rock falls to the overall outline of the island itself ŽBrunsden et al., 1996.. The sequence of rocks shows a rapid alternation between consolidated, fissured, high plasticity clays, siltstones, limestones, and sandstones of varying thickness and permeability. The overstep of the permeable, Cretaceous fine sands and thick chert beds capped by residual flint gravels of Eocene age accentuates this feature. As a result, there exist many varieties of the classic landsliding formula of permeable beds overlying less permeable aquicludes. As the sequence changes, so do the landslide types, from the mudslides in the Lower Lias to the rockslides of the Chalk and Middle Lias, to the rockfalls, topples, and sags of the Portland Stone and Kimmeridge Clay, and the blockslides of the Upper Greensand in the Landslide Nature Reserve between Axmouth and Lyme Regis. The Dorset coast shares with other coastlines the fact that it was abandoned by the sea during the last glacial period, and for a time, evolved under periglacial conditions. Major mudsliding occurred,

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and at the foot of the old cliffs, an apron of debris accumulated. These old slopes, which are still susceptible to reactivation, remain today at the Landslide Nature Reserve, Lyme Regis, the Spittles, behind Chesil Beach ŽFig. 1. and on the side slopes of the major rivers. Since ca. 5500 BP, the rising sea has initiated the removal of the solifluction deposits and destabilized many of the ancient slides so that coastal erosion is rapidly diffusing inland. The current rates of coastal erosion are 0.1–0.2 mpa on the vulnerable Lower Liassic Clays. A current rise of sea level on this coast at ca. 2 mm pa enhances basal erosion ŽTable 1., and there appears to be a rising trend in the activity of the landslides, which is spreading inland along the paleo-landslide systems ŽBrunsden and Ibsen, 1993.. Local Experience 2: The vital point for slope management is that there is a particular structural and lithological setting which favors landsliding. A more subtle point is that a legacy of pre-existing shear surfaces, extruded clays, cambering, valley bulging, landslide mantled slopes, and residual strength clays diffuse into the slopes above the current active cliff and shore. Susceptibility to landsliding is the most obvious geomorphological fact to be considered. However, whether the inland extent of paleo-coastal landsliding can be investigated in the early stages of a commission or utilized for costing the investigation budget, or cost-benefit, will depend on a willingness of the responsible authority to recognize that the inland geomorphological system boundary is the same as the administrative consideration. General Lesson 2: When determining the geotechnical setting of a site, correctly determining the exact area of coastal process interaction and administrative responsibility is vital. 2.3. The coastal change legacy The paleo-history is also important to our understanding of the time scales involved. This is particularly important to the interpretation of the beach systems of Lyme Bay. Although the geology and geomorphology of the coast are famous, some elements are strangely unknown. This is particularly true of the wave and tide conditions and their rela-

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tionship to the sediment transport system, and the development of the coast over the Holocene is poorly documented. For example, Chesil Beach is a 28-kmlong barrier storm beach and enclosed lagoon formed from flint and chert ŽFig. 3.. There is considerable discussion over the origin of the beach. Carr and Blackley Ž1973, 1974. and Carr Ž1980. suggest that the structure was driven ashore as sea level rose across Lyme Bay during the last 7500 years. If this is true, it is a fossil accumulation that is still being reworked by overtopping in storms and slow onshore migration. Other authors ŽBrunsden and Goudie, 1997; Bray, 1992; 1996; Brunsden, 1992. believe that the coarse upper beach was derived mainly from the flint and chert capping of the hills to the west. The investigation of these subjects proves significant because they will clearly determine the success of any structural designs and management systems. Local Experience 3: The Dorset coast is strongly affected by the history of sea level rise during the Holocene. Possible coastal management strategies for beaches must recognize that the beaches may be relict sediment stores with a limited sediment supply from offshore and that they are the downdrift terminus of a littoral drift system that is not longer being supplied. General Lesson 3: The appropriate lesson for the early stages of a project is the essential need for a desk study to determine the extent of knowledge about the legacy of coastal change, determining how these affect the current trends, and to write caveats associated with any ‘scope of survey’ decisions.

3. The coast as used And God said, ‘‘Let the waters be gathered together unto one place, and let the dry land appear’’, and it went on the market at six hundred pounds a square foot. ŽThe Bible: The Old Testament according to Spike Milligan, 1994.. 3.1. The historical legacy The fourth general contextual matter influencing the investigation design is an understanding of the historical legacy of human use. Human actions may be regarded as an attempt to improve the coast; the

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Table 1 Coastal erosion rate data for the Dorset coast Žcollated by Brunsden and Ibsen, 1993. Location

Budleigh Salterton Budleigh Salterton Budleigh Salterton Peak Hill–Branscombe Haven Cliffs—West Haven Cliffs—East Culverhole AxmouthrBindon Bindon Dowlands Dowlands Dowlands Rousden Charton Bay Whitlands–Humble Point East Pinhay Ware Cliffs Dorset StonebarrowrFairy Dell

Time

Coastal retreat

From–To

Max Žm.

1933–1937 1981–1985

75.00 100.00

Remarks mpa range

18.75 25.00 1.0–2.0

1905–1958 1905–1958 1905–1958 1905–1958 1904–1958 1904–1958

40.00 23.80 8.75 74.00 30.00 27.50 0.1–0.25 0.075–0.1

1904–1957 1904–1959 1904–1959 1904–1958 1904–1958

9.75 12.50 10.00 7.50 27.50 1.0–3.0 0.29–0.71

1887–1964

mpa average

Stonebarrow–Black Ven StonebarrowrFairy Dell StonebarrowrFairy Dell Charmouth Lyme RegisrBlack Ven Lyme regis Church Cliffs Lyme Regis–Charmouth Charmouth–Golden Cap Golden Cap–Eype Spittles

1887–1972 1928–1960 1946–1969 1914–1970 1958–1988 1803–1934

0.4–0.5 0.34–1.4

1901–1985 1901–1985

0.05–0.3 2.5–8.0

Thorncombe Beacon West Cliff East CliffrBurton Cliff West of Seatown East of Seatown Isle of Portland Furzy Cliff Redcliff Point Swyre, Bats Head Warbarrow Bay Kimmeridge Bay Durlston–St. Albans Durlston Bay Durlston Bay Handfast Point Hengistbury Head

1901–1985 1887–1962 1902–1962 1901–1985 1948–1985 1867–1960 1850–1973 1888–1963 1882–1962 1888–1982 1888–1963 1888–1963 1986–1988 1954–1986 1882–1962 1938–1986

0.3–0.5

27.45

0.2–0.3

0.46 0.11–0.16

1.50 0.02 0.74 0.44 0.16 1.40 0.55 0.50 0.18 0.09 0.18 0.22 0.18 0.13 0.50 2.00 0.50 0.45 0.87 0.13 2.40 3.14 0.89 0.71 0.38 0.30 5.25

0.40 0.37 0.03 0.05 0.25 negligible 0.32 0.41 0.22 0.14 0.38 0.00 6.00 0.44 0.23 0.20

Cliff top, major basal erosion 11 surges, 5–15 m per surge from small events average 2.5 m per century

For toe block of chalk Main elements of landslide

At least 7 small failures between 1887–1953 Steady erosion Suggesting stable period

Reactivation of ancient slips by beach erosion late 1900’s east part stabilised late 1980’s

Landsliding in the past Partially protected in 1984 Most post 1949 Eastern bay

Reduced by protection, rates increase to the west

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Table 1 Ž continued . Location

Time

Coastal retreat

From–To

Max Žm.

Remarks mpa range

mpa average

Hengistbury Head Barton Cliff Barton-on-Sea Barton

1867–1959 1970–1980

1.10 0.96 1.00 1.90

Barton-on-Sea

1971–1987

3.00

93.60

structures, uses, and management procedures are a real part of the contemporary behavior system and may be treated in the same way as the natural components. The following examples are used to describe the main changes to the Dorset coast. Improvement a1: In the 13th century, the first ‘improvement’ was made to the coast when a wooden haven wall was built at Lyme Regis. Since that time,

93.6 in 97 years Increased retreat where unprotected

there has been a succession of modifications. The wooden haven was replaced by a stone jetty, the Cobb Žsee Fig. 4. which was finally joined to the land in 1756. Since that time, the supply of sediment from the west has been interrupted, and any east–west exchange has ceased. Very coarse limestone and chert debris has gradually accumulated on Monmouth Beach and has been partly built over. The

Fig. 3. Chesil Beach from Portland. The vulnerability of the villages, if the beach is no longer being supplied, can be seen.

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Fig. 4. Air photograph of Lyme Regis 1972. The harbour wall called the Cobb is bottom left. Beach loss to the east is evident. The bare area to the right of the Cobb is the 1962 landslide. The shore platform is called Broad Ledge and has been extensively quarried for limestone. The fields with degraded rock terraces are the late glacial landslides of the Spittles now actively failing and the two dark arcs are the Black Ven mudslides.

beach to the east rapidly eroded. Increased erosion at the foot of the cliff may also have reactivated a large translational slide in 1962 that destroyed a house and a seawall. This slide is still moving; the remedial works are deteriorating, and small, slow movements episodically take place along the whole sea frontage. Over time, a succession of sea defense works, two generations of seawall, offshore rock armor, stone and timber groynes, and retaining walls have been

erected. Beach feeding took place in 1967 and 1992 ŽHydraulics Research, 1985; 1991.. Improvement a2: The Lyme Regis foreshore was used in the 19th century as a source of construction infill and high quality stucco for the decoration of fine buildings. Between 1840 and 1903, 20,000 tonsryear were cut from the platforms ŽFowles, 1991.. The lowering of the shore platforms caused serious acceleration of coastal erosion and landslides.

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The human response has been the construction of a jetty, seawalls, and groyne systems. Upslope, the undercutting effect caused the collapse of a carpark, the destruction of two houses, and heavy remedial works. Today, the effects are still being felt along the coast as the down drift loss of material causes beach lowering and a higher rate of cliff erosion. Improvement a3: The flint, chert, and quartzite shingle and cobbles of the west Dorset beaches were in demand for aggregate, ornamental, water filtration, and grinding purposes for 300 years until licenses were finally revoked in 1987 ŽCarr, 1980; Bray 1996.. A conservative estimate is that over 1.1 million tons were extracted between 1930 and 1977, which Bray Ž1996. estimates might be as much as 4% of the beach resources between Charmouth and Portland. Unlicensed gravel mining probably raises the totals to ca. 3 million tons, or 12%, of the beach volume Žsee Fig. 5.. It is difficult to estimate the effect this has had on the shore systems. Together with the natural processes and the effect of the

399

structures, however, it is certain that the cliffs, beaches, and public facilities along the entire coast from Lyme to Portland are in a fragile state Žsee Fig. 6.. Improvement a4: At West Bay in 1740, two jetties were built out across the beach to develop a harbour for Bridport ŽFig. 7.. Unfortunately, the natural movement of shingle along the shore formed a bar across the harbour mouth that impeded the entrance of ships. In 1924 to 1926, Francis Giles added masonry to the piers which interrupted the transit of beach material along the shore. The record of the ensuing loss of beach material on the western Župdrift. side of the harbour is one of the most extensively documented examples of erosion on the British coast. The historical record of coastal protection, extension, and repair is equally impressive ŽBrunsden, 1996.. Local Experience 4: It is clear from these examples that the Dorset coast has been seriously damaged by past engineering works. In particular, the

Fig. 5. Beach mining for gravel on West Bay Beach in 1937.

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Fig. 6. The disastrous state of Seatown Beach which lost sediment after the cessation of supply from the west after landsliding blocked the pathway. The picture shows the exposed beach foundation and the very rapid erosion of the clay cliffs into a storm ramp following exposure during easterly storms.

closure of the Cobb, sea quarrying at Lyme Bay, and the West Bay piers have effectively closed the sources of supply of new material, and the beach is regrettably thought to be on the brink of major change ŽBrunsden and Goudie, 1997.. Here, it is easy to blame past generations for taking action which, in hindsight, we can see were mistakes. Perhaps the lesson to learn is that our own time has come, and our decisions are about to be subjected to the test of time! As academics, we might expect our work to be superceded and to merely become part of the history of science. The trouble with applied work is that the action is real and remains for all to see and criticise. General Lesson 4: The historical legacy of human use of the coast may have introduced new trends of landscape change or unexpected ground conditions. It is also worth noting that there may be modern political consequences deriving from the new trends

of landscape change. If historical uses have generated trends that are not yet recognized and these have a physical effect after the installation of new works, it may be that the ‘blame’ will be misplaced. It is essential to recognize such legacies at the inception of a new project. 4. Historical coastal attitudes And God saw the light and it was good; He saw the quarterly bill and it was not good. ŽThe Bible: The Old Testament according to Spike Milligan, 1994.. 4.1. Historical standards The fifth general context to be established at the outset of a new project is to appreciate the historical

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401

Fig. 7. The evolution of the beaches and cliffs at West Bay following the infilling of the harbour walls. ŽA. 1867 Žunknown.; ŽB. 1929 Žunknown.; ŽC. 1987 ŽHydraulics Research..

402

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attitudes to coastal planning, engineering, protection, and defense. As noted above, in the UK, it is not unusual for public opinion to lay blame Žrarely credit. on an unspecified collective of people who are held responsible for the perceived problems. This is not a new sentiment, and there is no profit in extending the practice. It is perhaps sufficient here to state that past attempts at coastal protection did not always appreciate the regional context and evolutionary framework of the coastal system, and that individual developments were associated with a generally uncoordinated historical development process. It is almost certain that the engineers concerned did carry out investigations at the professional standards of the day. For example, Sir John Coode Ž1853. published a detailed description of the geomorphology of Chesil Beach before designing remedial works to West Bay Harbour. What was not known was what would happen to the system after the construction period ŽFig. 7.. It is still true that the weakest element of geomorphology practice is prediction, perhaps because of the geological roots of the subject. 4.2. Traditional solutions and inertia There is still a tendency for the traditional, hard engineering solutions to be adopted. There are four reasons for this. First, where the Earth science community is weak or the scientific knowledge of the coast is poor, the safest practice is to use an engineering solution. Second, there is a need for the solutions to be seen to work. The effective and visible solutions are often ‘heavy’ solutions, typically in the UK involving rock armour. The present managed coast, therefore, often consists of strong points, sediment barriers, and inefficient storage systems. These designs are provided as a reaction to experience or to facilitate a development irrespective of the needs or character of the coast itself. Third, because structures have a design life, there is a need for maintenance and continuity, and the range of options is heavily constrained by cost. Finally, for some managers, there is still a sense of defending against an enemy rather than a willingness to work with the system. An important consequence of this is that there is a tendency to respond only when there is a developing risk, structural failure, or new planning application. In the past, the controlling attitude has

been one of civil defence, which handles risk as it occurs. It was a clean-up operation rather than a planned response with forward planning and hazard mitigation in place. Local Experience 5: In the experience of West Dorset, much has gone wrong with the coastal protection schemes, despite the use of the best practice of the day. The historical solutions are mainly those of ‘heavy’ engineering, which demand maintenance. This factor, plus the investment already made, limits future choices. General Lesson 5: There is an inbuilt inertia associated with maintenance which constrains the options available. This is true even where it can be shown that the methods used have not been successful. Usually, the controlling factor is the cost, and the traditional attitudes to coast protection that the cost can and should be met from the public purse.

5. The coast as it ought to be ‘‘None of these!’’ he caught me up, ‘‘Not conservation, not planning, not even geography. Your subject is geotechnics.’’ And then with a lunge he resumed speed, but only for a few strides. Again he stopped short. ‘‘Geography,’’ said he, ‘‘is descriptive science Žgeo — earth, graphy — describe.; it tells what is. Geotechnics is applied science Žgeo — earth, technics — use.; it shows what ought to be.’’ And on he bounded. ‘‘But what’s the matter with ‘conservation’,’’ I pleaded, ‘‘or regional planning?’’ ‘‘Nicknames,’’ he retorted. ŽBenton Mackaye to Patrick Geddes, Mackaye, 1968.. 5.1. Contemporary attitudes The remaining context for project inception is an awareness of the current guidelines and attitudes to coastal management. This is particularly true in the UK where the governmental attitudes are rapidly changing in response to the influence of European Directives and privatization of public services. As a direct consequence of the lessons of the historical legacy, both the planning system and the engineering profession have made significant advances in the way they make decisions. Today, attitudes to the

D. Brunsden, R. Moorer Geomorphology 31 (1999) 391–409

Fig. 8. Elements of earth science investigations required for coastal development. ŽRendel Geotechnics, 1995a,b,c,d,e,f..

403

404

D. Brunsden, R. Moorer Geomorphology 31 (1999) 391–409

coast are changing under the influence of several factors. First, there is an improÕed scientific knowledge and technical ability and willingness to measure the processes involved in erosion, transport, and deposition due to the remarkable advances in micro-electronics and environmental data loggers. There is no longer any excuse, other than survey time, for coastal works to be designed in the absence of real time data on waves, tides, currents, and sediment movement patterns. Second, there are comprehensiÕe goÕernmentsponsored research programs to clarify the earth science needs and methodologies required to develop the essential planning and management strategies ŽUK examples include Department of the Environment, 1990; Rendel Geotechnics, 1993,1995a,b, c,d,e,f.. Third, there is a strong planning legislation with planning policy guidance to protect. Areas of Outstanding Natural Beauty, Heritage coast, Sites of Special Scientific Interest, Special Marine Conservation Areas, and Ramsar Wetland Sites ŽWest Dorset County Council, 1996; Department of the Environment, 1992a,b.. This is supported by a willingness to consider conserÕation and enÕironment priorities

supported by environmental assessment procedures and legislation ŽDepartment of the Environment, 1988.; the educatiÕe influence of local authority discussion groups such as the Standing Conference on Problems Associated with the Coastline ŽSCOPAC., or the Dorset Coast Forum. Finally, there is an awareness of alternatiÕes in coastal management to heaÕy engineering solutions ŽBrampton, 1992; House of Commons, 1992; Ministry of Agriculture, Fisheries and Food, 1993,1994., including a long-term integrated strategy and a wider consideration of ‘soft’ or ‘green’ engineering, such as sediment feeding, bypass systems, the use of flexible barriers, and managed retreat solutions ŽEnglish Nature, 1996.. How far these are driven by the economic and cost benefit consideration of modern attitudes to the control of public expenditure is unknown ŽPenning-Roswell et al., 1992.. 5.2. The contemporary guidelines A welcome new approach is emerging in many countries. In the UK, for example, the Department of the Environment has issued a statement of the earth science information requirements for sustainable coastal planning and management ŽFig. 8. ŽTables 2 and 3.. The central thesis is not new to coastal

Table 2 Support data required prior to a coastal development ŽRendel Geotechnics, 1995a,b,c,d,e,f. Že.g. farcoastal landsliding. Support data

Required?

Indication of report’s review Report is acceptable

Ø Ø Ø Ø Ø Ø Ø Ø Ø Ø Ø Ø Ø Ø Ø Ø Ø Ø

Regional setting Surface geology Geomorphology Slope steepness Groundwater Hydrology Erosion rates Ground movement rates History of landsliding Foreshore conditions Marine processes Littoral cell processes Stability analysis Sediment transport modelling Recession potential Landslide potential Environmental impact Risk assessment

U U U U U U U U

Additional data needed

U U U U U U U U U

Comment

Table 3 Questions that should be asked in a review of coastal stability prior to a development ŽRendel Geotechnics, 1995a,b,c,d,e,f. Area of interest

Site review Yes No

Comment

Is this conclusion Is further supporting documented in information required attached reports? Yes No Comment Yes

Ø Is the land capable of supporting the loads to be imposed? Ø Could the development be threatened by instability within the site? Ø Could the development be threatened by instability on adjacent slopes? Ø Could the development be threatened by erosion during the lifetime of the building?

Adjacent land Ø Could the development initiate instability by unloading adjacent slopes? Ø Could the development initiate instability by loading adjacent slopes? Ø Could the development initiate instability by uncontrolled discharge of surface water? Ø Could the development initiate instability by uncontrolled discharge of foul sewerage?

D. Brunsden, R. Moorer Geomorphology 31 (1999) 391–409

Site

No

Broader coastal zone Ø Could the development increase erosion or flood risk elsewhere by reducing the supply of littoral sediment from cliffs? Ø Could the development increase erosion or flood risk elsewhere by disrupting the transport of littoral sediment along the foreshore?

405

406

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consultants, and the attitudes have been stated in academic textbooks for a long time, but it is refreshing to a geomorphologist working in the UK system to finally see the following criteria listed as good practice in the latest goÕernment publications. Ž1. People are a major player in a very dynamic physical system, and each coast has a unique combination of resources and constraints which must be taken into account in managing any development or use. Ž2. The physical character, natural heritage, and past and present use form the system which has to be managed within local, regional, national, and international scales. The operation of the system extends beyond the interests of the individual sites or local authority boundaries, and it is essential to adopt a good neighbour principle. Ž3. Sustainable development requires adherence to a number of critical principles, among which is the crucial statement that decisions should be based on the best possible scientific information and analysis of risks. Ž4. Developers should not affect the natural operation of coastal processes to the extent that the level of erosion or flood risk is increased in neighbouring coastlines or that costly coastal defenses need to be built or maintained. The Ministry of Agriculture, which is responsible for coastal protection in the UK, is also introducing new legislation, notable the Shoreline Management Plan. This concept examines specific sediment transport cells in a holistic manner to draw together data about natural processes, condition surveys, land use, environment, and coastal defense impacts. Typical MAFF projects include the Mapping of Littoral Cells Project, the Coastal Area Modelling for Engineering in the Long-Term ŽCAMELOT. scheme, and the Soft Rock Cliffs: Prediction of Recession Rates and Erosion Control Techniques Research Project. Local Experience 6: The current UK Žand Dorset. coastal managers are receptive to the use of methods based on sound geomorphological principles, and there is a willingness to evolve new approaches if they are required by the special conditions identified by the environmental surveys. General Lesson 6: It is essential to be certain that the legislative parameters are fully understood at the start of a project. Failure to do this may mean that

the design of the investigative program does not satisfy the funding managers or steering committees and, at worst, may mean that the managers can be judged to be negligent. 5.3. Opportunities A common complaint of geomorphologists is that developments often take place without consideration of the geomorphological conditions or the benefit of the appropriate scientific knowledge. The Dorset experience is that the modern attitudes are creating an environment in which the latest schemes are being based on full available knowledge of the dynamic system, with due weight being given to the nature of long-term change and sediment flux. At Lyme Regis, for example, there is a four-phase coast protection scheme to improve the condition of the coastal defences and landslips in which the geological and geomorphological surveys are seen as the conceptual basis for the site investigation. This means that the exciting chance exists for geomorphologists to ensure that design solutions to coastal management problems are based on certain natural principles, and it is worth asking what these should be. 5.3.1. Where possible, allow the coastline to operate in the natural state This is the obvious first principle for an undeveloped Heritage coast. Where there is development, reversion is possible but rarely achievable because the current behavior is incompatible with human use or because the developments are already controlling the system. If structures are removed and the coast allowed to revert to a natural state, there may be a detrimental response because the system has adjusted to the altered conditions. If reversion means displacing homes or businesses to a safer or less visual place, a second set of problems arises, usually involving compensation. This is almost a prerequisite for ‘setback,’ but it has serious implications and is not yet in practice in the UK. 5.3.2. Structures should, as far as possible, replicate or enhance natural materials The purpose is to produce human landscape components that are compatible with their surrounding

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but also fill the functional need. This may involve the selection of materials that are aesthetically suitable but not as durable, or require innovative construction techniques. 5.3.3. Structures should, as far as possible, replicate or enhance natural landforms The central question, which may well become a dominating challenge for geomorphology in the Third Millennium, is: Is it possible to design and construct new landforms, landscapes, and efficient process systems to replace or improve those provided by nature? For example, the design of seawalls Žcliffs!., shore platforms, beaches, and headlands could be based on natural appearance but utilize modern research methods to improve performance, much as aerodynamic structures are designed in a wind tunnel or computer model. A great challenge is to find an aesthetic design or replacement for rock armour, which is widely regarded as intrusive, but is nevertheless effective. A compromise is to design in the local color, to use softer, more compatible materials, and to arrange the armour to replicate natural patterns Že.g., boulder arcs, mudslide lobes, and imbricated storm ramp armors.. The constraint will be coat because functionality, not aesthetics, may drive the choice. The challenge is, therefore, to design so that there is cost-benefit in the overall appearance or functionality in the forms Že.g., rock pools and shellfish.. Examples of ‘natural design’ are included in several practical research projects in the UK and elsewhere for the replacements of natural meanders, salt marsh set back, wetland water levels, and quarry restoration ŽDepartment of the Environment, 1992a,b; Walton, 1994.. In each case, however, the requirement is to restore or revert to a natural condition. Here, the challenge is to design a better landform or to replace a poor or damaged one. An example in Dorset is the removal of the shore platforms by sea quarrying. The restoration principle would suggest that we put them back. The research challenge is can we design and build them? It may be necessary to make the landforms more resistant or efficient. A seawall, for example, can be designed to look like a natural cliff, but shaped to minimize erosion or scour. A guideline should be to regard new coastal structures as new landforms and to therefore make

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sure that they are compatible with the existing assemblage. 5.3.4. Rates of change should be understood, and designs should be based on a full knowledge of the operation of the system The most successful designs are those that fulfill the functional needs of the system. To achieve this requires that the ‘behavior units’ of the coast are established so that both investigation and control techniques are tailored to the requirements of each unit. For example, for a cliff behavior unit, it is necessary to know the nature of recession events, their frequency and magnitude, the rates, trends, and large formative event occurrences, event sequences, preparatory factors, triggers, sensitivity, sediment flux, relationships to neighbouring systems and components, behavioural time scales, and spatial patterns ŽBrunsden and Chandler, 1996.. Above all, it is essential to know the forcing function; if these can be controlled, then the system can change. An example is foreshore lowering as a control of cliff retreat: if the shore platform can be strengthened or protected, novel ways of preventing cliff erosion may be developed. A key behaviour unit is the sediment cell. The structures should be compatible with the local and regional sediment transfers, the system should sustain the sediment fluxes, and a good neighbour principle should prevail. It is a common practice to attempt to impede sediment transport by building groynes or other barriers. It is less common to see ‘natural’ barriers being removed to enhance supply from source materials, although beach feeding and structure bypass systems are used. A Dorset example is the option to remove a mudslide lobe beneath the headland of Golden Cap to restore a connection between the cliffs to the west and the beaches to the east. Another provocative question is whether a geomorphologist could design a beach? When a beach on a high flux coast is replenished by beach feeding, there is often disappointment at the lack of success in beach maintenance. It is possible that this is because the new material does not fall on the beach with a natural internal structure or grain size distribution which is compatible with the energy system. Can we provide a lorry load of shingle dredged from

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offshore or dug from a quarry and simply expect the sea to sort it out into a stable beach? The challenge is to discover stable beach designs that can bear the applied stresses and deformations, including the foundations, internal structures, materials, drainage, flux patterns, and maintenance requirements in exactly the same manner as we would design a building or dam. 5.3.5. Establish the true inland extent of the aggressiÕe coastal system so that there is a full understanding of the relationships between land and sea Erosion at the base of a cliff leads to a diffusion of the impulse inland along rivers and through the undercliffs and coastal landslide systems. Design teams must recognize whether an aggressive wave of erosion is already moving inland perhaps to provide a lagged, complex response effect of structures that were not recognized as being in the sphere of concern of the coastal manager. In has been shown that in Dorset ŽBrunsden and Chandler, 1996. and in the Isle of Wight ŽLee et al., 1992. that the palaeo-coastal slope system is a strong link between the currently active shoreline and the old systems which might be reactivated by erosion. It is, therefore, a major responsibility of the coastal geomorphologist to determine the true depth of the coastal zone. It is worth noting that the Isle of Wight study ŽGeomorphological Services, 1991. was accepted by the funding agency ŽMinistry of Agriculture, UK. as a precedent for the basis of cost-benefit analysis.

Acknowledgements The authors wish to thank all those people who have shared the privilege of studying the Dorset coast. We also thank Spike Milligan for his originality and for helping us to keep academe in perspective and perhaps for helping us to make this paper more readable. The paper was originally written with a certain freedom of expression in the hope of provoking a lively discussion in Bologna. Following a strongly worded referee’s report, it has been revised. Because we lost the contents of a disk to a bug, it has also been rewritten. This sanitized version is therefore partially the work of the referee who is

thanked for his contribution and may place the paper on his cv. if he wishes. The quotations are the selection of the authors. The missing quotations by Douglas Adams Ž1980. and the omission of the geomorphological question to the Answer No. 42 are the choices of the referee.

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