Journal of Coastal Research 1035-1049 Fort Lauderdale, Florida Fall 1997

Episodic Shingle Supply and the Modified Development of Chesil Beach, England Malcolm J. Bray

Department of Geograph y University of Port smouth Portsmouth, POI 3HE, England ABSTRAC T _

BRAY, M.J., 1997. Episodic shingle supply and the modified development of Chesil Beach, England. Journal ofCoastal ,tllllllll:. Research, 13(4), 1035-1049. Fort Lauderdale (florida ), ISSN 0749-0208. ~ ~. This paper illustrates a budget approach to investigate and manage littoral sediment for coastal defence within an integrated process system in west Dorset, England. The budget is quantified in terms of inputs, transfers, storage ~ ~-'" and outputs of sediment within a litt oral cell. Complex, long established links are demonstrated between eroding cliff =+ ?F' sediment sources and a sequence of pocket shingle beaches that they supply. Sediment input s and subsequent tran s­ fers are found to be episodic so that the beaches natu rally alterna te between open and closed system states according to prevailing transport conditions. Interestingly, the major storm barrier of Chesil Beach is identified as the ultimate shingle sink. These results suggest that the beach did not simply develop as a product of the Holocene tra nsgression as often envisioned, but until recently, it formed part of a larger nat ural process system with the periodic input of additional shingle from the west, derived from the erosion of massive unstable cliffs. However, several interventions have dislocated these natural linkages, unwittin gly reinforcing the closed system states. In the absence of natural replenishment, the modified beaches are becoming increasingly sensitive to the continuing relative sea-level rise and storm activity that characterises this region. Attention is drawn to the need to esta blish such understanding prior to undertaking additional interventions. Details are provided of the ways in which th is information has assisted in the control of beach mining and futur e management policies are suggested.

ADDITIONAL INDEX WORDS: Cliff. bluff. sediment budget, erosion, shingle, gravel, beach, shorelin e managem ent , lit/ oral , cell, drift, protection, Dorset.

INTRODUCTION Iy inde pendent littoral sedime nt cells and partially dep en­ dent sub-cells according to transport boundaries (BRAYet al., Managem ent strategies based upon tradition al structural 1995), Th e se dime nt sources, stores, sinks and linking pa th­ mean s of coastal defen ce impl em ented at site -specific sca les ways are investigated to develop a geomorphologica l inter ­ are increasingly being qu estioned in terms of their functions, pr etati on of the long term trends tow ards wh ich the processes envi ronme ntal impacts a nd costs (PILKEY and HOWAR D, are working. A final stage is to qu antify the components and 1981; NORDSTROM , 1994 ). In ide ntifying alternat ives , most formulate a sedim ent budget (BOWEN and INMAN, 1966 ; authorities advocate mainten ance of a st abl e natural process CLAYTON , 1980), Future cond it ions can be estima te d by ex­ sys te m, assuming that this is known or can be reinstated . trapolation of contemporary trends, a nd adjus tments a re pos­ For example, a healthy bea ch is ofte n cit ed as the best form sible to incorporate th e effects of changi ng environmental of coastal defenc e (BRA..VI PTON , 1992), as well as pro viding for cond iti ons te.g; risin g sea-level), or managem ent methods the maximum recreational benefit. However, the health of (e.g., coastal defence stru ctures). the beach frequ ently dep ends upon cont inue d erosion of ad­ Thi s pap er presents a case study covering the wes t Dorset jacent coasts. It is also necessa ry to consid er th e historical coast of southe rn En gland including Che sil Beach . It has legacy of past activities that in many cases has modified nat­ been developed from work initially finance d by local author­ ural systems and significantly cons traine d future manage­ iti es to investigate sedime nt supply and transport (BItAY. ment optio ns . Long-t erm sus ta inable occup ation and use of 1986, 1990 ). It identifies dep endent sub-cells, their main sed­ shorelines without recourse to wid espread hard protective iment budget eleme nts, and outlines a ppropria te meth ods of structure s therefore dem ands inn ovative managem ent found­ inves tigation, data analys is and element coupling need ed for ed upon sound pro cess and landform understanding. Littoral qu antification . Th e impacts of past human activit ies a nd pos­ sediment mu st be managed as a valu ab le resource. sible future inte rventions are examined using the results . In working towards th ese objec tives, this pap er illu strates Such information is essential to address growing conflicts he­ th e value of a sys te ms approac h (BRUNSDEN a nd THORNES, tw een the need s for conservati on of the unique geomorphol­ 1979 ) in which coastal changes are characterised in term s of ogy and geological exposures of this coast as against the re­ inputs, tran sfers, storage and outputs of material s and en­ quirem en ts for coas tal defen ce. Th e diverse nature of th e ergy. Th e method is based up on t he identificati on of re la tive- coas tal st udy area mean s th at the methodology and results are poten ti ally of wid er significance an d th eir a pplica ti ons 95062 received 4 May 1995: accepted in reris ion 2 1 Augu st 1995. else whe re are discu ssed . 1036 Bray

Backsca r of coastal slope/cliff Lyme Bay ~ km

r-' over 150m N '1 100m to 150m If ' CHESIL 50m to 100m t D~ I BEACH 0 10 km 4 I I I

Figure 1. Location of the west Dors et coas t and the detailed stu dy area (inset).

THE WEST DORSET STUDY AREA (BRUNSDEN and J ONES, 1976). Its spectacular landslide to­ pography (Plate 2) is of great geomorp hological value an d is Attention is focused here (Figure 1), on a series of linked internationally imp ortant for its geological exposures. process un its in the eastern part of the Lyme Bay "mac ro­ Ori ented to face the southwes t, the site occupies one of the cell" (M o TYKA and BRAMPTON, 1993). Bounded to the east most exposed locations on the southern English coast. Pre­ by the major tra nsport bound ary of the Portl and Bill head­ dominan t wave direction is from the sout hwes t, coinciding land and to th e west by harbour structures at Lyme Regis, with th e maximum fetch which exte nds into the northeast th e shoreline comprises discontinuous shingle beach es with Atlantic. Maximum wave heights approaching 9 m have been contra sti ng character to either side of West Bay. Chesil Beach , a linear shingle storm barrier exte nds 28 km east­ recorded during severe storms (HARD CASTLE and KING, wards from West Bay to Chiswell (Isle of Portl and) and is for 1972; DRAPER and BOWNASS, 1983). The differ ence in th e 13 km backed by th e shallow Fleet Lagoon (Plate 1). Rising na ture of the coast to the eas t and west of West Bay reflects to over 15 m above mean sea-level and exhibiting exceptional th e degree of protection afforded by the shi ngle beaches. The longs hore pebble size grading (CARR, 1969), the beach is of huge volume of Chesil Beach almost completely protects the internationa l scientific importance and also defend s vulner­ la nd behind, so cliffs only exist close to West Bay where the able low-lying land and ecological habitats from flooding beach is lower . To the west, the pocket beaches offer only (BRAY, 1992a). It is thought to be a finite product of the Ho­ partial protection so the coast is highly dyn amic and a prod­ locene transgression th at exhibits reworking and slow on­ uct of contemporary marine erosion, landslid ing, sediment in­ shore migration as present relative sea-levels continue to rise put and littoral transport. (CARR and BLACKLEY, 1974). By contras t, the coast to th e Most of th e study area remains natural an d unprotected, west is fringe d by mu ch smaller pocket beaches at Cha r­ but with some notable exceptions . Small parts have been de­ mouth, Seatown and Eype, separated by headl ands an d veloped as harbours and seaside resort s, resulting in provi­ backed by high eroding cliffs (BIRD, 1989). The geology com­ sion of breakw ater and sea-wall struct ures at Chiswell, West prises impermeable Jurassic clays overlain by permeable Bay an d Lyme Regis (Figure 1). Such practices interfere with Cretaceous sa nds in a classic lan dslide generating sequence natu ral sediment tran sport an d can resu lt in detrimental ef-

Journal of Coast al Research, Vol. 13, No.4, 1997 Development of a Shingle Bea ch

iden tified. Neighbo uring littoral sedime nt sys te ms could th en Define research objectives be excluded safely from detail ed ana lys is. Th e main objective was to investigate how th e rapid sedime nt inputs from th e management aims dyn amic sub-cells between Lyme Regis and West Bay might relate to th e comparatively stable and apparently closed sed­ ime nt circulation system of Che sil Beac h. Identify littoral cell and sub-cells When compiling a sedime nt budget, a necessa ry ta sk is to identify its elements to form a qua litative model of all sedi­ I geomorp hologica l interpertation ment inputs, outputs, transport paths, stores and sinks (Fig­ , literature rewiew ure 3). Th is is best accomplished by reviewing existing liter­ ature in combination with a site inspection and geomorpbo­ Qualitative model of budget elements logical la ndsca pe assessm ent te.g.;JACOBSEN and SCHWARTZ, 1981; TAGGART and SCHWARTZ, 1988 ). In West Dorset, cliff

literature review erosion is an obvious input and supplies material to th e landfonn and proce ss measurements beaches following storage in large landslides. Fluvial inputs are limited by th e absenc e of significant riv ers. Fine sands , silts and clays are winnow ed rapi dly from cliff toe deb ris a nd Quantify elements lost offshore. Gravel remains to contribute to t he beach es where it is subject to longshore tra nsport a nd loss by attrition sediment flow a nd beach mining (Seatown), This gr avel (>2mm dia meter ) model is therefore the focus of attention. Landslide s that surge across th e foreshore at headla nds form temporary longshore Formulate sediment budget barriers to beac h drift but are eroded peri odically to permit I connections between beach es. Losses to, or gain s from . sub­ • alter bUdget compon tents merged offshore ba nk s were not known at thi s stage . Artifi ­ sensitivity testing cial beac h replen ishment has not been practised . A second step is to quantify th e main fluxes and flows of' Evaluate past activities Examine future management materials a nd analyse t he timescales over which they oper­ or natural process scenarios ate. Th erefore, res ea rch had to examine th e qualities a nd Figu re 2. Syste ms methodology fill' coasta l st udies . quantities of sediments yielded from cliff erosion, together wit h its fate once it reac hed th e shore. A holisti c approach is advocated that includes inten sive searches for relevant ex­ fects elsewhe re. Two piers modified in IHGG to protect th e tant data coupled with original field investi gations to fill harbour entra nce at West Bay Isle of Portland ), five sub-cel ls comprising Spit­ Sed iment yield is therefore a function of th e cliff geometry tles, Charrnouth, Seatown, Eyp e and Ches il beac hes were a nd rate of recession. Th e types of sediment liberated are a lso

,Journa l of Coasta l Resea rch. Vol. 13. No. 4, 1997 1038 Bray

IcoMMERciAll R. Char L. ~:!!1AC_!.iQ..NJ Stoneba rrow Gold en Cap Bl ack Ve n Broo m Cli ff Thorncombe Beacon

gravel released by landsliding of backscar

sea-cliff retreat and movement of mudslides Dog hou se Hi ll West Bay The Cobb Head lan d Piers I I I I I I I- SEATOWN BEACH I EYPE BEACH I CHESIL BEACH - ~ I '----r---;---....,....---' I '-,---;-- -.,..--.1 I I I I -+ I A I I I .t. I 1---- I I I - _1. I I __1.__ I I __1.__ L~~~I~~ ~ . l ~~~~~ . _ . J~~~~~~~ . U~~~~~~~. .l . ~~~~~~~~:: : 1. _. i. _._._._._._._._r _._._. _I _ _ ._ . t.J. _._t .i TEMPORARY GRAVEL BANKS WITHIN ~--; TEMPORARY GRAVEL BANKS WITHIN r<-i TEMPORARY i THE LITTORAL ZONE L~ THE LITTORAL ZONE '- ~ GRAVEL BANKS ._ ._ ._ ._ ._ ._ ._ ._ . _ ._. - '1 ' _ .-.- A-'-'- '- ._._._ .- I . - . _ . _. _. _ . - '1- ' _ . - J;'- ._ ._ ._ ._._ .1 . _ ._ . _ .- . _ ...... I I I i I I I I ._ . _ . _ . _ . _ . _ . _. _ ._ ._. _ .~. _ ._ . _ .1_ ._ ._ . _. _ ._ ._. _ ._ . _ . _ ._ . _ ._ ._ . _t.: _._.1_. _ . _. _ ._. _ . _ . _ ._ . I I i OFFSHORE GRAVEL BANK i ' -'-' - ' -' - ' - ' - ' -' - ' -'- '_ . _ . _ . _ . _ . _ . _ . - . - . _ .-.-. _ . - . _ . - ' - ' - '- ' - ' - ' - ' - ' - '- ' -'-'- ' - ' - '- ' - '

'- ' _ . _, Possible. but Barr ier to transfer 1- - - I Loss of gravel Possible. but Gravel Store of gravel allowing +-- Transfer of unp roven gravel CJ l .J from the system ~~~:~~ = t~ re + -- - I. _. _ .1 intermittent passage gravel tra ns fe r

Figure 3. Sediment bud get model of the West Dorset litt oral cell. Thi s forms a val uable framework withi n which to ident ify the component elements and th eir int errelations. It facilitates th e planning of research to qua ntify th e budget.

impo rtant beca use this affects their fate once they reach th e backscar recession has been inte rmittent and cyclic with sin­ beac h. The geology comprises Jurassic clays , marls and sa nds gle failures involving up to 30 m of retreat followed by long dipp ing very gently to the southeast. On the major hill tops, peri ods of relative stability (BRUNSDEN and JONES, 1980). these strata are unconforma bly overlain by Cretaceous sa nds Sea-cliff erosio n is more steady and continuous, but over a including the Upper Gree nsand Che rt Beds, a major source complete erosi on cycle, a simila r am ount of retreat is of beach forming gravel (Figu re 4 and Table 1). Variable su­ achieved so th at the two cliff lines remain in equilibrium perficial deposits ma ntle the cliff-tops and also contain che rt (parallel retreat). Usi ng this data, long te rm retreat ra tes on an d flint gravel. The qua ntities of th e differ ent mater ial ty pes the order of 0.3 ma" to 0.5 ma - I wer e calculated for the that would be released per un it of cliff retreat wer e deter ­ whole coast between Lyme Regis and West Bay. However , mined by exa mination of existing geological map s (6" Geolog­ increa sed rates of ret reat are gene rally noticeable since 1960, ical Survey fieldsheets) a nd lit erature (e.g., WILSON et al., especia lly at Black Ven where a phase of inte nse landsliding 1958 ), followed by detail ed field section ma pping of selecte d has per sisted since 1957 (BRUNSDEN and GOUDIE, 1981). geological units. A program me of sa mpling and sediment The study area was divided into some 180 longitudinal seg­ an alysis were necessary to accurate ly assess these source ma ­ ments of 100 m. Precise details of th e natu re and occurrence te rials. Resu lts reve aled that th e th ickest and richest gravel of ground forming materials (grain size, lith ology, cross-sec­ depos its exist in the backscars at Black Ven and Sto neba rrow tion area, etc.) were summed within each segment and en­ Hill. tered into a spreadshee t togeth er with the appropria te seg­ Cliff erosion rates have been determined by ana lysing ment eros ion rates. In tegr ation of these paramet er s produced changes of th e backscar (cliff-top) and sea-cliff positions plot­ sediment supply rates (compiled in Table 2) tha t wer e the n ted from aerial photog ra phs , old map s and a rece nt field sur­ plotted usin g a standard graphics package (Figu re 4). It vey, altogether covering the period 1901-1987 (Figure 4). Re­ should be noted that on a complex (compound) cliff coast, th e sults reveal major zones of persistently rapid retreat at the supply process comprises three distinct pha ses : (i) release I I Spittle s (2.2 ma - ) and Black Ven (0.9 ma - ) sys te ms, where from the backscar; (ii) trans port through the landslide sys­ ground conditions are especia lly favourable and massive tem; and (iii) deposition on the beach from landslid es (BRAY, lands lide embayments have forme d (e.g ., Plat e 2). Elsew here, 1992b). Th is means that short term variations in the material

J ourn al of Coastal Resear ch, Vol. 13, No.4, 1997 Developm ent of a Shingle Beach 1039

Metres retreat 250 250 Cliff Retreat 1 1!l1901-'960 . ' 960-1987 I 200 200

Thousands cubic metres 25 25

Cliff Erosion Sediment Yield 20 20

15 • Gravel > 2mm 15 mLimestone o Sand • Clay 10

0 96 90 84 78 72 66 60 54 48 Segment Number Cliff Geology: Melres 0 .0 . [] Cretaceous Black 200 • Middle Jurassic Thorncombe Ven ~ Upper Lias Beacon 150 o Middle Lias El Lower Lias 100 Eype West Mouth Cliff

4800 9600 metres East

Figure 4. Analysis of ground-form ing mat eri als: Geology, cliff retreat and sedime nt yield.

act ually reaching the beach are possible due to storage within proximate balance should exist between material inputs from land slide systems. In fact , only 50% of the gravel released by the backscar and outputs from landslides to the beach when rapid retreat at Black Ven since 1957 has yet reached th e the full erosion cycle is covered (parallel retreat model). beach. A further 15 to 20 years of rapid supply are probably Overall material yields are substantial, amounting to over required for equilibrium to be established. Nevertheless, re­ 300,000 m3 a- 1 (Table 2). Clay is the dominan t sediment (78%) sults over the full 87 yea r study period showed that an ap- with significant qua ntities of sand (17%), but only very small

Tab le 1. Geological succession of the west Dorset coast.

Maximum Thickness at Period Series Formati on Lithology Coast (m) Quarternar y Sup er ficial Angul ar chert and flin t in a sandy clay ma ­ 5 Deposit s trix. Per turbat ed and fissured Cretaceous Upper Chert Beds Yellow-grey cher t ba nds in coarse sa ndy 10 Gree nsand clay mat rix Foxmould Fine, yellow silty sand 35 Gault Gault Clay Soft, silty clay 13 UNCONFORMITY Jurassic Middl e Jurassic Clays, shales and limestones 74 Upper Lias Yellow sandstones 64 Middl e Lias Soft clays, ma rls and hard sandstones 130 Lower Lias Soft clays, marls and th in limestones 150

J ournal of Coastal Research, Vol. 13, No.4, 1997 1040 Bra y

Tah l« 2. LOll I-: term sediment yield.

Stoncbarrow­ Colden Ca p Doghouso Hill- Lyrn c-R . Cha r Golden Cap a nd Sea town Wost Bay Total

Mat er ial 'It m :1a , 11, rn-a , (.It rrr'a , fir

Crave! :1,890 1.21 2,290 0.71 140 0.04 40 0.0 1 6,360 1.97 l.imcston o 7,800 2.42 840 0.26 120 0.04 740 0.23 9 ,:;00 z.ss Sand 17,600 fi.47 14,6fiO a.ss :;,820 1.81 17 ,040 :;.:10 :;fi,110 17.13 C la y 134 ,710 4 1.86 76 ,fi10 23.79 17,1:10 :;.:!:1 22,420 6.97 2:;0, 77 0 77 .95 To la l 164 ,000 fiO.96 94, 290 29 .3 1 23 ,2 10 7.22 40 ,240 12.51 321.740 100

proporti ons of lim estone (3',1,) a nd chert and flint gravel ( 2 ',1,). foresh ore as mudsl ide lobes wh ich form new littoral tran sp ort Yields a re strongly conce ntrate d in the rapidly retreati ng boundaries. At most points on th e coas t, marine eros ion ex­ western parts (Figure 4).Especiall y imp ortant are the high , ceeds sedime nt input, fines are lost offshore and shi ngle eroding cliffs of Black Ven (P late 2) that account for 50',1" of beaches develop . Th e complete nea rshore sedime nt circula­ th e total yields. Particle size a nd abrasion res istance of t he t ion sys te m is th er efore chara cte rised by complex inter ac­ di fferen t materi al ty pes determine th eir fates once supplied tions betw een the coasta l landslides a nd littoral t ra ns port of to t he sho re. Th e sa ndy and clayey strata are poorly cons ol­ the materials th at they deli ver. idated a nd ea sily disin tegrate in to their constituent parti cles which a re t ra ns porte d offshore by wave action. Onl y che rt, Beach Storage flint and occasionally limestones a re sufficiently coarse a nd durabl e to form pebbles and boulders th at contr ibute to th e Th e qu antities and nat ure of th e shingle store d on th e beach . Long term gravel supply is estimate d as 6.4 X 10:' beaches represen t the net result of th e various fluxes and rnta " alt hough, a slight adjust me nt for storage within land­ flows wit hin th e st udy area. Th e beaches th erefore were in­ slide systems wa s necessary to det ermine yie lds to the shore vestigated by series of measured beach profil es an d a n inten ­ over th e period 1901-1987 , giving a rate of 4.9 X 10 ' rn-a ' . sive pebbl e sa mpling pro gramme tha t involved a na lysis of Gravel yields are conce ntra te d almost exclus ively in wes te rn 12,000 beach pebbl es across 14 tran sects (SHAY, 1990 ), Re­ pa rts and a re negligible eastwards of Cold en Ca p wh ere grav­ sults arc summa r ised in Tabl e :~ a nd compared with corr e­ el bearing deposits arc thin. Th e landslide complexes of Bla ck sponding detail s of th e cliff gravel sa mples and also with data Vcn (61',I,) a nd Stone harrow ( 2 8',1, ) for m the major sites of from Chesil Beach obt a ined from th e literature (CAHH an d input reflecting th e distributions of the thic kes t gravel bear­ BLACKL EY, E174; CAlm , 19R3), Th e volumetric compa risons ing dep osits a nd th e zones of most rapid retreat. Sediment suggest that coastal landsliding could easily be th e source of inputs should increase in th e near future whe n th e large vol­ all sh ingle on the three pocket beaches. In fact , a mu ch larger u nu- of materi al current ly engaged in throughput within th e accumulation of beach shi ngle would be exp ected , if cliffinput Black Ven landslide sys te m reaches th e fronting beach . had been maintained at current rates since sea- leve l ap­ Th e landslide s a long the west Dorset coast ca n therefore pro ached its pr esent position 4,000- 5,000 years ago. Since be cons idered in terms of a flow of material s from back scar cliff erosion ap pea rs long es tablished on this coas t, th e mis ­ to the shore, Most materia l is rapidly lost offshore, bu t debris matc h between cliff input a nd beach volume clea rly suggests rema ini ng on t he fores hore affords pr otect ion against marine tha t major losses (out put) mu st occur, a nd Ches il Beach is ero sion to the cliff toe . thus insti gat ing negative feedback and the only substa ntial shi ngle deposit in th e area th at could se lf-rcgulut ion of retreat. Onl y at th e toes of very active land­ receive th is alongs hore tran sfer. It is also shown that pebbl e slid!' sys tems is the debris supply sufficiently rapid to te m­ lithol ogy a nd longshore size gra ding were si mila r on all West pora rily exceed removal so t ha t material acc umulates on the Dorset beaches including Chesil Beach . Slight variat ions are

Ta hit':l. Tlu: uv»t /Jors,,1

'f Chert lk a"h Size Gradi ng Sort ing Houndnoss a nd Sp lH'l'icity a nd Flint Volume t rn': Cl iff g ra ve! in pu t non e, mixed sizes very poor un a br a ded a nd ve ry a ng u la r 99 .:; "':32 mi llion th rough ou t Churmout h east ward (well de­ very poor in west, but im provin g ea stward, very un gu- H4.4 277 ,Ollll finod i improvin g ea stward la r in west Seatow ll eastward (s ligh t: im proving ea st wa rd s light east wa rd imp rovemen t HH.fi rsv.ooo Eyp e eastw a rd (we ll de­ imp rov ing ea stward slight eas t wa rd improveme n t (Hi. I 164 ,OllO fined : Che s il eastward (exception­ good throug hout, but not st ud ied (18.:; '"'' ](i-fi :3 mi llion a ll improvin g eastward

':'Long term s u pply ex t ra pola te d over past 5,000 ye a rs ., ,',Im precis ion ca used by va r ia ble th ick ne ss and com pos it ion a t de pth

J ournal of Coas ta l Research , Vol. 1:1, No.4, 1997 Development of a Shingle Beach 1041 attributable to short-lived limestone pebbles supplied directly Onshore-Offshore Transport from the eroding cliffs. The beach pebbles are of similar li­ Investigations of the offshore and nearshore zones were un­ thology and size range to gravel supplied to the coast by land­ dertaken to identify any submerged gravel deposits that slides. Clast roundness and sphericity are greater at sea level might offer evidence of onshore feed or offshore loss (BI{AY, due to marine sorting and attrition. Roundness and spheric­ 1986). Intertidal and nearshore diver inspections revealed ity both increase to the east, perhaps indicating progressive relatively little gravel seaward of the well defined beach toe, abrasion of the angular cliff gravels as they are transported but several zones of large interlocking limestone and sand­ in that direction. Results therefore suggest that the west Dor­ stone boulders (boulder aprons) were located. These had set beaches, including Chesil, were previously connected and trapped small quantities of gravel and appeared to act as shared a common shingle source. transport barriers, effectively isolating the beaches from the offshore zone. An offshore hydrographic and sediment sam­ Beach Shingle Transport pling survey also failed to locate any significant gravel de­ posits, but again identified boulder aprons and revealed that Littoral drift was measured directly by a series of experi­ they extend to a point some 3-4 km seaward of Golden Cap. ments employing aluminium tracer pebbles (BRAY, 1990), us­ These are interpreted as the residue of ancient mudslides ing the technique described by WRIGHTet al. (1978), Tracers that operated on an earlier retreating coast. Similar deposits were efficiently recovered to a maximum depth of 0.45 m be­ are still being formed by erosion of the present coast. Other neath the beach surface using metal detectors. Recovery surveys of the wider offshore area of Lyme Bay and off Chesil rates of between 60% and 100lk, were achieved per sampling also failed to locate gravel banks (DARTON et al., 1980; DOB­ occasion. Tests were conducted simultaneously on 100lkJ shin­ BIE and PARTNERS, 1981; BRITISH GEOLOGICAL SURVEY, gle (St Gabriel's) and mixed sand and shingle (Charmouthl 1983), so it is concluded that most of this material must have portions of Charmouth Beach during high (storm) and low remained at the shoreline as the coast retreated. wave energy conditions. Tracer recoveries were undertaken Gravel that does become trapped within the boulder aprons on 40 sampling dates covering a year so as to encompass a is immobilised and lost from the beach system as the coast wide and representative range of conditions. The data were retreats (entrapment). The quantities involved have been es­ analysed using multivariate techniques to relate tracer trans­ timated by integration of measurements of the extent of the port (dependent variable) with size, shape and position vari­ boulder aprons and their gravel trapping capacity with long ables. Results indicate that shingle transport is most rapid term coastal retreat rates. Results reveal entrapment losses on the upper beach near the high water mark and larger trac­ to be very slow. er pebbles are the most rapidly transported. The observed increase in pebble size from Charmouth to Golden Cap could Outputs by Attrition therefore have developed by preferential transport of larger pebbles during eastward littoral drift. Similar results are re­ Impacts between pebbles during transport by wave action ported from Chesil Beach and have been used to explain its result in fractures and the grinding off of small surface ir­ unique size grading (CARR, 1971, 1974). regularities (attrition). Losses occur as pebbles are reduced Longshore transport volumes were calculated from the ve­ in size and fines are transported seaward. Laboratory simu­ locity, thickness and width of the moving shingle layer as lations suggest that rates of loss vary directly as a proportion of gross transport and inversely, according to the amount of defined by the tracers. The volumes varied from 2 m'dav 1 attrition a pebble has already undergone (KUENEN, 1964 l. to 22 m'day 1 during frequent periods of low wave energy These parameters were estimated in the field using the trac­ westward drift, increasing to a maximum of 168 m-day 1 dur­ er data (gross transport estimate) and pebble sampling data ing less frequent periods of high wave energy eastward drift. (rates of rounding estimate) to develop a site-specific calibra­ Results were used to calibrate sediment transport equations tion of the laboratory studies (BRAY, 1990). Results suggest (e.g .. NICHOLLS and WRIGHT, 1991), so as to facilitate shingle that freshly supplied angular cliff gravel suffers an approxi­ transport predictions at the two sites. Integration of results mate 10rk loss within its first year on the beach, whilst well with a representative wave climate originally developed for rounded pebbles are abraded very slowly. Although relatively West Bay over a 10 year period (HYDRAULICS RESEARCH, small, both attrition and entrapment outputs are important 1985) indicate a net eastward drift of 3.5 X 10:! rn-a 1 at St because they both result in losses from otherwise closed sys­ Gabriel's. At Charmouth, net eastward drift is estimated at tems. 4.7 X 10:{ mia 1, but 40(;' of the material is composed of sand and grit so shingle drift is 2.8 X 10:! m''a 1. Drift of the entire Outputs by Beach Mining beach sediment size spectrum decreases towards the east due to the progressive offshore loss of fines. It should be noted Seatown Beach has been the main focus of the mining ac­ that the long term validity of these rates might be questioned tivity, with substantial undocumented losses having occurred because of growing evidence that wind and wave regimes can during World War II for airfield construction. Eyewitness re­ shift over decadal timescales (BACON and CARTER, 1991; ports state that the beach was stripped to bedrock so that at BRAMPTON, 1993), Virtually no beach monitoring has been least 170,000 m' must have been removed, depending on the undertaken in this area, so it is not possible to independently past beach volume. Operations resumed in 1950 and involved check the values against long term volumetric changes. removal of a further 34,000 m' of the largest, best rounded

Journal of Coastal Research, Vol. 13, No.4, 1997 1042 Bray

W. Black Yen Black Yen R. Char Stonebarrow Broom Cliff Golden Cap 445 2130 240 1750 370 175 ~ _--.J~,---t

2150 Littoral Drift (8600m3 pa when eastward transport is permitted)

685 270 Accretion (up to 3,000 rrr 'a: Attrition when eastward travel 770 transport is prevented) Accretion 200 Accretion 740 Attrition 380 All shingle volumes are in rrr 'a: Attrition

1800'00,00000 k !81000,0,00000 4060,000 6040,00,0000 20,000 ------= 20,000 o - ---- r------,------,------r------.---..j0 o 2 3 4 5 Distance (to scale) km

Fig ure 5. Shingle flow model of th e Cha rm outh Beach sub-cell. Inputs from cliff sources in the west are transported eastwa rds towards th e one-way va lve of the Golden Ca p head land. Bea ch volum e fluctu ates according to wh ether tran sport is "open" (ou tput a nd beach deplet ion ), or "closed" (storage a nd accret ion ). Th e reco rded improvem en t in beach volumes ea st wa rd reflect s th e closed condition th at has prevail ed since 1962.

pebbl es for use as grinding media for th e ceramics industry. If Charmouth Beach were a fully closed syste m, substanti al Mining ceased in 1987 following a Public Planning Inquiry accretion should have occurred since 1901. This is not sup­ (BRuNDELL, 1985 ). Unlicensed rem oval of some 8,000 m' of ported by the comp ari son s with old maps, field reports and shingle is estimated from Eype Beach betw een 1954 and the contemporary beach volume. The imb alance can be ex­ 1974. plained by intermittent pulses of eastwa rd littoral drift (out­ put) ben eath Golden Cap. Major mudslid es at th e he adland BEACH SEDIMENT BUD GET ANALYSIS currently act as a total barrier to tran sport. Howev er, obser­ vations along this coas t have shown that mudslides evolve by A Flow Mode l for Charmouth Beach active ph ases of surging (e.g., Plate 2), separa te d by long Th e Cha rmouth Beach system is examined in detail, be­ ph ases of low movement and active marine ero sion. Th e bar­ cause it is the most dyn amic a nd receives by far the gr eatest riers form ed are liable to ret reat. Old photographs show that in puts from cliff erosion (Figu re 4). In compiling the budget, landslid e debris blocking the foresh ore beneath Golden Cap it is necessa ry to integrate various elem ents , including th e was erod ed sufficiently between 1934 and 1949 to allow a differing magnitudes and frequencies of their component pro­ continuous beach to exist from Charmouth to Seatown cesses. This is accomplished by modelling t he flow of gravel C'open" trans port condition). Th ereafter, minor mudslide through the syste m over the study period 1901- 1987 (Figu re surges intermittently cut the bea ch until a maj or phase of 5). Inputs are prim arily from cliff erosion in western parts. surging activity finally severed all connections in 1962 Net littoral tra nsport is to th e east, an d cons equently the (BRuNs DEN, 1985). During "open" tran sport. th e Golden Cap wes te rn part of th e beach is subject to slight depletion despite headland operates as a one-way valve and delivers pul ses of its proximity to sup ply. Accretion (an output in terms of flow) shingle to Seatown Beach. All shingle drift is eastward at is conce ntra ted on the ea stern part of the beach , explaining rates equivalent to the gross tran sport in this direction esti­ the eastward increase in beach volume (Figure 5). Output of mated by th e tracer experiments. An analysis of shoreline gravel from th e beach by offshore transport is assumed to be orien ta tion and dominant wave approach directions based on negligible, as suggested by the tracer expe riments and sea the West Bay data indicates that westward counter-drift floor sampling. Other gravel out puts from the beach by at­ should be minimal. Charmouth Beach therefore alternates trition a nd ent rapment are compa ra tively small. between being an open and a closed system , and its beach

Jo urn al of Coastal Resea rch,Vol. 13, No. 4, 1997 Development of a Shingle Beach 104:3

Table 4. Beach gravel budgets 19(}1-~1987.

Whole Area (long term Charmouth Seatown Eype assuming no human Budget Element Beach Beach Beach intervention)

Inputs Coastal Erosion 4.87 0.03 negligible 6.:36 (rn' a 1 X 10:1) Fluvial (River Char) 0.24 0.24 Littoral Drift 2.15 small from East Devon 0.70 Onshore Transport TOTAL 5.11 2.18 13.~30 Outputs Attrition 1.26 0.08 0.08 1.4:3 (rn' a 1 X 10:;) Littoral Drift :::2.15 to Chesil 11.58 Entrapment 0.19 0.05 0.05 0.29 Beach Mining 2.37 0.09 Offshore Transport small TOTAL 3.60 2.50 2.22 13.30 Beach Store (rn' X 10:1 ) (1987) 277.00 167.00 164.00 500.00-800.00 Balance (rn' a 1 X 1UQ 1.51 -0.32 -0.23 0 "Pulsed input beneath the Golden Cap headland volume fluctuates accordingly. The model indicates signifi­ activity should have diminished, allowing mudslide barriers cant beach accretion due to its "closed" state since 1962. At­ to be eroded. The scientific evidence of net loss and closed tention is drawn to the importance of establishing such an system status (since 1962) was critical in proving damage and understanding, because the likely impacts of future human led to revoking of the long-standing planning permission for interventions should differ significantly according to the pre­ shingle mining (BRuNDELL, 1985). vailing system state. In the longer term, Eype Beach is part of the larger Ii ttoral The model also demonstrates that the spatial distribution transport system receiving shingle from Seatown and then of cliff inputs and beach accretion zones are themselves im­ passing it on to Chesil. However, it has been separated from portant regulators of the coastal system. Beaches afford pro­ Chesil Beach by construction of the West Bay jetties (Plate tection to the cliff toes. If retreat accelerates, gravel supply 3), and from Seatown Beach by depletion of connecting beach­ increases: so in theory, beaches should accrete and marine es. It is now an entirely closed pocket beach that is isolated erosion should reduce. This idealised negative feedback from all new shingle sources and is suffering net loss (Table mechanism cannot operate efficiently on Charmouth Beach, 4). Present trends for increasing cliff erosion are therefore because eastward littoral drift prevents shingle accretion on likely to continue, but gravel inputs cannot increase accord­ the foreshore beneath the major landslide supply areas. The ingly because no suitable material is present in these cliffs. western part of the beach system is therefore characterised by high sediment throughput and relatively low volumes of Long-Term Coastline Evolution shingle storage. Clay and sand are supplied in large quanti­ The three pocket beaches have been studied by sediment ties but are easily eroded and transported offshore. Lime­ budget analysis for an 87 year period, long enough to signif­ stone boulders, chert and flint gravel provide only temporary icantly reduce variability arising from spatial and temporal protection because of the low durability of the former and the changes in their budget elements. Budgets must be consid­ potential for longshore transport of the latter. The active ered over longer periods to understand the implications of' phase of landsliding initiated at Black Yen in the late 1950's this research for Chesil Beach. Retreat of the West Dorset is therefore likely to continue, because natural basal protec­ coast has undoubtedly been long established, as indicated by tion cannot keep pace without additional landslide through­ the submerged boulder aprons that extend 3 to 4 km seaward put. It must be considered as an inherently eroding site that of the present coast..Although difficult to date, it is suggest(·d functions as a valuable regional sediment source. that they represent the amount of cliff recession since seh level approached its present elevation in this region approx­ Gravel Budgets for Seatown and Eype Beaches imately 5,000 years ago (HEY\VORTH and Kmso», 198:2~. If Gravel budgets have been compiled for Charmouth, Sea­ this is correct, coast retreat based on the position of offshore

town and Eype beaches (Table 4 l. Intermittent littoral drift boulder arcs has averaged 0.6 rna I to 0.8 rna lover the last outputs from Charmouth Beach are revealed as the main in­ 5,000 years. Since this long term mean rate is comparable puts to neighbouring Seatown Beach, so that it too fluctuates with the present day values te.g. 1901-1987 retreat from between closed and open system states according to condi­ Stonebarrow to Black Ven was between 0.4 rna : and o.~ tions at the Golden Cap headland. In spite of these contri­ rna 1), current shingle budgets might be projected back over butions, a net shingle loss has prevailed duke to substantial this period (Table 4). mining outputs. Transport connections around Golden Cap Harbour structures at Lyme Regis and West Bay are recent are unlikely to be restored until at least 2020, when landslide developments on this timescale, so shingle inputs would also

-Iournal of Coastal Research. Vol. 13, No.4. 1997 1044 Bray have been possibl e from th e eroding Ea st Devon coast to th e vent ions have been the harbour struct ures at Lyme Regis and west of Lyme Regis (BRAY, 1990 ). Without th e jetties at West West Bay that inter cept littoral dr ift a nd isolate beaches from Bay, Ches il Beach its elf would have extended uninterrupted th eir natural sources of supply. Well maintained structures at least as far westwards as th e Doghouse Hill headland. The form perman ent tran sport boundaries. Downdrift beaches combined cliff yields from th e East Devon and West Dorset th us affected suffer net loss and become sensitive to further coasts are consid erabl e (Ta ble 4). Assuming th at yields a re interfer en ce and the cumulative effects of risin g sea- level and typical of the land now eroded and th at losses by attrition storm activity. Cres t lower ing and landward migr at ion ha ve a nd entrapment have remained constant through time, 58 been recorded for Ches il Bea ch (CAR R and SEAWARD, 1990, million rn" of gravel could have been produced as these coasts 1991), and numerous flooding events have occurred over th e retreated. Pr esent day shingle stora ge bet ween Lyme Regis past 30 yea rs at Chiswell and West Bay (JOLLIFFE , 1979). and West Bay is estimated at less th an 1 million m", so again The shortage of beach shingle is clea rly identified as a major there is a disparity between input and storage. probl em, but th e cha nges to the transport pathways for fresh It see ms likely th at surplus gravel could have drifted east­ shingle are such th at th e natural syste m is not easily re­ wards along a ncient pocket beaches to accumulate on Chesil, establi sh ed. Sh ingle bypass ing systems might have reduc ed which operate d as th e main sediment sink. There are no al­ ea rly problems, but at West Bay, serious beach loss has oc­ ternati ves eithe r at the shore line or offshore in Lyme Bay. curred on both sides of the a rt ificial barri er (BRUNSDEN, Ches il Beach is the closes t shingle deposit of a ny size, with 1992 ). An alte rnative option at Chis well has been to adopt its volum e esti mated at 16 to 63 milli on m" (CARR and vari ous engineering measures to reduce flood ha zards (HOOK BLACKLEY, 1974); and allowing for differ ences in exposure to and KEM BLJ<:, 1991), but thi s further interferes with natural marine attrition, the characteri stics of its pebbl es are iden­ processes a nd could rein force commitm ents to interven e more tical to those produced by th e eroding cliffs. Whilst th e cliff widely (RRUNS DEN, 1992 ). Recycling is not an option, because erosion inputs a re clearly sign ificant by comparison with th e Ches il is a sink and has alrea dy accumulated all ava ilable present volume of Ches il Beach, th ey were unlikely to have coarse sediment within its cell. Replenish ment with exte r­ been th e form ative source. Ches il had already formed by nally deri ved materi al could compromise th e integrity of thi s 7,000 years BP (CARR and BLACKLEY, 1973, 1974) before sig­ unique landform. To do nothing could threaten human assets, nificant cliff ret reat. Subseque nt input from cliff sources but might allow th e beach to achieve a new quasi-st able equi­ would th erefore have nourish ed and enlarged the bea ch in librium. All options have asso ciated risks, becau se th ose few spite of continuous attritio n losses. The original sour ce ma­ gravel barrier s previously studied show a propensity for nat­ ter ial was probably fluvial , periglacial and perhap s anci ent ural migr ation, with possible catastrophic breakdown und er beach deposits on the floor of Lyme Bay , which gradually extre me stress (ORFORD et al., 1991, 1995). decreased in imp ortanc e as th e rate of sea level rise slowed Research should aid man agement in avoiding future ac­ in the late-Holocene. The closed system status of Chesil tions th at interfere with key natural processes so th at th e Beach is th erefore a more recent phenomen on th an sus pecte d difficult problems outlined above do not develop. The present hitherto. It dates from alterations to th e West Bay pier s in study has identified th e importanc e of cliff erosion in yielding th e mid 1860's th at effect ively isolated Ches il from its re­ much of th e region 's beach-forming sediment. Coastal plan ­ maining shingle source. Mining of Seatown Beach has further deplet ed th e supply pathway, making tran sport impossibl e ners might th erefore formulate setback zones (KAy, 1990; a round th e Doghouse Hill headl and (a relict beach isolated NATI ONAL RESEARCH COUNC IL, 1990) to ens ure th at th e on th e headland indicates th e form er conn ection ). Ren ewed main source areas ie.g., Black Yen ), remain free to erode. materi al inputs to Chesil a re unlikely in th e foreseeable fu­ However , such policies should also ens ure that pathways ture and will only be possibl e following restoration of the full linking sediment sources, mobile stores and sinks remain free tran sport pathway. to oper ate. Shingle bypassing should th erefore be included as an essentia l part of th e operation of any new struc tures th at might form artificial boundaries. Using th e budget and flow MANAGEMENT APPLICATIONS OF THE models presented her e, future changes can be assessed. For BUDGET ANALYSIS exa mple, an empirical model study of th e effects of sea-level In treating th e coas t as an integr ated sys te m, the research ris e on the West Dorset cliffs indicates th at, in places, erosion has indi cated th e adve rse imp acts of some past activities and might double by 2050 (BRAY and HOO KE, 1995 ). Resultant provides a basis for anticipa ting th e likely effects of future increase d sediment yields can th en be esti mate d, and tr aced interventio ns . Pocket beaches such as Seatown have been through th e coastal process syste m to ind icate the locations identified as closed syste ms over planning tim escales , so a and timings of th eir potentially beneficial downdrift effects. strong basis is established for identifyin g and controlling An integrated managemen t stra tegy might be developed to da maging practices such as beach min ing . Th is has ass iste d include different approaches operating over different tim e­ Dorset County Council in th eir min erals planning process. sca les. Restoration of a stable natural process syste m is iden­ It is inter esting to not e th at all th e West Dorset beaches tified as the major objective; but du e to past damage a nd beh ave natur ally as open systems over long timescales. Al­ natur al lags in restoring processes, it is only possibl e in th e though headl ands act as barrier s to drift, th ey periodically long term . Meanwhile, it might be justifi able to employ en­ allow pul ses of shingle to pass, so th eir long term effects a re gineering inte rventions to reduce hazards in the short-term not significant. In th is contex t, th e most problematic inter- provid ed th at natural sys te ms are not dam aged irrevocably

J ournal of Coas ta l Research, Vol. 13, No.4, 1997 Development of a Shingle Beach 1045 in the process. The long term objective should be to allow Jones at the London School of Economics and funded jointly time for a stable natural system to be restored. by Dorset County Council (DCC) and West Dorset District Council. Special thanks are due to staff within the Planning CONCLUSIONS Department (DCC) for extensive logistic support. Professor D. Brunsden, Kings College, London is thanked for his en­ An improved understanding of coastal processes, landforms couragement and specialist advice. and landscapes is needed to manage littoral sediment in a sustainable manner and to minimise needs for structural in­ terventions. In working towards these objectives, a geomor­ LITERATURE CITED phological systems approach has been applied successfully to investigate a complex and dynamic coastal system at a va­ BACON, S. and CARTER, D.J.T., 1991. Wave climate changes in the North Atlantic and North Sea. International Journal of Climatol­ riety of scales. At the strategic level, it is sufficient to identify ogy, 11, 545-558. independent cells and partially dependent sub-cells for shore­ BIRD, E., 1989. The beaches of Lyme Bay. Proceedings ofthe Dorset line management units. At regional and local levels of oper­ Natural History and Archaeological Society, 111, 91-97. ational responsibility, it is important to apply a more rigorous BOWEN, A.J. and INMAN, D.L., 1966. Budget of Littoral Sands in the approach to quantify a littoral sediment budget. Analysis of Vicinity of Point Arguello, California. C.E.R.C. Technical Memo­ randum No. 19, 41p. the processes, rates and timescales of material flow can then BRAMPTON, A., 1992. Beaches-the natural way to coastal defence. be integrated with details of the resulting landforms to iden­ In: Coastal Zone Planning and Management, Chapter 19. London: tify the long term trends toward which the landscape is evolv­ Thomas Telford, pp. 221-229. ing. Only when such an understanding has been achieved can BRAMPTON, A., 1993. Design implications from the South Coast past modifications and future impacts be fully assessed. shingle study. In: Proceedings of MAFF Conference of River and Coastal Engineers. London: Ministry of Agriculture Fisheries and In West Dorset, complex links have been demonstrated be­ Food, pp. 3.1.1-3.1.13. tween eroding cliff sediment sources and the beaches they BRAY, M.J., 1986. A Geomorphological investigation of the South­ supply, including Chesil Beach. Future research should re­ west Dorset Coast. Volume 1: Patterns of sediment supply. De­ cognise that Chesil Beach has been sustained by and has partrnent of Geography, London School of Economics. Report to evolved as part of a larger process system. Boundaries to sed­ Dorset County Council and "est Dorset District Council, 144p. BRAY, M.J., 1990. Geomorphological investigation of the South-west iment transport systems are not always clearly defined and Dorset Coast. Volume 2: Sediment transport. Depart.ment of Ge­ can evolve naturally in a complex manner, as at Golden Cap. ography, London School of Economics. Report to Dorset Cou ntv Others can be produced artificially, i.e., the West Bay jetties. Council and West Dorset District Council, 798p. Failure to recognise these features has resulted in human BRAY, M.J., 1992a. Chesil Beach. In: ALLISON, R.J., (ed. The Coast­ al Landforms of West Dorset. London: Geologists' Association, pp. interventions having serious unintended side-effects that 106-118. have modified the natural littoral sediment system and iso­ BRAY, M.J., 1992b. Coastal sediment supply and transport. III: AL­ lated Chesil Beach as a separate unit. As a closed system, LISON, R.J., (ed.r, The Coastal Landforms o] W)st Dorset. London: the beach is now more sensitive to direct interventions. Al­ Geologists' Association, pp. 94-105. though it has been possible to control damaging beach min­ BHAY, M.J.; CAHTER, D.J.. and HOOKE, J.M.. 1992. Sea-Level ris« and global warming: Scenarios, physical impacts and policies. De­ ing, shortages of shingle remain a major problem. Current partment of Geography, University of Portsmouth, Report to S('()­ trends for increasing cliff erosion are unlikely to replenish PAC,205p. the depleted beaches in the short term due to lags in the BHAY, M.J.; CAHTEH, D.J., and HOOKE, J.M., 199;). Littoral cell def­ process system. Meanwhile, pressure is likely to intensify for inition and budgets for central southern England. .lou rnul o] further short term engineering solutions. Restoration of the Coastal Research, 11,381-400. BHAY, M.J. and HOOKE, J.M., 1995. Coastal cliff erosion with accel­ full natural system therefore needs to be viewed as a long erating sea-level rise. Journal of Coastal Research (in press I. term objective that is additional to any short term remedial BI{I'l'ISH GEoLO(;rCAL SUI{VEY, 1983. Sea Bed Sediment", and (Illu­ actions. ternarv Geology. Portland and Lyme Bay, 1:250,O()() Series AlufJ. The Dorset coast demonstrates the problems that can re­ Southampton: Ordnance Survey. sult from the differences between geomorphological and plan­ BHUNI>ELL, M.J., 1985. Inspector:" Report on a Public l nquirv Into an Appeal Against the Refusal of Dorset County Council to Permit ning timescales. It should be appreciated that management the Continued Winning and Working ofPebbles and Graded Shingle based on natural process systems demands forward planning at Seatouin Beach, Seatoion, Chideoch. London: Depart.ment of En­ over longer intervals than hitherto contemplated. Coastal vironment. managers should realise that this type of approach is not sim­ BRuNsIH:N, D., 1985. The supply of beach material to Seatown Beach, Dorset. Report to Dorset County Council, Dorchester, UK, ply a research tool but has practical management value and 8p. is widely applicable elsewhere. Many coastal environments BIUJNSDEN, D., 1992. Coastal and landslide problems in west Dorset. have been modified by human activities or face imminent in­ In: Coastal Instability and Deoelopment Planning, Papers and Pro­ terventions, and it is valuable to apply similar methods to ceedings of the SCOPAC Conference. Portsmouth 24 October 1991, understand the spatial and temporal dimensions of such pp. 29-44. BRlJNSDEN, D. and GOUDIE, A., 1981. Classic Coastal Landforms o] modifications when planning future management strategies. Dorset, Landform Guides No. 1. Sheffield: The Geographical As­ sociation, 39p. ACKNOWLEDGEMENTS BRUNSDEN, D. and JONES, D.K.C., 1976. The evolution of landslide slopes in Dorset. Philosophical Transactions Royal Society London, This paper has been developed from work undertaken dur­ A283, 605-631. ing a research studentship supervised by Professor D.K.C. BRlJNSDEN, D. and JONES, D.K.C., 1980. Relative time scales and

Journal of Coastal Research, Vol. 13, No.4, 1997 1046 Bray

formative events in coast al landslide systems. Zeitschrift fur Geo­ HYDRA ULICS RESEARCH, 1991. West Bay Harbour:Analysis ofRecent morphologie, S upp. Band, 34, 1-1 9. Beach Changes East of the Harbour. Wallingford, UK: Hydraulics BRUNSDEN, D. and THORNES, J .B., 1979. Landscap e sensitivity and Research Ltd , Report; EX 2272 to West Dorset Dist rict Council, cha nge. Tran sactions of the Institut e British Geographers, 4, 463­ 16p. plus 13 ta bles , figur es an d plates. 484. JOLLIFFE, LP., 1979. West Bay and the Chesil Bank, Dorset . Coast al CARR, AP., 1969 . Size grading along a pebble beach: Chesil Beach, regimen conditions , resource use and the possible environmental En gland. Journal of Sedimentary Petrology, 39, 297- 311. impact of mining activities on coas tal erosion an d flooding. De­ CARR, A P., 1971. Experimen ts on longsh ore transport and sorting partment of Geography, Bedford College, Univers ity of London. of pebbles: Ches il Beach, Englan d. Journal ofSedimentary Petrol­ Report to West Dorset District Council, Dorset County Council, 87p. ogy, 41, 1084-1104. J ACOBSEN , E.E. and SCHWARTZ, M.L., 1981. The use of geomorphic CARR, A P., 1974. Differen tial movement of coarse sediment parti­ indicators to determine the direction of net sh ore-drift. Sho re and cles . Proceedin gs of the 14th Conference on Coastal Engin eering, Beach, 49, 38-43. ASCE, Copenhagen, pp. 851-870. KAY, R., 1990 . Development cont rols on eroding coastlines: Reducing CARR, A.P., 1983 .Chesil Beach: Environm ental, economic and socio­ the future impact of green house-ind uced sea level rise. Land Use logical press ures. Geographical Journal, 149, 53---B2. Policy, 7(2), 169-172. CARR, A P. and BLACKLEY, M.W.L., 1973. Investigations bea ring on KUENEN, P.H., 1964. Experimental abrasion: 6. Surf action. Sedi­ the age and development of Chesil Beach, Dorset , and the asso­ mentology, 3, 29-43. ciated area. Transactions, Institut e British Geographers, 58, 99­ MOTYKA, J .M. and BRAMPTON, AH., 1993. Coastal Management: 111. Mapping ofLittoral Cells. Report S R 328. Wallingford: Hydr aulics CARR, AP. and BLACKLEY, M.W.L., 1974. Idea s on the origin and Research Ltd, 102p. development of Chesil Beach, Dorset. Proceedings of the Dorset NATIONAL RESEARCH COUNCIL, 1990. Managing Coastal Erosion. Natural History and Archaeological Society, 95, 9-17. Wash ingto n DC: National Academy Press . 163p. CARR, A P. and SEAWARD , D.R., 1990. Chesil Beach: Cha nges in NICHOLLS, R.J . and WRIGHT, P., 1991. Longshore transport of peb­ cres t height, 1965- 1990. Proceedings ofthe Dorset Natural History bles: Experimental estimate s ofK. Proceedings ofthe Coastal Sed­ and Archaeological Society, 112, 109- 112. iments of '91, ASCE, Seattle, pp. 920-933. CARR, A P. and SEAWARD, D.R., 1991. Chesil Beach:Lan dward re­ NORDSTROM, K.F., 1994. Beaches and dunes of human- altered cession, 1965-1 991. Proceedings ofthe Dorset Nat ura l History and coasts . Progress in Physical Geography, 18, 497-516. Archaeological Society, 113, 157- 160. ORFORD, J .D.; CARTER. R.W.G., an d FORBES, D.L., 1991. Gravel bar­ CLAYTON, K.M., 1980. Bea ch sediment budgets and coastal modifi­ rie r migration and sea-level rise: Some observations from Story cation. Progress in Physical Geograp hy, 4, 471-486. Head, Nova Scotia , Canada . Journal of Coastal Research, 7(2), DARTON, D.M.; DINGWALL, R.G., and MCCANN, D.M., 1980. Geolog­ 477-488. ical and Geophysical Investigations in Lyme Bay, Report No. 79/10, Om'oRD, J .D.; CARTER, R.W.G.; J ENNINGS, S.C., and HINTON, A C., Institute of Geological Sciences, UK, 24p. 1995. Processes and timescales by which a coas tal gravel-domi­ DOBBIE and PARTNERS, 1981. Chesil Sea Defence Scheme: Investi­ nated barrier responds geomorphologically to sea -level rise: Story gation of Offshore Gravel Deposits. Consultan t's report to Wessex Head barri er , Nova Scotia. Earth S urface Processes and Land ­ Water Aut hority and Weymouth and Portland Borough Council, forms, 20, 21-3 7. 5p. PILKEY, O.H. and HOWARD ,J .D.,(conveners) 1981. Saving the Ame r­ DRA PER, 1. and BOWNASS, T.M., 1983. Wave devastation behind ican Beach: A Position Paper by Concerned Coastal Geologists. Che sil Beach. Weather, 38, 346-352. Skidaway Institute of Oceanography Conference on America's HAHDCASTLE, P.J . an d KiNG, AC., 1972 . Chesil Beach sea wave re­ Eroding Shoreline, Savannah, Georgia, 12p. (reprinted in Geo­ cords. Civil Engineering and Public Works Review, 67, 299-300. times, 26 (12), 18-22). HEYWOHTH, A and KiDSOK, C., 1982. Sea-level chan ges in south­ TAGGART, B.E. a nd SCHWARTZ, M.L., 1988. Net shore-drift direction west En gland an d Wales. Proceedings of the Geologists' Associa­ determination: A syste matic approach. Journal Shoreline Manage­ tion, 93, 91-111. ment, 3, 285-309. HOOK, B.J . and KEMBLE, J .R., 1991. Chesil sea defence sche me. Pa­ WILSON, N.V.; WELCH, F.B.A.; ROBBIE, J .A and GREEN, G.W., 1958. per 1: Concept, design and const ru ction. Proceedings of the Insti­ The Geology of the Country Around Bridport and Yeovil. Memoir tution of Civil Engineers, Part 1, 90, 783-798. of th e British Geological Survey, Sheet s 327 and 312. London, HYDRAULICS RESEARCH, 1985. West Bay Harbour. A nu merical HMSO, 239p. st udy of beach changes east of the Harbour entrance. Wall ingford , WRIGHT, P.; CROSS, J .S., and WEBBER, N.B., 1978. Alum inium peb­ UK: Hydraulics Research Ltd , Report EX 1301 to West Dorset Dis­ bles: A new type of tracer for flint and chert pebble beac hes . Ma­ trict Council, 33p. rine Geology, 27, M9-M17.

Journal of Coastal Research, Vol. 13, No.4, 1997 Development of a Shingle Beach 1047

Plat e 1. The Che sil Beach shingle barri er. Ext ending some 28 km westwards to West Bay in the dist an ce, it affords protection to th e Fleet Lagoon and a low-lyin g developed hinterl and (foreground).

Journal of Coastal Resear ch, Vol. 13, No.4, 1997 1048 Bray

Plat e 2. The cliff landslide complex of Black Ven . Major failures involving ma ssive mud slid e surges deliver lobes of sediment to th e shore. Their erosion produces characteristic residual boulder aprons . Note th at th e lobes cut th e beach a nd intercept littoral drift.

Journal of Coast al Research, Vol. 13, No.4, 1997 Development of a Sh ingle Beach 1049

Plate 3. The shingle t ran sport barrier form ed by the jetties at West Bay . Exten sive coas t prote ction structures and cliff regr ading have been undertaken following major shingle losses from th e west ern (Eype) beach. Note th at th e accumulation pattern agains t th e jetties is not a reliabl e guide to net drift becau se of th e depl eted an d isolated nature of Eype Beach. Nu merical modelling studies sh ow th at net drift has actua lly been toward s the cam era (eastw ards) sin ce 1982 (HYDRAULICS RESEARCH, 1991).

J ournal of Coasta l Resear ch, Vol. 13, No. 4, 1997