Journal of Coastal Research 761-7n Fort Lauderdale, Florida Summer 1996
Shoreline Salients, Cuspate Forelands and Tombolos on the Coast of Western Australia
Peta G. Sanderson and Ian Eliot
Department of Geography The University of Western Australia Nedlands 6009, Western Australia Australia ABSTRACT _
SANDERSON, P.G. and ELIOT, 1., 1995. Shoreline Salients, Cuspate Forelands and Tombolos on the Coast of Western ,tllllllll:. Australia. Journal of Coastal Research, 12(3),761-773. Fort Lauderdale (Florida), ISSN 0749-0208. ~ Shoreline salients, cuspate forelands and tom bolos on the Coast of Western Australia were examined photogrametr ~ ~ ically to determine the suite of landforms that comprised the structures and whether there were regional differences euusit' in their geometries. Aerial photographs from three regions were examined, including the South Coast, from Cape Arid =+ S- to Esperance; the Central West Coast, between Guilderton and Dongara; and the Ningaloo Coast, from Point Cloates to Exmouth. The landforms were broadly classified according to morphological and genetic criteria, such as growth mechanism, degree of mobility, contemporary activity/processes, main processes involved in the supply of material, sources of supply, conditions of wave regime and stage of development. Second, morphometric information was taken directly from the aerial photographs. Following work reported by SILVESTER and HSU (1993), this was analysed to determine the constant and exponential values in the curvilinear relationship between the length of the offshore structure relative to its distance offshore and the difference between offshore distance and the ratio of salient protrusion to island length. Separate graphs have been compiled for all observations from Western Australia as well as for each region to indicate geographic differences. An examination of the geometric differences between each coastal region was undertaken using analysis of variance techniques. At the 5% significance level, the results indicated that, there are significant differences between the coastal regions for most ratios when tombolos are excluded from the data sets. Most of the South Coast forelands and tombolos are formed by the deposition of sediment resulting from the conver gence of swell behind an obstacle, whereas on the Central West and Ningaloo Coasts the submerged reef provide an offshore barrier. Swell is complexly diffracted and refracted by the reefs and sediment is deposited in a less predictable manner. Flushing of lagoonal waters behind the reef either by longshore currents or offshore movement of water through breaks in the reefs appears to impede the formation of tombolos and provides an explanation for travelling versus stationary forms in the respective environments. It has been shown that the development of these forms cannot be attributable to the length of the offshore obstacle or the distance of the obstacle offshore. Explanation of this requires further investigation of the combined oceano graphic processes occurring leeward of the reef chains on the Central West Coast and on the Ningaloo Coast.
ADDITIONAL INDEX WORDS: salient, cuspate {oreland, tom bolo, morphology, geometry, regional variation, Western Australia.
INTRODUCTION of the three regions would highlight geographical differences in the geometries of the forms and raise questions concerning Cuspate forelands and tombolos were first described by the nature and intensities of processes affecting their for GULLIVER (1896; 1899), Originally, the term foreland was ap mation. plied to the Dungeness foreland in Britain. The term tombolo which is of Italian origin (JOHNSON, 1919), was applied to a COASTAL LANDFORMS IN WESTERN AUSTRALIA spit of sand or shingle which joins an island to the neigh bouring coast. It has since been recognised that low ampli No systematic and comprehensive study of the occurrence tude shoreline salients, cuspate forelands and tombolos are of salients, cuspate forelands and tombolos has been under part of a hierarchy of coastal sedimentary landforms. Such taken for Western Australia, although individual landforms landforms occur on the West and South Coasts of Western have been described in detail. Further, there are few, if any Australia and are common in three regions: on the Ningaloo studies of depositional landforms from the South Coast. How Coast in association with an active, fringing coral reef; along ever, a number of studies have examined sediment distribu the Central West Coast where semi-continuous Pleistocene tion, reef morphology and the relationship of the reef to in reef formations shelter the shoreline; and on the South Coast shore depositional features on the Rottnest Shelf between in the vicinity of granitic islands (Figure 1). It was anticipat Busselton and Geraldton (SEMENIUK and JOHNSON, 1982; ed that a broad scale investigation of the shoreline features SEARLE, 1984; SEARLE and SEMENIUK, 1985; SEMENIUK and JOHNSON, 1985; SEMENIUK and SEARLE, 1986; COLLINS, 95144 received 23 May 1994; accepted in revision :W May 1995. 1988; and SEMENIUK et al., 1988). They indicate that erosion 762 Sander son and Eliot
ma inland toward th e advan cing bank. The mechanics of th is
1 10~ · are obscure and SILVESTER (1987) offered a counter expla lOaS ,--- _ V 124°E 128'[ Continenta l Shelf 200m ••• • .• . nation for th e formation of th e structure . He stated that, while some forelands may be formed by th e above processes,
20'S 20'S Becher Point itself is maintained by th e balanc e in wave en ergy from the south and the diffracted wave energy through
.~ the gap in th e offshore reef. 30'S Processes occurring in the Ningaloo reefsystem are similar to those on th e Central West Coast. However their intensities
0 are different as the oceanic and reef systems operate within 40 S 119°E 1200E 1300E 140'E\],SO'E different environmental settings. Headlands and zones of INDIAN .tJ1'" sediment accumulation in th e Ningaloo lagoon are discussed OCEAN( i by HEARN et al., (1986 ). They are consid ered to form as a NORTHWEST / result of diffraction through bre aks in th e reef. Much of the CAPE i t: Exmout h 22'SI energy of waves incident on the seaward reef slope is dissi NINGALOO N;noslooi ~ 0~~ 1' REEF Root f _ pated at the seaward face of th e reef. However, overtopping of the reef by surf beat, wave and wind set-up and tidal ac ----I;/ WESTE RN I tivity driv es water into the lagoon and establishes a lagoonal '·Sha Carnarv on • OG circulation. The resulting current contributes to longshore DIRKSHELF HART I'ii. \&.ys:'10\, AUSTRALIA 26'I S transport of sediment and usually exits the lagoon through breaks in the reef. Hence, development of cuspate forelands i and salients in this region is controlled by a combination of i wave generated currents, refraction and diffraction of waves, JO's io, °s as well as by alongshore flow and large rip currents operating through breaks in th e reef.
SOUTHWESTERN AUSTRALIA
0S . ~~~ ~~.~~~ 34 . •, ? APE ARII:) 34'S Climate
o 2OOkilom etre s Southwestern Australia encompasses a range of climatic l--L---.I 11ZOE 116°E 1200 E 124°E 12S0E conditions (GENTILLI, 1971) which establish a context for re gional differences in depositional processes around the coast. , Figure 1. Regional Setting . Weather conditions in West ern Australia are principally de termined by movement of a belt of anticyclonic high pressure systems that move sea sonally between latitudes 26°S and of reefs, particularly during the Holocene sea level rise, as 45°S. Prevailing wind s on th e South Coast in summer are well as the bioproductivity of existing reefs and seagrass southerly to southweste rly and easterly on th e Central West banks, has substantially contributed, and continues to con Coas t. The Ningaloo Coast experiences quiescent weather tribute, calcareous sandy sediment to beach and nearshore conditions during summer but in winter th e anticyclonic belt areas of the Central West Coast. brings strong easterly to southwesterly wind s. During winter , As described by SEARLE (1984 ) and SEMENIUK et al. (1988), strong southerly winds on th e South Coast and northwest erly the Central Southwestern Coast of Western Australia is pro to westerly winds on the Central West Coast are associated tected by a broken chain of offshore reefs. The reefs dampen with winter storms. Strong sea breezes are experienced in th e effects of swell and give ris e to an intricate pattern of summer on th e South and Centra l West Coasts and in winter wave refraction and diffraction in the lee of th e obstacles. on the Ningaloo Coast. SEARLE (1984) concluded that Holocene sand accretion in th e southwest of Western Australia ha s been controlled by inter Oceanographic Setting action of th e shelfwave climate with the complex and eroding ridge and depression bathymetry, abundant sources of sa nd Following tidal nomenclature describ ed by DAVIES (1980), and evolving bank structures. SEMENIUK et al. (1988) pro th e Central West Coas t and South Coas t are in a microtidal posed that under th e influence of prevailing southwesterly environment which experiences a mixed mainly diurnal tidal swell and wind wave s, a net northward sediment transport regime (DEPARTMENT OF DEFENCE, 1993). Spring tidal rang has occurred along the exposed seaward faces of th e main es are generally less th an 1.0m (Table 1). In contrast to thi s land ridge and the first offshore ridge. Becher Point, a cus the Nin galoo Coast experiences meso-scale tid es, with a pate foreland on the Southwest Coast of Western Australia spring tidal range at Exm outh of 1.8m (Table 1). is discussed as forming as waves pass through th e breach and Incident wave energy is largely determined by the protec impel sediment landward to form lobate subma rine banks. tion offer ed to th e shore by offshore reef cha ins or islands. Disruption of th e swell and longshore transport by th ese The South Coast is domin ated by a persist ent southweste rly structures cau sed progradation of a sandy cusp from th e swell which combines wave activity with more variable wind
J ournal of Coastal Research, Vol. 12, No. 3, 1996 Shoreline Sa lien ts 763
Tabl e 1. Tidal ranges between Esperan ce and Exm outh. iment accumulation, mainly as deposits of calcareous sa nds and gravels (WYRWOLL, 1990). Predicted Tidal Ranges (metres) The objectives of the project are to: Neap Tides Spring Tides Highest Astron. Standard 1. describe th e distribu tion and form of salients, cus pa te Port MHLW MLHW MLLW MHHW LAT HAT forelands and tombolos in the three coastal regions of Exmout h 1.1 1.7 0.5 2.3 0 2.8 Western Australi a; Geraldton 0.4 0.9 0.3 1 0 1.3 2. morphometrically exa mine the geometric relationsh ips of Fremant le 0.7 0.7 0.5 0.9 0.1 1.3 the landform s with their assoc iated stru ctures; and Bunbury 0.7 0.7 0.4 0.9 0.1 1.3 Albany 0.7 0.8 0.5 1.1 0.1 1.5 3. determine if morphometric variation between th e three Esperance 0.6 0.8 0.5 1.1 0.2 1.5 regions is greater than within each region. Source: Department of Defence (1993) PREVIOUS RESEARCH The formation of coastal sedimentary accumulation form s (STEEDMAN, 1977; H EGGE, 1994). It s beaches are protected have been reviewed by J OHNSON (1919), ESCOFF1 ER (1954), from the ocean swell by islands and th e configu ration of the GUILCHER (1958) , ZENKOV1 CH (1967), KING (1972 ), SUNA coastline. In contrast to th e South Coast, th e West Coas t is MURA and M1SUZO (1987) and HORIKAWA(1988), and broad protected by a semi-continuous offshore reef barrier , includ scale classification of the form s have been reported by ZEN ing reefs of th e Southe rn Rottnest Shelf, Houtm an Abrolhos, KOVICH (1967) and KING (1972). The earlier authors distin the Dirk Hartog Shelf and th e Ningaloo Reef Sys te m (HARRIS guish bet ween forelands and tombolos. More recent research et al., 1991). Wave energies incide nt on the shorelines of both including that by SUNAMURA and MISUZO (1987) and HOR1 the Central West Coast and the Ningaloo Coas t are low due KAWA (1988 ) recogn ise low amplit ude accretiona ry features, to the attenuation of incident swell wave energy by the off shoreline sa lients, as part of a hier archy of depositional land shore reef system (STEEDl\1AN an d CRAIG, 1979; HEARN et forms . al., 1986). Much of the work on coastal accumulation forms has been geomorphological (J OHNs ON, 1919; ESCOFFIER, 1954; Geology and Sediments GUILC HER, 1958; ZENKOVI CH, 1967; KING, 1972; and SNEAD , The South Coast of Western Australi a from Ca pe Leeu win 1982) dealing with th e shape and genes is of th e subae rial to Cape Arid consists of exte nsive areas of Pre-Cambrian and portion of th e accretio na ry body. J OHNSON (1919) began a Cambrian crystalline cliffs and islands inte rs persed with genetic study of coas tal environments, and his work was fol sandy beaches (HARRIS et al., 1991). The shoreline is char lowed by ESCOFFIER (1954) who exa mined "travelling" fore acte rise d by rocky headl ands, mainland coastal sa nd barrier s lands, and by GUILCHER (1958) in a study oflandforms which and transgressive onshore dune syste ms . Occasional rock develop following erosio n of coastal headlands or nearshore platfo rms and nearshore reefs occur along the exposed sec isla nds. ZENKOVICH (1967 ), DALLYand POPE (1986) and SIL tions of th e embay ments (WOODS et al., 1985). The massive VESTER and Hs u (1993) have exa mined conte mpora ry pro headl ands control much of the foreland and tombolo devel cesses maintaining sediment supply to th e coas tal area, and opment while offering protection to th e southeaste rly facing processes affecting erosion. Why some form s travel and oth bays. Beaches of th e region are largely composed of quartzose ers are stationa ry remains open to conjecture. sandy sedim ent, which tends to become increa singly fine ZENKOVI CH (1967) provided criteria by which cuspate grained in an eas te rly direction along th e coast (HODG KIN forelands and tom bolos may be classified. The criteria in and CLARK, 1990 ). clud e: growth mechanism, degree of mobility, contemporary The Central West Coast, part of th e Rottnest Sh elf between acti vity/processes, main processes invol ved in the supply of Fremantle and Geraldton (Figure 2), supports ons hore and materi al , sources of supply, conditions of wave regime and offshore ridges of Pleistocen e limestone running subpa rallel stage of developm ent. From field studies, DALLY and POPE to the presen t coastline. The limestone outc rops as lithified (1986 ) describe combined refraction and diffraction process dun es, chai ns of reefs and offshore islands (PLAYFORD et al., es . Th ese give ri se to an alongs hore differ en ce in wave 1976). Structural control is provided by th e isla nds and bro heigh t in the lee of an island. Th e differ enc e induces con ken reef cha ins (HARRIs et al. , 1991), contributi ng to th e Ho vergi ng longsh ore curre nts, leading to the form ation of sa locene development of salients, cus pa te forelands and tom lients, including cus pa te forelands, and tombolos in the lee bolos alon g th e coast. Sedim ents are mixed quartzose and of the offshore structure . calcareous sands, th e latter der ived from reworked lime In contrast to the geomorphic classifications and broad stones and bioproduction from extensive seagrass mead ows descrip tions of form ation some studies, particularly th ose (SEARLE and SEMENIUK, 1985; SANDERSON, 1992). from wa ve tanks (ROSEN and VAJDA, 1982; SUH and DAL Further north , the fringing Ningaloo Reef tract runs par RYMPLE, 1987; and DDA et al., 1988) have concentrate d on allel to the coastline from Gnarraloo Bay to Point Murat the re lations hip between the dim en sions of the offsh ore ob (280km) (Figu re 3). The coral reef encloses a shallow sedi stacle (island or reef) and the size and type of accumula tio n mentary lagoon containing occasiona l patch and nearshore fea ture .formed in its lee. For example, SUNAMURA and MI reef platform s. The shoreline is characterised by Pleistocen e suzo (1987) examined the geometrical relationsh ips of de limestone outc rops interspersed with areas of Holocene sed- positional form s on th e shoreline in th e lee of isla nds. In
-Iourna l of Coasta l Research, Vol. 12, No. 3, 1996 764 Sa nderson a nd Eliot
NORTH WEST CAPE , //5 INDIAN OCEAN NORTHERN SECTOR ROTTNEST SHELF • PERTH Fremantle INDIAN OCEAN Becher PI. 8 o ~ Bunbury N (f I ""'-"" Submerged reef ~ ~!f -"-"'" Reef l - SOm - metre isobath --30m - metre isobath 7 /Goo;mlOO~r o 50 kilometres o 20 kilometres I . '---'---' Figu re 2. Centra l West Coa st of Western Australia . Figu re 3. Nin ga loo Coa st of Western Australia. Figure 4, I is the island length, A is th e len gth at the root have little relevan ce to th e accumulation feature form ing be of a tombolo or sa lient, lj is th e projecting len gth, J is th e hind a breakwater. SILVESTER and Hs u (1993) showed tha t offshore distance to an island and both lj and J are mea th e distan ce of th e sa lient from the obstacle (J -lj) divided by sure d perpendicular to the a-a' line. SUNAMURA a nd MI I plotted aga inst I divided by th e origina l shore line distance suzo (198 7) found th at a tomb olo form s if J/I < 1.5, a sa J provides a significant empirical relationship between the lient develop s if 1.5 < J/I < 3.5 and no island influen ce variables. They also exte nded previous studies by examining appears if J/I > 3.5. This is demonstrated when lj/A or A/I th e plan form of salients to det ermine its relati onship to th e is plotted ag ainst J/I. Th ese studies have been reviewed by form ation of zeta-form embayments (Hs u et al., 1993). The SILVESTER and Hs u (1993). observations of SUNAM URA and Misuzo (1987) and SILVES It was shown by Hs u and SILVESTER (1990) that variabl es TER and Hs u (1993) provide a basis to compare observations other than the island length (I) and its offshore distance (J) from the different coas tal region s of Southwestern Australia. Journal of Coas tal Research, Vol. 12, No. 3, 1996 Shoreline Salients 765 KOVICH (1967), while KING(1972) affords both forelands and ( 1) TOMBOlO (2 ) SALIENT ( 3 ) STRAIGHT SHORELINE tombolos individual categories. :::~. I The dimensions of the cuspate forelands and tombolos in ?'I cluded attributes such as alongshore length of the island or (i obstacle; width of the root of the foreland or tombolo; pro ./ i jecting length of the foreland or tombolo; and the offshore distance to the island or reef. Third, geometrical attributes of the accumulation forms were analysed, using measured dimensions and graphing ~l techniques similar to those described by SUNAMURA and MI suzo (1987) and SILVESTER and Hsu (1993). Graphs of T1/A. vs J/I which compare the projecting length to foreland width ratio with the offshore distance to obstacle width, and A./I vs _ . - . - . - - Initial shoreline J/I (width of the tombolo to length of the island against off Figure 4. Geometry of salients and tombolos behind an offshore obstacle shore distance to length of obstacle) for each of the three (after HORIKAWA, 1988: 155). regions were compared with re sults from other authors. The geometric ratios for each of the three regions describing the relations hip of the coastal accumulation form with the obsta METHODS AND TECHNIQUES cle offshore, were then compared using analysis of variance techniques (SOKAL and ROHLF, 1981). This was done to de Several steps were used to assess geographic difference in termine if the differences between the three areas was great the occurrence of salient, foreland and tombolo forms of West er than the variation within each region. ern Australia. First, aerial photographs (Table 2) were inter preted to locate the sedimentary forms. Stereo-pairs were used to identify and describe the suite of landforms of each RESULTS accretionary structure, and the overall dimensions of the The Accretionary Structures. structure were measured with a graticule overlay. The over lay gave an accuracy of +/- O.25mm on the photographs, The South Coast of Western Australia is characterised by which converts to +/- 3.96m on the ground for the South attached forelands and looped tombolos (after ZENKOVICH, Coast region, and +/- 5m in the Central Coast and Ningaloo 1967) apparently formed by the interaction of nearshore is areas. lands with prevailing swell waves. The islands are located The description encompassed morp hological and genetic less than 100m from the shoreline. Measurements of these criteria, established by ZENKOVICH (1967) and KING (1972). South Coast accumulation features are shown in Table 3. They included: Some double tombolos are found, for example Vancouver Pen insula near Albany. However these are not common. Where 1) type of protection offered to the shore (none, reef, perfo they do form, their dimensions broadly fit categories defined rate reef); by SUNAMURA and MISUZO (1987). 2) shape of the feature (simple, double, triple); The reef chain protecting the Central West Coast is located 3) type of connection with the coast (attached, looped, free, up to 15km from the shore. Close to the shoreline however, barrier, detached); some reef is emergent or only partially submerged and these 4) orientation of the landform (symmetrical, asymmetrical); structures influence deposition of sedimentary material. The 5) its position (open ocean, behind islands, in bays, on capes, reefs are often discontinuous, and allow complex interference paired); currents and wave patterns to form. Tombolos do not often 6) size (ratio of length to width); form in this area, due to the broken nature of the offshore 7) the possible causes of accumulation (estimated from the obstacles and the broad space between the reefs and the aerial photographs); and shore. Almost all forms in this region are classified as at 8) stage of development (rudimentary, developed, decaying, tached forelands (See Table 4). The accumulation forms gen relict, regenerated); erally project up to 150m from the shoreline, but there are Each accumulation form was then classified according to significantly larger features such as the Cervantes foreland, both ZENKOVICH (1967) and KING (1972). Forelands are Jurien Headland and Wedge Island (Figure 2). The dimen classed as attached forms and tombolos as looped by ZEN- sional relationships between the length of the projection and Table 2. Aerial photographs used in the analysis. Photograph Description South Coast Central West Coast Ningaloo Coast Job number WA 944, Proj. E51 WA 2881(C), 900459 WA 2764, 890233 Run/photo numbers 5,148-5,156 Runs 1-7 Runs 1-5 Scale 1:15,840 1:20,000 1:20,000 Date 1965 27/6/90 12/8/89 Journal of Coastal Research, Vol. 12, No.3, 1996 -..] m m Table 3. Morphology and dimensions of salients, forelands and tambalas on the South Coast. Pro- tec- Connee- Orienta- tion Shape tion tion Position Size Accumulation Development King's Class Zenkovich's Class. l Im) A(m) n Irn) J (m) J/I none simple looped asymmet open/e mbay 2:01 lat eral displ rudimentary tombolo-normal looped tombolo 31.7 49.1 49.1 49.1 1.52 none simple looped sJ. asymm open 1.5:1 lat eral displ developed tombolo-normal looped tombolo ???? ? none simple attached symmet open/b ehind isl 1:04 lateral displ rudimentary cuspat e foreland att ached foreland 26.9 95 14.3 72.9 2.7 none simple attached asymmet open/b ehind isl 1:02 lateral displ developed cus pate foreland attached foreland 15 57 9.5 30.1 2 none simple attac hed symmet open/b ehind isl 1:01 lateral displ rudim-devl'd cus pate foreland att ached foreland 18.2 47.5 6.3 42.8 2.35 none simple attac hed symmet open/emb ay 2:01 lateral displ rudimentary cus pate foreland attached foreland 63.4 74.4 26.9 61.8 0.97 none simple looped asy mmet open/behind isl 3:01 lateral displ rudim-devl'd tombolo-n ormal looped tombolo 36.4 31.7 6.3 27.7 0.76 none simple looped asy mmet open/behind isl 3:01 lat eral displ developed tombolo-normal looped tombolo 33.3 74.4 41.2 41.2 1.24 c., none simple looped symmet open/behind isl 2:01 lateral displ developed tombolo-normal looped tombolo 15.8 31.7 9.5 14.2 0.9 0 "... none simple looped asy mmet open/behind isl 1:02 lat eral displ rudim-devl'd tombolo-normal looped tombolo 9.5 23.8 4.7 17.4 1.83 e:-::; none simple attached asy mmet open/behind isl 1:03 lat eral displ rudimentary cuspate foreland attached foreland 17.4 36.4 9.5 44.4 2.55 .....,o none simple looped asymmet open/behind isl 1:01 lateral displ developed tombolo-normal looped tombolo 19 36.4 20.6 20.6 1.08 o none simple looped asy mmet open/behind isl 1:02 lat eral displ? developed tombolo-norma l looped tombolo 53.8 68.1 23.8 23.8 0.44 0 co none simple looped asy mmet open/b ehind isl 1:01 alongsh sed mvt developed tombolo-normal looped tombolo 53.9 90.3 44.4 44.4 0.82 tn en co ~ none simple attached symmet open/b ehind isl 1:01 lateral displ developed cus pate foreland attached forela nd 50.7 142.6 47.5 72.9 1.44 ::s 0- ;>:l none triple looped asy mmet open/between isis 2:01 lat er al displ devl'd/devl'ing tombolos-normal looped tomb olos 142.6 28.5 60.2 60.2 0.42 -s en '"en '" 23.8 34.8 7.9 7.9 0.33 0 '"co ::s ... 82.4 74.4 25.3 25.3 0.31 co .::>" ::s " none simple looped asymmet open/be hind isl 1:01 lat er al displ developed tombolo-normal looped tombolo 23.8 39.6 26.9 26.9 1.13 0- < none simple looped asy mmet open/b ehind isl 1:02 lateral displ developed tombol o-norm al looped tombolo 23.8 50.7 15.8 15.8 0.66 ~ ~ none double looped asy mmet open/be hind isl ? lat eral displ developed tombolos-normal looped tombolos 45.9 74.4 36.4 36.4 0.79 g.' .'"- 28.5 30.1 26.9 26.9 0.94 Z none simple attached symmet open/be hind reef 1:03 lat eral displ rud imentary cus pate foreland attached foreland 17.4 28.5 6.3 7.9 0.45 !" none simple looped asy mmet open/behind isl 1:01 lat eral displ developed tombolos-norma l looped tombolos 80.8 95 34.8 34.8 0.43 ."" 23.8 41.2 25.3 25.3 1.06 <0 m none simple looped asymmet open/be hind isl 1:02 lateral displ developed tombolo-normal looped tomb olo 26.9 47.5 15.8 15.8 0.59 '" none simple looped asymmet open/behi nd isl 2:01 lat er al displ well devel tombolo-normal looped tombolo 72.9 103 63.4 63.4 0.87 none simple at tac hed asy mmet open/be hin d rock 1:02 lat er al displ developing cus pate foreland attached foreland 12.7 47.5 12.7 14.3 1.13 none double looped symmet open/be hind isl 1:01 alongsh sed mvt developed tombolo-normal looped tombolo 25.3 71.3 33.3 33.3 1.32 none simple at tac hed symmet open/be hind rock 1:02 lateral displ developing cus pate foreland attached foreland 30.1 55.4 12.7 31.7 1.05 none double looped asy mmet open/be hind rock 1:02 lateral displ developed tombolos-normal looped tomobolos 38 55.4 28.5 28.5 0.75 31.7 41.2 21.4 21.4 0.68 none simple at tac hed symmet open/behind isl 1:03 lateral displ developed cus pate forelan d attached foreland 23.8 72.9 11.1 80.8 3.39 none simple at tac hed symmet open/be hind isl 1:03 lateral displ developed cuspate foreland attached foreland 9.5 82.4 7.9 47.5 5 none simple attached asy mmet open/be hind isl 1:04 lat er al displ developed cus pate foreland attached foreland 15.8 82.4 29.3 50.7 3.21 none simple looped asy mme t open/be hind isl 1:02 later al displ developed tombolo-normal looped tombolo 11.1 60.2 17.4 17.4 1.57 none simple at tac hed asy mmet open 1:02 diffrcation developed cus pate foreland attached foreland 47.5 63.4 44.4 44.4 0.93 none sim ple looped asy mmet open 1:02 lateral displ developed tombolo-normal looped tombolo 34.8 53.9 15.8 15.8 0.45 none simple ? asy mmet open/be hind reef 1:03 lateral displ developing cus pate foreland attached foreland 95 134.6 34.8 47.5 0.5 none double looped asy mmet open 1:04 ? developed tumbolos-normal looped tombolos 74.4 15.8 72.9 72.9 0.98 221.8 118.8 218.6 218.6 0.98 Sho reline Sa lients 767 ~ to~8LQ~ ~b~LQ~gs~~~ th e width of th e obstacle do not fit the general model put ~ 0"";""';"";""';"";""';""'; 00 0""': 0 0 forward by SUNAM URA and MISUZO (1987). The Ningaloo Coast consists of a fringing reef barrier at varying distanc es from the shore. The reefis mor e continuous than that of the Central Coast, but closer to shore and broken by deep channels th at aid in flushing of th e shallow lagoon . The exchange of water between th e ocean and the lagoon aids formation of a distinctly differ ent suite of accumulation forms. They project from 100m to over 1.7km from th e shore, and consist of attach ed forelands and travelling forelands (Table 5). The travelling forelands are similar to those de l- ~ lQmQ')lQ~t-mMMMC"') -5 c.D .....;lQ~~c.Dc.Oaic.DO O~CO .....; scribed by ESCOFFIER (1954 ) from the USA. Again the di ~'o::1"O':l~C'OC\lC'Ot-~ ;::::O':l -~t- men sional relationships of the forelands do not fall into the categories described by SUNAM URA and MISUZO(1987). Geometrical Attributes Sediment accumulation occurs in the lee of an island or reef structure primarily as a result of wave refraction processes, and seconda rily in respon se to movement of sediment by nearshore curre nts . Man y people have examined thi s phe nomen on; for example see NOBLE (1978), DALLY and POPE (1986) and th e review by SILVESTER and Hs u (1993). Most authors acknowledge the importance of the length of the off shore structure parallel to the shore and its distance offshore as primary variables affecting th e basal size and distanc e the landform protrudes from the original shoreline . SUNAMURA and MISUZO (1987) have suggested that th eir results indi cated that tombolos a nd sa lients could be distin guished on the ba sis of the ratio between the len gth of the offshore structure (island or reef) and its distan ce offshore. Measurements from th e three coastal regions of Western Australia (Figure 5a-50, do not significantly support these findings. However , in observati ons from th e South Coast, tombolos all have J/I ratios of less than 1.83, which is close to the 1.5 ratio indi cated by SUNAMURA and MISUZO(1987). SILVESTER and Hs u (1993; 350) have demonstrated that ~C\l -~C'JC'l -C'J"O:1'M __ C\lC\l three geometric variables, nam ely I, J and Tj, best define th e '"N 00000000000000 i:ii ,.:..;..:..;..:..; ,.:.; ,.:..;,.:...;,.:...;.:.;,.:...;,.:...;..:.;,.:..;,.:...; ,..:..; apex position of a sa lient. Their reanalysis of publish ed in forma tion describ es a curvilinear relationship between length "iii of th e offshore structure rel ative to its distance offshore (l/J) C <-<-to- e..-.~r.-e-c-tS....::.::c..... and th e differ ence between offsh ore distanc e and the ratio of :~ ~~~~~ ~2~EE~~e~ sa lient protrusion to island length (J- Tj/I), such th at: d: ~""g]] EEEEE-gE-gE -g :.E:.E:.E:.E:.E :.E:.a :.a:.E :.E:.E:.c:..c :.E I1J = 0.6784(J - Tj/I)- L214 ..o~ ..o~ ..c ~ ...c~ ..c~ ..c~ ..c~ ..c~ ..c~ ..o~ ..o.~.o ~ ..o~ ..o~ In th is relationship, J - Tj/I = 0 for tombolo landform s that, by definition, reach th e stru cture and ti e it to th e shore line . Their approach offer s a basis for regional comparison since th e constant and expone ntial function may be reasonably ex pected to vary for landform s in differ ent phases of develop men t or which have been developed under different environ "'"c:: .0c::_ men tal conditions. o - U Accordingly, morphometric data from the three coastal regions of Western Australia have been plotted according to th e methods of SILVESTER and Hs u (1993) (Figure 6) to de termine whether the attributes of th e sa lients: a) conform with SILVESTER and HSU'S(1993) findin gs; and b) provide a basis to distingu ish bet ween th e landform s of each region. •Journ al of Coastal Research, Vol. 12, No. 3, 1996 m-:J 00 Table 5. Morphology and dimensions ofsalients, forelands and tambalas on the Ningaloo Coast. Protec Connec Orienta Develop tion Shape tion tion Position Size Accumulation ment King's Class Zenkovich's Class l Im) 'A (m ) TJ (m ) J (m ) J/I reef simple attached symmet behind reef 1:04 current converg developed cuspate foreland attached foreland 4,000 3,200 800 3,000 0.75 reef simple looped asymmet behind isl 1:02 lateral displ developed tombolo-normal looped tombolo 60 420 150 150 2.5 reef simple attached ' asymmet behind reef 1:04 alongshore currents developed cuspate foreland attached foreland 4,000 1,500 500 2,400 0.6 reef simple attached asymmet behind reef 1:04 alongshore currents developed cuspate foreland attached foreland 4,000 1,200 240 2,200 0.55 reef simple travelling asymmet behind reef 1:03 alongshore currents developing cuspate foreland attached foreland 5,000 620 180 2,200 0.44 reef simple attached asymmet behind reef 1:02 ? developed cuspate foreland attached foreland 4,000 400 100 1,000 0.25 reef simple travelling asymmet behind reef 1:02 alongshore currents developed cuspate foreland attached foreland 3,000 1,000 460 1,300 0.43 reef simple attached asymmet behind reef 1:04 ? developing cuspate foreland attached foreland 1,200 1,000 180 760 0.63 reef simple attached symmet behind reef 1:01 diffraction developing cuspate foreland attached foreland 2,000 500 140 1,100 0.55 reef simple attacjed symmet behind reef 1:01 diffraction developing cuspate foreland attached foreland 4,000 480 280 1,300 0.32 reef simple attached symmet behind reef 1:04 diffraction? developed cuspate foreland attached foreland 1,700 1,200 200 1,440 0.85 ~ reef simple attached asymmet behind reef 1:04 diffraction developed cuspate foreland attached foreland 2,200 1,300 200 2,200 1 8 reef simple attached asymmet behind reef 1:04 current converge nce developing cuspate foreland attached foreland 4,000 900 330 2,800 0.7 a reef simple attached asymmet behind reef 1:04 current convergence developed cuspate foreland attached foreland 2,500 1,600 360 1,800 0.72 o ~ reef simple attached asymmet behind reef 1:01 spit development developed cuspate foreland at tached foreland 4,000 2,200 1,700 2,600 0.65 Cl o $:I:) UJ tr: ("'t- $:I:) a ::s 0..ro ~ to; UJ oUJ ro ::s $:I:) ~ ::s ~"'%j q-~3 ~~ ~~ C-.('1) ~S- ~ o "'%j ~ ~ 0.. ro ~...... ~. "<::4 ~ ~ 0 " 0 0 ..0 0 ~~ . ~ ~ ~ ~ ~~ ~ ~ ~ ~ ~. tj cr '-..' 0.. S' 00 I m :::r'to; 0 o I\) I\) ~ UJ to; ~ ~ ~ p ~ o' M- 6 M- M- (Jq ('1) ('1) ~ 0 ("'t- I-'" $:I:) ro ro ~t-:l g:O ~gooM-aS-g:~~~ ~ ro Ol ~ o ::s m o . (1) 0..' ~ 0 . m Ul e. ::r~' ~ ~ ('1) .-; ~ Z . ~ 0('1)00;' ~ M-oo~ 0"" ~ ~ o 0 !=' S-~ t-3 ~ S~· ~ ~. ~ ~ (Jq ('1) ~ ~ ~O z 1+ 8 5-~:> ~ $:I:) ro 0> S ::r ~ (Jq ~ CJq M- <:...t (Jq .-; ~ 0 o ~ 0""$:1:) S. I\) I-'" ('1) o 0.. M- ~ ~ II ~ ~ ~ ~ CDS co ag: § S. . ro + 0 co ~ (J-T]/I) ooo..§oo~;,~~ M-~ >~ ("'t- m ::s ~1;: ~ c.. I\:> (J.) ~ 01 o..~ ~ ~ ~::r ::L en -f c.. ~e: o°r--_...--_ e.Zq-;'n £ o Q) 0 ...... '::: roO ~. ~ ('1) ~ 0 ~ xr -a <:...t ~ M- 00 to; + ~'"O o o ro ~ ~ - ~ r CP ~~ ~('1) ~ ~ ~~ ~~ g P5 ::r + 0"" s;- 5' I\) ~ m &r~ ~~ ~~ ("'t- ~lr rn~ G) M-S ('1) mOl '-; n ~ :6 m ~ ~. ~" ~ ~ ~ o' t"4 ro z " 0 S F c::; ('1) ::s ~ ~. 0 ~ ~ ~ :::: ~ UJ o t ro o dO;. ;t5 cr :::r' rn ::s S ~~. £ S ~. ~ o: I g.. ~ ~ ~ -a ' ~ ~*+ o UJ =-,"1;- 2S I\:> M-~ " ~~~;"1 ~3 ~ § ~ ~ UJ .'-_"""------'-_--'-....J (Jl I m 'L.---''___----'_--' ::0 $:I:) o ~Z()OO ::rM-M-('1)<:...t~>~~.-; n l-' n ~ ~ ~ ~ $:I:) ::s 9:~' ~ ('1)oo~sr l\n ~ I < ~ ~ O ::s 0.. s g 0.. 0 I\)-~ m 0 I\) ~ m <5 10> ~ :7 ~~~ ~~. ro 0 0 o..~ 8~ o::r M- 00 S '"0 6" g (J.) ('1) 0 ~ o' 0 ('1) :::: 0.. ~ o' ~ ~~. o o~ ~ I g~ ~ a~~~Cno...-;1-r'I ~ ('1) '-; 1-' ~ C3 g. ~~ ~M-cr~ ~~ oo~ ~ + ~ ~ QO>!e.- .-; ('1) ::r~. ~ ~ ~ s ~ ~ ~. ~!e.~ ~ e. 0 c:: ::r 0 ('1) ::s o o oo~ ~M-~ ,-.~ ;: ~ &~ a o I\) o + co::S 0> S ~ .. + 0, + <:.A:>C !e. ~ ~ ~ ~ ~ ~ 0 ~ ('1) ~ o' .-; .-; s; + ~~ ~('1)0<:...t 1-+o)~M-~ ~ ('1) ~ ::s -if. + + 0.. 0.. S' M- .-; S II V ~ ~ ce ::r § 0 0:9. :::: ~ c.. c.. + s crq "...... ('1) 00 1-' '-..'('1) M- 1-+o) 0 0 '::: '::: + ~ ~ ~ + 0...... l M- 0 W M- roO o 00 M- cr + o .-; ::r. ,-. ~ . ~ ~ 0 ::r ,-. 00 SUJ ~ ~ ~ ~ ~ ~ ~ I\) $:I:) n' ('1) cr M- p.. @ ('1) ('1) 0"" .t M- ~ 0 ~ aq ' 00 M- ~ 00 .-; aq' ~ ro + + ~ .-; 0.. ('1) ~ ~ a~. 0 ::r ~ ~ ~ ~ ~ :::r' o o ~ ~ -;:~Sg('1)~~ O-· .-; o: S· S ~~q-""" \IoI~~('1)M- oo O ('1) o 0.. UJ + L.---'-_~_ m 'L.-----''___----'_---' ~ ~ ~ e. I -:3 ~ ;5 ~ ~. S' ~ -:3 ~ § UJ ...... 0, Shoreline Salients 769 Tabl e 6. Result s from analysis of variance. 0 Geometric Tombolos Tornbolos :::: 0 Variable Included Excluded ~ 4:1~OC% O 0 O P = 0.098, F = 2.41 P = 0.001, F = 8.175 . 1 P = 0.199 , F = 1.65 P = 0.451, F = 0.813 4 o 1 2 I /J 3 4 P = 0.02 1, F = 4.11 P = 0.000, F = 20.86 P = 0.095, F = 2.436 P = 0.002 , F = 7.102 P = 0.955 , F = 0.046 P = 0.010, F = 5.184 ~:[ ~ ~: l Differ enc es are sign ificant when P < 0.05 ent between the coastal regions. In all instances, I (length of .. :23 4 I 0 :..1 2 3: 4 I o the offshore obstacle), J (distance to the offshore obstacle) and I /J I/J J - 11 (distance between the offshore obstacle and the apex LEGEND 0 South Coast + Central West Coast of th e salient) remain significantly different between coastal • Ningaloo Coast region s when tombolo s are excluded from the data sets. Figu re 7. Relationship between 1M an d J - lllI for sa lients in eac h coast It follows that th e forms of salients, cuspate forelands and al region. tom bolos on th e Rottnest Shelf and Ningaloo Coasts are markedly differ ent. Although much work has been conducted on th e cuspate forelands of the Central and Southern West from I/J = 0.5 to 4.0; wher eas th ose from the Ningaloo Coas t ern Australian Coas t, the models of their formation remain ran ge from I/J = 1.0 to 4.0. The empirical formula are I1J = locali sed and cannot be applied to th e Nin galoo Coas t where 0.7362(J - 11/I)-OBI4 and I/J = 0.984(J - 11/I) -om from the th e reef stru cture and nearshore processes differ gr eatly. The Central West Coas t and Ningaloo Coas t respectively. relative simplicity of th e form ation of th e South Coas t cus Results presented here are more consiste nt with those from pate forelands and tombolos can be accounte d for by th e lack observations presented by SILVESTER and Hs u (1993 ) th an of reef contro l an d th e direct relationship between offshore those from SUNAMURA an d MISUZO (1987). However, in con island an d sedimentary accumulation. With th e complex, bro trast to SILVESTER and HSU's (1993) resul ts the re is a scat ken ree f chains that exist on th e West Coas t it is anticipa ted ter of observations when J - 11/1 is plotted against I/J for all that a combina tion of processes including swell diffr action th ree coastal regions in Western Australia (Figure 6) and this and refraction, sediment distribution, nearshore circulation, remain s true when tombolo form s are excluded from th e clas curre nt flow and local weather conditions will eac h have an sification. The scatte r of data on th e graphs is appa rently effect on the resulting developm ent of the coastal sedimen wider than that reported by SILVESTERand Hs u (1993: 350). tary features. These processes require further investi gation However , thi s may be du e to errors involved in taking mea in th e field . surements directly from aerial photographs, inclusion of a range of forms that are not necess arily in static equilibrium DISCUSSION with local wave and nearshore current conditions and sedi General Morphology ment supply, or some combin ation of th ese two. Nevertheles s, the results gen erally agree with tho se reported by SILVESTER Initial analysis of the aeri al photographs of the three areas and Hs u (1993 ). indicated th at there are distinct differences between the An examination of th e geometric differ ences bet ween each South Coas t and th e reef protected West Coast. The devel coastal region was undertak en usin g ana lysis of variance opment of accumulation forms on the South Coast is directly techniques. Each of th e geometric ratios, JII , 11/A, All , I/J and attributable to th e offshore granitic islands, and changes in J - 11II wer e tested by non -param etric one-way analysis of bathymetry. Offshore reef protection is very limited, and thus variance usin g the Kru skal-Walli s test (SaKAL and ROHLF, th e sediment accumulates directly behind nearshore obsta 1981) to det ermine which ratios showed significantly greater cles. Cuspate forelands and tom bolos which are characteristic differ ences betw een than within coastal region s. A 5% level of the South Coas t are illustrated in Figure 8. Type A forms was adopted for determination of significance. The ana lysis are tombolos which link a rocky outcrop with the mainland. of variance for each ratio was conducted twice. First for th e The coas tline typically changes orientation at this point and complete data sets , including tombolos and salients, and sec th e headland is flanked by long sandy beaches. Type B tom ond for data sets excluding tombolos. bolos occur where a large granitic outcrop is found close to a Results (Table 6) showed that at th e 5% significance level sandy beach. A small amount of material is then needed to th er e are signifi cant differences betw een th e coas tal region s link the island with th e mainland. The se forms are usually for most ratios when tombolo s are excluded from the data large (800- 1000m width) and are situated within a sandy sets. Only All, th e ratio of th e length of the root of th e salient beach environment. Type C tombolos are very similar to type to th e length of the obst acle showed significant differ ences B but smaller in scale. They are quite common due to the between the coastal region s when tombolos were included in frequent occurrence of small islands close to the shore and the data sets. The ratio of 11/A, th e projecting length to the occur on average with a frequency of approximately 5 every length of the root of the salient, was not significantly differ- 100km. Type D sedimentary forms are cuspate forelands that Journal of Coastal Research, Vol. 12, No. 3, 1996 770 Sa nde rson a nd Eliot TYPE A TYPEB TYPE A Offshore reef ....· ~'I .·.·. :· · ~ u s p a t e ; \ ~~. I.:I.foreland i ~ '.. I dBroken reef N ":\ .. ~ Not to scale N egIJurabi Point eg Near Yardie Creek TYPEC TYPED TYPE C TYPE D LongSandy Beach ~ Tambala N I =:: . ~o/.F'==== Reef Gap Reef not ~ Bar close to shore Small Rocky Island 200km o Q?:D ~ Broken '------' Not to scale Offshore Island Reef N I N TYPE E ~ LEGEND eg Some in Northern Sector eg : Turquoise Bay II Foredune ridges Close Offshore Reef ~ Dunes LEGEND I I Spit Development Reef-submerged or ~ partially submerged f}· i : . :/(~':/1 Sandy beaches II Foredune ridges ~ Granite outcrop [§] Dunes Figure 8. Ty pes of cuspate forelands and tombolos cha ra cte ristic of th e k\'..}"' : ~:J Sandy Beaches South Coa st. ~ N eg Winderaba ndi Pl. Figures are not to scale . Figure 10. Types of salients and forelands characteri sti c of th e Nin galoo Coa st. form behind islands th at outcrop a greater distance offshore TYPE A TYPE B th an those of type C. The fore land is ofte n symmetrical, or Reef slightly asymmetrical, and appa rently is form ed by diffra c /Y~agoon ( partially submerged tion of waves around th e island . The geometry of each of th e /;W r~ or island , ,""Cuspatev> ~ o: [ ) types found on th e South Coast genera lly fits th e models de N ~~; fa"~~ ~ ) '~. scribed by SUNAMURA and MISUZO (1987). Type E coastal ..:.. .; ...... "- iS I~~ : · · : · ,·~ accumulation forms are complex double or triple form s. The Offsho re~ ~ sediments accumulate between offshore islands linking one ~ N eg : Junen eg Lancelin Region to another and to th e ma inl and. The areas are characte rised TYPEC TYPE D by gr anitic outcrops with few sa ndy beaches or onshore ac cumulations of sediments. z., In contrast, th e protection offered by th e broken reefs to l reef both th e Central and Nin galoo Coas ts allows complex inter 1 I chain ~ action of swell waves, wind waves and longshore curre nts, N causin g sediments to accumulate in areas which are not di ! rectly landward of th e offshore reef but skewe d to th e direc eg eg : Nambung Region tion oflongs hore tran sport. Closer exa mination of th e Central TYPE E Coas t and Ningaloo reef sys te ms shows tha t th ese two LEGEND regions are differ ent to those of the South Coast and from ~ ~:r~t~bs~~~~~ each othe r. The reefof th e Central Coast is discontinuous and II Foredune ridges ~ the nearsh ore bathymetry is irregul ar, leading to complex cir ;i",omoo. I"'Vz- I Dunes culation patterns. Sedim entary accumulation form s typical of r.'·::·;::\d Sandy Beaches th e Central West Coast are illu strated in Figure 9. Type A N HeliffS ~ Limestone are th e large cuspate forelands which form behind offshore eg : North Head Figures are not to scale . islands and reef chains. The island is usu ally quite large (lOO-200m long) and part of a longer reef. Although 2-3km Figure 9. Types of salients, forelands and tombolos characteri stic of the offshore , it still exerts a considerable influ ence on th e local Centra l West Coast. sediment trans port. These cus pate fore lands are found at Journal of Coastal Research, Vol. 12, No.3, 1996 Shoreline Sa lients 771 rocky shoreline ~ sandy shoreline Ningaloo Reef A E N 9 10 20 30 'km ', NINGALOO COAST km N o 50 100 150 • ! , , CENTRAL WEST COAST rock shoreline ...... sandy shoreline c . Cape Archipelago of the Recherche N Leeuwin 100 150 200 km Al ba ny ! I , SOUTH COAST Figure 11. The locati ons of the sedimen tary accumulation form s described in Figures 8, 9 and 10 on the coas t of Western Australi a. such areas as Jurien , Cervantes and Wedge Island. Type B West Coas t. Wave diffr action and refr acti on thro ugh breaks forms are sma ller scale cuspate forelands occurring behind in th e reef is important, water driven across the reef by tid es islands or exte nsive areas of partially submerged reef. Type and waves significantly contributes to circulation within th e C form s are low-amplitude sa lients which form when sedi flat lagoon. In particular th e wave dri ven wate r a ppears to ments accumulate behind broken reef chai ns . Type D fore be assoc iated with the longshore transport of sediment, and lands develop behind broken and partially submerge d reef with th e movement of wate r in and out of th e breaks in th e outcrops. The perfora te nature of the reef allows wave ene rgy ree f. It combines to form distinct coastal accumulation form s to cross the reef and imp ede development of the foreland.A (HEARN et al., 1986). The chara cte ristic sa lients and fore lagoon is often enclosed by the foreland as the flanks have lands of the Ningal oo Coast are shown in Figure 10. The type accumulated. Type E forms are tombolos which are formed A foreland is similar in sca le to the type A forelands of th e by accumulation of sediments behind limestone headl ands. Central Coast. It is form ed, however , beh ind reef with no is Longshore trans port appea rs to significantly contribute to de land influ en ce and consists of exte nsive barrier development velopment of these form s. Very few of these coastal accu including development of relic foredune plains. Type B sa li mul ation forms have dimen sions which a re comparable to ents are 200-300m in width and are found behind broken those of th e South Coast. offshore reef. Further contributi ng factors are not easi ly iden Ningaloo Coast accumulation forms are significantly dif tified from the ae ria l photograph ana lysis . Type C accumu ferent to those of th e South Coast and to those of th e Central lations are small scale forms occurring on th e shoreline in J ourn al of Coastal Research, Vol. 12, No. 3, 1996 772 Sanderson and Eliot areas where the reef is a considerable distance from the regions of Western Australia do not significantly support the shore. Travelling forelands are classified here as type D fore findings of SUNAMUf{A and MISUZO (1987) however in obser lands. They form behind broken reef chains close to the shore vations from the South Coast tornbolos all have J/I ratios of and are influenced by longshore currents operating within less than 1.83 which is close to the 1.5 ratio indicated by the lagoon. Type E forms are large forelands (2-3km length) SUNAMURA and MISUZO (1987). Empirical equations derived which project out to the close inshore reef. The foreland does for each of the three regions demonstrate a curvilinear rela not form a tombolo, and spit development is observed at the tionship that is similar to that reported by SILVESTER and offshore extremity. In some instances, a lagoon has been en Hst: (1993) but which have different constants and exponen closed by the development of the foreland at some time dur tial values. Significant differences have been shown to exist ing the Holocene. between the three coastal regions for the geometric variables From the broad classification of coastal accumulation forms I, J and ,J TJ when t.omholos are excluded from the data described it is evident that different coastal environments sets. give rise to different types of salients, forelands and tombolos, It has been shown that t.he development of these forms can Due to the irregular nature of the West Coast reefs and com not be directly attributable to the siz« of the offshore obstacle plex interaction of oceanographic processes, full classification or the distance of the obstacle offshore. This leads to the need and description of processes forming the forelands and tom for further investigation of the combined oceanographic pro bolos can only be undertaken following a wider examination cesses occurring leeward of the reef chains. Onshore geo of associated wave and current processes and sediment char chronologic work cornhined with an examination of nearshore acteristics. The locations of the landform types described currents. circulation. sediment distribution and type would above is shown in Figure 11. lead to a more complete understanding of the goomnrphic de velopment of these Holocene feature«. This is currently being Regional Variation conducted for landforms on t.ht- Central West and Ningaloo Coasts as part of an ongoing rosearch program. It is apparent from analysis of the aerial photographs that there is significant disparity between the landforms of t.he LITERATURE CITED South, Central Western and Ningaloo Coasts of Western Aus tralia. Most of the South Coast forelands and tomholos are ('OI.I.I~". L.B. 19S5. S"dinll'nh and hist orv of' t h« Rot t m-st Shelf. formed by the deposition of sediment resulting from the con southwe-st Austr.iliu: a swr-ll-dumin.uc-d. non-t rouicnl c.ubon.ue 1l1argin. Sedillli'nlrIlY (;('o/(),~y. ()O: li)-.t~) vergence of swell behind an obstacle. nearly always a granite DAI.I.Y. W.n. and P, >1'1': ••1. 19SIi. f)dllc!,,'d brrolurutcr» ji,r shor.- pro headland or island, whereas on the Central West and Nin tection. Technical ({qJOrt. ("I;lslal Engineering I{"";":llTh Cr-nt u-. galoo Coasts the submerged reefs provide an offshore barrier Wnterwavs Expc-rinu-nt Station. ('EI{('-Sfi-I. ti:2pp. to incoming swell waves which would normally transport sed DAVII';"..1.L. ]9S0. (;",,~mphicll! Vllr;ll!wlI III ('OIlS!Il! /)('l',,!op III I' II I. Longman. London, Second Edition, 212pp. iments onshore. The swell is then complexly diffracted and DEI'i\HTMI';NT OF LlJ.:FEN"E. 199:1. AIlHlm!;1l11 NIlI;OIlIl! Tide Table» refracted by the reefs and sediment is deposited in a less IYY..J: Au-uralui. I'a puo NI'II' (;11;111'11 and /vntantuo. Australian predictable manner. The distance of the reef offshore, the de Govn. Publi,.;hing Service. Cnnborr.r. pp :liiG. gree of continuity of the reefs. and the bathymetric variations E,,('(wl"II':IL F.F. ]~lG4. Trarcllinp [orclands a nd tlu- shoreline pro are the most prominent differences between the two regions, C"HH,'S assoc;al"d uith Ih"lII. Bulletin. US Br-ach Erosion Hoard, 9: 11-14. and these then lead to the different types and dimensions of GENTII.I.I ..I. r Ed : 1971. ('IiIllIlI"H ofAustral!« and N,,", Zrnlond. EI the forelands and tombolos forming behind them. Flushing of sevier. Amsterdam. the lagoonal waters behind the reefs either by longshore cur GIIJI.<'III·:li, A. 19!iS. ('oasla! 011.1 Submarim- iHIl/"ji!W!Ogv. Methuen rents or offshore movement of water through breaks in the and Co. Ltd., London. :274pp. GI'I.I.IVI<;I1. F.P. IS~)(). Cuspat« Fort-lands. !i1l!!"I;1I (;('()1. Soc. AIIII'r reefs appears to impede the formation of tombolos and pro ;('0, 7. vides an explanation for travelling versus stationary forms in GI'I.I.IVI':I<. F.I) IS99. Shorelim- Topography. 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