Seasonal and biennial fluctuation in subaerial beach sediment volume on Warilla Beach, New South Wales

Marine Geology, 48 (1982) 89--103 Elsevier Scientific Publishing Company, Amsterdam -- Printed in The Netherlands

89

SEASONAL AND BIENNIAL FLUCTUATION IN SUBAERIAL BEACH SEDIMENT VOLUME ON WARILLA BEACH, NEW SOUTH WALES

I.G. ELIOT and D.J. CLARKE

Geography Department, University of Western Australia, Nedlands, N.S. W. (Australia) Mathematics Department, University of Wollongong, WoUongong, W.A. (Australia) (Received April 14, 1981; revised and accepted November 11, 1981)

ABSTRACT Eliot, I.G. and Clarke, D.J., 1982. Seasonal and biennial fluctuations in subaerial beach sediment volume on Warilla Beach, New South Wales. Mar. Geol., 48: 89--103. The sediment budget for the subaerial beach at Warilla, New South Wales, has been monitored for 5 yrs by fortnightly surveys at 18 closely spaced beach profile stations. Long-term trends, annual and biennial cycles of sediment exchange, and aperiodic variations in sediment volume are identified from analyses of the resulting time series. The long-term trend accounts for approx. 13% of variation in the sediment budget over the 5 yrs of measurement; the annual and biennial components together account for approx. 70% of the total volume of sediment in active exchange between the subaerial beach and adjacent sand stores; and about 20% is estimated as aperiodic fluctuations associated with individual storm events. Phase differences in the periodic components show different patterns of beach response for the annual and biennial sediment transfers. These interact so that the locus of onshore--offshore sediment exchange shifts from the centre to the northern third of the beach in alternate years.

INTRODUCTION

Shoreline recession on the Central--South Coast of New South Wales is attributable to a long-term nett loss of sediment from the active zone of the coastal sand system (Thom, 1974; Davies, 1974; Gordon et al., 1978; Jones et al., 1979) and to infrequent, severe storm wave activity (Stockwell, 1969; Thom et al., 1973; McLean and Thom, 1975; Foster et al., 1975; Bryant and Kidd, 1975; Wright, 1976; Short, 1978, 1980). Storm wave effects are occasionally magnified by the simultaneous occurrence of high-water levels on the coast due to storm surge, changes in barometric pressure, and onset of spring tides (Bryant and Kidd, 1975; Foster et al., 1975; Gordon et al., 1978). Both the long-term trend and the short-term fluctuations are superimposed on shoreline oscillations occurring in response to seasonal (annual) shifts in mean sea level, such as those described by Radok (1976) and wave regime changes (Davies, 1957; McKenzie, 1958; Foster et al., 1963; Read, 1964; Langford-Smith, 1966; Short, 1967, 1980). Mathematical models describing beach change necessarily must account for all these factors. 0025-3227/82/0000-0000/$02.75 © 1982 Elsevier Scientific Publishing Company

90 A first step to the development of mathematical models involves detailed description of the temporal and spatial components of beach change. Temporal variation in the volume of sediment stored in the subaerial beach (above mean low-water level) on Warilla Beach, New South Wales, has been examined to identify long-term changes, periodic fluctuations associated with seasonal shifts in the mean sea level and wave regime changes, and irregular fluctuations caused by individual storm events. The strategy used follows that described by Sonu (1969), who argued that the dynamics of beach change may be best explained in terms of collective responses of sediments associated with sand bars migrating alongshore or in onshore--offshore directions. In this paper the term sediment flux is used to describe change in the subaerial beach sediment volume considered to be associated with bar migrations. The relative importance of any one of the factors affecting shoreline change on the embayed beaches of South Coast, New South Wales is not evident from the literature. Prior to studies reported by McLean and Thom (1975), descriptions of beach change have been restricted largely to shortterm studies. These describe individual storm events (Andrews, 1912, 1916; Stone and Foster, 1967), short-period, cyclic beach changes associated with the passage of weather systems (Short, 1967) or report beach profile studies with observations gathered infrequently over one or two years (McKenzie, 1958; Read, 1964; Baxter, 1969). Thom et al., (1973) note that short-term changes related to particular meteorological events often mask any tendency toward cyclic beach behaviour with a distinct seasonal rhythm. This is not a surprising conclusion because resolution of seasonal and long-term change cannot be achieved from such short records. Resolution of long-period cyclic changes, with periods of at least 12 months, and other long-term changes requires time-series analysis of data strings similar in length to the eight~year record reported by Thom and Bowman (1980). No such analysis has been reported from New South Wales. Thom and Bowman (1980), however, point out that apparent cyclic alternations between peak accretionary events have recurrence intervals of between 2 and 5 years on the subaerial section of a profile measured at Moruya. Their record shows short-term fluctuations, of less than 12 months duration and involving up to 100 m 2 of profile change, superimposed on long-term, 5-yr, oscillations involving approx. 250 m 2 of change. Proper interpretation of such data requires detailed analysis that is suited to the sampling frequency of the data collection. It also needs to be considered in the context of the complex, three-dimensional bar-trough beach and inshore zone topography that affects subaerial beach change on this part of the NSW Coast. Their observations underscore the urgent need for time series analyses of beach change data from New South Wales, similar to that recently reported from elsewhere by Dolan et al. (1979a, 1979b), Hayden et al. (1979), Winant et al. (1975) and Aubrey (1979), if beach processes are to be satisfactorily modelled.

91 REGIONAL SETTING

Seasonal and biennial fluctuations in the volume of sediment in the subaerial beach store on Warilla Beach, New South Wales, have been identified from a large-scale study of beachface geomorphology. Warilla Beach is a 2 km long, quartzose, sandy beach tied between headlands at Barrack Point and Windang Island (Fig.l). Within these limits the beach is aligned NNE-SSW, open to the prevailing SE swell, and is gently arcuate in plan form. The nearshore sediments of the bay are contained by extensive submarine bedrock outcrops skirting Windang Island and Barrack Point. The outcrops extend seawards for at least t w o kilometres before passing under shelf plain relict sands. Smaller localised bedrock outcrops occur within the bay and along the central and northern section of the nearshore zone. Between the headland outcrops the bay bathymetry is simple. The bathymetric contours are parallel to the shore so that the sea bed shelves gently to the 20-m isobath. Channels are adjacent to the headland outcrops and there is a very slight rise in the bay centre (Fig.2).

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Fig.1. WariUa Beach: regional setting.

Ex,'shng

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Urban Areas

0

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Fig.2. Warilla Beach bathymetry. (Compiled by A.W. Stephens, 1978.)

The beach was backed b y a large, continuous frontal dune prior to destruction of the dune vegetation in the 1930s and extensive sand mining on the northern part of the beach during the 1940s. Little now remains of the original dune morphology. On the southern half of the beach the dune crests have been levelled for housing subdivision and the sand cliff behind the beach is fixed b y a rockwall. Immediately north of the rockwall the dunes have been mined, replaced with landfill, and generally degraded. On the northern extremity o f the beach, incipient foredunes cover the old sand mining road and are intermittently established on a t o m b o l o linking Windang Island to the mainland. Sands constituting these dunes are derived from the active beach environment. Inshore and foreshore beach morphology at Warilla is closely linked with the nearshore water circulation pattern, particularly with the presence of rip currents. The beach exhibits the full range of morphologic states described for other New South Wales beaches by Wright et al. (1979). It changes from

93

a low-wave-energy, reflective beach state with a simple inshore morphology, through transitional sequences incorporating transverse bars and rip channels, to a high-energy dissipative system with longshore bars as the wave regime varies. Transitional states incorporating complex arrangements of transverse and longshore bar patterns are c o m m o n on the northern end of the beach; while broad, terrace shoals occur more frequently on the southern, rockwall section of the beach. The wave climate of Warilla Beach is similar to t h a t for other parts of the Central--South Coast of NSW as described by Thom et al. (1973), Lawson and Abernethy (1975) and Wright {1976}. The wave climate is dominated by a highly variable wind-wave climate superimposed on persistent highenergy, south to south easterly swell. Lawson and Abernethy (1975) analysed Wave Rider buoy information for deep-water waves off Botany Bay. Their results are generally applicable to the Illawarra Coast because of its proximity to Botany Bay (Warilla is approx. 65 km south of Botany Bay) and because the two locations share c o m m o n wave sources. They report a median wave height of 1.45 m. Wave heights of 0.3 m were exceeded 99.9% of the time, and 3.0 m for 5% of the time. These values may be compared with hindcast wave statistics for Shellharbour reported by Stone and Foster (1967) and the Public Works Department of NSW (1970}. The largest waves are generated by mid-latitude cyclonic storms which direct S-SE storm waves towards the coast while calmer conditions prevail under offshore winds associated with anticyclonic weather systems. The former occur most c o m m o n l y during May to July and the latter during October to November. The late summer m o n t h s are characterised by a more variable wind pattern in which NE winds prevail (Gentilli, 1971}. The wave climate is superimposed on low-frequency sea level shifts including tidal fluctuation, storm surge and shelf wave activity. Tides are semidiurnal and vary in range from neaps of 0.3 m to springs of 1.9 m. Variation in tidal range may be masked by combinations of storm surge and shelf wave activity. Foster et al. (1975) report water-level rises due to storm surge of as much as 10 to 20% of the incident wave height. This implies a water level variation of up to 60 cm! Similar set-up of water level, up to 30 cm in amplitude, may also be produced by shelf waves. Such waves are prevalent during periods of strong SE wind conditions (Clarke, 1974) and therefore may be coincident with storm surge effects. OBSERVATION AND ANALYSIS

Variation in the subaerial sediment store on Warilla Beach has been monitored over five years since July 1975 by fortnightly beach surveys. Eighteen profiles, spaced at 100-m intervals along the beach (Fig.3), were surveyed by measuring the elevation of slope breaks, together with their distances from fixed bench marks. Sand surface elevations were surveyed at 10-m intervals where slope breaks were difficult to discern or widely spaced. The surveys extended seawards to approx. 1.5 m below Australian Height Datum.

94

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ROCKWALL PROFILE LOCATION ISO BAT HS METRES

IN

Fig.3. Beach profile locations.

The volume of the subaerial sand store at each profile station was calculated as the cross-sectional area of the profile seaward of the bench mark and above A.H.D. zero for one metre wide strips. The volume of the sand store for the beach was obtained by integrating the eighteen profile cross sections along the beach for each survey. Sediment volumes obtained over the five years constitute time series for individual profile stations and for the beach. The time series for the beach is shown in Fig.4. The steps used in decomposition o f each of the time series are as follows:

95

%

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~ 24 N 22 k)

2(3 1975

1976

1977

1978 I

IOO

150

' 200

4&

9oo

,ooo

I

,,oo

I

,200

Days

Fig.4. Subaerial b e a c h s e d i m e n t v o l u m e : c u m u l a t i v e v o l u m e f o r 18 profiles p e r day.

(1) The long-term trend, measured over five years, is calculated separately for each profile and for the beach as a whole from the original volumetric data by linear regression techniques. The difference between the measured trend and a state of zero nett change is tested for significance in each instance. (2) The original volumetric data for each time series is then smoothed by applying a mathematical filter. This operation yields t w o sets of information: (a) a set of filtered data thought to correspond to high-frequency fluctuations induced b y storm-wave and rip-current activity; and (b) a smoothed curve, being the difference between the original data and the filtered data. This information corresponds to the sum of all cyclic fluctuations with frequencies between three months and two years. (3) The s m o o t h e d curves are then d e c o m p o s e d into sinusoidal wave components and the phases and amplitudes of the dominant cyclic c o m p o n e n t s identified. The amplitude of each c o m p o n e n t is then expressed as a percent° age of the deviation from the mean volume for the time series. (4) Fourier reconstitution of the smoothed data has been undertaken in s o m e instances to test the strength of the analytic techniques employed. The close fit between the reconstituted curves and the smoothed curves justifies the techniques used at this stage. The sequence of analysis and data reconstitution is illustrated for profile 18 in Fig.5. The procedure e m p l o y e d is as applicable to subsections of the shoreface profile as it is to the profile as a whole. The results of the primary analysis reported here describe variation in the subaerial beach sediment store, particularly the sediment volume above mean sea level. Interpretation relies on the assumption that changes on the subaerial beach profile are associated with changes lower on the shoreface. The classic model o f switching from berm to bar t y p e profiles with rising wave conditions, as described by CERC (1975), is held to be applicable in this instance. Following the observations of Short (1980) and Thom and Bowman (1980), we assume that losses on

96

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Fig.5. Data analysis sequence and fourier reconstruction.

i 1200

97

the subaerial beach are approximately balanced by gains lower on the shoreface where cyclic sediment patterns, such as those observed on Warilla Beach, are involved. Imbalances do occur where sediment is lost from the subaerial beach through dune building or exchange with adjacent beach systems. We assume t h a t these losses are apparent in the nett balance for the sediment budget although t h e y are n o t separately measured. DISCUSSION AND CONCLUSIONS

Time series for individual profile stations and for the beach as a whole are decomposed into a five-year trend, periodic oscillations, and aperiodic fluctuations. The contribution of each c o m p o n e n t to the sediment budget has been determined by expressing its amplitude as a proportion of the total deviation from the mean sediment volume for each time series. The results are listed in Table I. Percentages listed are n o t directly additive because the statistical treatments used to n o t apportion variance. Several periodic oscillations have been identified from the data, including oscillations with periods of 4, 6, 8, 12 and 24 months. Periodic beach responses vary markedly along the beach with no two portions of beach responding the same way. Strong annual and biennial cycles account for up to 46% of the variation in subaerial beach sediment volume at individual profile stations. For the whole beach, the biennial c o m p o n e n t has an amplitude of 18,500 m 3 and accounts for about 40% of the beach sediment budget; the annual c o m p o n e n t an amplitude of 15,800 m 3 or 30% of the budget, 13% is due to the long-term trend over the 5 years; and about 20% is estimated as aperiodic fluctuations mainly related to changes in the wave regime. Together, the seasonal and biennial components account for approx. 70% of the total volume of sediment in active exchange between the subaerial beach and adjacent sand stores (Table II). Strong seasonal oscillations, those with > 25% of the total annual sedim e n t flux, were observed at the beach ends and in the centre of the beach near the end of the rockwall. Peak ranges in the seasonal c o m p o n e n t were registered for profiles 1, 9, 10, 17 and 18, with the highest values being from the northern end of the rockwall (profile 10: 46% of the total sediment flux) and from the northern end of the beach (profile 18: 39% of the total sediment flux). The alongshore distribution of peak seasonal fluctuations in sediment volume accords with expectations of beachfront aggradation, or erosion, associated with seasonal switches in the d o m i n a n t wave incident direction as reported by Stone and Foster (1967) and Thom et al. (1973). The beach responds as a complete unit and as discrete rockwall and open sandy beach units. Strong biennial oscillations, those ~>30% of the total sediment flux, were measured from profiles 3, 7, 12 and 15, and are highest on profile 15. An appreciation of the amplitude and phase of biennial change is important to an understanding of shoreline change on Warilla Beach. However, the five year record is n o t sufficiently long to enable confident description of the

98 TABLE I C o m p o n e n t s o f t h e subaerial b e a c h s e d i m e n t b u d g e t for individual profile s t a t i o n s a n d t h e w h o l e b e a c h at Warilla, NSW, F r o m J u l y , 1 9 7 5 t o May, 1 9 8 0

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 1--18

11800 5400 4600 4100 4100 3900 4700 4700 2900 5500 9800 10000 12800 13300 13300 17500 14700 10500

362 619 447 317 297 87 190 195 --87 --52 --1113 --788 118 --74 --5 --583 --318 --937

15 56 47 38 35 11 20 20 15 5 56 38 4 3 0 16 11 43

1449 543 534 416 345 292 474 650 496 1261 969 486 1251 1392 1745 2460 2481 2048

25 20 23 20 17 15 20 28 34 46 20 10 20 21 27 28 34 39

577 844 732 547 458 464 713 257 156 513 1042 1615 1433 1675 2282 2799 1884 1274

10 31 32 27 22 24 30 11 11 19 21 32 22 25 34 32 26 24

101100

--2612

13

15820

31

18455

37

V o l u m e s for p e r i o d i c c o m p o n e n t s are listed for t h e a m p l i t u d e s o f e a c h c o m p o n e n t . Perc e n t a g e s are c a l c u l a t e d f r o m t h e r a n g e (2 X a m p l i t u d e ) o f t h e c o m p o n e n t .

biennial component. Further surveying is necessary to confirm its full effect along the beach. The results reported here consequently provide propositions for closer scrutiny as more data become available and as the study proceeds. The annual sediment exchange generally accords with observations of beach change associated with seasonal variation in wave climate reported for Sydney beaches by Short and Wright (1981). However, the biennial sediment exchange is not simply explicable as a result of wave regime changes. Other oceanographic processes evidently play a role of equal importance, at least, to that of the regional wave climate. Several causal phenomena are being investigated including ocean--atmosphere interactions associated with the Walker Circulation or Southern Oscillation described by Pittock (1978); with biennial mean sea-level oscillations; and complex interactions between large-scale embayment circulations, such as those associated with storm-ripcurrent systems and their associated foreshore beach response.

99

TABLE II Components of the subaerial beach sediment budget for groups of profiles having similar temporal variation in sediment volume. Warilla Beach July, 1975 to May, 1980

1--2 3--5 6--9 10--12 13--15 16 17--18

13700 11500 13400 22600 34400 17500 24100

912 1079 428 --2298 260 --586 --1250

32 46 16 50 4 16 25

1950 1260 1814 2379 4245 2460 4635

28 22 27 21 25 28 38

1141 1763 1523 2942 5576 2799 3401

17 31 23 26 32 32 28

1-8

101100

--2612

13

15820

31

18455

37

Peak sediment volumes are recorded during October--December and the beach is in its most depleted state during May--July (Table III). This is consistent with what reasonably might be expected from seasonal variation in the wave climate when sediment is moved onshore or offshore. During this seasonal exchange some sediment is also shunted from one end of the beach to the other as the dominant direction of wave incidence varies. The alongshore transfer is n o t simple. The pattern of sediment flux is further complicated by other onshore and offshore movements of sediment in response to changes in wave power; by interaction with other periodic fluctuations; and by rip current activity. The contribution of each of these processes requires more detailed examination. The pattern of sediment m o v e m e n t within the subaerial beach sand store is controlled by interaction between the seasonal and biennial patterns of sediment exchange. In the seasonal cycle peak sediment volumes are recorded between profiles 6 and 12 during November (Fig.6). Sediment is then spread north and south from the central area so that the beach ends register peak volumes during January. The erosion phase, similarly begins earliest in the central section of the beach. Minimum sediment volumes are recorded on profiles 6 to 12 during May, while the beach ends hold sediment until July. The biennial sediment exchange pattern contrasts with the seasonal pattern. It is largely determined by sediment exchanges centred on the open beach, between profiles 13 to 16, and is most marked on profile 16 (Fig.6). Maximum and minimum sediment volumes are alternatively registered during July and August in successive years. During each phase sediment accumulates or erodes first on the open beach and is then transferred to, or drawn from,

100 TABLE III Phases of seasonal Beach, July, 1975

a n d b i e n n i a l c o m p o n e n t s o f b e a c h s e d i m e n t v o l u m e c h a n g e f o r Warilla to May, 1980 Seasonal c o m p o n e n t

Biennial c o m p o n e n t

Profiles

Phase

Peak m o n t h

Phase

Peak m o n t h (odd years)

1--2 3--5 6--9 10--12 13--15 16 17--18

175 ° 179 ° 120 ° 121 ° 162 ° 161 ° 180 °

January January November November December/January December/January January

33 ° 61 ° 48 ° 31 ° 120 7° 15 °

September November October September August July/August August

1--18

157 °

December

31 °

September

the southern rockwall section of the beach. Maximum and minimum volumes are registered on the southern end of the beach during November. Interaction between the seasonal and biennial cycles produces an asymmetric pattern of shoreline change. The biennial cycle alternatively reinforces deposition and erosion in successive years (Fig.6). During the depositional phase of the biennial cycle, sediment accumulation may approximately balance erosion associated with the seasonal cycle on the open beach. This is most pronounced near profile 16 during June through to August. Later in the year, peak depositional events for both cycles approximately coincide on profiles 6--9. At this time, from October to November, the beach is in its most fully accreted condition. During the following year, when the biennial cycle is in an erosional phase, erosional events for the seasonal and biennial cycles are coincident on profile 16 between June and August. The subaerial beach sediment store is in its most depleted condition at this time. The pattern of nett change over the five year survey period and dislocation of the zones of peak seasonal and biennial sediment flux indicate that the locus of onshore--offshore sediment exchange shifts from the centre to the northern third of the beach in alternate years. At this stage of the study, it is not possible to determine whether this pattern of shoreline change is typical of other NSW South Coast beaches with similar topography, or linked with the geometry of the Warilla embayment, or is a localised response to rockwall construction. Information describing beach changes prior to construction of the rockwall are lacking and comparative studies need to be undertaken to isolate regional effects from more localised beach responses. The methods of data analysis reported here provide an invaluable tool for a comparative study.

101

YEAR TWO

YEAR ONE PROFILE JANUARY

JULY

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~2

IN WHICH PEAK OR MINIMUM SEDIMENT VOLUME [ REGISTERED

JULY

Erosion

DEPOSITION

t

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}

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Erosion

I

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PROFILE GROUPS WITH SIMILAR PATTERNS OF TEMPORAL /~RIATION IN THE SUBAERIAL ACH SEDIMENT VOLUME.

Fig.6. Patterns of erosion and deposition for the combined seasonal and biennial cycles of sediment exchange.

102 ACKNOWLEDGEMENTS Financial s u p p o r t has been p r o v i d e d b y the University o f W o l l o n g o n g , the C o u n c i l o f t h e M u n i c i p a l i t y o f S h e l l h a r b o u r , the D e p a r t m e n t o f Public Works, NSW, a n d the U n i v e r s i t y o f Western Australia. M a n y p e o p l e f r o m t h o s e f o u r i n s t i t u t i o n s have p r o v i d e d invaluable assistance. We are grateful f o r their s u p p o r t a n d c o - o p e r a t i o n . In particular, we t h a n k E. Lee, P.J. DeanJ o n e s , J.A. L a n y o n and L. Metcalfe f o r assistance w i t h surveying a n d d a t a r e d u c t i o n . P. K e n d r i c k o f t h e C o u n c i l o f the Municipality o f S h e l l h a r b o u r has c o n d u c t e d t h e surveys over the last 12 m o n t h s . This i n f o r m a t i o n has p r o v e n invaluable t o t h e s t u d y . We also t h a n k A n n e R a y n o r and Michelle L e y for the cartographic work. REFERENCES Andrews, E.C., 1912. Beach formations at Botany Bay, J. Proc. R. Soc. NSW, 46: 158-185. Andrews, E.C., 1916. Shoreline studies at Botany Bay. J. Proc. R. Soc. NSW, 50: 165-176. Aubrey, D.G., 1979. Seasonal patterns of onshore--offshore sediment movement. J. Geophys. Res., 84: 6347--6354. Baxter, L.S., 1969. Kiama Downs Beach: a Morphological Appraisal. Thesis, Dept. of Geogr., University of Sydney, NSW (unpubl.). Bryant, E.A. and Kidd, R.W., 1975. Beach erosion, May--June, 1974, Central and South Coast, NSW. Search, 6: 510--513. Clarke, D.J., 1974. The oscillations of Port Kembla harbour. Dock Harbour Auth., 54: 383--384. Coastal Engineering Research Centre, 1975. Shore Protection Manual. U.S. Army, Corps of Engineers, U.S. Govt. Printing Office, Washington, D.C. Davies, J.L., 1957. The importance of cut and fill in the development of sand beach ridges. Aust. J. Sci., 20(4): 105--111. Davies, J.L., 1974. The coastal sediment compartment. Aust. Geogr. Stud., 12: 139-151. Dolan, R., Hayden, B. and Felder, W., 1979a. Shoreline periodicities and edge waves: J. Geol., 87: 175--185. Dolan, R., Hayden, B. and Felder, W., 1979b. Shoreline periodicities and linear offshore shoals. J. Geol., 87: 393--402. Foster, D.N., Stone, D.M. and Munro, C.H., 1963. Preliminary study of Beach Erosion on Cronulla Beach. Univ. N.S.W., Water Res. Lab., Techn. Rept., 65, 130 pp. Foster, D.N., Gordon, A.D. and Lawson, N.V., 1975. The storms of May--June, 1974, Sydney, N.S.W., Proc. 2nd Aust. Conf., Coastal and Ocean Eng., Gold Coast, Qld., Inst. Eng., Aust., Nat. Conf. Publ., 75/2: 1--11. Gentilli, J., 1971. Climates of Australia and New Zealand. Elsevier, Amsterdam, 405 pp. Gordon, A.D., Lord, D.B. and Nolan, M.W., 1978. Byron Bay--Hastings Point Erosion Study, P.W.D., NSW Coastal Eng. Branch, Rept. P.W.D. 78026, 227 pp. Hayden, B., Dolan, R. and Felder, W., 1979. Spatial and temporal analysis of shoreline variations. Coastal Eng., 2: 351--361. Jones, B.G., Young, R.W. and Eliot, I.G., 1979. Stratigraphy and chronology of receding barrier-beach deposits on the northern l]lawarra Coast of New South Wales. J. Geol. Soc. Aust., 26: 255--264. Langford-Smith, T., 1966. On teaching coastal geography. In: G.H. Dury (Editor), Aspects of the Content of Geography in Fifth and Sixth Forms. Dept. Geogr., Univ. Sydney, PP. 5A--5A18.

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