coastal erosion on sydney’s southern beaches study report · beaches form and change due to...

Coastal Erosion onSydney’s southern beaches

Study Report

at the Water Research Laboratory of the

University of New South Wales, Sydney, Australia

in association with theBergische Universität Wuppertal

Univ.-Prof. Dr.-Ing. H. Kaldenhoff

by cand.-Ing. Marcus Dätig

Sydney, January 2001

Contents

1 Introduction 1

2 Beaches in the coastal zone 2

3 The Beach System 5

4 Coastal erosion and beach processes 6

5 Human Response to Natural Coastal Hazards 9

5.1 The Establishment of Buffer Zones . . . . . . . . . . . . . . . . . . . . . . . . 9

5.2 Beach Protection Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

5.2.1 Seawalls . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

5.2.2 Groynes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

5.3 Sand Nourishment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

5.4 Dune Stabilization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

6 Three Southern Beaches of Sydney 13

6.1 Clovelly Beach . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

6.2 Coogee Beach . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

6.3 Maroubra Beach . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

7 The Coastline Hazards of these beaches 20

7.1 Clovelly Bay . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20

7.1.1 Zone 1: hazard level: minor to moderate . . . . . . . . . . . . . . . . . 20

7.1.2 Zone 2: hazard level: minor to serious . . . . . . . . . . . . . . . . . . 20

7.1.3 Zone 3: hazard level: minor . . . . . . . . . . . . . . . . . . . . . . . 21

7.1.4 Zone 4: hazard level: minor to serious . . . . . . . . . . . . . . . . . . 22

7.1.5 Zone 5: hazard level: low . . . . . . . . . . . . . . . . . . . . . . . . 22

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CONTENTS ii

7.2 Coogee Bay . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23


7.2.2 Zone 2: hazard level: serious . . . . . . . . . . . . . . . . . . . . . . . 24


7.2.4 Zone 4: hazard level: moderate to serious . . . . . . . . . . . . . . . . 25

7.3 Maroubra Bay . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26

7.3.1 Zone 1: hazard level: moderate . . . . . . . . . . . . . . . . . . . . . 26

7.3.2 Zone 2: hazard level: serious . . . . . . . . . . . . . . . . . . . . . . . 27

7.3.3 Zone 3: hazard level: moderate to serious . . . . . . . . . . . . . . . . 28



7.4 Final Statement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29

Bibliography 31

List of Figures

2.1 Coastal Environment and processes . . . . . . . . . . . . . . . . . . . . . . . 2

2.2 Sediment gain and Sediment loss . . . . . . . . . . . . . . . . . . . . . . . . . 3

3.1 The Beach system . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

4.1 Generation and Propagation of a wave . . . . . . . . . . . . . . . . . . . . . . 6

4.2 Swell and Storm Profile . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

5.1 Description of a Buffer Zone . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

6.1 Location of the southern beaches . . . . . . . . . . . . . . . . . . . . . . . . . 13

6.2 Coogee beach subdivided in different areas . . . . . . . . . . . . . . . . . . . 16

6.3 Maroubra Beach, part of the ’Plan of Management’ . . . . . . . . . . . . . . . 19

7.1 Zones of the Clovelly Bay . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

7.2 Clovelly Bay . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22

7.3 Clovelly Beach . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23

7.4 Zones of the Coogee Bay . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24

7.5 Coogee Beach, view from the south . . . . . . . . . . . . . . . . . . . . . . . 25

7.6 Coogee Bay, view from the north . . . . . . . . . . . . . . . . . . . . . . . . . 26

7.7 Zones of the Maroubra Beach . . . . . . . . . . . . . . . . . . . . . . . . . . . 27

7.8 Maroubra Beach . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28

7.9 Maroubra coast . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29

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1 Introduction

This report about the 3 southern beaches of Sydney starts by giving a brief introduction aboutthe coast of New South Wales. The state of NSW is located in the southeast of Australia andis one of the oldest and most populated states in Australia. Consisting of an area of 801.506square kilometres, which can be regarded as only 10 % of the whole continent, approximately30% of the Australian inhabitants live there.

The New South Wales coast extends from Tweed Heads in the north to Cape Howe in the south,a distance of 1590 km. Sixty percent of the coast, or 975 km consists of 721 sandy beaches. Theother 615 km can mostly be described as rocky coast. The beaches range from long sweepingbeaches on the north coast, up to 26 km in length, to small often deeply embayed beaches, manyonly a few meters in lengths. The coastal region of Sydney north for example with a length of45 km has got 20 sandy beaches with an average length of 625m, compared to the coastal regionsouth of Sydney, being 46 km long, but showing just an average length of 359m within 19 sandybeaches (1).

Coastal Protection and coastal management being neglected in the early years of our century,by the 1960s it was becoming evident that coastal erosion and its effects are a serious problem.Private homes, commercial buildings, public facilities and even roads were all endangered.The New South Wales government initiated an investigation in which a study had been madeabout the coastal processes regarding the coastal recession. This study revealed average rates ofcoastal recession of 0.5 to 1.0 meter a year, an amount of the coast to be lost in the ocean, whichis quite threatening. This study has been one of several reasons why the New South Walesgovernment introduced the Beach Improvement Programme in 1975 to assist local authoritiesin restoring and improving the recreational amenity of the state’s beaches. This program wasbased upon technical work carried out by the Public Work Department (nowadays changed tothe Department of Land and Water Conservation) and was used also as a means for increasingpublic awareness of coastal problems (2).

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2 Beaches in the coastal zone

The coastal zone includes the underlying geology, the coastal hinterland, the inner continentalshelf and the coastline including all coastal bays and beaches. The coastal environment isthe most dynamic part of the earth surfaces. It contains elements of all spheres that make upearth namely the atmosphere, the hydrosphere, or ocean, the lithosphere, or geology and thebiosphere. As the 4 spheres interact, (see figure 2.1) at the coast they produce a wide spectrumof coastal systems ranging from muddy tidal flats to rocky headlands to sandy beaches (2).

Figure 2.1: Coastal Environment and processes (1)

The atmosphere contributes the regional climate, the winds, rain and temperature and indirectlythe ocean temperature. The hydrosphere determines sea level and due to this also the positionof the shoreline, as well as contributing the major energy sources waves, tides and currents.Finally the biosphere includes the flora and fauna that inhabit either permanently, or in transitthe coastal zone and contribute shell, coral and algal fragments that help to build the beaches.As this report will describe three of the sandy beaches of the southern beaches of Sydney, it firstof all will show some facts about sandy beaches in general.

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They consist of lithospheric elements namely sand lying ultimately on bedrock geology whichis permanently been influenced by the interacting spheres mentioned above. Beaches form andchange due to several processes that interact at the coast to produce beach systems. Two ofthose are to be regarded as climate and atmospheric processes. Climate interacting with thegeology together with the physical forces of the rain let the part of the land surface runoff aswell as rivers erode and transport sediment to the coast (2).

Figure 2.2: Sediment gain and Sediment loss (9)

At the coast it is also climate, particularly winds that interact with the ocean to generate wavesand currents that are as already mentioned essential to build this sediment into beaches anddunes.

Particularly on the coast of New South Wales the beaches are predominantly composed of quartzsand grains together with other rock fragments. These sediments originated in the coastal hin-terland. Over many millennia they have been delivered by rivers and streams, to the coast andcontinental shelf, and subsequently moved by waves on- or along-shore to be finally depositedas beaches and dunes (1).

The regional geology therefore acts as a source for most of the sand on NSW beaches, theremainder being derived from shell and algal fragments. The rocks of the NSW coast that formthe headlands and cliffs range in age from 500 million to 60 million years. As the coast is only60 million years old, most of the rocks predate the coastline by many million years (1).

Age of NSW coastal features:

• Rocks: from 500 million years old

• Beaches: from 12.000 years old

• Most beaches: less then 6.500 years old

The rock of the cliffs in the area that is going to be described in this report is known as theHawkesbury Sandstone. It was laid down as sediment in a large river delta, which stretched


from north of the Hawkesbury River south almost to Nowra and west to lower Blue Mountains.This Sandstone was forming about 200 million years ago. The rock is made up mainly of sandand quartz in layers which vary according to what else the rivers brought down at different timesand the way they were flowing. There is also an occasional band of shale, composed of moremuddy material. Unlike the rock itself, the cliffs are very young regarding the geological timedimensions. During the last ice age the shoreline was about 12 km east, across the coastal plain.As the ice melted around the globe, sea level rose across the plain to plateaux of sandstone alongthe present shoreline. By the time it stopped rising about 6.000 years ago, the sea had floodedinto a series of river valleys cut into this sandstone, creating bays and harbours along the newcoast (1).

3 The Beach System

Different types of beaches show different types of profiles, depending on the influence of thelittoral zone. The figure below illustrates a typical NSW beach system

Figure 3.1: The Beach system (2)

On the left hand side of figure 3.1 you can see the subaerial beach which is a dry zone above theshoreline, only influenced by the sea through storm waves, or when there are high tides beingexceptionally high. The sediment on the subaerial beach becomes dry quickly and createsa series of coastal sand dunes with the help of wind, presupposing the coastline is nearly flat.Within the surf zone, containing bars troughs and breaking waves, some parts are exposed at lowwater when the tide is out and covered when the tide is in. The nearshore zone is permanentlycovered by water and extends seaward of the breakerzone out to the modal wave base. Thewave base describes the point, regarding the figure shown above is approximately 20 m depthon the NSW coast, to which ocean waves can move beach sands. Seaward from the wave baselies the inner continental shelf with no explicit influence on the beach system (1).

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4 Coastal erosion and beach processes

Coastal erosion is the result of a complex interaction of physical processes. Depending on thecircumstances, the water motions of waves, tides, storm surge, and nearshore currents com-bine and interact with the coastal land, which in turn has considerable inherent variability. Theprimary agent in coastal erosion, the waves, generate nearshore currents, which in turn trans-port the beach sediments, a movement which results in a rearrangement of the shoreline withpossible sites of erosion. Waves, who are, as in most cases, generated by winds blowing overthe water surface, are important as energy-transfer agents. They first obtain their energy fromwinds, transfer it across the expanses of the oceans and then deliver it to the coastal zone whereit can be the primary cause of erosion or can generate a variety of nearshore currents and sandtransport patterns (3). The generation of the waves is primarily dependent upon three stormfactors. First of all the speed of the wind, second the duration of the storm and last but not leastthe fetch area over which the storm occurs (see figure 4.1). The duration is important in that thelonger the winds have been blowing, the greater the amount of energy that can be transferred tothe growing waves. The fetch area has a similar effect, once the waves travel out of the stormarea, they no longer acquire additional energy. That means, the larger the fetch area, the moreenergy the waves can potentially obtain.

Figure 4.1: Generation and Propagation of a wave

By a process called wave dispersion, the highest-period waves in the spectrum where the stormtakes place, means the fetching area, move out rapidly and would be the first to arrive and bemeasured at some distant coastal site. In other words, you can say, that the complex sea inthe storm area is progressively transformed into regular swell waves as you can also see in the"Propagation period" of figure 4.1. These swell waves are known to travel over the expanseof the oceans with relatively little loss of energy. Important to the coastal erosion, the energythe waves have obtained from winds is thereby efficiently carried to the nearshore zone where

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it expended over a relatively narrow area. Reaching from the offshore to the nearshore zonethe wave crests become narrower and peaked, the troughs becoming wide and flat (3). Dueto a decrease in the wave length and an increase in the wave height, eventually the wavesoversteepen, become unstable and break, generally either by plunging or spilling. The nature oftheir breaking depends on their initial steepness and on the slope of the beach. By breaking onthe shore, the ’wave swash’ pushes sediment up to the beach face, which is dragged back due tothe ’backwash’. Because of the water percolating into the surface, the backwash can’t take asmuch water back as the swash brought up to the beach face. Therefore the onshore movementof sediment is higher than the backshore movement, until the slope reaches a state of dynamicequilibrium. Having reached this state, the same amount of sediment is moved landwards as isreturned seawards. The amount of the percolating water depends primarily on the size of thegrain. Hence the size of the grain influences the time it takes to reach the state of the dynamicequilibrium. Usually you can say, the coarser the sediment grain size, the steeper the overallbeach-slope. On steep, coarse-sand to cobble beaches the waves normally break directly at thebase of the beach face and swash up the slope, a surf zone with a bar being almost completelyabsent. The beach profile also depends on the wave energy level. Steep-wave conditions tendto shift sand offshore, eroding it from the beach berm and depositing it into bars in the regionof the breaker zone. The swash of a steep wave breaking onto the beach does not move farup the beach. Consequently, less energy is lost in transporting the sediment up to the beach,as well as less percolation of the water into the sand can take place. Therefore sediment canbe moved seawards. The sand removed from the beach is normally deposited offshore, to beslowly returned to the beach during periods of calm weather and constructive waves. If an areais affected by several storm surges during a season, then the beach may not have enough timeto recover, and erosion of the beach is cumulative (2).

The different wave energy level that may occur on the coast, depend on the time of the year.Wave heights tend to be larger during the storms periods, producing a change in the beachprofile, in so far that the sediment is removed from the beach face and transported seawards tobuild the longshore bar (see figure 4.2. During the periods with predominantly swell waves thesediment of the bar is moved back landwards to reconstruct the beach berms. But neverthelesssuch changes between the so called swell and storm profile, are important to coastal erosion,because the loss of the berm in the storm period profile permits the wave swash to more directlyattack the coastal property.

Figure 4.2: Swell and Storm Profile


Another aspect concerning coastal erosion has to be mentioned as the storm surge. It is causedby meteorological factors such as strong winds and abrupt atmospheric pressure reduction lead-ing to a significant change in the water level.

The rise in water level mostly is rather abrupt, induced by strong onshore winds and low atmo-spheric pressures accompanying a cyclone. In addition to generating large surface waves, thewinds of the cyclone can push water toward the coast, holding it there as a set-up of the meanwater level. The exceptionally low pressures of the storm system also contribute to increase thewater level. (Water is going to rise 0.1 meter for every 10 millibars the central pressure is belowthe surrounding air pressure.)

The storm surge may raise the water levels by several meters above the highest tides normalfor the coastal zone, even covering areas generally not affected by wave attack. Considerabledestruction results from the large waves superimposed on the exceptionally high levels sinceshoreline structures are now in the surf zone. Coastal erosion propagates. Additional to theaspect described above the continuous increase in the water level due to the greenhouse effectcontributes to the coastal erosion in a slowly but significant way. Nevertheless the coastlineof New South Wales is attacked by severe storms originating over the Tasman Sea. Thesestorms are capable of causing rapid erosion along the south- eastern coastline. The low pressuresystems from Tasman sometimes generate secondary lows, which intensify the storm systems.Under these conditions gale force winds, with a minimum wind speed of 50 kilometres an hour,are generated. In may 1974 for example a secondary low developed off the New South Walescoast, creating winds of over 140 kilometres an hour between North Sydney and Newcastle.This storm caused severe erosion, especially of Newcastle’s beaches (1).

5 Human Response to Natural Coastal Hazards

The most pressing problems associated with these natural hazards are the destruction of nature,property and the risk to life. These are usually the results of the accelerated erosion of the coast-line that occurs during intense storm periods. Attempts that have been made to find solutions tothese problems are the following:

5.1 The Establishment of Buffer Zones

A study of the processes responsible for the shaping beaches and the impacts of storms alongthe coastline demonstrates the need to accommodate the fluctuations in beach width when de-veloping sites in the beach zone. This can be done by creating buffer zones. The width of theland needed to accommodate natural beach movements is the buffer zone. The establishmentof buffer zones acknowledges that beaches fluctuate in extent as a result of the ’cut and fill’processes that accompany certain weather conditions. Buffer zones mean that erosion can oc-cur without damaging property. These zones are effective methods of reducing storm damage,for not only are developments outside the areas subject to erosion, but also the natural reservoirof sand, the dunes are not isolated from the beach zone, and during calmer conditions the beachcan be replenished naturally (2). In Figure 5.1, a description of a ’Buffer Zone’ is shown.

5.2 Beach Protection Systems

5.2.1 Seawalls

These are walls constructed from boulders and, or other structural devices along the beach, nor-mally fairly close to the surf zone. These walls are necessary in areas where development hastaken place close to the beach zone and so property is threatened whenever the beach is attackedby storm waves. The disadvantage to be mentioned concerning seawalls is, that the sand be-hind the seawalls, in many cases a dune system is removed from the active beach system, thuslimiting the amount of sand available for renourishing the beach. The limited sand supply maybe quickly lost to the beach system and the level of beach reduced, so after storms, the beachcannot rebuilt and it may remain below water level. It may also alter nearshore topography andso the wave conditions (2).

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5.2.2 Groynes

Groynes are rock walls or other structures built out into the ocean. They are designed to alterthe natural longshore movement of sand by acting as dams for sand. As sand is moved sidewaysby the longshore transport system, the groyne intercepts it. The sand is trapped on the updriftside, and the size of the beach is increased on this side of the groyne. The downdrift side of thegroyne is starved of sand and the beach width there is reduced. Groynes help to stabilize themovement of sand along the coast. They also help to protect that part of the seabed closest tothe shore from erosion. A problem caused by the use of groynes may be that they are designedto impound sand, which leads to an accumulation of sand on the updrift side and a reduced sandflow on downdrift side. If groynes extend beyond the breaker zone, they may divert sand into theoffshore zone, where it may become lost to the beachface. They actually can cause deepeningand steepening of the offshore seabed and increase the angle of wave approach, allowing sandto be moved along the beach for longer distances, and so increasing sand loss near the groyne.Longshore currents may be deflected seawards, creating rips, which drag large volumes of sandbeyond the offshore zone and remain out of the local beach system, being transported to othercoastal areas (2).

5.3 Sand Nourishment

This is the artificial return of sand to eroded beaches by pumping, Groynes will trap the sandbeing moved along the beach, but if the sand has been moved into the offshore zone and is notbeing returned to the shoreline, then sand is brought from other areas to replenish the beach.It is believed that this will not only return sand to a particular beach, but will also supply sandto the longshore transport system. Sand nourishment requires huge volumes of sand, and it isan expensive method of beach reconstruction. These enormous quantities of sand are obtainedfrom other coastal areas, but the most satisfactory source of sand, because it adds sand to thesystem, is ’off-shore dredging’. This takes sand from the offshore zone, which is not a partof the present beach system. Sand pumped on to a beach from offshore is usually left at anunnaturally steep angle. Nature strives to reduce this by smoothing out the sand, that is, thesand is taken offshore. As much as 30-50 per cent of renourishment is lost in this way. It doesnot provide any long-term solutions to beach erosion, for the wave climate is still the same andleads to the need for ongoing renourishment at required intervals, every 5 to 10 years (2).

5.4 Dune Stabilization

Dunes that are well covered by vegetation are resistant to wind erosion, because the vegetationbinds the sand. If vegetation is removed naturally by storms, wave overwash, strong winds,drought and bushfires, or artificially by clearing for building construction, the sand becomesmobile and can blow inland. Once it is away from the active beach zone, it is no longer capableof replenishing the shoreline. This is very important if beaches along the coastline are to bemaintained, for the sand in these dunes provides much of the sand to the beach system. When


sand is removed into the offshore zone, sand from the dunes can be used to replenish the beachface. Construction in this zone is also significant, for it effectively removes the sand from thesystem. If the dunes are reduced in size, storm waves can travel further inland and erosion isincreased. Plants are also important, because they act as a trap for wind blown sand, whichallows the dune to increase in size, providing a bigger reservoir for the beach system (2).


Figure 5.1: Description of a Buffer Zone (2)

6 Three Southern Beaches of Sydney

This chapter deals with three southern beaches of Sydney who are located in the eastern suburbsof Sydney extending from Clovelly in the north, via Coogee, to Maroubra in the South. Itdescribes the beaches and their surroundings and reveals facts about the coastal management ofthe Randwick City Council. The exact location of each of the three beaches, Clovelly, Coogeeand Maroubra is indicated in figure 6.1.

Figure 6.1: Location of the southern beaches (1)

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6.1 Clovelly Beach

Clovelly Beach is one of the smallest and most unusual beaches in Sydney. The beach itselfis only 70m long, backed by 100m of bare sand and edged by two walking path. However theentire beach is locked between two rocky ridges that extend like two arms for 300m seawardof the shoreline, and almost meet at their seaward end. The end result is an almost landlockedbeach. Most wave energy is expended breaking on the beach on the northern side. What littlewave energy gets into the bay eventually laps up against what is the lowest energy beach inSydney. Clovelly Beach has essentially no waves and consequently no rips, which makes it tobe a very save beach, as long as you don’t venture near the entrance of the bay, where the openocean begins (5).

Clovelly Bay has undergone a number of manmade modifications over the time, the most sig-nificant being the construction of concrete promenades over the natural rock to both, the northand the south sides of the bay. The cliffs, which line a large portion of the northern side of thebay, are composed of Hawkesbury Sandstone, which was mentioned in the introduction. Theyellow sandstone darkened from the effects of weathering to the brown colour it has got today.The cliffs are generally vertical with some variations due to undercutting or collapse of walls.The cliffs extend from the headland to the northernmost point of the bay, creating a ruggedcoastline. The top of the cliffs are relatively flat, barren and exposed to strong winds. Thisenvironment is quite harsh, yet attractive due to its natural qualities and the spectacular views.The cliff tops are bounded to the west by a small stand of remnant vegetation. Uncontrolledaccess over the cliff top areas has led to the destruction of large areas of endemic vegetation.Consequently wind and water erosion has removed the fragile surface soils and exposed areasof clay subsoil. The sandy beach occurs at the western end of the bay, its width is restrictedby surrounding slopes. Randwick City Council carried out a beach replenishment programmeapproximately nine years ago. Sand excavated from a building site in Bondi was transportedand dumped on the Clovelly Beach, raising the sand level of the beach by nearly 0.5 meters.Because of the bay being protected against extremely large waves, a great deal of this sand stillexists on the beach (5).

The following three statements are quotations being made in the " Preliminary InvestigationReport about the Clovelly Bay" (4), which reveal an appropriate description of the CoastalExposure, the Breakwater Effect and the Sea wall reflection:

• Coastal Exposure: The shoreline adjoining Clovelly Bay is exposed directly to waveaction from the Tasman Sea and lacks protection from any natural or artificial off-shorestructures. In turn, this wave action has progressively eroded the original rock formationsgiving rise to the essential form of the existing inlet with its narrow sheltered beach.

• Breakwater Effect: It is understood, that the breakwater was installed across the mouthof Clovelly Bay approximately 67 years ago. This breakwater trapped a pool of waterwhose behaviour was largely independent of off-shore wave action. The partial destruc-tion of the breakwater has resulted in the transmission of wave energy and unimpededtidal movement of water into the Bay. Accordingly, the conditions under which the inter-nal concrete structures in Clovelly Bay were developed no longer pertain.


• Sea wall Reflection: The existing concrete sea walls within Clovelly Bay are nearly verti-cal and gradually neck towards the west. Water waves entering the Bay are able to reflectfrom the sea walls with little energy dissipation. The reflected waves interact, resultingin local peaks in excess of the incoming wave train. The necking of the body of waterbetween the sea walls in the direction of the waves may increase the wave energy per unitwidth of the Bay can actually increase with distance from the breakwater.

Investigating the area, two facts which are in urgent need to be improved have to be mentioned:The surface of the walkways are of mixed quality, with some areas being in a quite dangerousstate due to missing concrete pieces, which contain exposed reinforcement within them andcreate trip hazards. The seawall along the southern side is in a poor condition and some partsrequire attention, as they are cracked and have collapsed undermining the slabs.

6.2 Coogee Beach

The name Coogee seems to have been derived from an Aboriginal word, which means "badsmell". This would be of course due to the decaying seaweed, which is washed up onto thebeach, even in these modern times. It is one of Sydney’s smaller, more intimate beaches, yetin the summer it can be as crowded as any. Maybe not as famous as Bondi Beach, but a largenumber of eastern suburbs inhabitants prefer it to the more popular, high-profile Bondi. CoogeeBeach is located about 12 kilometres south east of the Central Business District, is 400m long,and backed by a recently redeveloped park and promenade. In figure 6.2 certain area’s of theCoogee Bay are marked, which will be described on the following page (6).

The sandstone seawall in the ’Goldstein Reserve’ behind the beach dates from the late 19thcentury, and is perhaps Coogee’s most visible evidence of the historical development of thesite during the 19th century. Despite the removal of some of its length, in the late 1980’s, itsurvives virtually intact, and in remarkably good condition considering its age and exposure.The four sea pools in the describing area - Giles Bath and Ross Jones Pool at the ends ofCoogee Beach, as well as the Women’s bath and Wylie’s Bath below the Grant Reserve- arelisted by the National Trust. The ’Giles Bath’ has traditionally been regarded as part of theGiles Health Centre, built in 1928, and has significance because it is the largest of three poolsin the Sydney region, which is predominantly made from natural rock. The ’Ross Jones pool’was built in 1947 and has a unique design, which includes concrete piers, which extend beyondthe top of the walls resembling to a castle. Due to a rather large amount of seaweed remainingin the pool it is not the aesthetic pool, as it once must have been, anymore. The pool of the’Women’s Bath’ was constructed in 1886, substantially cut out of the rock shelf and retainedwith concrete walls in the south east corner. The pool has high aesthetic value due to its sitingnext to the cliff face and on the rock platform. It is the last remaining example of a segregatedpublic swimming pool occurring on the New South Wales coast. Finally the ’Wylies Baths’is one of the earliest swimming pools constructed on the Sydney coast, starting in 1902 andcompleting in 1907. It has got an elevated timber deck, built about eight meters above the pool.Although the original change facilities have been altered several times, the spectacular cliff sidesite, unique deck structure and association with the development of recreational facilities of thearea have ensured that the complex has remained a well known landmark.


Figure 6.2: Coogee beach subdivided in different areas

Nevertheless apart from these pools most of the people visiting the Coogee Bay certainly wantto enjoy the beach. Waves coming towards the beach are quite low, making the beach a rathersafe place. The reason Coogee is a safer beach, is due in large part, to the presence of WeddingCake Island, located 800m off the beach. The island intercepts much of the wave energy outof the south east, resulting in an average breaker height of only 0.6m. This fact combined withthe medium sized beach sand, produces a steep beach often fronted by a continuous narrow bar,usually devoid of rips, apart from those adjacent to each headland. Direct east swell howevermisses the island and produces higher seas (6).

6.3 Maroubra Beach

Maroubra Beach is located at the southern end of the eastern suburbs of Sydney, 12km south-east to the Central Business District. The name also originates from an aboriginal word, mean-ing ’Bay of Big Waves’. The beach is 1 km in length and can be subdivided into two parts.The northern half, curving to a rocky north headland is backed by a vertical seawall and prom-


enade. In comparison, the southern half has a more natural form with a vegetated frontal dunebacked by a grassed reserve. Apart from the very southern end the Maroubra Beach receivesthe full force of the Tasman Sea, producing the most hazardous beach in the area. The seawallat Maroubra was constructed during the 1920’s. Walls of this type are a quite familiar sight onmany of the beaches in the region of Sydney. It is a concrete structure with a stepped upper sec-tion facing seaward. Facilities such as roads, pavilions, surf clubs and shops are built behind theseawall. The area behind the southern end of the beach was previously used as a garbage tip andhence the beach didn’t attract much usage. The tip was converted to a large open reserve and thefrontal dune was preserved with its vegetation in poor condition. The beach has three zones ofconcentrated use, with its associated car park. These are located at the two ends and in a centralsection where swimmers are served by the facilities of the beach pavilion. The northern andcental section of the beach are dominated by 4 to 5 rip systems, which are particularly strongin the north and against the northern headland. Areas between are used by the board riders andare very popular as Maroubra has a reputation of having the most consistent surf south of theharbour (7).

A beach management study found that the promenade was popular with beach users as a walkingand viewing area. It also provided protection to the surf club and the car parking area. ThePavilion and car parking area had deteriorated to a state where they didn’t adequately caterfor the users needs and detracted from the scenic quality of the beach. Works were proposed toimprove the facilities with paving of the promenade, building a new pavilion, (which can be seenon the picture of Maroubra beach) and extensively landscaping the car park and surroundingareas.

At the southern end, the opportunity existed to use more natural beach management techniquesand provide facilities to enable the beach to be used to it’s full potential without adverse envi-ronmental impacts. Accordingly, the frontal dune was revegetated and fenced to control accessacross the dune. Crossing this fence line is supposed to be a crime and is punished by a highpenalty of 40.000 AUD (7).

The configuration of Maroubra Bay, with the major headland to the South and a lesser but stillsubstantial headland to the North, allows a reasonable assumption to be made that the MaroubraBeach system is a closed one.

This implies, that there are no net long-term losses or gains to the sand supply of the system,and that the quality of sand available for onshore and offshore movements is fixed. On thebeach itself, the three beach zones described earlier are varied in their form and thus in theirresponse to wave and wind forces. The southern and central zones, where the beach bermconsists of sand down to indeterminate depths, recede and develop a steep beach face aftersignificant wave attack. Later accretion in calm periods is quick to occur, from substantialavailable sand quantities observable offshore. The southern zone being more sheltered fromstorm waves usually recedes less than the central zone. Typical rips and channels are presentall along the beach, but are particularly evident at the northern end of the central zone, where arock shelf projects seaward of the normal waterline.

It is on this rock shelf that the northern beach zone is perched. The beach berm here is athin layer of sand overlying rock at very shallow depths. Even moderate swell conditions canremove a sufficient quantity of sand to render this zone unusable as a swimming resource,


and subsequent accretion is slow to occur. The seawall along the northern part of the beachprovides protection from storm wave attack of the beachside amenities, such as the pavilion,the promenade or the surf clubs, as well as a sand dune does along the southern half. In thenorthern half, the seawall merges into a structure known as the ’Colosseum’ in the northernbeach zone. The Colosseum is protected by the rock shelf projecting seawards in front of it,and also provides its own protection by being founded on the shelf. However, in extreme stormevents, broken water has flowed across the floor level of the structure.

Nevertheless the beach is one of the most popular surfing beaches in Sydney and during thesummer months is subject to intensive use. Because of its intrinsic scenic and recreationalvalues, the beach is highly valued by the community. Despite these considerable attributesand the communities concern for its protection, Maroubra Beach has not achieved its potentialas a premier coastal attraction and recreational resource. Its inherent natural qualities havebeen lost severely compromised by progressive urban development. Past attempts at redefiningthese qualities to achieve a resource complementary to the natural environment and capable ofwithstanding urban pressures have been largely unsuccessful. These pressures and the desirefor enhancement of the site have created the need for a revised plan of management. Parts ofthis plan are shown on the appendix of the Maroubra Beach plan of management (7).


Figure 6.3: Maroubra Beach, part of the ’Plan of Management’ (7)

7 The Coastline Hazards of these beaches

At the end of this report, the hazards are mentioned, which exists on the three beaches Clovelly,Coogee and Maroubra. In the appendix of this report there are 3 maps, which divide the areasof the beaches into certain zones. These zones characterize the hazards that exist in this certainsector, ranging from minor over moderate to serious kind of hazards. Most of these zones areshown in a picture, also to be found in the appendix. The description is been made from mypoint of view as well as I have tried to find a possible solution or precaution to decrease thehazard. Additionally to the figures in which the subdivision into the described zones of thebeaches is given, 2 figures marking a general overview of every beach investigated are shown.The methods to work against these hazards are taken from "Coastal Management of NSW":

7.1 Clovelly Bay

7.1.1 Zone 1: hazard level: minor to moderate

Within the whole zone 1 (see figure 7.1) there are no buildings that may be endangered, so thehazard concerning the loss or collapse of buildings in this zone is minor or almost not existing. It is moderate to serious regarding the danger for people who may underestimate the strongwinds that can occur during a storm surge. When they walk along the sandstone cliff duringa strong storm they can either be blown over the edge of the cliffs, or be surprised by suddencliff instability. Sings who prevent people from walking to near to the edge could be a possibleprecaution. Fences would be far to exaggerate because they disturb the beautiful view to theocean. Otherwise as long as pedestrians stay on the footpaths along that zone the hazard is low!One hazard to be mentioned on the southern end of that zone is the storm water outlet, whichcould be a danger for incautious people who walk near to it during a storm and will be surprisedby the large amount of water that suddenly will come out of the outlet. One possible solutioncould be to build the concrete pipe a little bit longer, to end up into the ocean.

7.1.2 Zone 2: hazard level: minor to serious

First of all the hazard for buildings in this area is minor because they are provided with enoughspace to the shoreline. More important in this zone is the danger for people who may walk alongthe concrete platform during a storm surge. They are endangered because of two reasons, firstof all the really bad shape of the concrete which, apart from a storm surge, can cause seriousinjuries for people who would walk along the platform barefoot. The only improvement to bedone on that hazard would be a complete new surface either with concrete or another materialthat is able to cope with the permanent oncoming water, like asphalt for example. Secondly,

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Figure 7.1: Zones of the Clovelly Bay

the danger for people walking along the platform is to be mentioned. The existing breakwaterstonewall on the northern side of the entrance of the bay cannot cope with the strong wavesduring a storm surge and will allow the large waves to flood the whole platform. Generally agood precaution would be a small (approx. 1m high) fence to protect the people to be drownedin to the ocean. The fence should be interrupted at the 4 stairs that allow people to step into thewater.

7.1.3 Zone 3: hazard level: minor

This zone shows no danger, neither for people nor for buildings because the strong waves willhave lost most of their power in the narrow bay. The only hazard to be mentioned is beach


Figure 7.2: Clovelly Bay

erosion, which takes place during a strong storm surge. Sand renourishment is the only methodto prevent the beach from eroding to far.

7.1.4 Zone 4: hazard level: minor to serious

Zone 4 is very similar to zone 2 apart from the Clovelly Surf Life Saving Club (S.L.S.C.),which is located on the eastern end of the zone. It is build very near to the shoreline, on top ofan almost vertical sandstone cliff, which is endangered to collapse due to cliff instability duringa storm surge. A semi flexible seawall could be a possible precaution as well as special kind ofconcrete, that will last on an existing wall, over the surface of the cliffs to strengthen them andto make them last longer.

7.1.5 Zone 5: hazard level: low

The hazard within this zone is very low because there are no footpaths along the cliffs and aswell there are no buildings in this sector that could be affected by a storm surge. The car parkcould even be regarded as a buffer zone in which the only loss could possibly be a forgotten car.

To draw a conclusion on the hazards existing in the Clovelly Bay a proposal would be to in-crease, or to improve the existing breakwater seawall to decrease the power of the waves. Fur-


Figure 7.3: Clovelly Beach

thermore, the building of a similar kind of seawall on the southern end of the entrance of thebay would become necessary. They both would decrease all the hazards mentioned above.

7.2 Coogee Bay


The hazard in this zone (see figure 7.4) is low, because neither people nor buildings couldbe endangered by a possible cliff instability that may occur in this area during a storm surge.Footpaths as well as buildings are located in an appropriate distance to the edge of the cliff.


Apart from that, signs warn the people to stay away from the unstable rock face are set alongthe edge, as well as a white wooden fence leads along the edge, to prevent people from falling.

Figure 7.4: Zones of the Coogee Bay

7.2.2 Zone 2: hazard level: serious

Much higher is the danger for people regarding zone two. Here, the footpath protected by awooden fence leads exactly along the edge of the vertical sandstone cliff. People, who may walkalong the path, or stand at the wooden fence to watch the storm takes place, could be surprisedby a sudden collapse of the cliffs. The at the moment existing fence should be removed at least2 meters further away from the edge of the cliff. Additionally signs have to mark, that it isprohibited to walk or sit on the space between the fence and the edge. Methods like for exampleconcrete walls to stabilize the sandstone are an inappropriate solution, because it wouldn’t fit


Figure 7.5: Coogee Beach, view from the south

into the landscape, especially this part, which is visible to the whole beach. The further inlandpart of this zone, like the Barbecue Area or the parkland are not endangered at all.


This part of the Coogee Bay has a very low hazard concerning people and buildings. Besidesthe beach erosion, which can be regarded as a hazard, no really danger has to be mentioned.The vertical seawall, which has been rebuilt some years ago, protects buildings, as well aspedestrians who walk along the promenade. The beach itself can be seen as a buffer zone, inwhich the strong waves are supposed to lose at least some of their power, to be then reflectedby the seawall. On the southern end of the beach, where the beach is rather narrow, there areconcrete steps to break the waves, and an even higher seawall to guarantee the safety.

7.2.4 Zone 4: hazard level: moderate to serious

On the western end of this sector the Coogee Surf Life Saving Club is located exactly abovethe shoreline, build on a sandstone cliff, only about 1.5-2 meter above the mean high tide level.Therefore this building is in a very hazardous area off cliff instability and may collapse into theocean in not too many years. The only precaution to protect the S.L.S.C. could be a flexible, orsemi-flexible seawall consisting of rocks or concrete blocks to be placed in the ocean with theintention to break the strong waves and decrease their power. Otherwise, cliff stabilization with


Figure 7.6: Coogee Bay, view from the north

the help of concrete could be a possible precaution, but again the aspect of a rather uncomfort-able visual effect has to be regarded. The other building, or facility endangered in this zone,is the Wylie’s Baths, with a saltwater swimming pool on the same level as the ocean. Apartfrom swimming in the pool during a storm surge being very dangerous, also the building of thebath is highly endangered. It consists of a little kiosk, change rooms and a platform to take asunbath. It is build on several rather thin wood columns, which are fixed with concrete in thesandstone cliff. When these cliffs will erode and be washed out by the ocean water during thetime, they may be not fixed properly anymore and the building will collapse. Protection in theway of little concrete walls to prevent the water to reach the bottom of the columns could be apossible precaution. Otherwise the rest of this zone is not endangered.

7.3 Maroubra Bay

7.3.1 Zone 1: hazard level: moderate

The space between the edge of the sandstone cliffs and the nearest building or the footpath forthe pedestrians is wide enough, measuring in between approx. 50-100m. Even if the nearlyvertical cliff would suddenly collapse the danger for people or buildings is low. No precau-tions/preparations have to be worked out (see figure 7.7).


Figure 7.7: Zones of the Maroubra Beach

7.3.2 Zone 2: hazard level: serious

The danger of destroying the buildings by a collapsing sandstone cliff is high, because thenearest house is only about 10m away from the edge of the vertical cliff, hence quite near to theshoreline.[picture 11] During a storm surge these sandstone cliffs can break and therefore erodeinto the ocean. Houses and other buildings will collapse and be destroyed. Also the dangerfor people like pedestrians or drivers on the street is very high because they can be surprisedby a sudden collapse of the cliffs. People do not expect cliff instability while watching thestorm from the footpath and underestimate the danger.[picture 12] The measurement againstthis hazard could be a flexible or semi-flexible seawall to prevent the really strong waves toreach the sandstone cliff with all their power and hence to decrease the possible cliff instability.Nevertheless, road signs should prevent people from walking along the footpath during a stormsurge.


Figure 7.8: Maroubra Beach

7.3.3 Zone 3: hazard level: moderate to serious

The North Maroubra Surf Life Saving Club as well as the Beach Pavilion are highly endangeredduring a strong storm surge because they are both almost unprotected in any way. The onlyprecaution that slightly prevent the waves to reach these buildings are two concrete stairs, thefirst one with 4 and the second one with 3 steps. It is rather easy for the strong waves to reachthese buildings because the shallow and not very wide reach cannot be seen as a buffer zone. Apossible precaution could be a vertical seawall on the platform between the two stairs. It mightbe rather difficult to add a concrete wall to the existing concrete platform in short distances.The waves would break on the first stair and would be reflected by the new seawall to protectthe two buildings. The danger for people or pedestrians is rather low, because the danger won’tcome abrupt and is obviously predictable visually. They can see the large waves approach tothe platform more and more. Last but not least beach erosion takes place so that even the nowmore or less existing buffer zone of the beach will decrease in the future.


There is almost no danger either for buildings in this zone or for people. The only existingbuilding is the South Maroubra Life Saving Club S.L.S.C, which is located with enough spaceto the shoreline. Also people are not endangered by a possible storm surge because there areno ways or footpaths leading through the dunes that lead from the beach to the hinterland. Theonly hazard may be beach erosion and the loss of the dunes caused by the lack of vegetation


Figure 7.9: Maroubra coast

on the dunes. Methods against this procedure can be dune stabilisation by providing the duneswith enough vegetation and sand renourishment to restrain the appropriate amount of sand onthe beach.


The hazard in this particular zone is quite low, because here are neither buildings nor footpathsalong the edge of the cliffs. The footpaths that lead through this zone are built within an ap-propriate distance from the edge. Only incautious people who walk to or along the edge ofthe sandstone cliffs could be endangered by strong winds or a possible cliff instability resultingfrom a storm surge. No precautions have to be done except for signs to make the people realizethe danger while walking on the edge of the cliffs.

7.4 Final Statement

Finally I want to say, that the investigation I did in this report has been very interesting forme, I definitely learned a lot about coastal erosion and beach processes. Also the researchabout the beaches in the Randwick City Council and outside on the beaches themselves hasbeen very interesting, because I have become a more deeper insight into the beaches and theirsurroundings, than a ’usual’ beach visitor. The problems of coastal erosion and cliff instability


has become a very dangerous hazard, especially along the coast of New South Wales. Methodshave to be done in the near future to prevent this piece of beautiful nature from being destroyed.The public awareness, which is rather low concerning these problems, has to be increased inorder to let the people who live along the coast realize how dangerous it could be to build theirhouses straight along the edge of the cliff.

Bibliography

[1] Beaches of the NSW Coast; Andrew D. Short;1985

[2] History and Heritage of Coastal engineering; Nicholas C.Kraus; 1989

[3] CRC Handbook of Coastal Processes and Erosion; Paul D. Komar; 1996

[4] Randwick City Council Preliminary Investigation Report; 1996

[5] Clovelly Beach, Plan of Management; 1997

[6] Coogee Beach, Plan of Management; 1995

[7] Maroubra Beach, Plan of Management; 1995

[8] Randwick City Council Library: Maps; 1984

[9] Waves, tides and Shallow-Water Processes; Open University Course Team; 1997

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