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Contributions Storm damage on Black Rock Sea Wall, April 2009 Eric Bird Geostudies,Australia.343BeachRoad,BlackRock,Victoria3193 Abstract InrecentyearsepisodesofstormdamagetotheseawallatBlackRockhaveoccurredinAprilandMay.when theadjacentsandybeach hasdisappearedbecauseofnorthwardlongshoredriftingduringtheprevioussum- mDearm.aSgoeuitshlwiakerldytdorirfetciunrgifnrAopmriAlprainldtMoaNyouvnelmesbsearbtehaecnhrceasntobreesaratifpircoitaelclytimvaeinbteaaicnhedininfrfornotntoofftthheesseeaawwaallll.. (TheVictorianNaturalist127(5)2010,196-200). Keywords:stormdamage,seawall,longshoredrift,beacherosion Introduction The north-east coast of Port Phillip Bay con- Headlands divide this coast into several natu- sists ofalternating headlands and sandy bays. ralbeachcompartments,ineachofwhichsand Thecoastalgeologyconsistsofasoftpaleclayey drifts northward during the summer half-year sandstone, the Red Bluff Sand, over a harder from November to April (Fig. 1), and south- dark brown ferruginous sandrock, the Black ward during the winter halfyear from May to RockSandstone,bothwellexposedinRedBluff October (Fig. 2). Black Rock Beach, extending (Kenley 1967). The contact betw'een the Red from Black Rock Pointsouth to Quiet Corner, BluffSand and the Black Rock Sandstone un- is one ofthese. By late summer the northern dulates gently: it protrudes on headlands with halfofthebeachhaswidened,whilethesouth- rocky shore ledges where it is slightly above ernhalfismuch reduced, and hasan extensive mean sea level at Black Rock Point and Quiet beach-less sector (Fig. 1). During the winter Corner, and it is a little below mean sea level half-year, sand drifts southward, so that the along Black Rock Beach, where the darksand- northern halfofthebeach isnarrower, andthe rockispartlyexposedatlowtide. southern halfhasabeachextendingin frontof theseawalltowardsQuietCorner. Fig. 1. Black Rock Beach at the end of summer (April)aftersixmonthsofdominantnorthwarddrift- Fig.2. BlackRockBeachattheendofwinter(Octo- ing. ABisthesectorofseawall thatwasnotbeach- ber)aftersixmonthsofdominantsouthwarddrifting fringed, and was thus damaged during the storm of has establishedaprotectivebeachinfrontofthesea 25-26April2009. wall. 196 TheVictorianNaturalist Contributions Theextentofseasonaldriftinghasvariedfrom It has been suggested that cliffs were more yeartoyear. InApril 2000, northward drifting extensive around Port Phillip Bay during the during the summer had been so pronounced early Holocene, between 6000 and 4000 years that the beach disappeared along the whole ago, when sea level was slightly higher than it length of the sea wall and became exception- is now, and that a subsequent fall in sea level allylow and narrowin the central sector, near (which promoted beach accretion) resulted in theBlackRockLifeSavingClub. Inmostyears their being reduced to steep, vegetated slopes. a shortsectorofbeachpersists inlatesummer Cliffs persisfed onlyon exposed sectors, nota- belowtheBlackRockcarpark,butinvariablyit blyheadlands(Bird 1993). disappears from the seawall sectorbetweenA A storm surge on 29-30 November 1934 and B in Fig. 1,which is then exposedto wave caused extensive erosion along the east coast attack. of Port Phillip Bay, and in the following year ThenorthernhalfofBlackRockBeachstands the state government set up a Foreshore Ero- infrontofascrub-coveredbluffwhichwasfor- sion Board,whichsurveyedsectorswhere ero- merlyarecedingcliffcutinsoftRedBluffSand, sion had been rapid (Mackenzie 1939). It was whilethesouthernhalfwasanactive,receding decided that sea walls should be built to pro- cliffwhenthefirstEuropean settlerscamehere tectthemostvulnerable sectors, includingone in the 19th century. The contrast is probably extending from Black Rock south to beyond related to the evolution of the beach system, Quiet Corner. This was constructed between with aperennialbeach ofvaryingwidth in the 1936and 1939,andtooktheformofamasonry northern half, and seasonal exposure to wave wallandundercliffwalk,thebackingcliffbeing action along the southern half, where the cliff graded to a 30° slope and planted with grasses wasunprotectedbyafringingbeachforseveral andshrubs. monthseachsummer. Fig.3.WavesbreakingovertheseawallatQuietCorneron26April2009. Vol 127 (5) 2010 197 Contributions Quiet Corner (Fig. 3). In the northern halfof the Black Rockbeach compartment the waves brokeontheseaward marginofthewidesandy beach and had littleeffect,thewaveenergybe- 5i)ngabsorbed bythesandybeach (Fig.4). Inthe southern halfa longsectorofthe sea wall (AB in Fig. 1) had no protective beach, and this is whythewavescausedsuchseveredamage(Fig. 6). Within a few days, southward drifting of sandbegantobuildabeachin frontofthedam- aged sea wall. By the end ofMay the sea wall was bordered by a narrow protective beach, and duringthe winterthis became wider, until in November the wall was well protected (Fig. Fig. 4. The 26 April 2009 storm had little effect on . Bayside Council decided to repair the sea thesandybeachnorthofBlackRock. Seaweedlitter wall and restore the features that existed prior marksthelimitofstormswash onthatday. to the storm, and this workwas completed on Thestorm of25-26April 2009 20November. A deep depression passedacrosssouthernVic- The storm damage on 25-26 April 2009 was toria on 25-26 April 2009, generating asouth- not unprecedented. Therehad previouslybeen westerly galeover Port PhillipBay. For several severalepisodesofstormdamage,particularlyin hours, waves up to 2.5 m high broke heavily AprilandMay,thetimewhenthereislittleorno on the shore between Black Rock Point and beach in front ofthe seawall. Hie storm of30 April 1986inflictedsimilardamage(Fig.7). The Fig.5. DamagedseawallsouthofBlackRock,27April2009. 198 TheVictorianNaturalist Contributions beach became very wide in late summer, and southward (round Quiet Corner) when itwid- enedatthesouthernend inlatewinter. In due course these losses would deplete the beach, andafterafewyearstheseawallbetweenAand B wouldbeagain exposed to stormwaves. An alternative would be frequent renourishment ofthe AB sectorwith sand pumped or ferried from the northern end ofthe beach, but this would be expensive, and such perennial recy- clingisunlikelytobemaintained. Itwouldbepossibletostopsanddriftingaway northwardfromthesouthernhalfofBlackRock Beach each summer by building large stone FBilga.ck6.RoPcrko,teNcotivveembbeearch20i0n9.frontofseawallsouthof groynes at A and B to enclose a compartment containing deposited beach sand (Bird 1990). Suchgroyneshavebeensuccessful in retaining repaired sea wall between A and B on Fig. 1 is artificial beaches at Hampton, and have been stillvulnerabletostormdamageinearlywinter, introduced (despite some local opposition) on beforedriftingsandarrivestobuildaprotective Sandringhambeach. Itislikelythattheywould beachinfrontofit. prove successful in maintaining a beach and ensuringstabilityoftheseawallbetweenBlack Seawallprotection RockandQuietCorner. One way ofprotecting this sea wall would be to dump large boulders in front ofit, but this wouldcausewavereflection andpreventbeach accretion (as it did on the Hampton shore in the 1970s). Analternativewouldbetobuildan offshorebreakwaterparalleltothecoastlineand m about30 seaward.ITiiswouldprotectthesea wall from storm wave attack and also induce beach accretion along the sea wall, shaped by waves refracted round its ends. Eitherofthese measures would be criticised as introducing unsightlystructurestotheshore. Anotherwayofpreventingdamagetothissea wall would be to form and maintain a protective beach in front ofit all year round. When theseawallwasoriginallyconstructed,aseries ofwooden groyneswasbuilt,protrudingabout 20metresseaward,inthehopeoftrappingsand and retainingaprotectivebeach,buttheywere not effective, and soon deteriorated. Onlymi- norremnantscannowbeseen,forexamplejust northofQuietCorner. A previous attempt was made in Decem- ber 1969 to maintain this beach by dumping numerous lorry-loads of sand in front ofthe sea wall (Fig. 8), but it all drifted away to the north during the following summer. It might bepossibletomaintainabeachherebydump- ing a very large quantity ofsand (ofthe order of200000 m^), but there then would be losses Fig. 7. Damageto sea wall bya previous storm, 30 northward (round Black RockPoint) when the April 1986. Vol 127 (5) 2010 199 Contributions Fig.8. SanddumpedontheshorenearQuietCorner,December1969. Itdriftedawaytothenorthduringthe nextfourmonths,anddidnotprovidewinterprotectionfortheseawall. ThisanalysisofthestormdamagetotheBlack BirdECF(1993) JheCoastofVictoria. (MelbourneUniver- mRaoncakgesreas waanldl ielnlguisntreaetress ttohebeneaewdarfoerocfoagsetoa-l Kestnrilitceyty,PrPVeisRcst:(or1Mi9ea6l,7b)popuT.errn3te1ia)-r4y6..InGGeeoololgoigcyaolfStuhervMeeylboofuVrincetoDriisa-, morphologicalprocesses. BulletinNo.59. MackenzieAD(1939)Coastalero.sioninVictoria. Transac- References tionsojtheInstituteofEngineersofAustralia20,229-236. BirdECF(1990)Artificialbeachnourishmentontheshores ofPortPhillipBay. JournalofCoastalResearch,SpecialIs- sue6,55-68. ReceivedJDecember2009;accepted11May2010 Onehundredyearsago SANCTUARIESFORSEABIRDS By a recent Gazette notice the Tasmanian Government has proclaimed Foster and Albatross Islands as sanctuariesforsea-birds.TheformerissituatedinBanksStrait,offthenorth-eastcoastofTasmania,andis theresortofPelicansandCapeBarrenGeese;whileAlbatrossIsland,offthenorth-westcornerofTasma- nia,isthebreedingplaceoftheSootyAlbatrossandotherbirds.CatandStorehouseIslands,portionofthe FlindersGroup,onwhichthereareextensiverookeriesofgulls,gannets,penguins,andmuttonbirdshave alsobeenreserved,sothatoursea-birdsshould nowreceivesomemeasureofprotection, andnaturalists shouldbedeeplyindebtedtotheTasmanianGovernmentforitsaction. From TheVictorianNaturalistXXVII,p. 30,June9, 1910 200 TheVictorianNaturalist