COASTAL COMPARTMENTS, SEDIMENT CELLS AND VULNERABILITY ASSESSMENT: A Progress ReportPresentation toWALIS MARINE GROUP

MATT ELIOT AND IAN ELIOTDamara Pty Ltd, Innaloo , WA

19 July 2011

BASIC CONCEPTS

Tata Perencanaan Unit Pengembangan Pantai Berdasarkan Kondisi Geologi Pantai.

Setting Unit Perencanaan Pengembangan Pantai dipisahkan berdasarkan atas kondisi geologi, struktur, bentuk/fungsi/potensi lahan (tata guna lahannya).

Detail Perencanaan di identifikasikan berdasarkan atas sel-sel sedimen yang akan di analisa sumber sedimen, arah transport dan deposisinya.

Perpaduan antara Pembagian klasifikasi Pantai dan sedimen sel dalam satu kesatuan. Dibagi sesuai dengan tujuan Pengembangan Pantai : (a) Perencanaan dan manajemen SDA lingkungan pantai (nearshore marine and coastal environment) (b) Penilaian Kerentanan (assessment of vulnerability) terhadap bencana pantai , perubahan iklim dan kenaikan muka laut.

Zones: Broad sectors of the Australian continent based on climateDivisions: Provides an overview of the whole state suitable for maps at scales of about 1:5,000,000Provinces: Areas defined on geomorphologic or geological criteria suitable for regional perspectives at scales of about 1:1,000,000Regions: Areas with recurring patterns of landform and geology suitable for regional mapping at scales of approximately 1:250,000Land Systems: Areas of characteristic landform patterns suitable for mapping at regional scales of 1:50,000 to 1:100,000 Compartments: A local unit based on one or more definite landforms suitable for mapping at scales of about 1:25,000 to 1:50,000Landforms: A local unit based on one or more landforms suitable for mapping at scales of about 1:5,000 to 1:15,000Sediment Cells: A local unit based on several linked landforms suitable for mapping at scales of about 1:5,000 to 1:25,000

PRIMARY COMPARTMENTS AND SEDIMENT CELLS

POTENTIAL APPLICATIONSCOMPARTMENTSLandforms (Framework) & Processes (Drivers)PLANNING PURPOSESMarine & coastal planningHabitat descriptionMarine & coastal risk assessmentMarine conservationEBFM

Major Landform Assemblages(After: Searle & Semeniuk 1985)

Nearshore MorphologyIslandsLinear reefs and submarine ridgesPavementsSand banks Sand flats and seagrass meadows

Landforms of the Shore Shoreline shapes (straight, irregular, arcuate and zeta-form)Rocky coasts (cliffs, ramps and platforms)Beaches (sheltered and exposed forms)

Onshore LandformsLimestone plateaux and outcropsForedunes Frontal dunes (blowouts and parabolic dunes)Barriers EstuariesDeltasCoastal lagoons and wetlands

An extreme event or events may change the type or location of a land system.eg. Avulsion (channel switching) and delta shiftGradual landform change associated with land surface instability ultimately results in structural change.eg. Barrier evolutionSTABILITYSUSCEPTIBILITYLikelihood of erosional change to landforms related to current land surface condition Likelihood of structural breakdown leading to a change in the land systemLikelihood/Kemungkinan of landform and/or land system changeVULNERABILITY=+

SUSCEPTIBILITY Long-term Structural ChangeCliff & talus slopeClimbing dunesAshburton River Delta 1963Open river mouthActive spitSpitPerched barrier and climbing dunesNo barrier. Perched beach and old dunesAshburton River Delta 2009Open river mouthActive chenierSTABILITYShort-term Landform ChangeMouthMouth

The susceptibility of rocky coast refers to the intrinsic propensity of a coastal land system or landform structure to alter in response to projected change in metocean conditions over a long period, commonly extending to millennia.

Variation in structure may occur spatially, due to differences in rock type; or temporally as a result in the differences in the strength of the same rock type and exposure to disparate processes.Rank 1: High cliff (>10m) plunging to subtidal levelRank 2: Moderate to high cliff (>10m) with an intertidal platformRank 4: Rock pavement or intertidal platform and low bluff (

SANDY (BARRIER) COAST SUSCEPTIBILITYThe sequence illustrated here follows that described by Roy (1994).

The susceptibility of a sandy barrier refers to the intrinsic propensity of the structure comprising the barrier system to alter in response to projected change in metocean conditions, particularly sea level rise over.

Barrier formation occurs over a long period, commonly millennia, although structural change from one type to another may occur within tens to hundreds of years.Rank 1: Episodic Transgressive BarrierNested blowouts and parabolic dunes. Rank 2: Prograded BarrierLow, foredune ridge plainRank 3: Stationary BarrierLow or narrow ridge of blowout Rank 4: Receded BarrierLow narrow dune ridge & old shoreline Rank 5: Mainland BeachNarrow duns & beach abutting bedrock.

STABILITY ON MIXED SANDY AND ROCKY COASTThe sequence illustrated here follows that described by da Silva (2010). Estimates of beach instability are based on the exposure of the beach to metocean processes.

The variability of sandy beaches in different settings has been described by Nordstrom (1992) and Short (2005).

The stability of sandy beaches perched on rocky substrates is not as well known, although such beaches are common features of the Australian coast. The sequence shows beaches subject to increasing exposure to wave and sea level variation.Rank 1: No beach OR a foredune is located on a high rock platform (>HAT)Rank 2: Perched beach is located on a supratidal rock platform Rank 3: Perched beach adjoining a low bluff Rank 4: Perched beach on an intertidal platform or beachrock rampRank 5: Perched beach on shallow inshore pavement

Rank 1: Undisturbed dune sequence OR Fully vegetated (>75% cover on barrier). Rank 2: 50 to 75% vegetation cover on barrier OR

Land system and landform description andRanking for susceptibility and instability

SUSCEPTIBILITY STABILITY 1 NEARSHORE MORPHOLOGY (Depth

SEDIMENT CELL DESCRIPTION

CellSouthNorthINSHORESHORELINEAND BEACHFACEBARRIER24 7 Mile Beach 9 Mile BeachBetween Seven Mile Beach and Bobs Hole at Nine Mile Beach the 20m isobath is approximately 7km offshore. The ridge of limestone reef, which includes Nine Mile Break, trends NNW and parallel to the coast. It becomes more irregular with distance north but continues to enclose a lagoon. Multiple ridges of shallow limestone reef, platforms and stacks shelter the coast and close with the shore at Bobs Hole.The shoreline has a shallowly-indented arcuate form and is zeta-shaped to the south. In the south, the beach abuts a 2km long, high platform. The northern section of the coast faces WSW with the nearly continuous beach sheltered by reef close to shore. The exposed, reflective beach is rhythmic with shallowly indented embayments between shoreline salients associated with inshore reef outcrops close to shore.An episodic transgressive barrier comprised of nested parabolic and blowout dunes overlie a limestone basement of unknown depth and distribution. Its vegetation cover is between 25 and 75%. The frontal dune is partly scarped or steeply faced to seaward, and its 25 to 75% vegetation cover disturbed by numerous access tracks. The foredune is absent from much of the coast, particularly south of Getaway Beach.

M-H

CellSouthern Boundary of CellInshoreShoreline PlanAspectBarrierSusceptibility ScoreSusceptibility RatingInshore SubstrateBeach ProfileBarrier VegetationFrontal DuneInstability ScoreInstability RatingMATRIX SCOREVulnerability34 CAPE BURNEY SOUTH445114M454316H433 West Bank 423110M344415H4M-H32 Phillips Road Coast423110M444315H4M-H31 Lucys423110M444416H4M-H30 Duncans Pool423110M444416H4M-H29 Flat Rocks 423110M334313M3M28 Headbutts13318L334313M2L-M27 Shire Boundary23319L354315H3M26 Bookara South31318L354315H3M25 NINE MILE BEACH433111M444517H4M-H24 Seven Mile Beach12328L333211M2L-M23 Harleys Hole12328L332210M2L-M22 Dongara North 12328L332210M2L-M21 LEANDER POINT32319L233311M2M-H20 South Leander Point334111M554317H4M-H19 White Point334111M554317H4M-H18 CLIFF HEAD325111M444315H4M-H

CONSEQUENCES FOR COASTAL MANAGEMENT

SUSCEPTIBILITY (STRUCTURAL INTEGRITY)Susceptibility ScoresIndicative SusceptibilityProjected Site Implications4 - 9Low Structurally sound geologic or geomorphic feature. Determination of susceptibility may require resolution of metocean processes 10 14Moderate Some structural features are unsound. Detailed assessment of coastal hazards and risks is advised.15 - 20High Structural features are extensively unsound. Development is not recommended.LANDFORM INSTABILITYInstability ScoresIndicative InstabilityPresent Actions on Similar Sites4 - 9Low Resilient natural system occasionally requiring minimal maintenance (eg. Alfred Cove, Milyu Reserve & Scarborough).10 - 14Moderate Management responses are required to accommodate a range of occasional major events, regular moderate events or frequent minor events. (eg. Broun Bay).15 - 20High Current management responses require ongoing installation or repair of major stabilisation works (eg. Esperance, Port Geographe).

INDICATIVE VULNERABILITY MATRIXMIXED SANDY AND ROCKY COAST

INSTABILITY (CONDITION)(Existing morphologic change to land surface)Low (Stable)ModerateHigh (Unstable)ExampleSUSCEPTIBILITY (STRUCTURE)(Potential change to geological structureLowBarrier perched on extensive tracts of coastal limestone(1) Vegetated swales in parabolic dunes landwards of a vegetated frontal dune ridge overlying coastal limestone above HWL(2) Vegetated dunes landwards of a vegetated frontal dune ridge and perched on coastal limestone at HWL(3) High foredune ridge and/or vegetated foredune plain overlying coastal limestone below HWLModerateWeakly lithified barrier with intermittent limestone outcrops (2) Mainly vegetated swales in parabolic dunes landwards of a mainly vegetated frontal dune ridge(3) Vegetated dunes landwards of a mainly vegetated frontal dune ridge (50 to 75% cover) and overlying coastal limestone(4) Cliffed or discontinuous foredune fronting moderate numbers of mobile blowouts and sand sheets (50% of the alongshore reach)

KEY Combined estimate of vulnerability Low Low-to-moderate Moderate Moderate-to-high High

CellSouthern Boundary of CellSusceptibility RatingInstability RatingVulnerabilityRating34CAPE BURNEY SOUTHMHM-H33West Bank MHM-H32Phillips Road CoastMHM-H31LucysMHM-H30Duncans PoolMHM-H29Flat Rocks MMM28HeadbuttsLML-M27Shire BoundaryLHM26Bookara SouthLHM25NINE MILE BEACHMHM-H24Seven Mile BeachLML-M23Harleys HoleLML-M22Dongara North LML-M21LEANDER POINTLML-M20South Leander PointMHM-H19White PointMHM-H18CLIFF HEADMHM-H

KeyVulnerabilityImplications for DevelopmentLowCoastal risk is unlikely to be a constraint to developmentLow-to-moderateCoastal risk may present a low constraint to developmentModerate Coastal risk may present a moderate constraint to developmentModerate-to-highCoastal risk is likely to be a significant constraint to developmentHighCoastal risk is a highly significant constraint to development

KeyVulnerabilityImplications for DevelopmentLowCoastal risk is unlikely to be a constraint to developmentLow-to-moderateCoastal risk may present a low constraint to developmentModerate Coastal risk may present a moderate constraint to developmentModerate-to-highCoastal risk is likely to be a significant constraint to developmentHighCoastal risk is a highly significant constraint to development

VULNERABILITY ESTIMATESCOMPARTMENTS AND CELLS

INDICATIVE VULNERABILITY MATRIX BASED ON LARGE LAND SYSTEMSVULNERABILITY = SUSCEPTIBILITY + INSTABILITY

KEYRanked estimateLowLow to ModerateModerate Moderate to highHigh

INSTABILITY(Existing Landform Change)SUSCEPTIBILTY(Potential Change to structure)Low(Apparently accreting) Medium(Apparently unchanging)High(Actively eroding)Rocky CoastLowHard rock (granite)cliffs and rocky shoresSoft rock (sandstone) cliffs and rocky shoresWeakly lithified rock (calcarenite) cliffs & rocky shoresSandy CoastMediumShoreline advance greater than 1.0 m/yrPrograded & episodic transgressive barrierVegetation cover >75% on barrierShoreline change from -1.0 to + 1.0 m/yrStationary barrierBetween 25% and 50% vegetation cover on barrier. Foredune presentShoreline retreat greater than 1.0 m/yrRetreating barrier& cuspate foreland. Vegetation cover

VULNERABILITY ESTIMATESPRIMARY COMPARTMENTS

POTENTIAL APPLICATIONSCOMPARTMENTSLandforms (Framework) & Processes (Drivers)PLANNING PURPOSESMarine & coastal planningHabitat descriptionMarine & coastal risk assessmentMarine conservationEBFM

AS NZS (2009) ISO 31000Risk Assessment Framework Adapted to Coastal Management

From: Rollason et al. (2010) and Rollason & Haines (2011)

Commonwealth Climate Change AssessmentsNCVALAPPANUGAPNPState Government Coastal AssessmentsSPP2.6 ReviewCoastal Process StudiesCoastal Planning StudiesCoastal Hazard AssessmentsPilbara CitiesCities ProjectRegional StrategiesLocal Government Coastal AssessmentsDIVERSE!!

The framework divides the coastal regions into scales appropriate to natural resource management at a State level. It focuses on the State Waters, and particularly the shoreface - the nearshore component of the inner continental shelf in which benthic sediments are moved by waves and currents.The land system hierarchy is similar to that described for soils mapping in Western Australian agricultural regions by Schoknecht et al. (2005) and van Gool et al. (2005).It spans very large (big) land systems and small land form elements. The large land systems are subject to slow change over decades to millennia, unless massive change is triggered by a extreme event or a sequence of extreme events.In contrast to the big systems, the small landforms are subject to change at sub-decadal scales, including seasonal events.The framework divides the coastal regions into scales appropriate to natural resource management at a State level. It focuses on the State Waters, and particularly the shoreface - the nearshore component of the inner continental shelf in which benthic sediments are moved by waves and currents.Landform mapping follows the WA Coast maps prepared by Bob Gozzard (GSWA).Descriptions of the landforms are done in terms of published identification of land system (eg Barriers) and landform (eg dunes) change, respectively over long and short periods. These accord with the concepts of susceptibility and instability applied in the approach used to determine vulnerability.Susceptibility involves incremental change occurring over decades to millennia and involves a change in the type of land system present. Commonly, it is due to gradual sediment loss from accretionary landforms such as beaches and foredune plains adjoining or climbing cliffs. The example suggests a structural change from a mainland barrier system to a cliffed coast without a barrier.

Stability refers to short term changes at sub-decadal scales, including singular events, without change to the type of land system present. The example shows the outcome of an extreme event: A large volume of sediment of sediment deposited during flooding of the Ashburton River prior to the 1963 has formed an elongate spit extending eastward from the river mouth. Subsequent migration of the spit is apparent by 2009.