COASTAL GEOMORPHOLOGY

NORTHERN DEVELOPMENT TASKFORCE

Environment Experts Working Group

Presentation: Ian Eliot - July 2008

Tasks

1. Analyse, classify and map the coastal geomorphology of four locations, and consider the characteristics of each area relative to the coastal landforms of the surrounding region

2. Provide:

(a) information on the relative stability of the coastline with regard to historical and current relative rates and processes for erosion and or deposition of sediment associated with the location; and

(b) indicate how the location is likely to respond in extreme natural events, particularly cyclonic conditions storm surge and extreme rainfall events.

Approach

The approach adopted was to undertake a preliminary assessment of potential environmental change following steps recommended by the National Committee for Coastal and Ocean Engineering for assessment of coastal vulnerability to climate change (NCCOE, 2004)

It involves:

1. Identification of primary variables

These are the driving forces affecting change and include fluctuation in sea level, tides, severe weather conditions, and the wave regime

2. Determination of landscape components

Secondary process variables, such as sediment transport, operate on large landscape components such as sandy cliffs, beaches, barrier dunes, tidal creeks, mangals and mudflats.

3. Estimation of potential relationships between the primary variables and the landscape components

Describe any apparent evidence for impacts of primary variables on the large landscape components & establish potential relationships between them.

PRIMARY VARIABLES GEOLOGICAL STRUCTURE

SEDIMENTS

SECONDARY VARIABLES LANDFORMS

Interrelationships

Morphodynamic System

Primary Variables

Primary Variable Climate Change Scenario Potential Regional Effect

Sea Level CSIRO (2007)

2030 Range 0.19 to 0.28

2070 Range 0.26 to 0.60

2100 Range 0.28 to 0.79

Includes allowance for dynamic glacial

melting.

Local tide gauge observations suggest

a larger relative sea level rise for

the Kimberley than the global

average.

Ramifications for estuaries and tidal

creeks include evolution of coastal

floodplains and shoreline retreat.

Local effects may be particularly

significant on tombolos beaches

perched on rock platforms or

immediately landward of reefs.

Weather Systems CSIRO (2007)

Ambient summer wind conditions are

projected to increase by 2% to 5%

Tropical cyclones are projected to

decrease in frequency by up to

44% and increase in intensity.

The significant uncertainty associated

with forecasting tropical cyclone

intensity and frequency has been

identified by the WMO International

Workshop on Tropical Cyclones

(2006) and should be noted.

Changes in seasonal and longer term

average barometric pressure,

rainfall and wind conditions

associated with monsoonal activity

will affect a wide range of

secondary variable (processes)

acting on the coast.

The effect of tropical cyclones is highly

episodic and related to the intensity

and path of each event. Locally,

tropical cyclones may produce

extreme surges.

Primary Variables

The National Committee on Coastal Engineering

(2004) lists the primary (key) variables as follows:

1. Mean Sea Level

2. Ocean Currents

3. Ocean Temperature

4. Wind Climate

5. Wave Climate

6. Rainfall & Runoff

7. Air Temperature

Blue text indicates those used in assessment of

potential coastal change.

Geological Structure

Packer Island

Quandong to Coulomb Point

Perpendicular Head

Gourdon Bay

PRIMARY VARIABLES

LANDSCAPE

COMPONENT

Sea Level Tropical Cyclones Monsoonal Winds Rainfall Wave Regime

Embayments

and Sandy

Beaches

Inundation due to

sea level rise will

affect the coastal

sediment budget

while

unconsolidated

sandy coast

adjusts to the

change

Local impacts of

tropical cyclones

may include mass

movement of

sediments and

shoreline retreat.

The balance of

erosion and

deposition alters

with intensity and

duration of onshore

winds associated

with monsoonal

activity.

Surface run-off and

gully formation is

apparent on Pindan

soils.

The balance of

erosion and

deposition alters

with intensity and

duration of

onshore winds

activity. Hence

coastal aspect is

significant in the

region.

Tidal Creeks

and Mangals

There is potential

for a large change

in zonation of the

mangal as well as

increased tidal

exchange and

salinisation of

ground water with

an increase in sea

level

Short term changes

in flow patterns

occur during

inundation due to

storm surge.

Wrack deposition

occurs at high

levels on mudflats.

Sediments are

recirculated

between in-channel

sand flats and

inshore bars with

seasonal switching

between onshore

(monsoonal) and

offshore (trade)

wind conditions.

Scouring of tidal

creeks may occur

during high rainfall

events. The salinity

gradient associated

with tidal exchange

is re-established

under dry

conditions.

Waves are locally

significant at the

mouths of tidal

creeks where they

affect sediment

transport.

Relationships: Primary Variables & Landforms

Packer Island

Washover channel & fan

Rock bar & sand flats

Chile Creek platform

Cliffs & rock platforms

Packer Island

LANDFORM COMPONENT EXTENT & CONDITION KEY PROCESSES DISTURBANCE FACTORS

Rocky Coast: Cliffs. Both the

seaward and landward

sides of the island are

cliffed.

An extensive, approximately

18km long and 500m

wide, limestone and

sandstone barrier

formation comprises

Packer Island. Other

outcrops are smaller.

Storm surge associated with

fluctuations in sea level,

and oceanographic

changes associated

with extreme

meteorological

conditions overwash the

barrier at elevations less

than 10 m.

Surge overwash channels

and fans are present on

the northern and

southern parts of

Packer Island .

A tidal channel abuts the rock

platform on the inland

side of the island.

Rocky Coast: Outcrops and

reefs forming local rocky

headlands

As above - Packer Island and

Chile Head –the rocky

headland north of

Packer Island has

several erosion al

benches which may be

related to Pleistocene

changes in sea level.

Packer Island & Chile Head

are structures

supporting formation of

tombolos, control the

location of Lombardine

Creek and Chile Creek,

influence the function of

the local sediment cells

and provide sheltered

marine conditions,

supporting mangrove

creeks and mudflats.

Sea Level fluctuations are

likely to affect the

stability of the tombolo

and sand spits at the

mouth of the tidal

creeks, including

Lombardine Creek and

Chile Creek behind the

barrier formations and

stability of the coast

between them.

Inshore Features: Sand

flats

An extensive sand flat is

impounded by a rock br

extending over 2 km

from Lombardine Point

to the shore.

Sea level fluctuations

associated with tidal

ranging and

meteorological process

drive inshore currents.

Any loss of sediment from

the embayment

landward of Lombardine

Point is likely to

exacerbate breaching of

the tombolo.

Perpendicular Head

NORTH HEAD PERPENDICULAR HEAD

North Head – Tappers Lagoon

Tappers Lagoon

Middle Lagoon Emeriau Point – Chimney Rocks

Embalgun Weedong Lagoon

Perpendicular Head

LANDFORM COMPONENT EXTENT & CONDITION KEY PROCESSES DISTURBANCE FACTORS

Rocky Coast:. Unstable

sandstone cliffs

North Head and

Perpendicular Head are

substantial headlands

with an elevation over

10 m.

There is substantial evidence

cracking and block fall

around North Head.

Oceanographic processes

operating at mean sea

level are apparently

undercutting the cliffs at

North Head.

Cliff erosion would be

exacerbated by ocean

processes during

extreme meteorological

events.

Sandy Coast: Dunes . Coastal dunes are located

south of Cliff Point, at

Middle Lagoon,

Mercedes Cove and

either side of Bell Point.

The barrier dune and wetland

at Weedong Lagoon is

an unusual landform in

the region.

Storm surge, onshore winds

associated with tropical

cyclones and monsoonal

activity contribute to the

formation of composite

storm bars and dune

formations.

Sea level rise is likely to

cause landward retreat

of the dunes in each

location.

Destruction of dune

vegetation by vehicle

tracking, fire and coastal

erosion may cause

instability.

Hinterland: Pindan Cliffs On the western end Pinder

Bay, near Embalgun, the

Pindan soils have been

eroded by coastal

processes

Sea level fluctuations

associated with extreme

meteorological events

bring coastal processes

to the base of the

Pindan. Cliffs formed by

ocean processes are

then degraded by

slumping and gullying.

Scalloping of the coast

indicates wave

refraction around

Perpendicular Head

and, perhaps higher

than average set-up of

water levels during

extreme storm events.

Coulomb Point to Quandong Point

Quandong PointJames Price Point - erosionJames Price Point - dunes

South of Coulomb Point North of James Price PointCoulomb Point

Coulomb Point to Quandong Point

LANDFORM COMPONENT EXTENT & CONDITION KEY PROCESSES DISTURBANCE FACTORS

Rocky Coast: Outcrops and

reefs forming local rocky

headlands

Four small headlands, less

than 0.5 km outcrop

from Coulomb Point to

Quandong Point.

Other outcrops occur as

linear, shore-parallel

rock platforms

underlying sandy

beaches.

Storm surge associated with

fluctuations in sea level,

and extreme

meteorological

conditions interact with

the geology to affect

shoreline development

and stability in nearby

embayments.

Storm surge and tidal

currents during spring

tides may erode

beaches perched on the

rock platforms.

Sandy Coast: Dunes Coastal dunes are located at

Quandong Point, Close

to James Point and in

the embayment

immediately south of

Coulomb Point

Storm surge, onshore winds

associated with tropical

cyclones and monsoonal

activity contribute to the

formation of composite

storm bars and dune

formations.

Destruction of dune

vegetation by vehicle

tracking, fire and coastal

erosion may cause

instability.

Hinterland: Pindan Cliffs In the 10 km north of James

Point the Pindan soils

have been eroded by

coastal processes and

terrestrial run off.

Sea level fluctuations

associated with extreme

meteorological events

bring coastal processes

to the base of the

Pindan. Cliffs formed by

ocean processes are

then degraded by

slumping and gullying .

The effects of storm surge

and heavy rainfall may

be exacerbated by

drainage along tracks

and off the Pindan.

Gourdon Bay

SW Cape Latouche Treville Wrack deposit – Port Smith Extension of tidal creek

Gourdon Bay – view SE Cape Du Boulay - erosion Cape Du Boulay – geology

Gourdon Bay

LANDFORM COMPONENT EXTENT & CONDITION KEY PROCESSES DISTURBANCE FACTORS

Rocky Headlands: Talus and

boulder outcrops are

located at headlands and

in embayments

Storm deposits flank cliffs and

rocky headlands in

Gourdon Bay. These may

underlie and be partly

covered by beach sands

Fluctuations in sea level, and

oceanographic changes

associated with extreme

meteorological conditions

will affect the exposure

and transport of storm

deposits along the beach

Any cross shore development

would need to consider

the potential impacts of

boulder transport during

extreme mind, wave and

sea level conditions.

Embayments: Sandy beaches

and tidal flats

Small bay beaches are located

in the vicinity of Cape

Latouche Treville & long

sandy beaches with some

rocky headlands in

Gourdon Bay.

Tidal reworking of sediment.

Fluctuations in sea level,

and oceanographic

changes associated with

extreme meteorological

conditions

Cross shore movement of

sediment apparently

occurs with fluctuations in

sea level and the wave

regime.

The zeta form of Gourdon Bay

indicates long-term

sediment transport

alongshore to NE. This is

apparently small in

volume.

Stream Mouths: Permanently

open streams draining

mangals and mudflats

Tidal creeks in Port Smith drain

mangrove wetlands and

vegetated mudflats. The

creeks discharge over a

well developed ebb tide

delta

Extreme winds and waves;

Storm surge

Sea level fluctuations and storm

surge associated with

severe weather conditions

impact on the upper

reaches of the tidal

creeks.

Sediment exchange may occur

between the flood tide

distributaries and the ebb

delta with changes in

weather and tides.

Thanks for your attention