| Abstract | The 290 km long segmented, fringing Ningaloo Reef of Western Australia lies between
latitudes 21°47’ and 24°S along longitude 113°30’E. Nearshore currents, controlled by
the reef, dictate both marine and terrestrial sedimentary systems and provide a modern
analogue for the adjacent uplifted and preserved paleo-reefs. The present day reef
records Holocene and Last Interglacial phases of reef growth in a tectonically stable
environment, overlying uplifted Tertiary carbonates of the Cape Range, which is flanked
by raised Plio-Pleistocene terraces and reefs.
The coastal plain adjacent to Ningaloo Reef and the Cape Range region, provides
evidence of coastal evolution, tectonic uplift, global sea-level changes, coastal aeolian
processes, desert aeolian processes and karstic processes. Interactions between these
processes have determined the geomorphology and stratigraphy of the region. The
Holocene evolution of the coastal plain adjacent to Ningaloo Reef records five
depositional stages; shelf erosion and shore face retreat, transgressive deposits,
highstand deposits, regressive deposits, and modern beach and foredune development.
As a reflection of these influences, large parabolic dune fields were deposited during the
transgression and highstand, relic coastal features generated during highstand, and beach
ridge plains formed during the regression.
The regional geomorphology varies from rugged Tertiary limestone cliff coasts adjacent
to the southern extent of Ningaloo Reef, to Holocene sandy active beaches on the coast
adjacent to the northern extent of the reef. The pre-existing topography has largely dictated Holocene depositional regimes. An expansive Pleistocene desert dune plain
dominates the regional inland geomorphology and is indicative of past aridity. The
coastal plain in mapped areas is typically characterised by a narrow coastal strip of
Holocene dunes, including rocky and sandy shorelines, modern foredunes and relic
foredunes, beach ridges and parabolic dune fields. However, sections of coast adjacent
to the southern extent of Ningaloo Reef have no Holocene deposition where high
Tertiary cliff coasts abut the waters edge.
The coast adjacent to Ningaloo Reef is rapidly increasing in popularity as a preferred
tourist destination and this has led to increasing degradation of the fragile coastal
environment. This degradation is primarily related to nodes of activity, in the forms of
uncontrolled proliferation of access tracks and clearing vegetation for camping sites.
Geomorphological mapping of the coastal zone, integrated with a land classification
scheme based on substrate capacity, provides a regional data base that enables natural
and anthropogenic coastal environmental impacts to be assessed. The development of a
land classification scheme based on substrate capacity was incorporated with land
system units (geological units, further defined by environmental characteristics) to assist
in future land management and environmental monitoring. Land system units with low
substrate capacity are unconsolidated, have little to no vegetation, are commonly mobile
units that take form in steep slopes and undulating topography, making them prone to
sediment remobilisation and hence degradation. Land system units with a medium to
high substrate capacity consist of consolidated limestone with a thin to non existent
cover of colluvial material and significant vegetation cover.
Based on GIS analysis, risk zones were delineated, and areas which are particularly at
risk of degradation due to a combination of the level of land use and substrate
characteristics were highlighted. This study is of direct benefit for land management and
planning purposes as it quantifies the impacts on the coastal zone and allows for the
development of more effective management strategies. It is expected that the geological,
environmental and geographic information system (GIS) data produced in this study will
form the platform for further research work in this area. |
