Darwin City and its suburbs are bounded along the western shore by sea cliffs, between 1-30 m in height, and shore platforms at the base of headlands along with small pocket beaches and some longer beaches up to 10 km in length. The low lying coastal cliffs at East Point and Nightcliff consist sedimentary rock commonly known as Porcelainite which as been naturally eroded, largely by wave action from the ocean to form horizontal to gently undulating bedded strata of varying colours with large and small caves which are common at East Point and Casuarina to the north.
Darwin Harbour Catchment has a total area of 3230 km2 approximately 20% of the area is developed for urban and rural land uses. Darwin Municipal boundary fringes on approximately 36 km of coast line, made up of mangrove forest, beach and dune foreshore areas and cliffs. The current population living in the Darwin Harbour catchment is estimated at 110,000 people. ABS figures show in 2026 more than half of the projected NT population (165,000) will live in the Darwin Harbour catchment .
Cliff erosion is a natural process which occurs in stages. Firstly, fresh water surface runoff, groundwater flows and seawater gradually erode the lower to mid cliff areas containing soft dolomitic/carbonate and siltstones forming fissures and cracks within the rock.
Over a period of time the cracks become enlarged and break up large sections of rock from the parent material. At high tide the waves break on the lower cliff face which break the joints in the rock even further until eventually large sections of rock collapse onto the beach.
The caves formed by this process then tend to concentrate the wave energy resulting in even greater cliff collapses and more erosion with larger embayments along the coast.
Cliff erosion along the Darwin harbour coastline can also be increased by surface, stormwater and groundwater flows at particular points over the cliffs which also dissolve the fragile carbonate/silicate rocks leading to cliff instability. This process is enhanced by the acidic nature of the ground water in the Darwin region.
Nutrient rich stormwater and effluent discharging from sewerage outfalls near East Point are also the likely cause of algal staining and pitting of the dolomitic layers of the cliffs and are contributing to the bio-erosion occurring in these areas.