Environmental Change And Management
The purpose of this report is to explain the extent of human induced change to both the Collaroy and Long Reef area and to discuss the strategies implemented by Northern Beaches council to manage coastal erosion. This is relevant to environmental change and management as human induced change significantly alters our global environments for the worst while responsible human management reverses these effects. This is especially true for Collaroy and the Long Reef Area as there are various human induced changes that the Northern beaches are trying to reverse. This report will cover the geographical context, natural processes operating, human induced changes, and management strategies of the Collaroy and Long Reef area.
Collaroy is a suburb located approximately 22km North of the Sydney CBD at the coordinates 33.7315° South and 151.3002° East. It has a land area of 273 hectares and an estimated population of 8463 people, meaning a population density of 30.93 per hectare. The land at Collaroy and its surrounding area is being used for mainly residential, commercial, and recreational use. The area is also crucial for transport from manly to the northern beaches. These human uses sometimes interfere with the area’s natural features of Collaroy and its surroundings include the beaches, sand dunes, lagoons, and headlands that are crucial to the native environment and ecosystem.
There are a plethora of natural processes operating in the Collaroy and Long Reef area along the coast:
One of these natural processes is the formation of bays and headlands due to coastal erosion. Bays and headlands only form along coastlines when there are alternating bands of hard and soft rock. Hard rock is more resistant to erosion than soft rock. As a result, overtime destructive waves will have much heavier impacts on the soft rock. This is caused by coastal erosion processes such as hydraulic action (where rock is broken down by the forces of deconstructive waves) and abrasion (where stones and rocks are thrown at the coast by waves). Eventually a deep bay is formed while the hard rock sticks out as headlands. The bays are now protected from further erosion by the hard rock of the headlands. A beach will form in the sheltered bay as the waves are much weaker. See Figure 3 for a visual aid on the formation of bays and headlands. An example of a headland and bay observed from Collaroy Beach can be seen in figure 4.
Another natural process is long-shore drift and how it transports material along the coastline. This process occurs when constructive waves strike the shore at an angle due to the wind direction. Deposits of sand and other material within the waves are taken by swash and put further down the beach. The deposits are then pulled straight back by the backwash because gravity. This occurs many times so that eventually the deposits travel further down the beach in the direction of the long-shore drift. A diagram showing long-shore drift can be seen in figure 5.
Finally, the natural process of deposition and the coastal landforms it creates. This process occurs when the waves, currents, winds and any rivers connected to the sea transport sediment. Whenever any of these sediment carriers lose their energy deposition occurs. In other words, any sediment being transported is dropped. Along coastlines this can result in the emergence of landforms such as beaches, dunes, spits, and tambolos. Beaches form when the sediment is deposited on the shore by the swash of constructive waves. Dunes form when wind carries sand up the beach and deposits it in a heap around an obstacle like vegetation or driftwood. Spits develop when long-shore drift occurs primarily in one direction and then meets a river mouth or change in direction of the coastline forming an extension of the coastline. Spits turn into tambolos when waves diffract around islands taking sediment with them, eventually sediment will build up connecting the spit to the island (forming the tambolos).
A human induced change to the beach at Collaroy is the erosion of sand dunes caused by the development of manmade factors that extend seaward to the beach. One of these factors are the sea walls which are used to prevent property damage by residents/owners. However, due to deposition of sea walls under the sand dunes, the amount of sand at the Collaroy beach has been significantly lowered. This has resulted in a lack of sand to protect against surging waves, ultimately making it vulnerable to wave damage. In demonstration of this vulnerability, the 2016 June East Coast Low storm event (See Figures 8 and 9) resulted in 10 houses and 1-unit block along the Collaroy-Narrabeen coastline being evacuated.
Another human induced change is the increase in global warming caused by our extensive carbon emissions. This change occurs mainly because of the greenhouse gas effect, an effect where gases in the atmosphere trap the suns light and heat on Earth. When we release carbon emissions into the air it builds up these greenhouse gases in the atmosphere, trapping even more heat. We have managed to increase the amount of greenhouse gases in our atmosphere by more than a third since the industrial revolution (See Figure 10). If the global temperatures go up too much it causes the oceans to warm up and sea waters to expand. This takes up more space in the ocean basin and causes a rise in sea level. The warm water causes ice sheets, ice caps and glaciers to melt, adding to the rise in sea levels. Warmer temperatures also increase the likelihood of freak weather such as strong storms. These impacts have heavily affected the Collaroy areas coastline as rising sea levels submerge its coast while the storms damage the man-made assets and environments.
Beach replenishment is a process where sand lost through longshore drift or erosion is replaced from other sources. The northern beaches council sources sand from local building sites to supplement sand and build up sand on eroded beaches. Sand is also taken from the entrance of Narrabeen Lagoon and is used to replenish Collaroy-Narrabeen Beach. Beach replenishment is fantastic for keeping the beach aesthetically pleasing. This can have the effect of heightening the economy as it is pleasing to tourist while also protecting the hotels they stay in. However, beach replenishment is very cost inefficient as $10,000 per 100 meters must be spent every 1-5 years to keep replenishing the sand.
Another strategy is dune management which involves re-introducing native plants and installing fencing to anchor sand in place and help the dunes grow. The northern beaches council manages the coastal dunes. They create dune pathways to stop people walking through the dune vegetation as that can destroy the plants, which in turn destabilizes the dunes, furthering erosion. Dune management is one of the most effective strategies in coastal management with high aesthetic, cultural & spiritual value. It is also decently cost effective at $20,000 per 100 meters every 50-100 years. However, not effective in storm surges and needs to intrude onto roads and housing.
As previously mentioned, the purpose of this was report was to explain the extent of human induced change to both the Collaroy and Long Reef area and to discuss the strategies implemented by Northern Beaches council to manage coastal erosion. The main points discussed were the specifics in the geographical context, natural processes occurring, human induced changes, and the management strategies implemented by the council. In the geographical context we discussed the specific location, its relation to Sydney, and the land uses. The natural processes section described and explained the formation of headlands and bays, longshore drift, and deposition and the coastal landforms it creates. Human induced change was then studied in the areas of erosion of sand dunes and global warming. Finally, the management strategies implemented by the council such as dune restoration and beach replenishment were viewed along with their positive and negative attributes. This report has addressed the topic of environmental change and management by conveying that the impacts of global warming and dune erosion were real and significant, it also showed that it was important to start managing these issues now before it gets too late. All in all, the findings of this report are important as they enlighten us on the current state of our coastlines in the Northern Beaches, and all Australia for that matter, this will hopefully give us an incentive to start making dramatic changes to our global footprint.