Claudia Stark will be discussing the different perspectives revolving around the erosion issue in Lake Cathie.
   This poster along the fence of Ilarroo Road shows the public's disapproval of the planned retreat option.  Revetment Wall  Destructive Waves at Lake Cathie while year 10 SCAS students did field work on the erosion issue in the area.
 Lake Cathie 2012
 Illaroo Road 2012
 Residents along Illaroo Road.
 | Physical and Human Geographical processesOperating along the Lake Cathie coastline are many physical and human processes which contribute to the growing erosion issue along Illaroo road. Some physical factors include: Long Shore Drift is the geographical process where the waves approach the beach at an angle and effectively carry sand up the beach in a particular direction and is later pulled vertically down the beach by backwash.It is the primary method of sediment transport along the beach.The result is that if the direction is constant then material will be gradually shifted along the beach until the beach is stripped bare. The predominant nearshore direction at lake cathie is from the south-southeast, more than 70% of the time. This suggests that the longshore sediment transportation is to the north. Coastal erosion is the wearing away of land and the removal of beach or dune sediments by wave action, tidal currents wave currents, or drainage. Storms, wind and fast moving water vehicles cause coastal erosion. Destructive Waves have high energy and high wave frequency. they have a weak swash which brings ashore little material but has a much stronger backwash than swash, which causes it to remove beach material. Destructive waves create a steep narrow beach. To be classified as destructive waves there have to be more than 8 in one minute. We observed this in our fieldwork and noted that the waves were destructive due to their size and surge. There was also strong water movement (rips and current). Constructive Waves have low wave frequency and energy, where strong swash carries materials onshore and the weak backwash removes very little material, this froms a wide sloping beach. Because their swash is much stronger than their backwash the beach is built up by the deposited material. They are less frequent reaching shore less than 8 times per minute. Human processes increase the speed of the issue in ways such as flattening the primary dunes, walking and recreational activities on the dunes and clearing of shrubs along the dunes.These processes have created the issue with erosion which endangers the houses along Illaroo road and those along Chepana street if Illaroo houses are taken out. We observed some of these human processes on our field trip to Lake Cathie earlier this term. We saw houses built along the primary dunes, and clearing of weeds like the Bitou Bush along the dunes also. Management Options
Planned retreat: the planned retreat option is where the government buys back the private land at risk, which would allow the natural process of erosion to occur. The Study suggests that Council should offer to pay each property owner an amount of $600,000 for their property. This amount is considered an insult to the property owners, and is substantially less than prices paid by residents for their properties up to 6 – 8 years ago. One property will be bought every 3 years, therefore it will take 51 years for all 17 properties to be bought. the total coast including demolition, relocation of services, and restoration costs will be $11.44 million. The benefits of the planned retreat option is it would allow the environment to erode naturally and the process to occur without human interference, the private owners of the houses along Illaroo road would no longer be at risk, and it would improve the public access and recreational amenity of the beach. The disadvantages of the planned retreat option is there is a high emotional impact on owners of the properties, difficulties on deciding the right price to buy back properties. Some opportunities resulting from the planned retreat option is the ability to rehabilitate the land on illaroo road and the dunes, and possibly improved public access and recreational amenity. Some possible threats due to this is the owners of the houses along illaroo road do not want to sell their properties, and this may cause protests etc. Beach Nourishment: The beach nourishment option is where sand from the lake is dredged and placed along Illaroo Road. The immediate advantage of beach nourishment is the beach stops shrinking
Although there are many disadvantages to the beach nourishment option; the new sediment erodes again and often more quickly than the original beach, meaning the process must be repeated, beach nourishment is very expensive and dredging may also harm neighbouring marine life.
an opportunity resulting from beach nourishment is more beach access for tourists and recreational activities. But some threats are the possibility of a reduction in the population of local wildlife,
Revetment: the revetment is a rock structure built across the beach that is designed to prevent storm erosion and shoreline recession which will protect the 17 houses as well as Illaroo Road. the advantages of the revetment is that is is considerably cheaper ($8.5 million cheaper) than the planned retreat option, and it will stop the effects of erosion immediately as well as landowners keeping their properties.
a disadvantage of the revetment is that they generally only last for 50-80 years and may limit access to the beach for tourism or recreational activities. it is also not as aesthetically pleasing to the general public.
Some opportunities from the revetment wall is the
Groyne: is another rock structure, built straight out to sea designed to minimize the effect of longshore drift. They trap sediment from longshore drift which builds up a beach, this then brings opportunities in tourism and creates a positive multiplier effect on the local economy (good for retail, catering and transport jobs). It also means that if there is a reduction in the erosion of the beach. Some disdvantages of the groyne structure is they starve beaches further down the coast of sediment which can result in coastal erosion in another location further down the beach, this could destroy buildings or private land in another area creating the same problem in a different area. the threats of this could be the coastal erosion in another area could mean house prices in another location would plummet in the region making it difficult for affected homeowners to move out. Revetment wall and Beach nourishment:this option incorporates both the revetment wall and beach nourishment which means that the revetment wall will have the benefits of being strong and providing good protection by
absorbing the waves energy, and the advantages of beach nourishment is that the immediate effects of erosion and longshore drift ( the beach shrinking) will be stopped. The disadvantages are that the revetments have a
relatively short life span (30-50 years) and are both will be expensive, leading to threats of not being able to afford the repairs. but this option brings many opportunities to the Lake Cathie residents and tourists as it still enables able access to the beach and room for recreational activities although the wall isn't largely aesthetically pleasing. Restore Lake Innes: The stakeholders all have different opinions and perspectives on the best form of coastal management in lake cathie. a resident living on Illaroo Road believes that the council has responsibility to protect the properties in this area and that the revetment or sea wall is the best option to be payed for by the council. residents have a great emotional attachment to these properties and believe that " the council allowed this land to be built on many years ago so it is their responsibilty to protect the properties in this area." But not all people involved agree with this course of action, a conservationalist from Coast Care believes that the many poor decisions made in the past shouldnt influence the decision making in the present and that this will not help find the most effective solution for the erosion issue in Lake Cathie. He believes " the council needs to consult with specialists and think through the actions before they rush into anything...they need to find a strategy that works in harmony with the dynamic nature of the coastline environment." This further consultation with informed specialists will help see the best and most effective solution, which may not be the sea wall as it will create even further erosion as it increases the power of the wave's action. the local council member shows a similar sympathy in the plight of the residents "we understand that people are upset." but believes that the buyers were aware of the threat of erosion when they purchased the homes, and that the action they take must be in accordance with local council development regulations. this in consideration they local council believes the best option is to purchase the properties and revegatate the land, acknowledging that this option isn't popular but it is sensible. Evaluation: Through this research and the fieldwork we completed at Lake Cathie i believe the revetment wall in combination with beach nourishment is the best option as it gives the beach time to repair and time for the council to consult more specialists and investigate other options. this issue is very complicated with varying perspectives form residents, local shop owners and council members and i believe this option fits in the best with everyone as well as being suitable for the environment's rehabilitation.
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