In Central coast scale, the study area is located at the south part of LGA area and close to the boundary where includes Ettalong Beach and Booker bay. In Brisbane water scale, it starts form rip bridge then end at the estuary of Brisbane Water where is close to the Broken Bay. This area has lower housing density and people who live here are almost at median age. It is also an area with highly car dependency. The Fishing and shipbuilding is the traditional culture of this area so it is not hard to see several private and public wharf along the Bookerbay eastern coastal area.
Figure1，2：Location of Study area
Tourism is one of the main industries in this area. The Booker Bay and Ettalong Beach as the famous tourist attractions in Central Coast attract people from all over the world to enjoy their holiday here. The public ferry wharf is the main starting point for whale watching every winter. Along the beach area, hotel composition subsidiary industry is also developing. However, as the current erosion annually happened, the coastal beach area is facing a crisis of damage and gradual disappearance.This will bring a huge impact to the local tourism industry and at the same time, it will cause huge losses to the local economy.
Figure 3：A view of public wharf beside Booker Bay
Figure 4：A view of Ettalong Beach
Figure 5：A view of cafe in Ettalong Beach
Main Problem
From the DEM data of Earth Explorer, it is clear that the average altitude of this area is not high that eighty percent of the area is less than thirtyfour meters above sea level(Figure 6). In addition, the gradient map(Figure 7) indicates the general gradient is also at lower degree so our study area has flat terrain. Actually the three main problem on this site is: areal flooding, coastal erosion and narrow economy. For the areal flooding(Figure 8), as the seabed is too high in this area, it is easier to be flooded than other regions in central coast. Affected by sea level rise and storm water, the east of Booker Bay and west of Ettalong Beach area are tend to be flooded in the future. For the coastal erosion, the soil types map indicates that the main soil types along the coastal area are Aeolian soil and Beach sand soil (Figure 9) so that they are easily eroded by the seawater. Moreover, from the data collected by Gosford Narara Research station, we found the Southeast winds prevail throughout the year in the study area(Figure 10) impact the coastal erosion along the southwest of Ettalong beach and the current movement in the seabed area. For the seasonal tourism, it is a general problem for beach area. Because of the cold wind and temperature, it brings shock to the beach tourism industry.
Figure 6: Elevation map of study area
Figure 7: Gradient map of study area
Figure 8: Flooding map of study area
This research wil mainly focus on the problem of coastal erosion. It will post several strategies based on the analysis of costal erosion. Figure 9: Soil types map of study area
Figure 10:
Coastal Erosion The coastal erosion is one of the most serious problems happened in our study area. Based on the analysis and research about the seabed elevation(Figure 11), the direction and pressure of flood tide and ebb tide(Figure 12,13), estuary area will face great shock from the south pacific ocean. Passing the sand bar area, the south pacific ocean currents will go to the deep area. Therefore, the main erosion area is located at the west of Ettalong Beach. The erosion types are short term cyclic erosion, realignment of tidal channels and abnormally high wave attack(Figure 14). The short term cyclic erosion is a general erosion type and it is influenced by the wave energy input which has seasonal variation. Realignment of tidal channels produced by human interaction ( grone constructure) and natural events (storms). Water passing through the sand bar will reduce the stabilization of adjoining beach. For the abnormally high wave erosion, extreme offshore waves can cause an increase in water depth on the shoal (by erosion or storm surge) and allow unusually high wave attacks. According to erosion study made by the local council, it divded the main erosion area into four main sections: Ettalong point, Ettalong point to Lemon Grove Drain, Lemon Grove Drain to Memorial Ave Stormwater Outlet, Memorial Ave Stormwater Outlet to Ferry Wharf. The strategy of dune construction and stabilization is highly recommended for those four areas. Channel nourishment is suggested to be applied in the areas from Lemon Grove Drain to Ferry Wharf. For the Beach Nourishment, the study recommends to apply this method in the areas from Ettalong point to Ferry Wharf. The Groyne and Revetment works are necessary for the areas from Ettalong point to Memorial Ave Stormwater Outlet.
Figure 11: Elevation map of seabed
Figure 12: Flood tide analysis map
Figure 13: Ebb tide analysis map
Figure 14: Erosion types analysis map
Figure 14: Proposed strateties for different erosion types in different area.
Report Goals This report engages to introduce and apply different landscape technologies to mitigate the coastal erosion problem in Ettalong beach area. It will seperately apply approperiate innovative landscape technologies for those four sections in Ettalong Beach area. As those four sections has different erosion types, they have different design goals: - Ettalong point : Defending from the Abnormal Wave Attack and Cyclic Erosion - Ettalong point to Lemon Grove Drain : stabilizing the beach to mitigate the erosion caused by Abnormal wave attack and Cyclic Erosion - Lemon Grove Drain to Memorial Ave Stormwater Outlet : Defending from the tidal erosion caused by channel realignment - Memorial Ave Stormwater Outlet to Ferry Wharf : mainly mitigate the Abnormal Wave Attack The next part will Sepcifically introduce different innovative landscape technologies for coastal erosion and evaluate several of them for our study area.
02 Innovative Landscape Technologies 02.1 Monitoring and Simulating technologies Hawk Eye II scanning device The Hawk Eye II scanning device can capture accurate data on both land and seabed topography in one aerial pass. Sounding and terrain data will be used to create continuous digital elevation models of ocean and continuous land. In addition, the fine details of the cloud point density produced by LiDAR measurements will help to identify very small scale changes in the height and roughness of the underwater surface, revealing the shape of the dune to identify any sandbank and produce a fluid power that can then be used to develop and learn to solve any local sediment accumulation problem. The Hawk Eye II laser data achieves an accuracy of +/- 25cm in the sea and a depth of between 3m and 55m. It can also be used to determine and analyze the geological conditions of the seabed. It can be used to accelerate the usability and accuracy of nautical charts, identify the shape of the seabed and pinpoint the location and exact dimensions of any man-made structure or obstacle. Its technology improves the viability, quality and speed of coastal and maritime mapping, and typically operates at 60% of traditional hydrographic cost, helping to provide high quality information for environmental and conservation projects, habitat management and coastal Area understanding of engineering and exploration.
Figure 15 : The operating principle of the Hawk Eye II airborne bathymetric and topographic laser scanning system
Pros: Improve the speed and quality of coastal mapping Cons: It can only be used to measure terrain.
Figure 16: LiDAR data captured with Hawk Eye II showing the morphology of both land and seabed.
Liminal machines Liminal machines is a method which need to adopt the technology of paramatric modelling and computational simulation to understand the pattern of process that produce specific performance and effects. A series of software skills such as Maya Particle Flow, Rhino Terrain, Grasshopper,Paneling Tools and GIS are also necessary for this technology.
Figure 17: Exploration of flow dynamics and vortex formation (left); understanding of forces that direct sand movement and failure (right)
Liminal machines is a method which need to adopt the technology of paramatric modelling and computational simulation to understand the pattern of process that produce specific performance and effects. A series of software skills such as Maya Particle Flow, Rhino Terrain, Grasshopper,Paneling Tools and GIS are also necessary for this technology. The Pattern of process is a model established by exploring the natural forces identified in the function/material cycle.It focuses on the organizational and qualitative characteristics of strength, mobility, transformation and adaptation.Using a time-based parametric model (generated by Rhino and Grasshopper), it is possible to create a vector field with attractors (points or curves) as influencing factors, resulting in changes in direction and intensity.By analyzing the subsequent patterns, an intuitive list can be compiled that records the forces of tidal and air movements as well as erosion, sedimentation and sedimentation processes. Pros: - It is more intuitive to see the direction of sand erosion and the accumulation area.
Figure 18 : The documentation of the Computational Fluid Dynamics (CFD) model highlights the loss of sand and the area of accumulation.
Cons: - The experiments of liminal machine in this book are site less and scale - less so when it is applied to a specific site more elements should be considered about.
Floating sensor network The drifts that makes up the floating sensor network have communication capabilities and integrate many sensors including GPS, pressure, Depth, temperature and salinity. The fleet will be deployed quickly to respond to emergencies such as floods, dam breaks and pollutant spills. Movable, portable, floating sensors are placed in the running water where they are needed.The data sent by the sensor is used to estimate and generate a water flow map. These devices send information to responders over mobile phone networks and short-range radios.Since the sensors are carried by sea water, their GPS receivers can track their movements.The combination of real-time information from multiple sensors provides a large picture of the entire system – a situational awareness map. Each drifter has a different trajectory; combining all of these paths provides more information than a separate section. Imagine the “traffic map� of the entire delta, showing the speed of the water, how deep the water is everywhere, and how much water is polluted.
Figure 19 : A view of device structure and functions for each part
Pros: Compact and convenient with multiple functions Cons: It might affect ferry routes Figure 20 : A view of device working in the water
02.2 Coastal Stabilisation Devices Artificial Dunes Coastal sand dunes are complex ecosystems formed by wind transport, located at the interface between the terrestrial and marine environments. Sand dunes play an important and recognized dual role in shoreline and beach stability: -They provide natural protection for beachfront property and assets from flooding and storm surges -They constitute the erodible sand source of the beach Sand dunes also provide a natural “trap” for wind-driven sand that precipitates and contributes to the growth of the dune system while reducing the potential blockage of rain drains. Another common practice to promote sand dune stability is to place an anti-storm surge in the dunes to provide a second line of defense during the storm. In fact, under normal circumstances, the “artificial armament” of this dune is still completely buried, invisible, and exposed to the outside as a strong revetment in the case of beach erosion. The core of the dune uses underground rock or concrete breakwaters, and various patented systems, such as stone-filled matrixes, meshes, cushions, and sand-filled geotextiles, are used as protective materials for underground sand dunes.There are several documented methods for the reconstruction and restoration of sand dunes, including the use of wind barriers, replanting vegetation and managing beach access points. Pros: - Buffering waves and flooding - Sand supply to the beach - Creating natural habitat - Preventing sand from moving inland
Figure 21 : A view of Dune reconstruction in Cadiz Spain
Figure 22 : A view of Delfland Coast The Netherlands
Cons: - It is Sensitive to sea level rise - Performance in the field of sand dune filling - Durability of reinforcement material - Stability of reinforcement material
Figure 23 : A view of coastal dunes at Aberffraw, Anglesey, UK
Beach Drainage Systems Beach Management System The Beach Management System (BMS) works on saturated beaches that are more susceptible to erosion than unsaturated beaches. When saturated, the density of individual sand particles is small and there is less contact between particles, making the beach material vulnerable to the effects of overshoot and undershoot. Therefore, if the beach is well drained, the particles will pile up more closely and the sand on the beach will be better consolidated. The BMS system is a drainage system that integrates a drain pipe and an electric pump. ( see Figure 24) The buried horizontal drainage ditch is in the form of a perforated pipe wrapped by geotextile. They are parallel to the shoreline, slightly above the average high tide line, and are located in the surge zone (wave surge zone). The drain drains the collected water into the collection basin, which then flows into the pumping chamber built on the far back shore. Once the water level in the tank reaches the preset water level, the sensor-activated submersible pump will begin to pump the drained water off the beach.
Figure 24 : A schematisation of beach management system
Pressure Equalisation Modules The Pressure Balance Module (PEM) system is another relatively new system and is currently being tested in Kuantan and Penghang. PEM acts on the uprushing area of the beach, and the waves flow upward along the beach. When they reach the limit, they flow downward and penetrate into the bed.
Figure 25 : A schematisation of Pressure Equalisation Module
The infiltration of seawater into the riverbed is limited by the existing groundwater level. Therefore, if groundwater can be reduced, more water can penetrate the bed from the run-up, and less water will drag the running surface away.The reduction of the local water table can be achieved through the PEM system, which physically “connects� the atmosphere to relieve stress inside the beach. In summary, PEM increases the vertical penetration of the upper punch in the oblique belt. Pros: -No visual impacts -Simplicity of constructability -Low cost Cons: -Only suitable for low energy wave areas -Durability -Easily to be damaged during storms
Figure 26 : Pressure Equalisation Module pipe at Teluk Cempedak beach
02.3 Wave Attenuation Devices "Natural" Defence Artificial Sea Grass The seagrass field appears as a current attenuator in its natural state, and several products have been produced as a flush prevention system. The leaves of the artificial seaweed or seaweed system are made of polypropylene, synthetic rubber or natural rubber. These systems are fixed to the bed in blocks or blocks to reduce the velocity of the water and induce sediment deposits in the water column. The University of Teknologi in Malaysia has successfully tested an artificial seaweed system consisting of leaves made of natural rubber.The blade has a specific gravity of 0.5 and floats on the water. The current emission reduction can reach 70% (Hadibah Ismail 2005). Because it acts like a resistance barrier that blocks the normally strong water flow, the success of an artificial grassland system relies heavily on the safe anchoring of the seabed. Concrete block foundations are often used as anchoring mechanisms.
Figure 27 : A view of Artificial Sea Grass
Artificial Mangrove Root Systems Mangrove roots play a key role in wave attenuation. Othman (Othman 1994) observed that the roots and trunks of Avicennia slowed the flow of water caused by tidal and inland emissions, leading to sedimentation. The closer the distance between the tree and the tree, the greater the attenuation of the wave energy.Local researchers are currently studying the effects of the strength, shape, and configuration (or alignment) of the “engineered� mangrove roots to determine how they interact with the waves. The preliminary sink test on the roots of artificial mangroves proved that the method can effectively attenuate wave energy.The model of the product is shown in Figure 29.
Figure 28 : A view of natural magrove roots
Pros: - Wave attenuation - Stabilize the seabed Cons: - Only suitable for shallow slopes - Construction time and Management of Bio-technical Projects - High cost - Effect on the Eco-system
Figure 29 : A model of an artificial mangrove roots system
Wave Eater Wave Eater is an innovative, convenient floating breakwater system designed for a variety of beachfront applications, easy to install and environmentally friendly.This breakwater equipment consists of linear low density molded polyethylene and high density polyethylene dies. The interior is hollow and filled with water during installation until the unit is submerged by two-thirds. There are a series of baffles on the outside that stir up and forth as the waves impact the system. Wave Eater's innovative design allows for a variety of different configurations depending on the amount of wave dissipation required (wave height and energy cancellation) when passing through the attenuator. When designing a wave attenuation system, the designer considers the wavelength, (distance from crest to crest), wave height, water depth, and acquisition distance. Based on these aquatic specifications, it can form a breakwater system that includes specific needs. It also offers both economical and practical protection. Facilities in the United States and other countries are designed to protect marinas, ship launch facilities, utility spillways, coastal erosion prevention, and even floating breakwaters in fish farms.Because the Wave Eater is made of plastic and filled with water, the “footprint� in the environment is minimal, allowing for accelerated processing when design and installation permits are required.
Figure 30 : A view of Wave Eater
Figure 32 : A view of Wave Eater working for coastal area
Pros: - low cost of management - Wave attenuation - low ecological impact - It is easily and fast to install Cons: - It is difficult for a single one to serve a large area
Figure 33 : A view of Wave Eater working for Peninsula Marina, Lake Buchannon, TX
03 Strategies and Technology Application 03.1 Ettalong point Applying technologies: Hawk Eye II scanning device, Artificial Dunes & Artificial Mangrove Root Systems The Ettalong point is located at the southwest of Ettalong Beach deside the estuary of Brisbane Water(see Figure 34) where is possible to get a higher pressure from south pacific ocean. The main erosion types here are cyclic erosion and abnomal wave attack.Therefore, it might need more firm and stable strategies and materials to fight with coastal erosion. The Hawk Eye II scaninng helps to capture the elevation of sea bed (see Figure 35)and finds the sea bed in front of the Ettalong point is higher than other areas so that it has basement to buid defense for the coastal area. The Hawk Eye II scaninng also can make real-time monitoring the dynamic change of the coastal erosion helping to find approperiate strategies for this area. After researching several reports, it is found that the Atificial dunes (Coastal stabilization devices) and Artificial Mangrove System (Wave Attenuation Devices) are suitable for the erosion mitigation in Ettanglong point(see Figrure 36). As this area has to face higher pressure of current and tide, it is necessary to construct a second line of defence during the storm event. The defense will mainly be buried under the sand surface structured by stone-filled matrixes. The Artificial Mangrove System will distribute along the coastal line and under the water. The devices will be put on the seabed with higher elevation and not only stabilize the sand base but also can be another defense for the beach area.
Figure 34 : Area of Ettalong point
Figure 35 : a Lidar Image of Ettalong point
Pro: - Sand dune stabilization - Wave Attenuation Cons: - Ecological impact Figure 36 : a map of strategies proposal Stone-filled Matrixes Mangrove Roots System
Figure 37 : a cross section of strategy proposal
03.2 Ettalong point to Lemon Grove Drain Applying technologies: Liminal machines, Artificial Dunes with green grid & Wave Eater The Ettalong point to Lemon Grove Drain area is closed to the estuary of Brisbane water. It has the highest pressure of the tide and currents. The main erosion types here are cyclic erosion and abnomal wave attack. There are already some vegetations on the beach but most of them are quite sparse. Through the explorations of flow dynamics and eddy formations, The liminal machines helps to form the sand movement on the beach based on the wind data collected by Gorsford Narara Research Station throughout the whole year. The generated analysis map will help assist in the generation of subsequent strategies.
Figure 38 : Area of Ettalong point to Lemon Grove Drain
During the design part, one of the methods of Artificial Sand Dune construction has been adopted in the coastal erosion mitigation in this area that is green - grid. The green grid means to plant vetations on sand beach and stabilize the sand dune by their roots that also has the function of ecological remediation. Another strategy for this area is Wave Eater. As this area might have the highest wave, the width and the length of the Wave Eater should increase and more dam boards should be stiched together that means the Wave Eater System shoudl be strong enough to face the tide and surge. Pros: - Ecological remediation - Sustainable - Wave attenuation - The Wave Easter System has low cost and easity install Cons: - The Green Grid might take long time to get effect - It is sensitive to sea level rise
Figure 39: Sand movement in beach area made by Liminal Machine
Figure 40: Schematisation of Artificial Sand Dune Construction with Green Grid
Figure 41: A view of Artificial Sand Dune Construction with Green Grid
Figure 42: A view of Wave eaters with more dam boards
03.3 Lemon Grove Drain to Memorial Ave Stormwater Outlet Applying technologies: Floating Sensor Network, Beach Management System & Wave Eater The Lemon Grove Drain to Memorial Ave stormwater Outlet has already been constructed into Ettalong Beach Waterfront Reserve which already has groyne to defense the tide and surge erosion. It has a certain effect but it does not completely solve the problem.Therefore, this area still needs innovative technology to improve the coastal defense system. First, the monitoring system here is composed of floating sensor network and the network is combined with Wave Eater (a component of coastal defense system)which means that the floating sensor will attach to the Wave Eaters. The Floating sensor helps to monitor the pressure and direction of tide. When the tide direction changes, the propeller of floating sensor will help to move the Wave Eater directly face the tide. As the surface of Ettalong Beach Waterfront Reserve has been changed into concrete, it is not an easy work to put a drainage tank underground. However, it is effective to improve the coastal defense system. The water in the tank has connection to the Brisbane Water and has the same hydraulic pressure. Thus, when the tide comes up the water in the tank will also rise up. If the water level touch the sensor in the tank, it will send out the signal and the Electrical Pump sation start to pump the water and dischage them into other pond areas.
Figure 43 : Area of Lemon Grove Drain to Memorial Ave Stormwater Outlet GPS and Compass
Radio Computer Motor Control
Twin DC motors with Propellers Battery Sensor Figure 44 : The components of Floating Sensor
Pro: - Wave attenuation - Erosion mitigation - convenient Cons: - The floating Sensor System might affect the ferry routes. - Higher cost to achieve the Beach Management System Figure 45 : A map of strategies proposal
Figure 46 : A schematisation of beach management system from Lemon Grove Drain to Memorial Ave Stormwater Outlet.
03.4 Memorial Ave Stormwater Outlet to Ferry Wharf Applying technologies: Floating Sensor Network, Pressure Equalisation Modules, Beach Management System & Artificial Sea Grass The area from Memorial Ave stormwater Outlet to Ferry Wharf is located at the north of Ettalong beach. This area has higher level sea bed and a large amount of sea grass along the underwater beach area. The main erosion type here is abnomal wave attack. The existing sea grass might already take some effect to defend the wave attack but that is no enough this area needs more strategies to optimize its defense system. The monitoring system in this area is composed by the floating sensor network. The floating sensors are mainly distributed below the sea grass area that not only can monitor the wave pressure and direction but also can monitor its habitat condition. To imrpove the defense system, the artificial sea grass will be a applied in areas where has no sea grass and areas in front of sea grass. Although sea grass has capability to reduce the wave pressure and mitigate the eorison, it still needs protection. ' Planting ' Artificial Sea Grass in front of the original sea grass can form a protective barrier to prevent the roots and body of sea grass from being damaged by wave attack. Meanwhile, for the area without real sea grass, Artificial Sea Grass fields can reduce the flow rate of water and induce sediment deposition in the water column.
Figure 47 : Area of Memorial Ave Stormwater Outlet to Ferry Wharf
Figure 48 :A map of strategies proposal
Another strategy is a combination of Pressure Equalisation
Modules and Beach Management System. As this area has higher level sea bed, it is hard to only rely on seawater infiltration to figure out the erosion problem. Thus, two levels have been set up. The Level 1 is mainly treated by Pressure Equalisation Modules and Level 2 combine the Beach Management System with Pressure Equalisation Modules. When the sea water start to flood the secend PEM pipe the water flowt the the underground water tank and start to be controled by the Beach Management System.
Pros: -Wave attenuation -Seagrass protection -Optimize the drainage system -Convenient monitoring system
Figure 49 :Artificial Sea Grass working with real sea grass
Cons: - Ecological impace - High cost
Level 2
Level 1
Figure 50 :a cross section of combination of Pressure Equalisation Modules and Beach Management System
04 Conclusion This report introduces and applies several innovative landscape technologies for the coastal erosion problem along the Ettalong Beach. Those technologies are divided into three types: Monitoring and Simulating technologies: - Hawk Eye II scanning device - Liminal machines - Floating sensor network Coastal Stabilisation Devices: - Artificial Dunes - Beach Management System - Pressure Equalisation Modules Wave Attenuation Devices: - Artificial Sea Grass - Artificial Mangrove Root Systems - Wave Eater After understanding and evaluating all the strategies, they are seperately applied in four main erosional area : Ettalong point,Ettalong point to Lemon Grove Drain,Lemon Grove Drain to Memorial Ave Stormwater Outlet and Memorial Ave Stormwater Outlet to Ferry Wharf. Each area has at least three strategies for monitoring, sand stabilizing and wave atteunating. However, the effectiveness of each strategy needs to be validated in future practice and research.
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