Dune Management Strategy for Alva Beach, Wunjunga and Beachmount Reserve - Burdekin Shire Council
←
→
Page content transcription
If your browser does not render page correctly, please read the page content below
Dune Management Strategy for Alva Beach, Wunjunga and Beachmount Reserve Draft for Public Comment 03 Sept 2020
JBP Project Manager Daniel Rodger Jeremy Benn Pacific Suite T46, 477 Boundary Street Spring Hill QLD 4000 Australia Revision History Revision Ref / Date Issued Amendments Issued to Draft Dune Appraisal LG, DM v1.0 / 21 Apr 2020 Draft Management Options LG, DM, OP V 1.1 / 26 June 2020 Draft For Public Comment LG, DM, OP V 1.2 / 03 Sept 2020 Contract This report describes work commissioned through Vendor Panel on 09 March 2020, under contract QBSC/20/003. Burdekin Shire Council’s representative for the contract Linda Goven. Clare Yang and Daniel Rodger of JBPacific carried out this work. Prepared by ................................................ Daniel Rodger BSc MEng CEng CMarEng MIEAust Prepared by ................................................ Clare Yang MEng Coastal and Civil Engineer Purpose This document has been prepared as a Draft Report for Burdekin Shire Council. JBP accepts no responsibility or liability for any use that is made of this document other than by the Client for the purposes for which it was originally commissioned and prepared. JBP has no liability regarding the use of this report except to Burdekin Shire Council. 2020s0406 - BSC - Burdekin Dune Management Strategy_Management Options 1.2.docx i
Acknowledgements JBP would like to acknowledge the previous work undertaken within the Draft Beachmount Coastal Land Management Plan by NQ Dry Tropics, and the Coastal Hazard Adaptation Strategy by Alluvium Consulting, which has provided a scientific and planning base for this project. Copyright © JBA Pacific Scientists and Engineers Pty Ltd 2020 Trading as Jeremy Benn Pacific and JBP Scientists and Engineers ABN: 56 610 411 508 ACN: 610 411 508 2020s0406 - BSC - Burdekin Dune Management Strategy_Management Options 1.2.docx ii
Contents 1 Introduction........................................................................................................ 1 2 Background to coastal values and processes ..................................................... 2 2.1 Values for traditional owners, residents and visitors ........................................................ 2 2.2 Alva .............................................................................................................................. 2 2.3 Wunjunga...................................................................................................................... 5 2.4 Other available reports and data for the Burdekin coastline ............................................. 11 3 Appraisal of dune system ................................................................................... 14 3.1 Drivers of coastal processes and erosion........................................................................ 14 3.2 Appraisal of the dune system ......................................................................................... 15 3.3 Location of infrastructure within the erosion zone ............................................................ 17 3.4 Dune crest in relation to storm tide levels........................................................................ 18 3.5 Dune disturbance, barren dunes or blowouts .................................................................. 18 3.6 Track density ................................................................................................................. 19 3.7 Assessment and prioritisation......................................................................................... 21 4 Dune management actions ................................................................................ 24 4.1 Management actions ..................................................................................................... 24 4.2 M1 - Enhanced partnerships .......................................................................................... 25 4.3 M2 - Revegetation of erosion zones ............................................................................... 26 4.4 M3 - Dune protection measures ..................................................................................... 30 4.5 M4 - Beach accessways ................................................................................................ 33 4.6 M5 - Beach traffic zone .................................................................................................. 33 5 Dune Management Strategy - Alva Beach .......................................................... 34 5.1 Summary of revegetation and protection zones .............................................................. 34 6 Dune Management Strategy - Beachmount Reserve .......................................... 37 6.1 Summary of revegetation and protection zones .............................................................. 37 Appendices .................................................................................................................... 40 A Appendix A - Beach appraisal ............................................................................ 40 B Appendix B - Fence technical drawings .............................................................. 48 2020s0406 - BSC - Burdekin Dune Management Strategy_Management Options 1.2.docx iii
List of Figures Figure 1-1: Alva, Wunjunga and the Beachmount Reserve. ......................................... 1 Figure 2-1: Alva map and local features ........................................................................ 3 Figure 2-2: Alva Beach lookout looking towards spit over dunes (left) and inner lagoon (right) ............................................................................................................ 3 Figure 2-3: Alva northern access track (between the two beach access points)............. 4 Figure 2-4: Alva Beach looking south (left) and north (right) .......................................... 4 Figure 2-5: Wunjunga map and local features ............................................................... 5 Figure 2-6: Beachfront houses at Wunjunga ................................................................. 5 Figure 2-7: The coastline looking south from Wunjunga ................................................ 6 Figure 2-8: The coastline of the Beachmount reserve near the Funny Dunny camping ground looking south (left) and north (right) .................................................... 6 Figure 2-9: Reduction in dune heights adjacent to informal camp sites (image from the Beachmount Coastal Land Management Plan) .............................................. 7 Figure 2-10: The evolution of Charlies Creek (source: Beachmount CMP) .................... 7 Figure 2-11: Analysis of historic images from the Beachmount CMP ............................. 8 Figure 2-12: Ebb shoals and channel formations between 1959, 1969 and present day 9 Figure 2-13: 4WD vehicles parked along Alva Beach .................................................... 10 Figure 2-14: Map from BSC beach vehicles guide......................................................... 11 Figure 2-15: Shoreline Analysis completed within the Burdekin CHAS .......................... 13 Figure 3-1: Drivers of coastal risk ................................................................................. 14 Figure 3-2: Conceptual diagram of different sediment transport mechanisms ................ 14 Figure 3-3: Conceptual diagram of blowout evolution (top) and example of blowout at Alva Beach (bottom). ............................................................................................. 15 Figure 3-4: Coastal segments ....................................................................................... 16 Figure 3-5: Infrastructure measured behind the dune .................................................... 17 Figure 3-6: Schematic of JEPA short-term erosion modelling using Vellinga (1982). ...... 17 Figure 3-7: Example dune disturbance mapping ............................................................ 19 Figure 3-8: Dune disturbances along Alva Beach........................................................... 19 Figure 3-9: Example track measurements...................................................................... 20 Figure 3-10: Alva hazard review .................................................................................... 22 Figure 3-11: Wunjunga and Beachmount Reserve hazard review ................................. 23 Figure 4-1: Lower Burdekin Land Care Association nursery and working bees ............... 25 Figure 4-2: Dune profile and preferred species (Beachmount CMP) ............................... 27 Figure 4-3: Sand fences in use at Wooli, NSW............................................................... 28 Figure 4-4: Sand fences in use at Kurnell, positioned within a blowout ........................... 28 Figure 4-5: Sequence for progressive installation of dune-forming fences (DLWC 2001) 29 Figure 5-1: Phase 1 revegetation works at Alva Zone 8-9 .............................................. 34 Figure 5-2: Overview of Alva Dune Management Strategy ............................................. 36 Figure 6-1: Phase 1 revegetation works at Beachmount Zone 19 and Zone 20-22 ......... 37 Figure 6-2: Overview of Beachmouth Dune Management Strategy ................................ 39 2020s0406 - BSC - Burdekin Dune Management Strategy_Management Options 1.2.docx iv
Figure 6-3: Alva Beach 10% AEP short term erosion map.............................................. 40 Figure 6-4: Alva crest level in relation to storm tide ........................................................ 41 Figure 6-5: Alva mapped dune disturbance .................................................................... 42 Figure 6-6: Alva mapped tracks through dunes .............................................................. 43 Figure 6-7: Wunjunga and Beachmount Reserve 10% AEP short term erosion map ..... 44 Figure 6-8: Wunjunga and Beachmount Reserve crest level in relation to storm tide ..... 45 Figure 6-9: Wunjunga and Beachmount Reserve mapped dune disturbance ................. 46 Figure 6-10: Wunjunga and Beachmount Reserve mapped tracks through dunes ......... 47 List of Tables Table 2-1: Tide levels from QLD Tide Tables ................................................................ 11 Table 2-2: Tide and storm tide levels for Alva Beach and Wunjunga ............................. 12 Table 2-3: Extreme wave conditions for Alva Beach and Wunjunga .............................. 12 Table 3-1: Scoring metric for infrastructure and erosion ................................................ 18 Table 3-2: Scoring metric for dune crest lowering ......................................................... 18 Table 3-3: Scoring metric for barren dunes or blowouts ................................................ 19 Table 3-4: Scoring metric for track density .................................................................... 20 Table 3-5: Scoring metric for each coastal segment ...................................................... 21 Table 4-1: Types of fencing .......................................................................................... 30 Abbreviations 4WD............................... Four Wheel Drive AEP ............................... Average Exceedance Probability AHD ............................... Australian Height Datum BRC ............................... Burdekin Shire Council CHAS............................. Coastal Hazard Adaptation Strategy DSAS ............................. Digital Shoreline Analysis System JBP ................................ Jeremy Benn Pacific (JBPacific) JEPA.............................. JBP Erosion Prone Area tool LAT ................................ Lowest Astronomical Tide LGA ............................... Local Government Area LGAQ............................. Local Government Association of Queensland MHWN ........................... Mean High Water Neap MHWS ........................... Mean High Water Spring MLWN............................ Mean Low Water Neap MLWS ............................ Mean Low Water Spring MSL ............................... Mean Sea Level NQDT ............................ NQ Dry Tropics TC.................................. Tropical Cyclone 2020s0406 - BSC - Burdekin Dune Management Strategy_Management Options 1.2.docx v
1 Introduction This report has been prepared by JBPacific (JBP) on behalf of Burdekin Shire Council (BSC) to develop a Dune Management Strategy for Alva beach, Wunjunga and the Beachmount Reserve. These locations are shown in Figure 1-1. The Burdekin coastline is dynamic, fed by the extensive sand supplies within the Burdekin River. The coastline has diverse community values and high expectations regarding recreational use of the beach, which present a range of challenges in coastal management. Collectively the Alva and Beachmount Reserve cover 10km of coastline, and are examples of un-urbanised, largely natural dune systems. They provide an ecological habitat for flora and fauna, an open-coast recreational area, and a buffer to coastal erosion and storm tide inundation. However, they are under increasing pressure due to complex coastal processes, ongoing human interaction, and a changing climate. These processes are causing localised erosion issues and are limiting natural dune recovery, which have the potential to threaten the ecological and community values of the coastline. This Dune Management Strategy builds on the recent Coastal Hazard Adaptation Strategy (CHAS) developed for Burdekin Shire Council, which aims to support the long-term management of the coastline. The Dune Management Strategy provides additional local context, new high-detail modelling, and builds on the range of dune protection works undertaken in the past. It aims to increase stakeholder coordination through the development of a strategic plan for ongoing dune management and increase community stewardship through organisations such as the NQ Dry Tropics (NQDT), the Lower Burdekin Landcare groups, and the residents themselves. This report contains the following sections: • Section 2: Background to the Burdekin coastline and townships • Section 3: Appraisal of the existing dune system • Section 4: Dune protection measures • Section 5: Dune Management Strategy Figure 1-1: Alva, Wunjunga and the Beachmount Reserve. 2020s0406 - BSC - Burdekin Dune Management Strategy_Management Options 1.2.docx 1
2 Background to coastal values and processes The Burdekin coastal system is renowned for its natural beauty and coastal processes. It is an area highly valued by traditional owners, residents, and visitors alike, and has been the subject of several relevant studies. This chapter reviews available information on the following: • The values for traditional owners, residents and visitors • The township of Alva Beach • The township of Wunjunga and the Beachmount Reserve • Available scientific reports and data for the Burdekin coastline. 2.1 Values for traditional owners, residents and visitors The Burdekin coast has been the traditional home of the Bindal and Juru peoples for thousands of years. Traditional owners have a deep connection with country and continue to have a shared living culture with their environment. The Gudjuda Reference Group Aboriginal Corporation represents the cultural heritage of the traditional owners of the land. In addition, indigenous land and sea rangers are employed through Gudjuda who has undertook a range of coastal management activities including pest and weed management, biodiversity surveys, turtle monitoring and protection, seagrass monitoring and maintenance of cultural heritage sites. Today the Burdekin residents also include families from some of the earliest pioneers of the sugarcane industry. The importance of water to the community is experienced through events such as the Burdekin Water Festival; held annually since 1957 annually to celebrate Burdekin’s lifestyle, economy and culture in relation to water. The coastline has been the focus of a large-scale Coastal Hazard Adaptation Strategy (CHAS) which conducted an online “Experience and values” survey to gather a community perspectives on the values of the region. Almost 150 responses were received, which provided the following information1: • Most residents visit the coast on a monthly to occasional basis. Alva Beach is the most popular beach to visit, followed by locations including Wunjunga and Groper Creek. • Recreational use of the coastline is an important feature of respondents, with 40% rating it as their most valued aspect of the coast. Having direct access to beaches is highly valued for supporting the 'beach lifestyle'. • Burdekin’s natural ecosystems, wildlife and conservation and the unique landscape were recognised as being significant by 85% of respondents. • The environment is considered the most important value within ~25% of surveys, with natural ecosystems, wildlife and conservation ranked highest (15%), and the regions unique landscape features and natural beauty ranked highest by 10% of respondents. • A large proportion (over 70%) of the community believe that the Burdekin coastline will be impacted by coastal erosion or coastal flooding in the future. Approximately 25% of residents had been impacted by coastal erosion or coastal flooding on several occasions, while another 24% had experienced an event once or twice. The Burdekin coastline provides important recreational opportunities that draw visitors to the region, with beach infrastructure and access points believed to be an important feature to meet the values of the local community and its visitors. Visitors have been travelling to the region since the early 1950s, using the beaches for recreation purposes such as fishing, beach driving and camping. These visitors currently contribute approximately $44 million annually to the local economy. Commercial and tourism operators hold assets that may be impacted by coastal hazards, hence, will benefit from an ongoing dune management. 2.2 Alva Alva is the main coastal township of the Burdekin coastline. Whilst one of the most visited beaches, the local township only has a population of under 300 people, however includes the Alva Beach Tourist Park and the Surf Life Saving Club. The township has been constructed along a sandy frontal ridge system, and currently has a degree of protection from a large sandy spit that has continued to build and extend to the north. Plantation Creek runs north between the beach and the 1 Alluvium (2020) Burdekin Shire Council Coastal Hazard Adaptation Strategy Phase 3 Summary Report 2020s0406 - BSC - Burdekin Dune Management Strategy_Management Options 1.2.docx 2
sandy spit and creates a lagoon, which limits beach width at high tides. To the north the coastline continues around 20 km to Cape Bowling Green, which is highly used by 4WDs driving along the beach. Figure 2-1: Alva map and local features Photograph taken 04 June 2018 02:38 Photograph taken 04 June 2018 02:49 Photograph location: -19.456284, 147.483383 Photograph location: -19.4536, 147.482483 Figure 2-2: Alva Beach lookout looking towards spit over dunes (left) and inner lagoon (right) Alva Beach allows recreational vehicle use. There are two formal beach access points to the beach, the first located immediately north of the town at the end of Causeway Street. A northern access track then continues 1km between the dunes and the Alva wetlands to a second beach access. The northern access track is shown in Figure 2-3, with the northern beach access point shown in Figure 2-4. A number of vehicle tracks and erosion blowouts can be observed along the dune system and the rear wetland, which is impacting vegetation establishment and dune recovery. 2020s0406 - BSC - Burdekin Dune Management Strategy_Management Options 1.2.docx 3
Figure 2-3: Alva northern access track (between the two beach access points) JBP Photograph taken 04 June 2018 JBP Photograph taken 04 June 2018 03:10 Photograph location: -19.442211 , 147.477371) Photograph location: -19.442177 , 147.477402 Figure 2-4: Alva Beach looking south (left) and north (right) 2.2.1 Coastal processes along Alva Beach The foreshore of Alva beach is constantly changing due to the northerly longshore drift and sediment supplied by the Burdekin River estuary. Over time a sandy spit has continued to build and extend north adjacent to Plantation Creek, current extending 2-3km before the creek breaks out into the ocean. The beach foreshore has been growing seawards in recent decades, with a historical rock seawall built to protect against coastal erosion now buried under the backshore dunes. Although Alva is vulnerable to coastal hazards, the sandy spit offers a large amount of protection to the township against erosion. The coastline to the north is considered more vulnerable, being exposed to storm tides and waves, and subsequently has a greater potential dune breaching during a significant event. An assessment of long-term shoreline change has been undertaken within the CHAS, which shows the coastline at Alva to be is relatively stable, but locations north of the spit have experienced up to -50m of landward movement over the last 50 years (see Section 2.4.2). 2020s0406 - BSC - Burdekin Dune Management Strategy_Management Options 1.2.docx 4
2.3 Wunjunga The Wunjunga settlement is situated towards the southern end of the Burdekin Shire coastline, on the southern slopes of Big Hill / Beach Mountain. The properties are a combination of permanent, holiday and weekend homes, with several beach huts holding an annual permit to occupy status. Access to the township is through Beachmount Road. Constructed in 1951, this road spans 10km through low-lying saltmarsh to the coastline, and then continues north to Wunjunga, running between 30m to 350m behind the dune system. Figure 2-5: Wunjunga map and local features JBP Photograph taken 05 June 2018 03:29 Photograph taken 05 June 2018 03:31 Photograph location: -19.731138, 147.592773 Photograph location: -19.731846, 147.593414 Figure 2-6: Beachfront houses at Wunjunga 2020s0406 - BSC - Burdekin Dune Management Strategy_Management Options 1.2.docx 5
The Wunjunga township is located adjacent to lands referred to as the Beachmount reserve. The reserve begins near the mouth of Yellow Gin and Groper creeks to the north and extends south approximately 7km. The reserve includes a large grazing leasehold block to the west of the foreshore, a quarry reserve covering 5.5ha located in the middle of the recreation reserve, and partially houses a small camping area called Funny Dunny Park. Along the reserve several areas are used as informal camping sites, which has led to damage to the dunes and crest lowering (see Figure 2-9). Beachmount Road extends through the Beachmount Reserve and provides four formal beach access points. Figure 2-7: The coastline looking south from Wunjunga2 JBP Photograph taken 05 June 2018 03:54 JBP Photograph taken 05 June 2018 03:54 Photograph location: -19.7514, 147.598587 Photograph location: -19.751366, 147.598602 Figure 2-8: The coastline of the Beachmount reserve near the Funny Dunny camping ground looking south (left) and north (right) 2 You tube (2020) " Home Hill Beach (Wunjunga, Queensland, Australia) Drone Video", accessed on 09 April 2020 from: https://www.youtube.com/watch?v=hS6VQdlCMuU 2020s0406 - BSC - Burdekin Dune Management Strategy_Management Options 1.2.docx 6
Figure 2-9: Reduction in dune heights adjacent to informal camp sites (image from the Beachmount Coastal Land Management Plan) 2.3.1 Coastal processes along the Beachmount reserve Two significant coastal processes have been observed along Beachmount Reserve, relating to the blowout of Charlie's Creek and the growth of a coastal salient. Towards the south of Beachmount Reserve, Charlies Creek is an area of significant coastal change. Prior to 1986 the area consisted of a very narrow dune and sparse vegetation, with a small creek draining into the ocean. These dunes were breached, vegetation lost, and the creek scoured during Tropical Cyclone (TC) Charlie, which made landfall to the north of Upstart Bay on 1 March 1988. Over time the channel widened to allow tidal flow behind the sand dunes, forming a coastal lagoon. The potential for this to extend further and erode Beachmount Road was a growing concern in the 1990's, and as a result tidal works were undertaken to construct a bund across the creek and reconstruct the eroded dune. Works included the used of debris placed along the dune area which has been trapping sand, facilitating vegetation colonisation, and has led to ongoing dune growth. The location is currently referred as Charlie's Gap. Figure 2-10: The evolution of Charlies Creek (source: Beachmount CMP) 2020s0406 - BSC - Burdekin Dune Management Strategy_Management Options 1.2.docx 7
Analysis of aerial images was undertaken within the Burdekin CHAS (see Section 2.4.2) and the Beachmount Coastal Land Management Plan (see Section 2.4.3). Within these studies, aerial images ranging from 1945 to present were obtained, geo-referenced and analysed. The photos show that above sea level, there has been a change from an initial long, relatively straight coastline, to one that includes a coastal feature known as a salient. This emerged in the mid 1980's and forms a bulge or ‘point’ along the coastline. Figure 2-11: Analysis of historic images from the Beachmount CMP The following mechanisms are proposed for the emergence of this salient, which is shown based on three historic aerial images between 1959, 1969 and present day (see Figure 2-12). • 1959: Images in 1959 show the lower delta of Yellow Gin Creek, which discharges through a primary channel in a south-easterly direction which opens into a fan shape. A relatively straight secondary channel runs south-southeast along the coastline which creates the first salient shape as a subtidal morphologic feature. At this location, the southward migrating channel meets northward longshore sediment transport, and allows sand to accumulate. Location “1” shows another small secondary channel discharging east from Yellow Gin Creek before being diverted north by the extensive ebb-tide shoals. These extensive shoals are a feature of the flood-dominated Burdekin River tributaries. Flood events allow the rapid deposition of sediment throughout the estuary mouth, which is then reshaped over tens of years as mobile sandbars. • 1969: The 1969 image shows the main Yellow Gin Creek channel continues to discharge in a south-easterly direction. The secondary channel discharging south-southeast along the ‘subtidal’ salient is no longer present, and the underwater salient has become disturbed. The secondary channel discharging easterly has now been diverted to flow in a southerly direction by a pronounced sand shoal system. This flow is now being directed at Location “2” and is likely to be the reason for the destabilisation of the subtidal salient. 2020s0406 - BSC - Burdekin Dune Management Strategy_Management Options 1.2.docx 8
• Present day: Over the course of 50-years the secondary channel becomes the dominant flowpath for Yellow Gin Creek. It continues its sweeping shape, which erodes the coastline at Location “2” before the channel is re-directed into a seaward direction. This sweeping “S” shape causes several morphologic changes. o The northern edge of the subtidal salient is eroded, which will have mobilised sand as a deep channel is scoured from the bed. o This mobilised sediment is deposited along the residual subsurface-salient. It becomes stabilised in a more southern location, and its elevation increases to become subaerial. o Once the salient becomes emergent is was stabilised by vegetation, allowing it to grow further seawards to become a dominant feature of the coastline • Future evolution: Predicting future coastal geomorphology is challenging. Whilst erosion rates at Location “2” (between the salient and Wunjunga) are not expected to match the significant historic shoreline change, further evolution of the ebb-tide channel is expected to occur. If the estuary follows a typical flood-dominated evolution, there is the potential for a new channel to break through the sweeping S shape, likely at Location “3” or “4”, which may result in accretion of the beach at "Location 2". However, the timeframe for this process is unknown and will depend on local conditions. Until that time the observed erosion/recession at Location “2” is expected to continue to some degree, causing a continued southerly migration of the salient. Figure 2-12: Ebb shoals and channel formations between 1959, 1969 and present day 2020s0406 - BSC - Burdekin Dune Management Strategy_Management Options 1.2.docx 9
2.3.2 Recreational beach access Alva beach and the Wunjunga coastline are areas allowing recreational vehicle access along the beach. Alva Beach has a history of vehicles accessing areas above the high tide mark, illegally driving over the dunes and rear salt flats. Amongst these vehicles are Quad Bike riders, who have been observed damaging, removing, or lifting fences to get bike access to the wetlands and dunes. 3 Along Beachmount h Reserve, the dunes to the south of Charlie's gap are known to be heavily used by 4WD's, in addition to illegal camping. There are no readily accessible, published QLD guidelines on the requirements for beach driving. However, under Queensland government legislation, driving on the beach should remain seaward of the high-water mark, which is the limit of state land. Above the highwater mark the land is owned by whoever holds the title of the land and is subject to their right of trespass. Figure 2-13: 4WD vehicles parked along Alva Beach4 Almost all dunes are sensitive to human disturbance and have almost zero tolerance to vehicles. Some general information is provided on the Queensland Government Parks and Forests webpage relating to driving on sand5. Most beaches in Queensland are backed by vegetated sand dunes. These dunes are very effective coastal protection features. They absorb the erosive energy of waves generated by cyclones and storms and are reservoirs of sand to nourish the beach during periods of wave erosion. Vegetation on the dunes traps and holds sand blown from the beach aiding dune build-up and stopping sand from being blown inland and lost from the active beach and dune system. Dunes with their covering of grasses and other plants are so fragile that even footsteps can damage or kill the plants and weaken the dunes. Driving vehicles on dunes has a worse effect and greatly increases the chance of dune destruction. Vehicle tires destroy dune vegetation exposing the sand to wind erosion which lowers the dunes and reduces their effectiveness as coastal protection features. Beach erosion increases because of the lower volume of sand in the dune directly behind the beach. 3 North Queensland Register (2015) "Quad riders warned off Alva", Accessed on 09 April 2020 from: https://www.northqueenslandregister.com.au/story/3365604/quad-riders-warned-off-alva/ 4 Source Youtube (2020) "ALVA BEACH, The Great Escapes". Accessed on 02 April 2020 from: https://www.youtube.com/watch?v=jOWdaVuhiHQ 5 Queensland Government (2020) "Four-wheel driving; Driving on sand", Parks and Forests, Department of Environment and Science. Accessed on 09 April 2020 from: https://parks.des.qld.gov.au/experiences/fourwheeldriving/driving_at_the_coast.html 2020s0406 - BSC - Burdekin Dune Management Strategy_Management Options 1.2.docx 10
The BSC has previously developed a hardcopy brochure describing requirements for vehicles when driving on beaches. It was developed in partnership with the Coastal Vehicle Management Steering Committee, an initiative of NQDT, and funded by the Australian Governments Caring for our Country Program. Initiatives like this brochure are important to provide information directly to vehicle users. Key information has previously included: • Legal requirements when driving on the coast. This includes requirements to only use vehicle access points, to not drive on privately owned land, and only drive on Council land where designated. • A vehicle beach access map, showing three access points at Alva, and four along Beachmount Reserve (see right) • Tips to protect native animals and their habitats. This listed requirements to keep off sand pans, fragile sand dunes, and to drive between the high and low water marks to prevent erosion, damage to the dune vegetation and to minimise disturbance to the local ecology. • Safety tips, describing safe distances, coastal hazards, 4WD driving etc. • Requests to report unlawful driving, with a contact list to report: i. Unauthorised vehicles driving above the high tide ii. Damage to Council property iii. Damage to marine plants iv. Disturbances to native animals. Figure 2-14: Map from BSC beach vehicles guide6 2.4 Other available reports and data for the Burdekin coastline 2.4.1 Tide conditions Tidal planes are published in the 2019 Queensland Tide Tables7 at Cape Ferguson, located to the north of the LGA. These are presented in Table 2-1. Table 2-1: Tide levels from QLD Tide Tables Tidal Planes at Cape Ferguson Tide level 2019 (mLAT) 2019 (mAHD) Highest Astronomical Tide (HAT) 3.8 2.2 Mean High Water Spring (MHWS) 2.9 1.2 Mean High Water Neap (MHWN) 2.1 0.4 Mean Sea Level (MSL) 1.8 0.1 Datum - Metres Australian Height Datum (mAHD) 1.7 0.0 Mean Low Water Neap (MLWN) 1.5 -0.2 Mean Low Water Spring (MLWS) 0.7 -1.0 Lowest Astronomical Tide (LAT) 0.0 -1.7 6 BSC (date unknown) "Vehicles on our beaches", brochure. Developed by Burdekin Shire Council circa 2010. 7 Maritime Safety Queensland 2019, Queensland Tide Tables. Published at: https://www.msq.qld.gov.au/-/media/MSQInternet/MSQFiles/Home/Tides/Online-tide-tables/2019/2019queenslandtidetables.pdf? 2020s0406 - BSC - Burdekin Dune Management Strategy_Management Options 1.2.docx 11
2.4.2 Coastal Hazard Adaptation Strategy This BSC Coastal Hazard Adaptation Strategy (CHAS) has been developed with the support of the Queensland Government and Local Government Association of Queensland (LGAQ), as part of the state-wide QCoast2100 program. The CHAS has eight key phases, encompassing a series of studies that seek to: • Identify coastal hazard areas (areas prone to coastal erosion and storm tide inundation) • Understand vulnerabilities and risks to a range of assets (built and natural assets) • Engage with the community to understand preferred approaches to adaptation • Determine the costs, priorities and timeframes for implementation of actions. A range of extreme wave and storm tide information is available within the Phase 3 Hazard Assessment, which produced new coastal inundation mapping throughout the LGA under a range of likelihood and planning horizons. Highest Astronomic Tide and storm tide levels are shown in Table 2-1 for both communities. Table 2-2: Tide and storm tide levels for Alva Beach and Wunjunga Alva Beach Wunjunga (m AHD) (m AHD) Present day HAT 2.1 2.1 Present day storm tide, 10% AEP 2.2 - 3.4 2.2 - 3.4 (excluding/including wave runup) Present day storm tide, 1% AEP 2.3 - 4.1 2.3 - 4.2 (excluding/including wave runup) Present day storm tide, 0.2% AEP 2.6 - 5.0 2.6 - 5.0 (excluding/including wave runup) The study undertook extreme wave modelling, with conditions shown in Table 2-2. This was used within a relatively high-level coastal erosion modelling with both Alva Beach and Wunjunga represented by a single cross section only. These models have now been enhanced within this DMS to provide additional detail along the coastline. Table 2-3: Extreme wave conditions for Alva Beach and Wunjunga Alva Beach Wunjunga Hs (m), T (s) Hs (m), T (s) Present day, 10% AEP wave conditions 2.05m, 7.37s 2.07m, 7.37s Present day, 1% AEP wave conditions 2.85m, 9.46s 2.30m, 10.71s Present day 0.2% AEP wave conditions 3.00m, 12.14s 2.88m, 12.14s Present day, 10% AEP general erosion width 20.2m 16.5m Present day, 1% AEP general erosion width 26.6m 19.5m Present day 0.2% AEP general erosion width 32.9m 29.3m As part of the CHAS, the rate of long-term recession was estimated using the Digital Shoreline Analysis System (DSAS) since the 1950's. This historical change is shown in Figure 2-15 for Alva and Wunjunga. Both coastlines are highly variable, each showing recession rates of up to -50m (a landward movement) and accretion rates of up to +50m (a seaward movement). 2020s0406 - BSC - Burdekin Dune Management Strategy_Management Options 1.2.docx 12
Figure 2-15: Shoreline Analysis completed within the Burdekin CHAS8 2.4.3 Beachmount Coastal Land Management Plan (NQDT) This Plan was prepared by the NQDT to define the values of the Beachmount Reserve, identify the impacts to the defined values, and consider management strategies to mitigate the impacts. A range of data has been produced within the Plan, with the following elements reused within this Dune Management Strategy: • The location of four beach assess points • The location of two informal camp areas which are disrupting the dunes • The location of existing fencing on the Wunjunga foreshore • The boundaries of the eight weed management areas • The ideal plant species for Burdekin region and planting specifications • Locations of photo monitoring points used by the NQDT. 8 Alluvium (2020) Burdekin Shire Council Coastal Hazard Adaptation Strategy Phase 3 Report 2020s0406 - BSC - Burdekin Dune Management Strategy_Management Options 1.2.docx 13
3 Appraisal of dune system 3.1 Drivers of coastal processes and erosion The range of studies described in Section 2 describe an area affected by ongoing coastal processes and morphologic change. Before considering the management of the dunes in great detail, it is important to first consider the underlying coastal processes affecting the site. Coastal and estuarine environments experience a range of hydrodynamic, sediment transport and morphologic processes that are linked through dependant and independent variables. This includes the underlying astronomical tide, local storms, the local wave climate, stormwater inflows, the sediment type (e.g. cohesive silts vs non-cohesive sands), sediment properties, and any regional sediment sources and sinks. Figure 3-1: Drivers of coastal risk Due to the complexity of these factors, there are several ways sediment can be mobilised, eroded, transported and deposited. As shown in Figure 3-2, sediment movement can itself be divided into several processes, including: • Longshore sediment transport, which is the transport of sediment parallel to the coastline due to the arrival of waves at an oblique angle. This can be separated into two mechanisms: sand moving in the swash zone (along the beach face) and further seaward in the surf zone. • Cross shore sediment transport, which is the on- and offshore movement of sediment between the nearshore zone and the dune system. • Suspended and bedload sediment transport, which is typically the through transport of sediment under tidally driven currents, that can flow along a shoreline and within estuaries, or flows. Figure 3-2: Conceptual diagram of different sediment transport mechanisms 2020s0406 - BSC - Burdekin Dune Management Strategy_Management Options 1.2.docx 14
Coastal blowouts are an additional process throughout the Burdekin region. A blowout depression within the sand dunes are typically defined by their shape, typically saucer-, cup- or trough-shaped. They develop when vegetation cover is lost, and the sand is shifted and deposited in the leeward edge. A blowout may be initiated in a variety of ways, most commonly wind erosion in areas of low vegetation cover, storm erosion of the beach face, and human activities. In a dynamic environment, any exposed dune will quickly revegetate before they evolve into a substantial blowout. However once a blowout is established, which may be caused by ongoing disturbance by beach users and the tunnelling effect of wind blowing across the dunes with increased speed, a feedback mechanism is triggered for the blowout to continue eroding. The evolution of a blowout is shown in Figure 3-3 (top) which can be compared to the large blowouts along Alva Beach which extend up to 150m inland. Figure 3-3: Conceptual diagram of blowout evolution (top)9 and example of blowout at Alva Beach (bottom)10. 3.2 Appraisal of the dune system The coastal dune system along Alva beach, Wunjunga and the Beachmount Reserve has an important role in mitigating against erosion, stabilising the surface against wind erosion, and provides habitat for wildlife. To support its ongoing management, each coastline has been split into 250m segments, as shown in Figure 3-4. This resulted in 15 assessment zones along Alva Beach and 30 zones along the Beachmount Reserve. Each coastal segment has been appraised in terms 9 Hesp, P. (2011). "Dune Coasts". Treatise on Estuarine and Coastal Science. 3. 193-221. 10.1016/B978-0-12-374711-2.00310-7. 10 You Tube (2020) "Alva Wetlands | Drone Footage [4K]", Accessed on 09 April 2020 from: https://www.youtube.com/watch?v=n6I9pGpZL7M 2020s0406 - BSC - Burdekin Dune Management Strategy_Management Options 1.2.docx 15
of its threats, which have been used to develop ongoing management actions (described in Section 4). Four threats to dune stability have been assessed and quantified. These include: • The location of any infrastructure in relation to the storm erosion zone. • The elevation of the dune crest in relation to storm tide and wave runup levels. • Any barren dunes, disturbances or blowouts. • The presence of informal tracks cutting across the dunes, either from frequent pedestrian or vehicle use. The approach used to quantify each hazard is described in the sections below. Figure 3-4: Coastal segments 2020s0406 - BSC - Burdekin Dune Management Strategy_Management Options 1.2.docx 16
3.3 Location of infrastructure within the erosion zone This assessment measured the distance of infrastructure behind the dune crest, created new beach erosion estimates, and identified the degree of infrastructure potentially at risk. Infrastructure distance behind the crest Spatial analysis was used to map the distance of the closest infrastructure behind each coastal section. This was based on aerial imagery flown in 2013, supplied by BSC11. Figure 3-5: Infrastructure measured behind the dune Potential erosion distance The potential erosion for each 250m segments has been assessed for a 10% Annual Exceedance Probability (AEP) storm (equivalent 1 in 10-year event). The assessment has assumed unprotected, unvegetated dunes, which represent a 'worst-case' for coastal management. This has supplemented the coastal modelling undertaken in the CHAS, by incorporating high detail along both the Alva Beach and Beachmount coastline. Figure 3-6: Schematic of JEPA short-term erosion modelling using Vellinga (1982). Calculation of the storm-based erosion and dune slumping was undertaken using the JBP Erosion Prone Area (JBPA) tool. This predicts the beach erosion at each coastal zone under extreme wave, period and storm tide conditions. The tool estimates the beach equilibrium profile during a storm based on the work of Vellinga (1982) 12, where the beach shape is described as: 0.5 7.6 7.6 ) = 0.47 [( )1.28 ( ( )0.56 + 18] − 2.00 0 0 0.0268 Where, 0 = significant ‘deep water’ wave height and w = fall velocity of sand. The input parameters for each calculation include initial beach profile, storm tide level, nearshore wave 11 BSC, supplied for the Coastal Hazard Adaptation Strategy within file: "Burdekin_Shire_50cm_2013_Z55_mosaic" 12 P. Vellinga (1982). “Beach and dune erosion during storm surges” Delft Hydraulics Laboratory 2020s0406 - BSC - Burdekin Dune Management Strategy_Management Options 1.2.docx 17
conditions, grain-size diameter, an upward slope stability threshold of 1:3, and a lower slope of 1:12.5. Under storm conditions, the erosion distance is simulated that would occur to balances the storm equilibrium profile and the pre-storm profile. This assumes sand is eroded from the dune and is deposited into the nearshore coastal zone. The erosion width is then measured landward of the Highest Astronomical Tide (HAT) level, all the way to the intersection with the dune escarpment. Location of infrastructure within the erosion zone The location of infrastructure in relation to the estimates 10% AEP erosion zone was used to categorise each section as Low, Medium or High hazard. This has followed the scoring metric shown in Table 3-1. Table 3-1: Scoring metric for infrastructure and erosion Metric: Beyond 200m from 10% Between 200m to 20m from Within 20m (or within) the AEP erosion zone the 10% AEP erosion zone mapped erosion zone. Score Low hazard Medium High hazard 3.4 Dune crest in relation to storm tide levels Primary coastal dunes are high, generally with a profile that is relatively consistent along the shoreline. Analysis of each coastline indicates this primary dune crest is approximately 2 to 5mAHD at Alva beach and 3 to 4m AHD along the Beachmount Reserve. During a coastal storm, these dunes are subject to additional processes due to storm tides and waves runup. If the storm and wave levels are higher than the dune crest they may lead to overwash and breaching. Overwash is the initial process of waves running up and over the dune crest or through localised depressions or blowouts, which will begin to erode the dune and move sediment landward. With enough wave energy this loss of sediment can lead to breaching of the dune, lowering the crest elevation of the beach profile, and substantial erosion. The minimum elevation along the frontal dune was measured within each coastal zone to identify any low points, and was compared to the present-day 10% AEP storm tide level (2.2m AHD) and the storm tide plus wave runup level (3.4m AHD). Dune crests with an elevation lower than the storm tide level (excluding waves) were identified as a high hazard, and below the run-up level as a medium hazard. This scoring metric is shown in Table 3-2. Table 3-2: Scoring metric for dune crest lowering Metric: Dune crest higher than Dune crest between storm Dune crest lower than 10% 10% AEP storm tide + tide and the wave setup AEP storm tide level wave setup level level Score Low hazard Medium High hazard 3.5 Dune disturbance, barren dunes or blowouts Disturbed dunes, barren dunes or blowouts have been mapped to identify any areas that may be losing sediment from the coastline. Blowouts can be natural features, commonly occurring in the foredune or within older vegetated dune systems, but are usually the result of human use along Alva and Wunjunga. Any blowout (natural or human made) can develop deeper in time, and cause the gradual collapse of adjacent dunes. The presence of any barren sand dunes or blowouts within the dunes has been mapped from aerial imagery, as shown in Figure 3-7. Often these were located along or near vehicle tracks, but also include areas that may have been disturbed from campsites. A relative scoring system was used to identify the largest areas, as shown in Table 3-4. 2020s0406 - BSC - Burdekin Dune Management Strategy_Management Options 1.2.docx 18
Figure 3-7: Example dune disturbance mapping Table 3-3: Scoring metric for barren dunes or blowouts Metric: No disturbance Up to 2000m2 mapped Over 2000m2 mapped disturbance or blowouts disturbance or blowouts Score Low hazard Medium High hazard Figure 3-8: Dune disturbances along Alva Beach13 3.6 Track density Vegetated primary dunes can be damaged by vehicles and frequent pedestrian use. The presence of tracks cutting across the dunes has been mapped to identify high-use areas that can be targeted for revegetation, fencing and educational signage. These were summed for each beach section, and a relative scoring system used to identify the most heavily trafficked areas, as shown in Table 3-4. 13 You Tube (2020) "Alva Wetlands | Drone Footage [4K]", Accessed on 09 April 2020 from: https://www.youtube.com/watch?v=n6I9pGpZL7M 2020s0406 - BSC - Burdekin Dune Management Strategy_Management Options 1.2.docx 19
Figure 3-9: Example track measurements Table 3-4: Scoring metric for track density Metric: No observable tracks in Up to 2km of mapped tracks Over 2km of mapped tracks in coastal segment in coastal segment coastal segment Score Low hazard Medium High hazard 2020s0406 - BSC - Burdekin Dune Management Strategy_Management Options 1.2.docx 20
3.7 Assessment and prioritisation 3.7.1 Alva Beach The beach appraisal of Wunjunga and Beachmount Reserveis shown in Appendix A. The new erosion modelling, at-risk infrastructure assessment, the dune crest level, mapped dune disturbance, and identified tracks have been quantified using the Low, Medium, High scoring matrix shown in Table 3-5. Table 3-5: Scoring metric for each coastal segment Metric: Low hazard Medium High hazard Beyond 200m from Between 200m to 20m from Within the mapped erosion Erosion to infrastructure 10% AEP erosion the 10% AEP erosion zone zone, or within 20m. zone Dune crest higher Dune crest between storm than 10% AEP Dune crest lower than 10% Dune crest level tide and the wave setup storm tide + wave AEP storm tide level level setup level Up to 2000m2 mapped Over 2000m2 mapped Dune disturbance No disturbance disturbance or blowouts disturbance or blowouts No observable Dune tracks Up to 2km of mapped tracks Over 2km of mapped tracks tracks The results are shown in Figure 3-10, which indicates the following: • Infrastructure erosion. The main erosion risk is to the northern access track, which runs directly behind the dunes (Segment 8-10) which are now experiencing trough blowouts. • Crest levels along the northern coastline (Segment 1-5) are the lowest, and have the greatest risk of wave runup, overwash and breaching. • A series of trough blowouts are present between Segments 3-10. These are deep sided, elongated disturbances running from the dune toe to crest (east-west), which extend up to 150m inland. The entire coastline is frequently used by vehicles. Several locations at the northern beach access, the Causeway Street beach access and the Alva Beach Tourist Park, are identified as where vehicles pass through and can be managed by signage. 2020s0406 - BSC - Burdekin Dune Management Strategy_Management Options 1.2.docx 21
Figure 3-10: Alva hazard review 2020s0406 - BSC - Burdekin Dune Management Strategy_Management Options 1.2.docx 22
3.7.2 Wunjunga and Beachmount Reserve The beach appraisal of Wunjunga and Beachmount Reserveis shown in Appendix A. The new erosion modelling, along with the assessment of at-risk infrastructure, the dune crest level, dune disturbance, and tracks, have been quantified using the scoring matrix shown in Table 3-5. The results are shown in Figure 3-11, which provides the following trends: • Infrastructure erosion. Infrastructure is threatened by erosion at Wunjunga, Beachmount Road (Segment 20-22), and the second bund at Charlies Gap. • Crest levels along southern Beachmount Road (Segment 20-23) are generally narrow and have localised areas of crest lowering that may form a weak point along the dune to wave overwash. Similarly, the berm at Charlie's Gap is considered relatively low and has the risk of being breaching during a storm. • Dune disturbances are mapped throughout Wunjunga, due to frequent traffic. Elsewhere, barren dunes are present along Segments 16-29 that may be due to natural processes, and along the southern coastline (Segment 26 to 30) due to frequent use by vehicles. • Access to the coastline is through four formal tracks which is open for recreational 4WD use. Two other informal beach access tracks were identified at Wunjunga (Section 4-5) and north of the Funny Dunny camping ground (Section 13). However, there are a large number of informal tracks running along the dunes along the southern beach (Segment 26- 30) that are leading to dune erosion. Figure 3-11: Wunjunga and Beachmount Reserve hazard review 2020s0406 - BSC - Burdekin Dune Management Strategy_Management Options 1.2.docx 23
4 Dune management actions The aim of this Dune Management Strategy is to create a coastline that is more resilient to coastal erosion, to be sustainable into the future, and provide benefits to multiple stakeholders. A set of targeted management objectives has been formulated based on the values of the coastline, and the hazards identified in the previous Sections. Specific management objectives have been formulated following six key principles discussed with the project steering committee: • Have a focus on nature-based or 'soft' actions rather than 'hard' infrastructure (seawalls etc). • Improve public information, education, and awareness of coastal hazards to build community stewardship • Plan for new signage at high use areas that can promote dune management and provide details for volunteers to contribute. • Any new fencing needs to consider vandalism and use different materials at high-use areas. • Prioritise erosion 'hotspots' for targeted revegetation, which may be used to measure progress. • Work with local organisations such as the NQDT, the Lower Burdekin Landcare groups, and the residents themselves. 4.1 Management actions A range of ‘Management Details’ have been developed, which can be used to address the hazards identified in the Dune Appraisal within Section 3. These include: • M1 - Enhanced partnerships, focusing on a greater collaboration with partner organisations • M2 - Revegetation of erosion zones, which will use native plant species, fencing and signage to stabilise key areas. • M3 - Dune protection measures such as fencing, signage and education, that can be used to support new revegetation. • M4 - Beach accessways, these would support walk-in beach access and allow rear-parking and foot traffic access to the beach. • M5 - Beach traffic review, which considers changes to existing 'traffic’ and ‘no traffic’ areas to address existing and future recreational needs 2020s0406 - BSC - Burdekin Dune Management Strategy_Management Options 1.2.docx 24
4.2 M1 - Enhanced partnerships This action aims to work with the capabilities of partner organisations. This would encourage and support local volunteers to carry out on-ground restoration works, such as weed removal, revegetation and general foreshore cleanups (i.e. working bees), which would also foster greater appreciation of the natural environment by participants. Several external groups will be able to contribute to the Strategy, including: • NQDT • Gudjuda Aboriginal Corporation • Lower Burdekin Landcare Group • Queensland Parks and Wildlife • Great Barrier Reef Marine Park Authority. Further opportunities should be sought with the range of other organisations working in the region. Collectively, these organisations have a large amount of capabilities, responsibility and internal skills that undertake a range of tasks to support the plan. These include: • All organisations can apply for funding for the implementation of the plan. • All organisations have websites that can support in promotion of dune management actions. • The Gudjuda Aboriginal Corporation are active throughout the Beachmount area. • The Lower Burdekin Landcare Group has a nursery that has a wide range of Australian native plants that would be suitable for dune revegetation. • The NQDT and Lower Burdekin Landcare Group have a paid and volunteer-based labour force that can undertake on-ground works and revegetation. Figure 4-1: Lower Burdekin Land Care Association nursery and working bees 2020s0406 - BSC - Burdekin Dune Management Strategy_Management Options 1.2.docx 25
You can also read
