Deviot Landslip Project
The Deviot Landslide Project was initiated by West Tamar Council in 2017 in response to the reactivation of a landslide that occurred in Brickmakers Point, Deviot as a result of the significant rainfall event of June 2016.
West Tamar Council was successful in securing funding through the Australian Government’s Natural Disaster Resilience Grants Program to initiate an investigation into the landslide.
Geotechnical Engineer, Dr Derek Pennington of Pennington Geotechnics was engaged by West Tamar Council in 2018 to conduct an investigation into the landslip to understand the casual factors related to the landslip and to provide recommendations for mitigating the risk of landslip in the future.
The project was overseen by a Steering Committee comprising representatives from:
- West Tamar Council;
- Department of Premier and Cabinet;
- Mineral Resources Tasmania;
- Crown Land Services; and the
- Deviot Community.
The key objectives and scope of the project was to:
- Design, supervise and peer review a geotechnical investigation program to achieve a greater understanding of landslip at Deviot;
- Coordinate a forensic review of the existing investigation (a timeline);
- Provide advice to Council with tender/contract process to appoint contractors to undertake field investigations and subsequent analysis and reporting; and
- Write a concluding report summarising the investigation findings and addressing the aims in a form able to be understood by relevant parties.
A particular focus of the project was to ensure community engagement provided the opportunity for landowners most affected by the Brickmakers Point Landslip in Deviot to have input into the project. Dr Pennington engaged one on one with the affected landholders and held numerous on-site visits as part of his investigation. The project also included two community meetings in Deviot and the opportunity for affected landowners to tell their story and have this reflected in the report.
Following release of the Draft Report in May 2019, Council invited public comment on the report. Prior to finalising the report, the nine submissions received during the public comment period were included as an Appendix to the report to acknowledge the personal impact of the Landslip on the individuals most affected.
A copy of the Pennington Report titled 'Lower risk development and living with landslide in the Tamar, Deviot Landslide Project, August 2019' is available upon request by contacting the West Tamar Council.
LANDSLIP PROGRAM IMPLEMENTATION:
The West Tamar Council is committed to building community resilience to natural hazards, providing information to people looking to develop or purchase properties in landslip areas and ensuring that council is actively managing and mitigating the risks of landslip that fall within its function and responsibilities to act on.
In December 2019 Council initiated a Landslip Program which has five key objectives. Council continues to work towards the implementation of actions to meet these objectives.
- Manage and mitigate the risks to council infrastructure from landslip including roads and stormwater assets whilst maintaining services to the community.
While Deviot was once a small village with a rural standard of infrastructure, the need by Council to proactively manage overland stormwater flows, road side drainage, ground water and road pavements in an area with at times significant land instability requires a considered and site specific approach to Council infrastructure design, construction and monitoring. During 2020 Council has invested considerable resources into investigating best practice approaches to the infrastructure required including the following actions:
- During 2019 and 2020 Council has invested in extensive road side drainage upgrades from Gravelly Beach through to Motor Road. This has included the installation of a flexible concrete matting system consisting of pyramid shaped, 50 Mpa concrete blocks to better manage and control overland flows and storm events (see pictures below).
- During the 2020 wet winter a section of road to the south of the Motor Road and Deviot Road intersection failed leading to emergency works to stabilise the area. Council subsequently commissioned a Geotechnical investigation to provide recommendations for stabilisation of the active landslip area. Stakeholder engagement with adjoining landowners will commence in early 2021. If the drainage works proposed prove successful at this site, they will form a test case for potential use in other areas of land instability in the municipality.
2. Establish integrated processes and controls across Building, Plumbing, Planning, Environmental Health and Engineering to mitigate the risk of landslip in new developments.
- Review of planning and development controls for Landslip including establishing a peer review process for Landslide Risk Management (LRM) reports submitted to Council for Planning Applications.
3. Build council's capacity, knowledge and awareness to effectively manage landslip mitigation programs and ensure sound advice and information is provided to customers.
- Continuing to build council staff awareness of Landslip to ensure technical reports provided to Council meet the Australian Geomatics Society guidelines for Landslip and accurate information and advice is provided to customers.
4. Engage and consult with the community to establish effective community monitoring programs and the development of educational tools and resources.
- Completion of 12 months of landslip monitoring at Deviot for 2019 and a community workshop in December 2019 to present monitoring results to affected residents in Deviot with the support of Mineral Resources Tasmania.
5. Act as an advocate on behalf of the community and those impacted by landslip.
- Proactively advocating for greater disclosure of information to perspective homeowners who are looking to purchase properties in landslip prone areas. To further this, council submitted a motion for consideration at the Local Government Association of Tasmania (LGAT), 2019 Annual General Meeting (AGM) calling on the disclosure of landslip information on 337 certificates and reform in the Real Estate industry to require upfront disclosure of these risks to prospective purchasers prior to entering into legal contracts. This motion led to a change in legislation and subsequent amendment to the 'Local Government (General) Regulations 2015' related to the prescribed questions for 337 certificates.
2021-2022 Future Focus
- Review of landslip monitoring requirements for Deviot to better inform Council infrastructure requirements and risk mitigation actions.
- Implementation of the recommendations in the geotechnical report commissioned by Council in 2020 to improve drainage and reduce landslip risk at the Motor Road, Deviot Road intersection at Deviot, including targeted engagement with adjoining property owners and affected residents regarding mitigation and rehabilitation works in the area.
- Commence road reconstruction and sealing works on Deviot Road and commence design work to replace the old retaining wall to the north of the Yacht Club.
- Design of drainage improvements and road reconstruction to the northern side of Motor Road to capture overland flow and stormwater for controlled discharge. This work is planned to be implemented in a staged capital works program of upgrades over the next 2-3 years.
- Review of development controls for Planning and Building required under the Tasmanian Planning Scheme and Local Provisions Schedule for West Tamar Council.
- Continued focus on building Council staff awareness and capacity to respond to Landslip.
Left: Flexible concrete matting stormwater drains -Deviot Road
Right: Flexible concrete matting stormwater drains –Gravelly Beach Road