Design Coastal Path - Gnarabup to Narda

The Shire requires the services of a suitably qualified and experienced Consultant to design a pathway along the Gnarabup coast between the Gnarabup Carpark and Riflebutts. The pathway is to be made up of a combination of crushed limestone and boardwalk.

Council, at their Ordinary Council Meeting of 17 December 2025, resolved to support the development of the Riflebutts to Gas Bay Concept Plan (the Concept Plan), encompassing the general arrangement and concept layout of the Gnarabup Coastal Path. The plan shows the reconstruction and realignment of the existing coastal path with the construction of a new alignment through a mixture of crushed limestone and a raised boardwalk. This included endorsing the outcomes of an Opinion of Probable Cost and Concept General Arrangement that was prepared earlier in the concept planning development. A copy of the concept General Arrangement is attached as an appendix to this request as Appendix 2.1.

The boardwalk is generally to be constructed with a treated pine frame and hardwood decking. Alternative materials were costed as part of the OPC development. The Shire requests the Consultant review the options and provide professional opinions with regards to durability and value for money for other materials. Discussions of alternative materials will be had with the Shire and the Consultant as part of the initial kick off meeting.

The proposed alignment, as presented in the Concept Plan, aims to reduce the ongoing maintenance of the existing path due to wind-blown sand, coastal erosion processes, and excessive vegetation growth. By locating the path higher up in the dune system, a greater visual amenity is achieved, but there is a trade off with the level of construction required. The section of crushed limestone is anticipated to be construction along the flatter sections of the dune system. Where the topography of the dunes becomes steeper and there is more vegetation, a boardwalk can be placed on the high side of the swale.

The Consultant is expected to undertake a feature survey of the surrounding area to ensure design levels can be achieved and to ensure accurate volumes and quantities. These are to be presented in a Bill of Quantities and Schedule for the purposes of procuring a construction contractor.

Geotechnical conditions of the subject area are unknown. Conditions are expected to be sandy and limestone in nature in a reasonably mobile coastal sandy primary dune system. The Consultant should allow for representative geotechnical samples to be undertaken to support the design development.

Disturbance to the coastal dunes should be minimised wherever possible during the investigation and design phases. The Consultant shall allow for any pedestrian and traffic management that might be required throughout these investigations noting that the coastal path and accesses are frequented by the community throughout the year.

Detailed design is required to be completed by 30 April 2026 to comply with the grant funding agreement.