Patawalonga Lock Timber Boardwalk Upgrade, Glenelg

The challenge

The boardwalk at the Patawalonga Lock wraps the northern and western sides of Marina East at Glenelg, part of it built out over the decommissioned lock gate at the southern end of the Patawalonga barrage gates. Constructed around 2001 for pedestrians and a modest maintenance allowance, it had since become the working access route for the vehicles and plant used to service the lock, the barrage gates and the public areas around them, from a rapid response truck to a spider crane and boom lifts. The City of Holdfast Bay needed to know whether the structure could take that duty under current standards and, where it could not, exactly what had to be replaced. That was not a question the eye could answer: joists, bearers and connections sat hidden below decking that in places was bolted through by the balustrade, and earlier reviews suggested some areas differed from the original 1998 documentation. Two decades of salt air, splash and weather had also left their mark on the timber and on the steel balustrade infills.

Our approach

Establishing what was actually built came before any calculation. Decking planks were lifted at selected locations so the framing beneath could be measured directly, with the rest read from the sides of the structure and through the gaps between boards, and every member recorded for size, spacing and condition. Material selection was then weighed on load capacity, durability, drainage, appearance and the practicalities of joining dissimilar materials, and the design settled on fibre reinforced polymer beams and joists supporting hardwood timber decking, with stainless fixings and isolation between dissimilar metals for a marine setting.

The outcome

The council came away with an evidence based picture of its asset: the areas needing full replacement, the framing that could stay in service, and the balustrade work required for compliance. Design and documentation followed, and the new boardwalk over the old lock is now being built, with Magryn supporting construction through requests for information, workshop drawing review and site inspection. What the City of Holdfast Bay ends up with is a public walkway rated for pedestrian crowds and for the service vehicles the site depends on, framed in a material chosen for a salt water environment and detailed to reduce long term maintenance. Just as importantly, it preserves reliable vehicle access to the Patawalonga Lock and barrage gates, infrastructure that needs regular maintenance and mechanical plant to reach it.