Sinclair Tunnel, situated beneath the dam wall in Wainuiomata, served as a drainage tunnel and was later supplemented by a relief tunnel.
A tunnel beneath the dam wall in Wainuiomata was constructed as part of the original dam project, completed in 1884, which served as Wellington’s first major water supply reservoir. Tenders for construction of this tunnel were to be submitted no later than 14 September 1882 with a Mr D Sinclair being the winning tender and the tunnel later being referenced as Sinclair Tunnel.
A further relief tunnel was discussed and reported on 10 November 1883 and again on the 24 January 1884 after massive damage to the dam, due to a serious flooding event. Today, there are 3 pipes next to Sinclair Tunnel which are likely the result of this proposed relief tunnel.
These tunnels / pipes serve two key purposes:
- Drainage and Outlet Control: Enabling the controlled release of water from the reservoir to facilitate maintenance by providing access to areas of the dam that are otherwise inaccessible when the dam is full.
- Structural Safety: The tunnel would help manage seepage and pressure that might build up behind the dam wall, ensuring the integrity of the structure.
Although the old Wainuiomata dam is no longer active as part of the water supply system, the site retains significant historical and recreational value. The dam and its tunnel stand as key elements of Wainuiomata’s heritage, reflecting an important chapter in the story of Wellington’s early water infrastructure.
