The old dam known as the lower dam including this spillway was constructed in the 1880s and was decommissioned in the 1950s. From the 1950s, Wellington’s water supply from Wainuiomata came from the Morton dam and the Orongorongo weirs. Around 1969-70, there was a reduction of approximately one meter in the spillways’ height to enhance safety measures, accompanied with opening of some sluices beneath the dam. Together, the sleuths below and spillway, channel the river flow. Today, a natural wetlands area is located behind the old dam wall.
A curious feature of the spillway is the presence of large metal pins protruding from the concrete. This suggests the possibility of a wooden structure like a bridge spanning one of the levels. Although no photographs have surfaced showing a bridge crossing the spillway, the pins clearly appear to have served a purpose such as a bridge or used somehow in the construction process. Interestingly, similar pins can also be seen embedded in the concrete at the boat ramp hut above the spillway, where they were evidently used to anchor the timber frame to its concrete foundation.
