Upgrades to cater for lake level management and to accommodate future climate change effects on Lake Ōkāreka in Rotorua has now been completed.
Toi Moana Bay of Plenty Regional Council have been undertaking a staged upgrade of the outlet structures and stream protection for the Lake Ōkāreka level control since 2016.
The initial upgrade involved replacing the old concrete pipes with a polythene and stainless steel pipe with greater flow capacity. This is to protect homes and infrastructure from high lake levels.
Toi Moana Bay of Plenty Regional Council Lakes Operations Manager, Andy Bruere said, Regional Council increased the outlet flows to more than double the normal flow as a result of high lake levels in 2017.
To enable this increased flow Regional Council undertook stabilising and strengthening works on the Waitangi Stream where the outlet pipeline discharges, on its way to Lake Tarawera. The next stage was to upgrade the remaining old pipeline to enable the lake levels to be controlled taking account of future predictions for climate change.
“As a result of climate change it is expected temperatures will rise and our wind, rainfall and seasonal patterns will shift and we will see more extreme events and unpredictability in our weather,” Mr Bruere said.
“This work will help to mitigate some of the effects of that.”
Modelling was undertaken to understand the possible flows with climate change scenarios through to 2090. The final stage of the project was to complete construction of the pipeline outlet, to ensure the water does not erode the discharge point. The connection between the lake and the inlet to the pipeline has been upgraded to make it a more natural rock structure and allow for the peak flows to be managed.
One of the key factors in enabling the works to cater for future climate events was the granting of a new resource consent for the potential increased flow. It is important to note that although the new consent “allows for” an increased flow, this high flow is only to be discharged when necessary to control the lake level and prevent infrastructure damage.