New weir to be built for Tairua flood scheme

Debris collecting at the floodgate inlet has resulted in damage to the spillway embankment and weir.

Waikato Regional Council will start work onsite constructing a new weir for the Grahams Creek flood scheme later this month, with works to be completed by early February.

The position of the weir, which is adjacent to the floodgate, is being shifted 50 metres downstream to prevent the accumulation of debris during flood events and damage to the infrastructure. An access track and fencing will also be installed as part of the project.

The council received $330,800 from the Local Government Flood Resilience Co-Investment Fund to support the project after the Government made the contestable fund available to regions affected by the North Island’s extreme weather events in early 2023.

The Grahams Creek Flood Scheme activated in all the weather events and performed well, however, the significant volume and velocity of the stream during these events, and debris carried, resulted in damage to the spillway embankment and weir and infilled the main channel.

With the current layout of the floodgate inlet and associated ‘weed screen’, there are frequent blockages during rain events which result in premature activation of the spillway.

This increases maintenance requirements, and ultimately cost.

By completing enhancement work and shifting the weir, the community’s resilience to future weather events will be further increased, and the overall performance of the flood scheme will be improved.

The Grahams Creek catchment is susceptible to short duration but high intensity rain events, which can cause flash flooding and debris flow with little or no warning.

The scheme, which was completed in 2016, protects many properties, State Highway 25 and the bridge from this hazard diverting floodwaters away from the residential areas and into a designated floodway, across the floodplain and into the estuary.