A new flood protection scheme aims to stop the Kerikeri River spilling into dozens of Waipapa homes - but the downside is that it may increase flood levels further downstream.

The Northland Regional Council project, if it gets the green light, will involve building a spillway and stopbanks to divert part of the river's flow during floods.

The proposed spillway will shortcut a sharp bend in the river and start about 300 metres downstream of the State Highway 10 bridge. The water will then follow a natural overflow channel, drop over a waterfall, and be discharged back into the Kerikeri River, 650m downstream of Rainbow Falls.

The scheme will greatly reduce flood risk for 41 buildings and 108 properties, mostly along Waipapa Rd and Waitotara Drive. It will also reduce flood levels at Waipapa Landing.

Advertisement

However, it will increase flood levels - albeit only by about 10cm - at some downstream properties. They include Quail Ridge (a retirement complex under construction off Rainbow Falls Rd), properties on Amokura Drive, Tuatahi Place and Peacock Gardens, and the historic Kerikeri Basin. Flood levels in a 1-in-100 year event are expected to increase at the Stone Store by 7cm and at Kemp House by 2cm.

The spillway is also expected to flood two farm properties off SH10, on average twice a year for 12 hours at a time. The project involves more than 50,000cu m of earthworks and requires eight new stop banks, mostly at Waitotara Drive.

Regional council land and rivers manager Bruce Howse said the scheme would cost $2.1 million and be paid for by a targeted rate over the 4300 properties in the Kerikeri-Waipapa catchment. That was roughly $80 per property per year for 10 years.

It would raise flood levels downstream but only at properties which were already at risk of flooding. Predicted higher flood levels at the Stone Store would be offset by recent work to improve flow and remove a boulder bank just upstream of the Kerikeri Basin footbridge.

The regional council is currently applying to itself and the Far North District Council for a raft of consents. A joint hearing before commissioners Bill Smith and Fraser Campbell was held at Kingston House in Kerikeri on May 27. Nine submissions were received, four of which opposed the scheme.

The commissioners adjourned the hearing to give the council time to respond to submitters' concerns. It will reconvene in about five weeks' time. No date has been set for the decision.

Major floods hit the Kerikeri River in 2007 and 2011. The biggest of recent decades struck in 1981.

The scheme will not protect the Waipapa commercial area. In its long-term-plan the regional council is considering a $13.8 million plan to build a detention dam further upstream for water storage and flood prevention in central Waipapa.