Quake-damaged stopbanks handle heavy rain

Waimakariri River. Photo / Herald on Sunday

The stopbanks on the Waimakariri and Kaiapoi rivers damaged in the September 4 earthquake have coped well with increased river levels this week, Environment Canterbury says.

Tony Boyle, ECans's principal hazard analyst, said the river engineers have made "excellent progress" repairing the stopbanks, with all major repairs completed this week.

Mr Boyle said the repairs ensure there is a minimal risk of the Waimakariri or Kaiapoi River stopbanks being breached for river flows of up to 3,000 cumecs, which is the equivalent of a 30-year flood event.

Heavy rain in the Southern Alps have resulted in increased river flows this week, peaking around 1100 cumecs.

Environment Canterbury will keep monitoring river flows over the Christmas and New Year period, with further significant falls expected early next week.

The earthquake damaged the stopbanks on the Waimakariri River downstream of the Old Highway Bridge, the stopbanks along the Kaiapoi River, and those at Kairaki Creek.

The remaining moderate and minor repair work on the stopbanks is due to be completed by March next year and this will increase the flood capacity to the original 4,700 cumec flow which is the equivalent of a 450-year flood event.

- NZ Herald staff