Coast rivers warning alarms in May

Nicole Mathewson Reporter from The Press

Brendon McMahon, Local democracy reporter

Hydrology data collected by the West Coast Regional Council underscores just how wet the month was.

However while the Hokitika and Haast rivers exceeded their 1-year annual return periods during heavy rain on May 9, high flows in the Grey and Buller rivers further north remained below their one-year annual return, a resource science report to the Resource Management Committee on Tuesday says.

"May has been a wet month of unsettled weather for the West Coast with the Hokitika and Waiho rivers triggering four flood warning alarm responses," the staff report says.

"On average, most flows recorded were above or near median annual flows".

On May 3 the Hokitika passed the first alarm threshold of 3750mm and peaked at 3793mm; six days later on May 9 it peaked at 4411mm.

The threshold of 8000mm at the Waiho (Waiau) River at Franz Josef was passed and peaked at 8474mm on May 3; it peaked slightly lower at 8144mm on May 9.

In April the Hokitika River at the gorge measuring point, surpassed its flood alarm threshold on the 11th, with a peak of 3762mm.