West Coast remarkably dry

Nicole Mathewson Reporter from The Press

From local democracy reporter Brendon McMahon:

Extraordinarily dry weather throughout the West Coast this summer has been reflected in very low flows in rivers across the region.

In contrast to the North Island in the wake of Cyclone Giselle, in the past seven days until Friday no rain had fallen in the Buller River catchment at Bald Hill and there has been 23mm in the Inangahua catchment, according to West Coast Regional Council river monitoring data.

For the Grey River and its inland tributaries no rain has been recorded for seven days; likewise, no rain has been recorded in the Hokitika River headwaters for the same period while further south the Waiho (Waiau) at Franz Josef only had 2.5mm.

Over December and January the council has been closely monitoring river levels, particularly in the Grey Valley.

"For the most part of January, the lack of rainfall has seen all the rivers drop near or below their seven-day mean annual low flows," a staff report to the West Coast Regional Council Resource Management Committee this week said.

As a result, hydrology staff conducted 18 'low flow' gaugings which would help the council to calibrate its current flow models for waterways in the region.

The council expected to start reporting long term flow data soon via its website, the report said.

It notified Grey Valley farmers last month they were on irrigation watch. The valley is one of the principal irrigated farming areas on the West Coast.

Meanwhile, the report notes that council only picked up one area of concern through its contact recreation water monitoring for popular swimming holes and beaches. That was at Marrs Beach, at the mouth of a major protected wetland off Martins Creek and opposite Westport township on the Buller River.

It exceeded the safe E coli threshold for swimming at the new year.

Increased coliform readings are often associated with rainfall but, "no significant rainfall occurred at the time," the report said.

In recent weeks, science staff had also been responding to public inquiries around potentially toxic algae after the council put out a public appeal to watch for and report toxic algae.

But so far no sites have been found that pose a health threat.

The threat was considered serious as rivers continued to drop and higher water temperatures and low flows can prompt harmful algae.

"Warm stable temperatures can favour growth of such algae. So far no sites have been found that pose a significant threat to human or animal health."

The West Coast council was liaising with Health NZ and Environment Canterbury on how to respond should a
significant threat be identified.

The council is also having to up its game around wetland assessment, with new national standards impacting.

Science staff had helped the compliance department with a wetland assessment last month.

"Council will need to increase capacity in identifying and validating wetland types and extent. Science and compliance staff are currently developing skills in wetland plant identification."

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