Wellington reservoir levels fall in downpour
Wellington’s long, dry spell ended with a torrent this week, leading to a paradoxical reduction in the city’s back-up supply.
But Wellington Water chief executive Tonia Haskell said the rainfall replenished the river catchment, meaning more water down the river and a “diminished” risk of a water crisis.
According to Wellington Water, the Hutt River, which the region takes much of its water from, was a mess of mud and debris during and after Monday’s downpour, making it unsuitable for treating for drinking water.
This meant Wellington Water had to take drinking water from Te Marua lakes, which are typically used as a back-up water supply. Levels in the lakes had fallen from 95% to 91% over the past few days.
An email from Wellington Water, attributed to regulatory services director Charles Barker but not actually said or written by him, advised here was a countering positive impact from the rain – water use dropped.
After years of under-investment in pipes, the capital has been inundated with leaks this summer, leading to a ban on sprinklers. As of last Thursday, there was a 43% chance of a complete ban on all outdoor water use and people being asked to reduce their usage inside.
There was a 17% chance of level 4 restrictions, under which people would have to halve their use and water regulator Taumata Arowai would be asked to declare a drinking water emergency.
Then Monday came. MetService and Greater Wellington Regional Council rain gauges recorded 62.8mm of rain on Monday in Kaitoke, which is the catchment area for Hutt River. That was nearing the entire rainfall in February (79.6mm), and compared with January’s 100.8mm.
Wellington Airport recorded 12mm on Monday, the only rainfall it has received this month. February’s rainfall was about half of the month’s average while January’s was about a quarter.
“Barker” said there was also the question about whether the rain “re-charged” the catchment area.
“Our experience of the system is that sustained rain over many days is required to have an impact.
“With the water catchments drying up, the type of rain we have seen has a tendency to predominantly run off directly into the streams. The dry, hard surfaces are unable to absorb and hold on to the rain from a short duration.
“As the weather clears and the rivers settle back into their rhythm we will continue to watch closely as to what impact, if any, the rain has had on their supply capacity.”