Rain too much for saturated soils

Taruheru on Pilmer Road

The district’s saturated soils cannot take any more water — this was clearly shown during Sunday’s burst of heavy rain.

While the amount of rain over Sunday was not particularly high, water levels rose rapidly, with surface flooding and waterways filling in half a day.

The rapid rise was evident at the well-known low spots around the city and flats,  such as the Taruheru catchment.

At the height of the Cyclone Gabrielle flood in February the Taruheru reached a peak of 4.6 metres at Tucker’s Road bridge. On Sunday it had reached almost 3.3 metres by mid-afternoon.

Soil data recorded by the  National Institute of Water and Atmospheric Research (Niwa) show soils everywhere in the district, apart from the tip of East Cape, are at or over carrying capacity.

The saturation area covers from Wairoa and inland through the Ureweras right up the coast to Ruatoria and the Raukumara ranges.

As a result, even small amounts of rain will immediately run off and start flooding the land and waterways.

In the seven-day period up to 9am Monday morning, the on-and-off rain had totalled over 200mm in the areas north of Tolaga Bay.

Puketoro Station has had over 250mm since June 5.

The southern part of the Gisborne district has had between 100 and 200mm over the same seven-day period, while just on Sunday, the Whareratas had over 65mm and the Waimata catchment had over 52mm.

With persistent rain and cloudy conditions, sunlight hours over the district are well down. Niwa’s daily climate maps show sunshine is down by as much as 85 percent of average in the region, so far this month.

The extended outlook from MetService  offers the chance of a sunny day on Thursday, but then the rain returns, and stays through the weekend to the following Wednesday, June 21.