Drastic drops in Wairarapa river flows

PARCHED: Lake Wairarapa's northern foreshore is dry and cracked, as river flows reach low levels and temperatures exceed 30C.

It is official, January was a very hot and cruelly dry month in Wairarapa.

Statistics just released by Greater Wellington Regional Council confirm the month brought sweltering days with little to no rain and knocked river levels for six.

A rain gauge at the Tanawa Hut, about 15km north of Tinui, totalled 8mm, the lowest total since 1981 and the third lowest since 1956.

Even in what is regarded as the green belt, rain was a scarce commodity.

The Tararua Ranges and foothills received between 10 and 20 per cent of the average January rainfall and northern and, on the valley floor, eastern parts recorded between 8-20 per cent of what normally falls.

The only significant rain in the month fell on January 21, when 20mm was dumped in central Masterton in less than two hours.

The exceptionally dry start to the year, coming on top of three consecutive months of drier than average conditions, has resulted in river flows dropping away drastically, and the regional council has warned low flows in rivers and streams usually happen later in February and extend through to April.

The Ruamahanga, Waipoua, Waingawa, Waiohine, Mangaterere, Tauherenikau and Kopuaranga have all fallen to levels rarely experienced and, with plenty of summer weather still ahead, there are increasing fears river flows will diminish still further. There has been a huge drop in soil moisture, with deficits much more severe than is normal for January.

Low river flows are starting to impact on the health of waterways and ecosystems, and Wairarapa has already been subjected to some toxic algae bloom outbreaks.

Elsewhere in the Wellington region, the lack of rain has seen the Karori Reservoir record the lowest rainfall since 1879 and Wainuiomata Reservoir its lowest since 1890.

All rain gauges run by GWRC in Wellington, Lower Hutt, Upper Hutt and Wainuiomata showed less than 6 per cent of average January rainfall amounts.

The regional council believes that, while unsettled weather next week may bring some relief, it is far from certain there will be enough to generate the sort of flushing needed to scour algae from river beds.