Exceptionally high king tides are forecast for the Manukau and Waitemata harbours later this week, and the NZ Transport Agency advises drivers that there is a risk some low lying sections of the city’s motorway network may flood.
In the Waitemata harbour, high tides of up to 3.7m - about 0.6m higher than normal – are expected for five days from this Friday until the following Tuesday (31 January – 4 February). King tides usually occur over a period of two days and peak at 3.6m.
Areas most at risk from flooding include a section of highway and adjoining cycleway on the Northwestern Motorway (State Highway 16) causeway between Great North and Rosebank Roads, and the Northern Motorway (SH1) near the Onewa Road interchange. In the city, some parts of Tamaki Drive could also flood.
The king tides will be at their highest on Saturday and Sunday mornings says the Transport Agency’s National Journey Manager, Kathryn Musgrave.
“Our advice to all road users, including cyclists and walkers, is to take extra care – especially during that hour-and-a-half either side of high tide. If necessary, we will divert drivers on to other roads to allow them to continue their journeys safely, and sections of the Northwestern cycleway will most likely be underwater which will make walking and cycling hazardous,” says Mrs Musgrave.
The Transport Agency’s SH16 Causeway Upgrade Project includes raising this section of the Northwestern Motorway 1.5m to prevent flooding in future.
The king, or perigean, tides occur when the moon is either new or full and closest to the earth. The weather – low pressures or strong winds – can also influence the height of the tide.