If we needed a reminder of how vital the Riverlink project is to Lower Hutt, Cyclone Gabrielle delivered it in February.
The flooding triggered by intense rainfall – well over 400mm in some parts of Tairāwhiti and Hawke’s Bay – engulfed homes and businesses and swept away infrastructure. Eleven people died. The properties of half the population of Wairoa were inundated when the Wairoa River breached stopbanks.
The warning from the regional council’s Manager Flood Protection, Graeme Campbell, in April was stark: If that cyclone had hit Lower Hutt, existing central city stopbanks would not have coped. Even with the higher, wider stopbanks planned under Riverlink, we might only have escaped a breach by the skin of our teeth.
It has been estimated that if a fully-flooded Hutt River burst through protections along our CBD, floodwaters in parts of the central city and further south could be a life-threatening half a metre-or more deep. Damage could total $1.1 billion (and that was the figure being used more than six years ago).
Except for the Riverlink stretch (south of Kennedy-Good Bridge to Ewen Bridge) stopbanks are in most locations able to contain 2,300 cumecs – that’s 2,300 cubic metres of water flowing past a given point every second. For the Hutt River that’s a size of flood with an AEP (annual exceedance probability) of 0.23%. A flood with a 1% AEP has a one in 100 chance of happening in any year.
Councillors were told we have the highest level of flood protection anywhere in New Zealand. But not yet at Riverlink.
The regional council has allocated $295 million for floodway improvements at Riverlink. Waka Kotahi has again confirmed the $420 million for a new grade separated interchange and bridge at Melling will not be affected by the massive cost pressures caused by cyclone damage further north.
Just remember, a new bridge at Melling is vital for flood reasons; the orientation of piers of the existing bridge present a flood debris hazard.
Hutt City Council is taking the lead on the promenade on top of the stopbank through the central city, the pedestrian/cycling bridge linking the relocated Melling railway station across the river to Margaret St (due for completion in 2024) and engaging the private sector on developing sites along the river corridor for residential, hospitality and leisure use. We’ve budgeted $129 million, but expect to get back about $40m on land parcel sales at project completion in 2027.
The preferred consortium to carry out works under an Alliance partnership model is now chosen. There is trepidation about final costs given inflation and construction workforce constraints but over the next six months, design, works schedule and cost will be finalised before main works start in October.
Traffic disruption, loss of carparks, etc., will be painful in the short term. Someone said it will be like carrying out open heart surgery on the city while we’re still running. But it will transform the central city, and when it rains hard, we’ll no longer have to look at our stopbanks with fingers crossed.