Cyclone Gabrielle: Bird’s eye view of flooding, silt damage in Hawke’s Bay and Tairāwhiti

Dragonfly Data Science's map showing silt in the Hawke's Bay. Photo / Supplied

Data scientists have created a new interactive map showing the layers of silt and flooding that inundated Hawke’s Bay and Tairāwhiti in the days after Cyclone Gabrielle.

The map is made by Dragonfly Data Science and combines satellite images taken February 19-21 with socioeconomic data. It shows the large deposits of silt throughout Hawke’s Bay and Tairāwhiti.

The government recently announced $172 million in funding to help process and dispose of the millions of tonnes of silt on roads and people’s properties, businesses and land.

Near Napier, the map shows silt covered extensive parts of Pakowhai, Awatoto and surrounding areas – with similar devastating realities for many communities through the two regions.

Dragonfly satellite data expert Dr Sadhvi Selvaraj said the map overlaid areas affected by flooding, slips and silt with information on population density and detailed information about the communities living in the affected areas.

The map uses the “statistical areas” – geographical boundaries defined by Stats NZ – and includes how many buildings, schools, supermarkets, hospitals, roads and hectares of farmland are in an affected area.

“This type of satellite data can ‘see’ through cloud and in darkness, so it acted like an eye in the sky, showing where the flooding was greatest,” Selvaraj said.

“Data from another satellite enabled us to map the silt and slips, providing a high-level picture of the damage.”

A taskforce has been set up to help get rid of the millions of cubic metres of silt that washed down Hawke’s Bay’s rivers from the hills devastating homes and properties. Photo / Supplied

Selvaraj understood the map to be a “New Zealand first” and said similar tools could be used to respond to future significant weather events. However, data scientists in New Zealand needed better access to satellite imagery to be able to produce maps of this nature consistently.

The imagery used to create the map came from European Space Agency satellites that were, coincidentally, over New Zealand at the right time in February to capture flooding, slips and silt from Cyclone Gabrielle.

Silt, debris and disaster in Hawke's Bay. Photo / Warren Buckland

The map was made in partnership with Social Wellbeing Agency (SWA) Toi Hau Tāngata. SWA deputy chief executive, policy, data and insights, Aphra Green said the map provided significant insights into the make-up of communities.

“This really matters in tailoring the best possible response and tailoring recovery efforts.”

Cyclone Gabrielle caused billions of dollars of damage across the North Island. MetService’s head of weather communications, Lisa Murray, said it was “one of the worst storms to hit Aotearoa New Zealand in living history”.

Nine red weather warnings – MetService’s most severe level of warning – were issued across the intensive three-day event, but almost three months later, people in the hardest-hit regions are still cleaning up after the cyclone condemned their homes and destroyed their livelihoods.

A wrecked car sticking out of mud and silt in Esk Valley this week. Photo / Paul Taylor

The Herald reported this week conversations with residents in these communities about whether they can rebuild their homes were being delayed.

Cyclone Recovery Minister Grant Robertson said earlier he hoped to initiate consultation on the government’s plan for regions impacted by the cyclone and the Auckland floods from the start of May.

He has since told the Herald he was now working towards taking that plan to communities towards the end of the month, but it could be even later.

“I’m very wary of putting out information that we can’t stand by,” Robertson said on Tuesday.

“I’m working towards the end of the month but I’m just wary of committing to that when there are so many moving parts.”