Future of our region’s landscape 'hard to predict': GDC principal scientist

This 3D-modelled image shows the erosion that caused the temporary closure of popular walking tracks on Makorori Headland last year. Picture by Murry Cave

Erosion reshaping the region after 2017 cyclone marked a ‘shift in storminess’.

A scientist says the future of this region’s landscape is hard to predict, but dramatic erosion experienced here could stall, at least for a while, if current El Niño weather conditions continue.

Gisborne District Council’s principal scientist Murry Cave said while last year’s closure of the Makorori Headland walks came as a shock to the community, who enjoyed free access to breathtaking views, it also highlighted the impacts of the multiplicity of storms the region had experienced — particularly since Cyclone Cook in 2017.

That cyclone marked a shift in storminess from what had previously been a relatively quiet period weather-wise for the region, Mr Cave said.

“This reflects a long-term cycle between periods of quiet and storms with the current phase of storminess exacerbated by an extended La Niña system."

The storms do not just bring rain and floods. Many recently have also included strong onshore winds and high waves, the impacts of which were exacerbated by storm surges from large blocking highs in the Pacific Ocean, Dr Cave said.

“This changes the sediment dynamics on our beaches, with some gaining sand but others having lost it or experienced remobilisation of it to other parts of the beach.

“This has happened even as the storms have increased the load of sediment being lost from the land and delivered to the ocean.

“And so, in places like in the Ūawa River mouth at Tolaga Bay, the increase in sediment has resulted in the build-up of sand bars immediately off the river mouth, but paradoxically the northern side of the river mouth experienced retreat with dunes and grassed areas lost while the southern beaches remained more stable.

“Now that situation has reversed, with the dunes at the southern end of Tolaga Bay experiencing loss of the sand dunes.”

Similarly, storm damage caused the closure of the playground and picnic area at Tokomaru Bay.

In 2022, the Waitangi weekend storm resulted in the closure of the East Cape road for some time and this area remained vulnerable during storm conditions, Mr Cave said.

'We live in a dynamic region where weather conditions can change rapidly'

“We are seeing it elsewhere as well with the partial loss of an urupa at Anaura, the beaches at Whangara experiencing erosion recently and in the loss of the coastal space between Pouawa and Tatapouri.”

That area between Pouawa was a favourite for summer camping but ongoing erosion led to New Zealand Transport Agency Waka Kotahi closing Turihaua Point for coastal protection work this summer.

Other erosion in the area resulted in summer camping spots being increasingly squeezed into smaller spaces between the road and the sea, Mr Cave said.

“Closer to town, the increase in storminess has accelerated the rate of erosion at Sponge Bay and a few years ago we also had the breach of protection at the southern end of Wainui Beach taken out by a combination of high tides coinciding with a storm surge.

“Further south at Whareongaonga, we have had other impacts where very large landslides in the steep coastal cliffs have resulted in the increasing loss of large areas where the Gisborne to Wairoa railway used to run.

“It is hard to predict what the future will bring,” Mr Cave said.

“Will the present El Niño phase result in an overall reduction in storminess and if so, how long will it last?

“All we know for certain is that we live in a dynamic region where weather conditions can change rapidly."