Dan Bloomer1, Alex Dickson1, Alec Mackay2, Alan Palmer3
1 LandWISE, 21 Ruahapia Rd, RD10, Waipatu, Hastings
2 Farm Systems & Environment, AgResearch, Tennent Drive, Fitzherbert, Palmerston North
3 Farmed Landscapes Research Centre, School of Agriculture and Environment, Massey University, Palmerston North
When Cyclone Gabrielle struck New Zealand in February 2023, agricultural land in Hawke’s Bay, Wairoa and Gisborne was inundated with sediment. A key challenge was understanding how to manage this sediment to return highly productive cropping and orcharding soils back to full production.
Previous studies, including those after the 2004 Southern North Island Storm, provide sediment management guidance but focused primarily on pastoral recovery. Information for high-value cropping and orcharding soils is sparse.
Baseline samples were collected thirty to ninety days after the event from 155 sites across 110 locations, representing different catchments, sediment types, and farm enterprises. Sediment depth, texture, fertility, structure, and earthworm abundance were assessed, growers’ actions recorded, and contamination samples collected from ten sites.
Some of the baseline sites were revisited to assess recovery progress. In spring 2023, ten Hawke’s Bay sites were resampled to assess winter changes in sediment and soil properties. These sites were paired by location and sediment characteristics but managed differently over winter. These ten sites plus six additional ones were resampled in autumn 2024, collecting both soil and crop-harvest measurements. Over two years, sixteen sites were sampled multiple times to track recovery.
Results demonstrate that land and growers are resilient, with most impacted areas returning to similar productivity within a short timeframe. Establishing annual ryegrass as soon as possible consistently enhanced recovery and accessibility. Light grazing does not damage structureless sediment and may help by incorporating organic matter and breaking up surface capping. Once conditions allow, successful crops can be established and good production achieved.
These findings align with earlier studies from 1938, 1948, 1988 and 2004, supporting expectations of similar recovery following the 2025 flood events impacting Nelson and Tasman growers.
Ideally, all 155 sites would be revisited to collect comprehensive information on soil recovery and grower experiences. Since Cyclone Gabrielle will not be the last such event, understanding optimal management responses is crucial for supporting future impacted communities.
This collaborative work involved LandWISE, Massey University, BSI – AgResearch, BSI -Plant & Food, and Gisborne District Council, with support from Ministry for Primary Industries and the Vegetable Research and Innovation Board.