AgResearch secures funding for sediment sampling project in Tairāwhiti post-Cyclone Gabrielle

Silt left behind when the Mata River, in the Waiapu catchment, flooded during Cyclone Gabrielle. GDC land management staff have been sampling silt in the Waiapu, Uawa and Waipaoa catchments to determine the effects of the flooding on productive land. Picture supplied

A new project to sample sediment post-Cyclone Gabrielle is under way.

Crown agency AgResearch has sourced funding to undertake silt sampling in Tairāwhiti.

The project aims to undertake a rapid assessment of flood-affected productive land impacted by long saturation and sediment deposition in Hawke’s Bay, Tairāwhiti and Northland.

It was recognised that there was an urgent need to establish ground cover to start to repair and restore land as soon as possible and provide guidance to landowners on remediation, land preparation and nutrient management.

Gisborne District Council land management staff have been undertaking the sampling work over the past few weeks.

The nature and depth of sediment have been assessed by catchment and proximity to river source points.

Sediment and soil samples were obtained along with information on the actions land managers have taken or are proposing to take. Suggestions have also been made to land managers around remedial options.

In total 55 samples of sediment and soil were collected from 39  locations throughout the region including the Waiapu, Uawa and Waipaoa catchments.

The results are still to be fully analysed, but early indications are that the sediment has  high PH and sulphur levels, and low Olsen P (a fertility indicator to assess on-farm nutrients), compared to the underlying soil.

The next steps are to collate and analyse the results, interpret the findings and look for opportunities to build resilience.

The data collected will provide baseline information for assessing and reviewing the effectiveness of various management strategies applied, in addition to the data from the 1948 Gisborne floods and the 2004 southern North Island storm.

Most of the data from 2004 comes from pastoral systems so it will be particularly useful to learn about the cropping and horticulture land use types this time around.