SedNet NZ modelling to assess sediment contributions from natural land cover areas and impacts of climate change in Taranaki

In 2021, Taranaki Regional Council (TRC) contracted Manaaki Whenua-Landcare Research (MWLR) to model several scenarios in regard to suspended sediment loads in streams and rivers in the Taranaki region. 

These were:

  • Mean annual suspended sediment loads under different land cover scenarios;
  • Mean annual suspended sediment loads required to meet the National Policy Statement for Freshwater Management 2020 (NPS-FM 2020);
  • Suspended fine sediment attribute states (visual clarity) at selected water quality monitoring sites and to estimate the future attribute state for the future soil conservation scenario consisting of fully implemented and mature Whole Farm Plans.

This work is reported in Neverman et al. (2021)[1]

Erosion in natural cover areas (TRC)

To further build on the 2021 work, TRC through the Envirolink scheme requested MWLR to estimate the impact of projected climate change on sediment loads at the selected water quality monitoring sites reported in Neverman et al. (2021).  TRC wished to use this work to provide a contemporary baseline and future soil conservation scenarios and also requested MWLR estimate the contribution of natural land cover areas to modelled loads. This work was completed under Envirolink Medium advice grants 2305-TRC004 and 2308-TRC005.

The objectives of the Envirolink work were to:

  • Model the effects of climate change on erosion and suspended sediment loads for mid-century and late century for: the contemporary baseline scenario (2018 land cover and the extent and maturity of soil conservation works completed to date) and the future soil conservation scenario (fully implemented and matured soil conservation works);
  • Compare model results with and without the effect of climate change to assess the extent to which soil conservation measures mitigate projected impacts from climate change;
  • Assess compliance with the NPS-FM (2020) for suspended fine sediment at selected water quality monitoring sites for the future soil conservation scenario under projected climate change;
  • Estimate the contribution of natural cover areas to suspended sediment loads at selected water quality monitoring sites for the contemporary baseline and future soil conservation scenarios;
  • Compare natural cover load contributions with the estimated load reductions required to achieve the NPS-FM (2020) attribute bands for suspended fine sediment reported in Neverman et al. (2021)

Stream sedimentation (TRC)

TRC Scientist Brian Levine says the work has provided information to move forward in the Council’s implementation of the NPS-FM.  Brian says “the work will help guide stakeholders in the process and shed light on what is achievable.  It will also provide the council with an idea about how much effort is necessary to achieve NPS-FM objectives”.

Read the full report [PDF, 2.8 MB]

[1] Neverman AJ, Smith HG, Herzig A 2021. Planning soil conservation for sediment load reduction in Taranaki. Landcare Research Contract Report LC3942 prepared for Taranaki Regional Council

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