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Catchment-scale LiDAR-based SedNetNZ modelling of erosion and suspended sediment loads in Waikato CEM catchments

TR 2025/10
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Report: TR 2025/10

Author: Simon Vale, Hugh Smith, Maksym Polyakov (Bioeconomy Science Institute)

Summary

Project and client

  • Waikato Regional Council (WRC) contracted Manaaki Whenua – Landcare Research (MWLR) to model erosion and suspended sediment loads in four catchments from the Catchment Environmental Monitoring (CEM) programme using the newly developed LiDAR-based version of the SedNetNZ model. The CEM catchments include the Kaniwhaniwha (100 km2), Karapiro (67 km2), Matahuru (110 km2), and the Moakurarua (200 km2).
  • The project involved generating a new digital stream network from a 5 m digital elevation model (DEM) for each catchment and developing a high-resolution landslide susceptibility model to predict shallow landslide erosion. These layers were used in SedNetNZ to model contemporary suspended sediment loads for CEM catchments as well as future erosion mitigation scenarios.
  • The project also assessed the load reductions required to meet National Policy Statement for Freshwater Management (NPS-FM 2020) targets.

Note: An economic analysis was included in the project, which evaluated the cost-effectiveness of erosion mitigation works in achieving visual water clarity targets defined by the National Objectives Framework (NOF) for suspended fine sediment. This analysis was not included in this abridged version of the report for release.

Objectives

The project had the following objectives:

  • update the contemporary suspended sediment loads for CEM catchments using the LiDAR-based version of the SedNetNZ model
  • model future erosion mitigation scenarios, including bush retirement/afforestation, space-planted trees, and riparian retirement under two implementation scenarios
  • assess load reductions required to meet NPS-FM (2020) attribute bands and the national bottom line (NBL) for suspended fine sediment at monitoring sites.

Read or download the report