Horizons Regional Council asked Manaaki Whenua – Landcare Research to document the use of SedNetNZ in the Horizons region; update the assessment of the impact of soil conservation work to date, and possible future work under the Sustainable Land Use Initiative (SLUI), on sediment load; assess the impact of SLUI works on water clarity; and update the assessment of the impact of climate change on sediment loads.
SedNetNZ has been used in multiple applications in the Horizons region since 2013.The model algorithms and parameterisation have largely remained the same, with subtle variations to SDR and time period of active landsliding.
The farm-scale version can be used for discussing soil conservation options with farmers but has limited use at a catchment scale.
SedNetNZ typically produces modelled SSY estimates within ¬±40% of measured SSY, but in some cases there were large overestimates.
SLUI works carried out up to 2017 are estimated to have reduced total regional sediment load by 6%.
With no further SLUI works it is estimated that by 2043 sediment load for the region will have decreased by 16%. However, with ongoing implementation of SLUI works (scenario 3) sediment load could be decreased by 30%.
Climate change is predicted to increase sediment yields by 41% to 179% depending on the climate change scenario, which reinforces the need for ongoing SLUI works.
SLUI works are predicted to increase mean visual clarity by between 11% (with no further SLUI works) and 29% (scenario 3).
Manaaki Whenua Landcare Research Contract Report LC3135