Author:Christoph D Matthaei
Source:University of Otago, Department of Zoology
Northland Regional Council with support from Auckland Council and Ministry for the Environment have contracted a consortium led by Streamlined Environmental Ltd and consisting of Streamlined Environmental, Landcare Research, NIWA and the University of Otago, to conduct the Kaipara Harbour Sediment Mitigation Study (KHSMS, the Study). The first aim of the Study is to develop a catchment economic model for use in assessing the economic costs and environmental benefits of a range of scenarios for mitigating sediment losses to rivers and estuaries within the Kaipara Harbour catchment. The second aim of the Study is to develop a management tool for use in formulating consistent farm-scale sediment mitigation plans. The tool will be easily usable by land management advisors in the field to identify appropriate actions to mitigate critical source areas of sediment under different land uses at the farm scale.
This report provides a narrative assessment of how changes in sediment attributes in freshwater in response to mitigation applied in the catchment will translate into changes in ecosystem health and functioning and certain values derived by humans from the use of water.
Daigneault et al. (2017) report on the catchment economic modelling done for the Study, which was performed with the spatially explicit economic land use model, New Zealand Forest and Agriculture Regional Model (NZFARM). The model incorporated data and estimates from economic and land use databases and biophysical models. Annual sediment loads into seven river subcatchments from various land uses have been estimated using the SedNetNZ model (Dymond 2016). A harbour sediment budget that takes as input those sediment loads has been constructed. Land-based mitigation costs and effectiveness in reducing sediment have been obtained from a range of sources.