Lake Rotokauri Integrated Catchment Management Plan

Streamlined Environmental undertook a water quality assessment and data analysis to support the development of an Integrated Catchment Management Plan (ICMP) for the Lake Rotokauri catchment on the fringes of Hamilton City. Our assessment included a synthesis of current knowledge, field investigation and analysis to identify urban contaminants of concern, and the design and calibration of a SLAM (Simplified Lake Assessment Model) to determine the potential effects of urbanisation on the lake. We developed a spreadsheet model to predict the potential loads of nitrogen, phosphorus and sediment that could runoff a greenfield urban development. These loads were then input to the SLAM model, which predicts phytoplankton biomass increases as a consequence of development without mitigation. We then used these potential effects to identify the critical pollutants, and predict the amount of stormwater treatment needed to avoid any increase in phytoplankton production in the lake. We concluded that phosphorus was the contaminant that most limited urban development (through transport of soil phosphorus into the lake) and that up to 70% treatment would be required to avoid any further deterioration in this already hypertrophic lake.