John Oldman (ASR)
Vernon Pickett (Waikato Regional Council)
The New Zealand Coastal Policy Statement (NZCPS) is used by central and local government to guide planning and resource consent processing. The focus of the NZCPS is to promote the sustainable management of the coastal environment. Three broad objectives of the NZCPS are that:
- Discharges to the marine environment should avoid adverse effects.
- Where water quality has deteriorated it shall be enhanced.
- Areas potentially affected by coastal hazards need to be identified.
The Waikato Regional Council (WRC), through the Waikato Regional Coastal Plan (RCP), implements rules and actions based on the principles of the NZCPS. One of the major coastal areas under WRC jurisdiction is the Firth of Thames. The Firth supports a range of fish and coastal bird species of recreational, commercial and conservation value and also supports a number of marine farms. Issues facing the WRC relating to the Firth include identifying and managing the environmental impacts of marine farming, nutrient enrichment and contaminant dispersal, effects of increased sedimentation especially in the southern Firth, and hazard management due to increasing sea levels with its implications for coastal erosion and inundation.
To enable informed decisions to be made on the future management of the Firth WRC has developed a hydrodynamic model of the Firth of Thames. Figure 1 shows the bathymetry grid for the model setup for EW by ASR Limited.
Figure 1. Area covered by the Firth of Thames hydrodynamic model. Shading indicates depths.
To ensure that the model provides realistic quantification of the physical processes occurring within the Firth it was calibrated against existing field data collected at a number of sites both within the Firth and the inner Hauraki Gulf. This process involves comparing measured data with the data predicted by the model. Once a good fit between the observed and predicted data is achieved the model can be used to quantify and understand broad scale processes affecting the Firth. Figure 3 shows the predicted average current speed within the Firth.
Figure 2. Predicted mean current speed from the EW Firth of Thames model.
The model will be used as a foundation for more focussed site specific studies. WRC staff, with the assistance of ASR, will use the model in house to carry out. Examples of the potential use of the model include:
- Define general circulation patterns within the Firth to better inform resource management policy and plan development.
- Quantifying the effects of winds and tides on extreme water levels. By understanding how the Firth reacts to tides and winds an analysis of extreme water levels under current or future climate scenarios can be carried out.
- Identify storm and tsunami inundation impacts for Civil Defence planning.
- Define sediment dispersal from the major river systems to help explain mechanisms governing mud accumulation in the southern Firth, and associated mangrove expansion and shorebird habitat reduction within the Firth RAMSAR site.
With increasing demands on the Firth and uncertainties relating to future climate forecasts the development of the Firth of Thames model will allow the WRC to better incorporate oceanographic information into Council’s policy development and resource consent decision-making.
John Oldman is a Senior Consultant with ASR Limited and Vernon Pickett is Coastal Earth Scientist with the Waikato Regional Council.